Metal organic compounds

Abstract

The Invention relates to a method Method for making a ruthenium catalyst comprising the steps of - Providing an aromatic dithiol substituted on adjacent aromatic carbon atoms with thiol groups, wherein in a first step an aromatic compound substituted with two leaving groups on adjacent aromatic carbon atoms are reacted with alkali trithiocarbonate to obtain an aromatic benzodithiole-thione, which in a subsequent step is reacted / hydrolysed with a base; - providing a zinc dithiolate compound by reacting the aromatic dithiol with a zinc carboxylate in an organic solvent; Reacting the zinc dithiolate compound with a ruthenium compound wherein X1 and X2 are, independently of each other, are anionic ligands and are the same or different; L and L2 are, independently of each other, neutral electron donor ligands and are the same or different; Ar is an aromatic group which may be substituted and that can be bridged with L, if L is an alkoxy group; - Obtaining a ruthenium catalyst of formula 4 or 4a, wherein R1 to R4 are, independently of each other, are selected from hydrogen, halogen, alkyl, aryl, or R.1 with R3, R3 with R4 or R2 with R4 are forming together an aliphatic or aromatic ring.

Description

Metal Organic CompoundsDescriptionRuthenium-based stereo- retentive olefin metathesis catalysts have more become of interest, so novel and more scalable, industrially suitable methods are needed.Aromatic dithiols are valuable compounds in various chemical industries due to their unique properties and applications, but have also become a key starting material in the field of ruthenium-based stereo- retentive olefin metathesis catalysts.EP3008078 shows the use of aromatic 1,2-dithiols as ligands in transition metal complexes for stereoselective metathesis catalysts.Known methods for synthesizing aromatic 1,2-dithiols often have the disadvantage to involve complex procedures and harsh conditions.1. Traditional Methods: o Processes: Traditional methods for synthesizing aromatic dithiols often involve multi-step reactions, including the use of thio- lating agents and strong acids or bases. o Conditions: These methods typically require harsh reaction conditions, such as high temperatures and the use of toxic reagents. o Examples: Common approaches include the reaction of aromatic halides with thiourea followed by hydrolysis, or the use of Grignard reagents with sulfur compounds.2. Use of Halogenated Aromatics: o Processes: Some methods utilize halogenated aromatic compounds as starting materials, which are then reacted with sulfur- containing reagents.o Conditions: These reactions often require high temperatures and prolonged reaction times. o Examples: The conversion of dihalobenzenes to dithiols using sodium sulfide or other sulfur sources.3. Catalytic Methods: o Processes: Catalytic methods involve the use of metal catalysts to facilitate the formation of thiol groups on aromatic rings. o Conditions: These methods can be more efficient but often require expensive and sensitive catalysts. o Examples: Palladium-catalyzed thiolation reactions of aromatic halides.4. Shortcomings and Problems1. Complexity and Efficiency: o Issue: Traditional methods are often complex, involving multiple steps and requiring careful control of reaction conditions. o Impact: This complexity can lead to lower overall efficiency and increased production costs.2. Harsh Reaction Conditions: o Issue: Many prior art methods require harsh conditions, such as high temperatures, strong acids or bases, and toxic reagents. o Impact: These conditions can pose safety risks, environmental concerns, and difficulties in scaling up the processes for industrial applications.3. Yield and Purity:o Issue: The yield and purity of the final aromatic dithiols can be variable and sometimes low due to side reactions and the need for extensive purification steps. o Impact: This variability can affect the consistency and quality of the final product, making it less reliable for commercial use.4. Cost and Scalability: o Issue: The use of expensive catalysts and reagents, as well as the need for specialized equipment, can increase the cost of production. o Impact: High production costs and scalability issues can limit the practical application of these methods in large-scale manufacturing.5. Environmental and Safety Concerns: o Issue: The use of toxic reagents and harsh conditions can lead to environmental pollution and pose safety hazards to workers. o Impact: These concerns necessitate additional safety measures and waste management protocols, further increasing the complexity and cost of the processes.Polyhedron 2016 (117) Seiten 265-272 shows several methods for the preparation of thiols and dithiols, focusing on three key approaches. In direct thi- olation, aromatic compounds are directly thiolated using thiolating agents such as thiourea or thiolacetic acid in the presence of catalysts like copper or palladium and are conducted under mild to moderate temperatures, which is straightforward and can be applied to a variety of aromatic substrates. Reduction of disulfides consists of a reduction to thiols using reducing agents such as sodium borohydride (NaBH4) or lithium aluminum hydride (LiAIH4) typically carried out in polar solvents like ethanol or tetra hydrofuran (THF), which provides high yields of thiols and is useful for synthesizing thiols from readily available disulfides. The hydrolysis of thioesters employshydrolyzation to thiols using bases such as sodium hydroxide (NaOH) or potassium hydroxide (KOH) in aqueous or alcoholic solutions at elevated temperatures, which is efficient and allows for the selective preparation of thiols from thioesters.Nature 2015 (517), Seiten 181-186 shows innovative methods for the preparation of thiols and dithiols. Catalytic Thiolation relates to thiolation of aromatic halides with catalytic systems involving transition metals such as palladium or nickel and are conducted under mild conditions with the use of ligands to enhance the catalytic activity. This method offers high selectivity and efficiency, making it suitable for complex aromatic compounds. In photochemical thiolation thiols are generated through irradiation of aromatic compounds in the presence of sulfur sources and is carried out under UV light or visible light, often in the presence of photosensitizers, resulting in reactions that are environmentally friendly and can be performed under ambient conditions. Enzymatic thiolation makes use of enzymes such as thiolases to catalyze the formation of thiols from precursor molecules. The reactions are conducted in aqueous media at physiological temperatures and pH. They are highly specific and operate under mild conditions, making them suitable for sensitive substrates.SU1421736 shows a method for producing aromatic dithiols by reduction of disulfonyl chlorides to dithiols by reduction with zinc and hydrochloric acid. However, the thiol groups of the aromatic dithiols are located on different aromatic rings of the compounds.Recently it was found that such stereo- retentive olefin metathesis catalysts can be prepared by using dithiolates such as (arene-l,2-dithiolato)(eth- ylenediamine)zinc(II) compounds, such as (3,6-dichlorobenzene-l,2-dithio- lato) (ethylenediamine)zinc(II), for example. Such catalysts and their preparation are shown, for example, in WO 2017 / 100585.Such dithiolate species need to be isolated in a separate step. This isolation is difficult and not possible on a production scale because the requiredfiltration is very slow, difficult and poses hazards as hot chloroform is needed to remove impurities.In addition, the product contains ethylenediamine, which is classified as a very toxic substance and has been added to the "Substance of Very High Concern" (SVHC) list of ECHA. Moreover, even in traces, ethylenediamine can have a detrimental effect on the catalyst properties, see for example Fogg et al. : Decomposition of Olefin Metathesis Catalysts by Brpnsted Base: Metallacyclobutane Deprotonation as a Primary Deactivating Event, J. Am. Chem. Soc. 2017, 139, 46, 16446-16449.Mauduit, M. et al., Org. Lett. 2018, 20, 6822-6826 uses diethyl zinc(Zn(ethyl)2) for the in situ generation of a Zn-dithiolate species. But Zn(Et)2is pyrophoric, sensitive to moisture and thus it is not well suitable for use in production.WO 2014 / 201300 shows a method for making zinc dithiolate compounds in section

[0602] from 3,6-dichlorobenzene-l,2-dithiol with a fourfold molar excess of zinc acetate and ethylenediamine at 22°C for one hour. The reaction product was assigned the following formula:Zinc dithiolates, however, exhibit bad solubility. The zinc dithiolate of WO 2014 / 201300 is washed with hot chloroform, confirming the bad solubility and thus are bad to characterize and to analyze.W02018 / 087230, section

[0084] shows an identical method of making the zinc dithiolate compound under the very same conditions from the very same educts as the zinc dithiolate of WO 2014 / 201300, but this time the structure shown is compound 10 having the structure given as follows:The differences in the structures of the dithiolate compound of WO 2014 / 201300 and W02018 / 087230 show the difficulties of characterizing and analyzing such compounds, but also their bad solubility.It was the objective to provide a synthesis of ruthenium-based stereo-retentive olefin metathesis catalysts that overcome the shortcomings of the prior art.This problem is solved with a method for making a ruthenium catalyst comprising the steps ofProviding an aromatic dithiol substituted on adjacent aromatic carbon atoms with thiol groups, wherein in a first step an aromatic compound substituted with two leaving groups on adjacent aromatic carbon atoms are reacted with alkali trithiocarbonate to obtain an aromatic benzodithiole-thi- one, which in a subsequent step is reacted / hydrolysed with a base; providing a zinc dithiolate compound by reacting the aromatic dithiol with a zinc carboxylate in an organic solvent;Reacting the zinc dithiolate compound with a ruthenium compound of formula 3Formula 3wherein XI and X2 are, independently of each other, are anionic ligands and are the same or different; L and L2 are, independently of each other, neutral electron donor ligands and are the same or different; Ar is an aromatic group which may be substituted and that can be bridged with L, if L is an alkoxy group;Obtaining a ruthenium catalyst of formula 4 or 4a, wherein the anionic ligands are a bridging dithiolate forming a ring via its sulfur atomsFormula 4a wherein R1 to R4 are, independently of each other, are selected from hydrogen, halogen, alkyl, aryl, or R.1 with R3, R3 with R4 or R2 with R4 are forming together an aliphatic or aromatic ring.As can be seen, a combination of two reactions that have never before been employed for the synthesis of ruthenium-based stereo- retentive olefin metathesis catalysts have been surprisingly found to solve the problem and allow such compounds to be made available to a broader customer base.The first reaction is a method for the preparation of 1,2-dithiols, wherein an aromatic compound substituted with leaving groups in the 1,2 position are reacted with an alkali trithiocarbonate to obtain an aromatic benzodithiole- thione, which subsequently is hydrolysed with a base. It is the first step ofthe method for making a ruthenium catalyst as claimed herein. This method also is a subject of this patent application.The second reaction is the method for the preparation of a zinc dithiolate compound by reacting the aromatic dithiol with a zinc carboxylate in an organic solvent. It is the second step of the method for making a ruthenium catalyst as claimed herein. This method also is a subject of this patent application.These methods will be discussed separately and they are connected in that they are used for the preparation of ruthenium-based stereo- retentive olefin metathesis catalysts.Thus, all the embodiments described separately for both the steps of preparation of aromatic 1,2-dithiols as well as the preparation of zinc dithiolates are also embodiments for the method for making a ruthenium catalyst according to the invention as claimed herein.Preparation of aromatic 1,2-dithiolsIt was the objective to provide a simple method for producing aromatic 1,2- dithiols (its most simple example being benzene-l,2-dithiol) in high yield and purity with few process steps, which allows preparation of these compounds from starting materials that are easily available in commercial quantities, avoids toxic compounds, without the need for a metal catalyst, which can be upscaled easily and wherein byproducts can be removed in a simple manner.This problem is solved by a method for the preparation of aromatic dithiols substituted with thiol groups on adjacent aromatic carbon atoms, wherein in a first step an aromatic compound substituted with two leaving groups on adjacent aromatic carbon atoms are reacted with alkali trithiocarbonate to obtain an aromatic benzodithiole-thione, which in a subsequent step is reacted / hydrolysed with a base to obtain an aromatic dithiol substituted with thiol groups on adjacent aromatic carbon atoms.This method addresses the shortcomings of the prior art by providing a more efficient, straightforward, and environmentally friendly approach to synthesizing aromatic dithiols. It allows for the use of a variety of aromatic andheteroaromatic compounds, offers flexibility in the choice of leaving groups and alkali, and employs milder reaction conditions, making the process safer and more scalable for industrial applications.The method provides a more efficient and straightforward approach to synthesizing aromatic dithiols. It allows for the use of a variety of aromatic and heteroaromatic compounds and offers flexibility in the choice of leaving groups and alkali. The milder reaction conditions and the use of polar solvents make the process safer and more environmentally friendly.Short Description of the InventionThe invention provides a method for the preparation of aromatic dithiols substituted on adjacent aromatic carbon atoms with thiol groups. The method comprises the following steps: a) Reaction with Alkali Trithiocarbonate: An aromatic compound substituted with two leaving groups on adjacent aromatic carbon atoms is reacted with alkali trithiocarbonate to obtain an aromatic benzodithiole- thione. b) Hydrolysis with Base: The aromatic benzodithiole-thione obtained in the first step a) is subsequently reacted or hydrolyzed with a base to yield the desired aromatic dithiols.More specifically, the Invention can exhibit the following embodiments:1. Method for the preparation of aromatic 1,2-dithiols substituted on adjacent aromatic carbon atoms with thiol groups, wherein in a first step an aromatic compound substituted with two leaving groups on adjacent aromatic carbon atoms are reacted with alkali trithiocarbonate to obtain an aromatic benzodithiole-thione, which in a subsequent step is reacted / hydrolysed with a base.2. Method of item 1, wherein the leaving groups are selected from the group consisting of halogens or pseudohalogens, or are selected from the group consisting of Cl, Br, I, -OCN and combinations thereof.3. Method of any of items 1 or 2, wherein the aromatic dithiols and the aromatic compounds are comprising an aromatic or heteroaromatic ring or ring system exhibiting 5 to 26 carbon atoms, or 6 to 22 carbon atoms, or 6 to 16, or 6 to 8 carbon atoms.4. Method of any of items 1 to 3, wherein the aromatic dithiols and the aromatic compound can be further substituted with halogen, more specifically with F, Cl, Br or I or alkyl groups having 1 to 5 carbon atoms.5. Method of any of items 1 to 4, wherein alkali is selected from lithium, sodium, potassium and combinations thereof, or wherein alkali is sodium or potassium.6. Method of any of items 1 to 4, wherein the aromatic dithiols are 1,2- dithiols or, if substituted, 2,3-dithiols.7. Method of any of items 1 to 6, wherein the aromatic compound is a di- halobenzene, a tetrahalobenzene, a pentahalobenzene or a hexahalo- benzene.8. Method of any of items 1 to 7, wherein the aromatic compound is a heteroaromatic compound.9. Method of any of items 1 to 7, wherein the aromatic compound is a quinoxaline, particular selected form the group consisting of 2,3-difluo- roquinoxaline, 2,3-dichloroquinoxaline and 2,3-dibromoquinoxaline.10. Method of any of items 1 to 7, wherein the aromatic compound is selected from the group consisting of hexahalobenzene, pentahalobenzene and 1,2,3,4-tetrahalobenzene, in particular selected from the group consisting of hexafluorobenzene, hexachlorobenzene, hexabromobenzene, 2,3-dichloro-l,4,5,6-tetrafluorobenzene, 2,3-dibromo- 1,4,5,6-tetrafluorobenzene, pentafluorobenzene, 2,3-dichloro-l,4,5- trifluorobenzene, 2,3-dibromo-l,4,5-trifluorobenzene, pentachlorobenzene, pentabromobenzene, 1,2,3,4-tetrafluorobenzene, 2,3-dichloro- 1,4-difluorobenzene, 2,3-dibromo-l,4-difluorobenzene, 1,2, 3, 4-tetrachlorobenzene, 1,2,3,4-tetrabromobenzene, 1,2,3,6-tetrafluoro- benzene, 2,3-dichloro-l,4-difluorobenzene, 2,3-dibromo-l,4-difluoro- benzene, 1,2,3,4-tetrachlorobenzene, 1,2,3,4-tetrabromobenzene.11. Method of any of items 1 to 10, wherein the alkali trithiocarbonate is employed in a molar excess over the aromatic compound, in particular in an excess of 1.1 to 2, in particular 1.2 to 1.9 or 1.3 to 1.5 equivalents.12. Method of any of items 1 to 11, wherein the reaction of alkali trithiocarbonate with the aromatic compound is carried out at a temperature of about 80°C to 120°C, in particular 90°C to 110°C or 95°C to 105°C.13. Method of any of items 1 to 12, wherein the reaction of alkali trithiocarbonate with the aromatic compound is carried out in a polar solvent, in particular water, dimethyl formamide or combinations thereof.14. Method of any of items 1 to 13, wherein the base is a solution of an alkaline hydroxide in an alcohol, in particular ethanol.15. Method of any of items 1 to 14, wherein the base is employed at an excess of 3 to 8, in particular 4 to 6 or about 5 equivalents versus the aromatic benzodithiole-thione.16. Method of any of items 1 to 15, wherein the reaction of the base with the aromatic benzodithiole-thione is carried out in an alcohol, in particular ethanol.17. Method of any of items 1 to 16, wherein the reaction of the base with the aromatic benzodithiole-thione is carried out at a temperature of from about 70°C to about 100°C.The embodiments described hereabove apply both to the method for making a ruthenium catalyst according to the invention as well as the method for the preparation of aromatic 1,2-dithiols.Detailed Description of the InventionThe method involves reacting an aromatic compound, substituted with two leaving groups on adjacent aromatic carbon atoms, with alkali trithiocarbonate. The leaving groups can be selected from halogens or pseudohalo- gens, specifically Cl, Br, I, or -OCN.The aromatic dithiols and the aromatic compounds used in this method can comprise an aromatic or heteroaromatic ring or ring system with 5 to 26 carbon atoms, preferably 6 to 22, more preferably 6 to 16, and most preferably 6 to 8 carbon atoms. These compounds can also be further substituted with halogens (F, Cl, Br, I) or alkyl groups having 1 to 5 carbon atoms.The alkali used in the reaction can be selected from lithium, sodium, potassium, or combinations thereof, in particular sodium or potassium, or sodium.The aromatic dithiols obtained can be 1,2-dithiols or, if substituted, 2,3-di- thiols, in particular compounds of formula 2 or formula 2a,Formula 2a, wherein R1 to R4 are, independently of each other, are selected from hydrogen, halogen, alkyl, aryl, or R.1 with R3, R3 with R4 or R2 with R4 are forming together an aliphatic or aromatic ring.R.1 to R4 independently of each other, are selected from hydrogen, F, Cl, Br, I, Cl to C8 alkyl, or C5 to C14 aryl, optionally substituted with one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C8 alkyl, or C5 to C14 aryl or combinations thereof.Alternatively, R.1 with R3, R3 with R4 or R2 with R4, taken together, are forming an aromatic ring or an aromatic ring system exhibiting 5 to 14 carbon atoms; or R1 with R3, R3 with R4 or R2 with R4, taken together, are forming an aromatic ring or an aromatic ring system with 6 to 10 carbon atoms.In particular, R3 and R4, taken together, are forming an aromatic ring or ring system which can exhibit 5 to 14 carbon atoms or 6 to 10 carbon atoms, optionally substituted with one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C8 alkyl, or Cl to C4 alkyl, or C5 to C14 aryl, or C6 to CIO aryl or combinations thereof.In particular, R2 and R4, taken together, are forming an aromatic ring or ring system which can exhibit 5 to 14 carbon atoms or 6 to 10 carbon atoms, optionally substituted with one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C8 alkyl, or Cl to C4 alkyl, or C5 to C14 aryl, or C6 to CIO aryl or combinations thereof.In particular, R1 and R3, taken together, are forming an aromatic ring or ring system which can exhibit 5 to 14 carbon atoms or 6 to 10 carbon atoms, optionally substituted with one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C8 alkyl, or Cl to C4 alkyl, or C5 to C14 aryl, or C6 to CIO aryl or combinations thereof.In particular, R1 and R3, taken together, are forming an aromatic ring or ring system which can exhibit 5 to 14 carbon atoms or 6 to 10 carbon atoms, optionally substituted with one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C8 alkyl, or Cl to C4 alkyl, or C5 to C14 aryl, or C6 to CIO aryl or combinations thereof; and additionally R2 and R4, taken together, are forming an aromatic ring or ring system which canexhibit 5 to 14 carbon atoms or 6 to 10 carbon atoms, optionally substituted with one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C8 alkyl, or Cl to C4 alkyl, or C5 to C14 aryl, or C6 to CIO aryl or combinations thereof.In this case, to avoid misunderstandings, the positions Rl, R2, R3 or R4 not part of an aromatic ring or ring system can be selected from hydrogen, halogen, alkyl, aryl and can in particular be selected from hydrogen, F, Cl, Br, I, Cl to C8 alkyl, or C5 to C14 aryl, optionally substituted with one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C8 alkyl, or C5 to C14 aryl or combinations thereof; or the positions Rl, R2, R3 or R4 not part of an aromatic ring or ring system can be selected from hydrogen, halogen, alkyl, aryl and can in particular be selected from hydrogen, F, Cl, Br, I, Cl to C4 alkyl, or C6 to CIO aryl, optionally substituted with one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C4 alkyl, or C6 to CIO aryl or combinations thereof.More specifically, Rl, R2, R3 and R4 are hydrogen, halogen (F, Cl, Br, I), methyl, ethyl n-propy, isopropyl, n-butyl, iso-butyl, tert. -butyl, or phenyl, naphthyl, fluorenyl, phenalenyl, anthracenyl, phenanthrenyl, which each can be unsubstituted or substituted with F, Cl, Br, I, Cl to C8 alkyl, such as, for example, methyl, ethyl n-propyl, isopropyl, n-butyl, iso-butyl, tert. -butyl, or combinations thereof.In a specific embodiment, Rl and R2 are hydrogen, halogen, methyl, ethyl or phenyl, R3 and R4 are hydrogen, halogen, methyl, ethyl or phenyl or R3 und R4, taken together, are forming an aromatic ring or ring system with 6 to 10 carbon atoms, which are optionally substituted with one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C8 alkyl, or C5 to C14 aryl, C6 to CIO aryl or combinations thereof; orRl to R4 are selected from hydrogen, F, Cl, Br, I, Cl to C8 alkyl, or C5 to C14 aryl, optionally substituted with one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C8 alkyl, or C5 to C14 aryl or combinations thereof.In yet another specific embodiment, R.1 is hydrogen or halogen, or together with R.3 may form an optionally substituted polycyclic ring; R.3 is hydrogen, or together with R.1 may form an optionally substituted polycyclic ring; R4 is hydrogen or together with R2 may form an optionally substituted polycyclic ring; R2 is optionally substituted Ce-io aryl, halogen, or together with R4 may form an optionally substituted polycyclic ring.[1] In one embodiment, R1 is halogen; R3 is hydrogen; R4 is hydrogen or together with R2 forms an optionally substituted naphtyl or phenantryl ring; R2 is halogen or together with R4 forms an optionally substituted naphtyl or phenantryl ring.[2] In one more embodiment, R1 is hydrogen, methyl or Cl, or together with R3 forms 2-phenyl-naphthyl or phenanthryl; R3 is hydrogen, or together with R1 forms 2-phenyl-naphthyl or phenanthryl;R4 is hydrogen or together with R2 forms 2-phenyl-naphthyl, phenanthryl, or methylphenantryl; R2 is Cl, 3,5-dichloro-phenyl, phenyl, t-Bu or together with R4 forms 2-phenyl-naphthyl, phenanthryl or methylphenantryl.[3] In a further embodiment, R1 is Cl; R3 is hydrogen; R4 is hydrogen or together with R2 forms naphthyl or phenanthryl; R2 is hydrogen, Cl, or together with R4 forms naphtyl or phenanthryl.[4] In yet one more embodiment, R1 is hydrogen or Cl; R3 is hydrogen; R4 is hydrogen or together with R2 forms naphthyl or phenantryl; R2 is Cl, phenyl or together with R4 forms naphthyl or phenantryl.[5] In yet a further embodiment, R1 is hydrogen, methyl or Cl, or together with R3 forms 2-phenyl-naphthyl or phenanthryl; R3 is hydrogen, or together with R1 forms 2-phenyl-naphthyl or phenanthryl; R4 is hydrogen or together with R2 forms 2-phenyl-naphthyl, naphtyl, phenanthryl, or methylphenantryl; R2 is Cl, 3,5-dichloro-phenyl, phenyl, t-Bu or together with R4 forms 2-phenyl-naphthyl, naphtyl, phenanthryl or methylphenantryl; or R1 is hydrogen or Cl; R3 is hydrogen; R4 is hydrogen or together with R2 form an optionally substituted naphthyl or an optionally substituted phenanthryl ring; R2 is Cl, phenyl or together with R4 form an optionally substituted naphthyl or an optionally substituted phenanthryl ring.In another embodiment, R.1 and R.2 are hydrogen or halogen, in particular Cl or Br and R.3 and R4 are hydrogen.In a further embodiment, R.1, R2, R3 and R4 are fluorine.In yet another embodiment, Rl, R2, R3 and R4 are so selected that the compound of formula 2 or formula 2a is selected from the group consisting ofThe aromatic compounds used can be dihalobenzenes, tetrahalobenzenes, pentahalobenzenes, or hexahalobenzenes. They can also be heteroaromatic compounds, such as quinoxalines, specifically 2,3-difluoroquinoxaline, 2,3- dichloroquinoxaline, and 2,3-dibromoquinoxaline.The aromatic compounds can be selected from hexahalobenzene, pentahalo- benzene, and 1,2,3,4-tetrahalobenzene. Specific examples include hexafluorobenzene, hexachlorobenzene, hexabromobenzene, 2,3-dichloro- 1,4,5,6-tetrafluorobenzene, 2,3-dibromo-l,4,5,6-tetrafluorobenzene, pentafluorobenzene, 2,3-dichloro-l,4,5-trifluorobenzene, 2,3-dibromo-l,4,5-tri- fluorobenzene, pentachlorobenzene, pentabromobenzene, 1,2,3,4-tetra- fluorobenzene, 2,3-dichloro-l,4-difluorobenzene, 2,3-dibromo-l,4-difluoro- benzene, 1,2,3,4-tetrachlorobenzene, 1,2,3,4-tetrabromobenzene, 1, 2,3,6- tetrafluorobenzene, 2,3-dichloro-l,4-difluorobenzene, 2,3-dibromo-l,4- difluorobenzene, 1,2,3,4-tetrachlorobenzene, and 1,2,3,4-tetrabromobenzene.In particular, the aromatic compound suitable as educts for the aromatic dithiols described above are compounds of formula 2b and 2cWherein Rl, R.2, R.3 and R.4 as defined above and wherein substituent A is a leaving group and can be the same or different, in particular A are the same. In particular, A is selected from the group consisting of Cl, Br, I, -OCN and combinations thereof, in particular if A are Cl and the same. More specifically, the aromatic compound can have the following structure, with A being as defined above, in particular with A being Cl or Br:The alkali trithiocarbonate has the general formulaWherein M is an alkali metal as defined above, in particular sodium or potassium, in particular sodium.The alkali trithiocarbonate is employed in a molar excess over the aromatic compound, specifically in an excess of 1.1 to 2 equivalents, preferably 1.2 to 1.9, and more preferably 1.3 to 1.5 equivalents.The reaction of alkali trithiocarbonate with the aromatic compound is carried out at a temperature of about 80°C to 120°C, in particular at 90°C to 110°C or 95°C to 105°C.The reaction of alkali trithiocarbonate with the aromatic compound is carried out in a polar solvent, such as water, dimethyl formamide, or combinations thereof.The base used for hydrolysis is a solution of an alkali hydroxide, in particular sodium or potassium hydroxide, in an alcohol such as methanol, ethanol, n- propanol or isopropanol, more specifically ethanol. The alcohol also serves as the solvent of the reaction of the aromatic benzodithiole-thione with the base.The base, that is, the alkali hydroxide, is employed in an excess of 3 to 8 equivalents, preferably 4 to 6, and more preferably about 5 equivalents versus the aromatic benzodithiole-thione.The reaction of the base with the aromatic benzodithiole-thione is carried out at the boiling temperature of the solvent, which usually is a temperature in the range of about 65°C to 100°C or 70°C to 97°C or 75°C to 85°C.In a specific embodiment, invention provides a method for the preparation of aromatic dithiols of formula 2 or formula 2a,Formula 2,Formula 2a, wherein R.1 to R4 are, independently of each other, are selected from hydrogen, halogen, alkyl, aryl, or R.1 with R3, R3 with R4 or R2 with R4 are forming together an aliphatic or aromatic ring comprising the steps of: a) Reaction of an alkali trithiocarbonate, in particular a sodium or potas- sium trithiocarbonate, with an aromatic compound of formula 2b or 2cwherein Rl, R2, R3 and R4 as defined above and wherein substituent A is a leaving group and can be the same or different, and wherein A is selected from the group consisting of Cl, Br, I, -OCN and combinations thereof, in particular if A are Cl and the same so as to obtain a benzodithiole-thione, and b) Hydrolysis of the benzodithiole-thione obtained in step a) with an alkali hydroxide, in particular sodium or potassium hydroxide dissolved in analcohol, in particular ethanol, to obtain the desired aromatic dithiols of formula 2 or 2a.The embodiments described hereabove apply both to the method for making a ruthenium catalyst according to the invention as well as the method for the preparation of aromatic 1,2-dithiols, but when appropriate may as well apply to the preparation of the zinc dithiolate described below as follows.Preparation of zinc dithiolateDue to growing demand for stereo- retentive catalysts, it was an objective of the Invention to provide a suitable method to provide zinc dithiolate species to allow a scalable process that delivers the production of stereo- retentive catalysts in good yield and purity.A further problem to be solved was the investigation of an in-situ preparation of a Zn-dithiolate species without addition of ethylenediamine or other bases. Alternatively, reaction with an isolated Zn-dithiolate species containing no amine residue, was another option to solve the problem. Yet another problem to be solved was the provision of a zinc dithiolate compound having improved solubility in organic solvents.This problem is solved by the conversion of a zinc carboxylate and dithiol to form a zinc-dithiolato complex, which can also be easily isolated. It was surprisingly found that in particular Zn-acetate or zinc pivalate can be reacted with dithiol and the zinc-dithiolato complex can be prepared without addition of ethylenediamine or other basesThis method provides a significant simplification of the process since no distillation is necessary anymore and no isolation of intermediate products have to be undertaken.The product is easy to isolate in very high yields and purities. A further remarkable advantage is that dithiol of poor quality and low purity can well be used and the production method of the zinc-dithiolato complex acts as a purification step. This is particularly important as the dithiol is commerciallyavailable in poor purity (60-90%). In this way the quality problems are solved by using the method of the Invention as means for purification, no distillation for product isolation is needed because a simple filtration and washing procedure for product isolation is sufficient and in addition, in- creased yield and space utilization is effected.The problem is solved by a method for making a zinc dithiolate compound by reacting a compound of formula 2 or formula 2a,Formula 2a, wherein R.1 to R4 are as described above in the section on Preparation of aromatic 1,2-dithiols. More specifically R.1 to R4 independently of each other, are selected from hydrogen, halogen, alkyl, aryl, or R1 with R3, R3 with R4 or R2 with R4 are forming together an aliphatic or aromatic ring, with a zinc carboxylate in an organic solvent.Brief Description1) Method for making a zinc dithiolate compound by reacting a compound of formula 2 or 2a,or u a a wherein R.1 to R.4 are, independently of each other, are selected from hydrogen, halogen, alkyl, aryl, or R.1 with R3, R3 with R4 or R2 with R4 are forming together an aliphatic or aromatic ring, with a zinc carboxylate in an organic solvent.2) Method of item 1, wherein R1 to R4 are, independently of each other, are selected from hydrogen, F, Cl, Br, I, Cl to C8 alkyl, or C5 to C14 aryl, optionally substituted with one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C8 alkyl, or C5 to C14 Aryl or combinations thereof.3) Method of item 1 or 2, wherein R1 with R3, R3 with R4 or R2 with R4, taken together, are forming an aromatic ring or an aromatic ring system exhibiting 5 to 14 carbon atoms.4) Method of any of items 1 to 3, wherein R1 and R2 are hydrogen, halogen, methyl, ethyl or phenyl, R3 and R4 are hydrogen, halogen, methyl, ethyl or phenyl or R3 und R4, taken together, are forming an aromatic ring or ring system with 6 to 10 carbon atoms.5) Method of any of items 1 to 4, wherein the zinc carboxylate is zinc acetate (Zn(OAc)2) or zinc pivalate.) Method of item 5, wherein the organic solvent is selected from the group consisting of alkohols, ethers, ketones, esters and combinations thereof. ) Method of item 5 or 6, wherein the organic solvent is selected from the group consisting of methanol, ethanol, isopropanol, tetrahydrofuran, acetone, ethyl acetate and combinations thereof. ) Method of any of items 1 to 7, wherein the reaction temperature is from 10°C to 40°C. ) Method of any of items 1 to 8, wherein the reaction time is from 2 hours to about 48 hours, in particular 4 to 36 hours or 6 to 24 hours. 0) A zinc dithiolate compound with a nitrogen content of less than 1 weight percent, obtainable by the method of any of items 1 to 9. 1) Method for making a ruthenium catalyst comprising the steps ofProviding a zinc dithiolate compound by a method of any of items 1 to 9;Reacting the zinc dithiolate compound with a ruthenium compound of formula 3Formula 3 wherein XI and X2 are, independently of each other, are anionic ligands and are the same or different; L and L2 are, independently of each other, neutral electron donor ligands and are the same or different; Ar is an aromatic group which may besubstituted and that can be bridged with L, if L is an alkoxy group;Obtaining a ruthenium catalyst of formula 4 or 4a, wherein the anionic ligands are a bridging dithiolate forming a ring via its sulfur atomswith R.1 to R4 being as defined in one or more of the preceding items.12) Method of item 11, wherein the zinc dithiolate compound is provided by a method of any of items 1 to 9 in situ in the reaction mixture with the ruthenium compound of formula 3 and the method is carried out as a one pot reaction.13) A zinc dithiolate compound of the formulawherein R1 to R4 are as defined in items 1 to 4, Y is nil or an electron donor ligand that is not a nitrogen compound and the zinc dithiolate compound is exhibiting a nitrogen content of less than 0.2 weight percent.14) A zinc dithiolate compound of item 13 of the structureDetailed DescriptionR1 to R4 independently of each other, are selected from hydrogen, F, Cl, Br, I, Cl to C8 alkyl, or C5 to C14 aryl, optionally substituted with one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C8 alkyl, or C5 to C14 aryl or combinations thereof.Alternatively, R1 with R3, R3 with R4 or R2 with R4, taken together, are forming an aromatic ring or an aromatic ring system exhibiting 5 to 14 carbon atoms; or R1 with R3, R3 with R4 or R2 with R4, taken together, are forming an aromatic ring or an aromatic ring system with 6 to 10 carbon atoms.In particular, R3 and R4, taken together, are forming an aromatic ring or ring system which can exhibit 5 to 14 carbon atoms or 6 to 10 carbon atoms, optionally substituted with one or more substituents selected from thegroup consisting of F, Cl, Br, I, Cl to C8 alkyl, or Cl to C4 alkyl, or C5 to C14 aryl, or C6 to CIO aryl or combinations thereof.In particular, R2 and R4, taken together, are forming an aromatic ring or ring system which can exhibit 5 to 14 carbon atoms or 6 to 10 carbon atoms, optionally substituted with one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C8 alkyl, or Cl to C4 alkyl, or C5 to C14 aryl, or C6 to CIO aryl or combinations thereof.In particular, Rl and R3, taken together, are forming an aromatic ring or ring system which can exhibit 5 to 14 carbon atoms or 6 to 10 carbon atoms, optionally substituted with one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C8 alkyl, or Cl to C4 alkyl, or C5 to C14 aryl, or C6 to CIO aryl or combinations thereof.In particular, R.1 and R3, taken together, are forming an aromatic ring or ring system which can exhibit 5 to 14 carbon atoms or 6 to 10 carbon atoms, optionally substituted with one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C8 alkyl, or Cl to C4 alkyl, or C5 to C14 aryl, or C6 to CIO aryl or combinations thereof; and additionally R2 and R4, taken together, are forming an aromatic ring or ring system which can exhibit 5 to 14 carbon atoms or 6 to 10 carbon atoms, optionally substituted with one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C8 alkyl, or Cl to C4 alkyl, or C5 to C14 aryl, or C6 to CIO aryl or combinations thereof.In this case, to avoid misunderstandings, the positions Rl, R2, R3 or R4 not part of an aromatic ring or ring system can be selected from hydrogen, halogen, alkyl, aryl and can in particular be selected from hydrogen, F, Cl, Br, I, Cl to C8 alkyl, or C5 to C14 aryl, optionally substituted with one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C8 alkyl, or C5 to C14 aryl or combinations thereof; or the positions Rl, R2, R3 or R4 not part of an aromatic ring or ring system can be selected from hydrogen, halogen, alkyl, aryl and can in particular be selected from hydrogen, F, Cl, Br, I, Cl to C4 alkyl, or C6 to CIO aryl, optionally substitutedwith one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C4 alkyl, or C6 to CIO aryl or combinations thereof.More specifically, Rl, R2, R3 and R4 are hydrogen, halogen (F, Cl, Br, I), methyl, ethyl n-propy, isopropyl, n-butyl, iso-butyl, tert. -butyl, or phenyl, naphthyl, fluorenyl, phenalenyl, anthracenyl, phenanthrenyl, which each can be unsubstituted or substituted with F, Cl, Br, I, Cl to C8 alkyl, such as, for example, methyl, ethyl n-propyl, isopropyl, n-butyl, iso-butyl, tert. -butyl, or combinations thereof.In a specific embodiment, Rl and R.2 are hydrogen, halogen, methyl, ethyl or phenyl, R3 and R4 are hydrogen, halogen, methyl, ethyl or phenyl or R3 und R4, taken together, are forming an aromatic ring or ring system with 6 to 10 carbon atoms, which are optionally substituted with one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C8 alkyl, or C5 to C14 aryl, C6 to CIO aryl or combinations thereof; orRl to R4 are selected from hydrogen, F, Cl, Br, I, Cl to C8 alkyl, or C5 to C14 aryl, optionally substituted with one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C8 alkyl, or C5 to C14 aryl or combinations thereof.In yet another specific embodiment, Rl is hydrogen or halogen, or together with R3 may form an optionally substituted polycyclic ring; R3 is hydrogen, or together with Rl may form an optionally substituted polycyclic ring; R4 is hydrogen or together with R2 may form an optionally substituted polycyclic ring; R2 is optionally substituted Ce-io aryl, halogen, or together with R4 may form an optionally substituted polycyclic ring.[6] In one embodiment, Rl is halogen; R3 is hydrogen; R4 is hydrogen or together with R2 forms an optionally substituted naphtyl or phenantryl ring; R2 is halogen or together with R4 forms an optionally substituted naphtyl or phenantryl ring.[7] In one more embodiment, Rl is hydrogen, methyl or Cl, or together with R3 forms 2-phenyl-naphthyl or phenanthryl; R3 is hydrogen, or together with Rl forms 2-phenyl-naphthyl or phenanthryl;R4 is hydrogen or together with R2 forms 2-phenyl-naphthyl, phenanthryl, or methylphenantryl; R2 is Cl, 3,5-dichloro-phenyl, phenyl, t-Bu or together with R4 forms 2-phenyl-naphthyl, phenanthryl or methylphenantryl.[8] In a further embodiment, Rl is Cl; R3 is hydrogen; R4 is hydrogen or together with R2 forms naphthyl or phenanthryl; R2 is hydrogen, Cl, or together with R4 forms naphtyl or phenanthryl.[9] In yet one more embodiment, Rl is hydrogen or Cl; R3 is hydrogen; R4 is hydrogen or together with R2 forms naphthyl or phenantryl; R2 is Cl, phenyl or together with R4 forms naphthyl or phenantryl.

[0010] In yet a further embodiment, Rl is hydrogen, methyl or Cl, or together with R3 forms 2-phenyl-naphthyl or phenanthryl; R3 is hydrogen, or together with Rl forms 2-phenyl-naphthyl or phenanthryl; R4 is hydrogen or together with R2 forms 2-phenyl-naphthyl, naphtyl, phenanthryl, or methylphenantryl; R2 is Cl, 3,5-dichloro-phenyl, phenyl, t-Bu or together with R4 forms 2-phenyl-naphthyl, naphtyl, phenanthryl or methylphenantryl; or Rl is hydrogen or Cl; R3 is hydrogen; R4 is hydrogen or together with R2 form an optionally substituted naphthyl or an optionally substituted phenanthryl ring; R2 is Cl, phenyl or together with R4 form an optionally substituted naphthyl or an optionally substituted phenanthryl ring.In another embodiment, Rl and R2 are hydrogen or halogen, in particular Cl or Br and R3 and R4 are hydrogen.In a further embodiment, Rl, R2, R3 and R4 are fluorine.In another embodiment, Rl, R2, R3 and R4 are so selected that the compound of formula 2 or formula 2a is selected from the group consisting ofThe zinc carboxylate can in principle be any soluble carboxylic acid salt of zinc, more specifically a zinc salt of a carboxylic acid exhibiting 1 to 8, in particular 1 to three carbon atoms, such as zinc formate, zinc acetate, zinc propionate, zinc isopropionate, zinc butyrate, zinc pivalate, zinc valerate, zinc caproate or zinc heptanoate, zinc octanoate, zinc 2-ethylhexanoate or zinc nonanoate, either water free or the hydrate. The use of zinc acetate (Zn(OAc)2) or zinc pivalate, either water free or as hydrate, has shown to be practical.Suitable organic solvents are polar solvents, such as polar aprotic or polar protic solvents. Usually, organic solvent are selected from the group consisting of alkohols, ethers, ketones, esters and combinations thereof. More specifically, the organic solvent is selected from the group consisting of methanol, ethanol, isopropanol, tetra hydrofuran, acetone, ethyl acetate and combinations thereof. Acetone has shown to be a practical solvent for the reaction since it dissolves the aromatic dithiol, its impurities and the zinc carboxylate, but the zinc dithiolate shows a poor solubility, so it can be easily precipitated and filtrated as well as washed. For washing, acetone and petrol ether have been found useful.The reaction can be carried out at temperatures of from 10°C to 50°C, in particular from 10°C to 40°C or from 15°C to 35°C or 20°C to 30°C. Generally, the reaction is quite robust and can be carried out at usual room temperatures so that normally no heating of the reation mixture is necessary.Reaction times vary from about 2 hours to about 48 hours, in particular 4 to 36 hours or 6 to 24 hours.Under the above conditions a zinc dithiolate compound with a nitrogen content of less than 1 weight percent can be obtained. Consequently, the Invention also relates to a zinc dithiolate compound with a nitrogen content of less than 1 weight percent, which is obtainable by the method above.The embodiments described hereabove apply both to the method for making a ruthenium catalyst according to the invention as well as the methodfor the preparation of the zinc dithiolate, but when appropriate may as well apply to the preparation of aromatic 1,2-dithiols described in the respective section above.Preparation of ruthenium catalystsThe Invention also relates to a method for making a ruthenium catalyst employing such a zinc dithiolate compound.The invention thus also relates to a method for making a ruthenium catalyst comprising the steps of- Providing a zinc dithiolate compound by a method as described above;- Reacting the zinc dithiolate compound with a ruthenium compound of formula 3Formula 3 wherein XI and X2 are, independently of each other, are anionic ligands and are the same or different; L and L2 are, independently of each other, neutral electron donor ligands and are the same or different; Ar is an aromatic group which may be substituted and that can be bridged with L;- Obtaining a ruthenium catalyst of formula 4 or 4a, wherein the anionic ligands are a bridging dithiolate forming a ring via its sulfur at- omswith R.1 to R4 being as defined above.Specifically, Ar can be an aromatic group bridged with L, wherein L is an alkoxy group being a substituent of Ar.For the compounds of formula 3, anionic ligands XI and X2, independently of each other, can be halogens selected from F, Cl, Br, I and combinations thereof, in particular Cl or Br. Usually XI and X2 are the same, in particular XI and X2 are the same and are Cl. Ar is aryl, in particular aryl with 5 to 14 carbon atoms, or aryl with 6 to 10 carbon atoms, in particular phenyl or naphthyl, which is optionally substituted, in particular substituted with halogen, nitro, aminocarbonyl, alkyl with 1 to 8 carbon atoms or alkyl with 1 to 4 carbon atoms, alkoxy with 1 to 8 carbon atoms or alkoxy with 1 to 4 carbon atoms, aryl with 5 to 14 car- bon atoms or aryl with 6 to 10 carbon atoms or combinations thereof. More specifically, aryl Ar can be substituted with one or more substituents selected from the group consisting of nitro, F, Cl, Br, I, Cl to C8 alkyl, Cl to C4 alkoxy, C6 to CIO aryl or combinations thereof. In particular, if Ar is substituted as described above, then Ar and L are bridged.In an embodiment, Ar is aryl with 5 to 14 carbon atoms, or aryl with 6 to 10 carbon atoms, in particular phenyl, which is substituted with halogen, nitro, or aminocarbonyl and if Ar and L are bridged.More specifically, aryl Ar is optionally substituted with one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C4 alkyl, Cl to C4 alkoxy, C6 to CIO aryl or combinations thereof.More specifically, Ar is a structure of formula 5, whereinFormula 5W is hydrogen, halogen selected from F, Cl, Br or I, particularly Cl, Br and I, or W is oxygen;R.19 is alkyl with 1 to 6 carbon atoms or phenyl, which is optionally substituted in the para position with nitro, Cl to C4 alkyl, Cl to C5 alkoxy, halogen selected from F, Cl, Br or I; or R.19 is methyl, ethyl, isopropyl or tert.- butyl, with the proviso that if W is hydrogen or halogen, then R19 is nil;R20, R21 and R23 are hydrogen, alkyl with 1 to 6 carbon atoms, aryl with 6 to 10 carbon atoms, or R20 is hydrogen, alkyl with 1 to 4 carbon atoms, aryl with 6 to 10 carbon atoms, or R19 is hydrogen, methyl, ethyl, isopropyl, phenyl or naphthyl.R22 is hydrogen, nitro, Cl, Br, I or trifluormethyl, or a group of the formula -NH(C=O)R30 or -S[(=O)2(-N(R30)2)], with R30 being selected from alkyl, cycloalkyl or perhaloalkyl with 1 to 6 carbon atoms, an aryl or perfluoroaryl with 5 to 10 carbon atoms optionally substituted with nitro, Cl, Br, I or F an aldehyde, nitrile, in particular R30 is selected form the group consisting ofmethyl, ethyl, trifluormethyl, cyclohexyl, pentafluorophenyl, p-nitrophenyl; orW is oxygen, R.19 is alkyl with 1 to 4 carbon atoms, R.20 is hydrogen or aryl with 6 to 10 carbon atoms, in particular phenyl, R.21 and R.23 are hydrogen, R.22 is nitro, Cl, Br, I or trifluormethyl; orW is oxygen, R.19 is isopropyl, R20 is hydrogen or phenyl, R21 and R23 are hydrogen, R22 is nitro or trifluormethyl; orW is oxygen, R19 is isopropyl, R20, R21 and R23 are hydrogen, R22 is nitro or trifluormethyl; orW is oxygen, R19 is alkyl with 1 to 4 carbon atoms, R20 is phenyl, R21, R22 and R23 are hydrogen; orW is oxygen, R19 is isopropyl, R20 is phenyl, R21, R22 and R23 are hydrogen.L and L2 are neutral electron donor ligands.In particular, L2 can be a phosphine or an NHC ligand.In another embodiment, L is a sulfoxide, such as DMSO (dimethyl sulfoxide), a phosphine, or L is a halogen or an alkoxy group -O-R19 with R19 being a Cl to C6 alkyl.In particular, L can be an alkoxy group -O-alkyl with alkyl having 1 to 6 carbon atoms, namely alkyl being selected from methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert. -butyl or -O-aryl with aryl having 5 to 10 carbon atoms, in particular phenyl, which can be optionally substituted with alkoxy as defined hereinabove, nitro, halogen such as F, Cl, Br, I, amino, alkylamino or dialkylamino with alkyl as defined hereinabove, more specifically with the substituent in the para-position to the oxygen atom.L can also be a sulfoxide carrying two alkyl substituents as defined above, or wherein the two alkyl are a saturated alkyl bridge so at to form a cyclicsulfoxide; suitable sulfoxides are, for example, dimethyl sulfoxide (DMSO) or the cyclic tetramethylensulfoxide. Other suitable embodiments for L is pyridine.In another suitable embodiment both L and L2 can be defined as phosphines having the structurewherein the groups R31, R32 and R33 are each independently for each occurrence selected from the group consisting of substituted or unsubstituted primary, secondary or tertiary alkyl or cycloalkyl with 1 to 20, in particular 1 to 10 carbon atoms; substituted or unsubstituted aryl or heteroaryl exhibiting 5 to 20, in particular 5 to 10 carbon atoms, or optionally two or more of the groups R31, R32 and R33 are fused to form a ring.More specifically, R31, R32, R33 may be substituted, for example once, twice, or three times, e.g. once, i.e. formally replacing one or more hydrogen atoms of the alkyl, cycloalkyl, aryl or heteroaryl group. Examples of substituents are halogen (e.g. fluoro, chloro, bromo and iodo), SFs, CF3, alkyl, aryl hydroxyl, nitro, amino, alkoxy, alkylthio, carboxy, cyano, thio, formyl, ester, acyl, thioacyl, amido, sulfonamido, carbamate and the like. Where the substituent is amino it may be amino, hydrocarbylamino or dihy- drocarbylamino, where the hydrocarbyl substituents on the nitrogen may be alkyl, aryl or heteroaryl such as substituted or unsubstituted Cl- C20 alkyl, aryl or heteroaryl or even C1-C10 alkyl, aryl or heteroaryl. Where the groups R31, R32, R33 are cycloalkyl they may be for example cyclohexyl or cyclopentyl. The cyclohexyl or cyclopentyl groups if present may be substituted as described hereinabove. As known to those skilled in the art, heteroaryl moieties are a subset of aryl moieties that comprise one or more heteroatoms, typically 0, N or S, in place of one or more carbon atoms and any hydrogen atoms attached thereto. Exemplary R31, R32, R33 arylsubstituents, for example, include phenyl or naphthyl that may be substituted. Exemplary R.31, R32, R33 heteroaryl substituents, for example, include pyridinyl, furanyl, pyrrolyl and pyrimidinyl. Further examples of heteroaromatic rings include pyridazinyl (in which 2 nitrogen atoms are adjacent in an aromatic 6-membered ring); pyrazinyl (in which two nitrogen atoms are 1,4-disposed in a 6-membered aromatic ring); pyrimidinyl (in which 2 nitrogen atoms are 1,3-disposed in a 6-membered aromatic ring); or 1,3,5- triazinyl (in which 3 nitrogen atoms are 1,3,5-disposed in a 6- membered aromatic ring).Examples of L or L2 as being phosphines are Triphenylphosphine, Tricyclohexyl phosphine, Tri(o-tolyl)phosphine, Tris(4-chlorphenyl)phosphine, Tris(3- chlorphenyl)phosphine, Tris-(4-fluorphenyl)-phosphine, Tris-(pentafluor- phenyl)-phosphine, Tris(4-trifluormethylphenyl)phosphine, Tris(trimethylsi- lyl)phosphine, Diphenyl(p-tolyl)phosphine, Tris-(4-methoxyphenyl)-phos- phine, Tri(p-tolyl)phosphine, Tris(2,4,6-trimethylphenyl)phosphine, Tris(3,5-dimethylphenyl)phosphine, Tri(l-adamantyl)phosphine, Tri(2-ada- mantyl)phosphine.In another embodiment L is a phosphite of the structurewherein R31, R.32 and R.33 are as defined above for the section relating to phosphines. Examples for phosphite include P(OMe)3, P(0Et)3, P(OPr)3 and P(OPh)3. Examples of group L as a phosphine include in particular PCy3 and PPhs - where Cy is cyclohexyl and Ph is phenyl. Examples of group L as a phosphite include P(OMe)3 P(0Et)3, P(OiPr)3 and P(OPh)3.Examples of combinations of L and L2 for the compounds of formula 3 or the catalysts of formula 4 described herein are where L2 is nucleophilic carbene, in particular N -heterocyclic carbene / phosphite, phosphine / phosphite and phosphine / phosphine.NHC ligands (N-heterocyclic carbenes) are well known in catalysis and a description thereof can be found, for example, in Frank Glorius, "N-Heterocy- clic Carbenes in Transition Metal Catalysis", Springer Verlag Heidelberg 2007, in particular the general definition on pages 10 and 11, figures 3 to 4.In one embodiment, L2 can be represented by the structure of Formula 6Formula (6) wherein :Rll, R.12, R.13 and R.14 are independently hydrogen, unsubstituted C1-C12 alkyl, substituted C1-C12 alkyl, unsubstituted C4-C12 cycloalkyl, substituted C4-C12 cycloalkyl, unsubstituted C5-C24 aryl, substituted C5-C24 aryl, unsubstituted C5-C24 heteroaryl, substituted C5-C24 heteroaryl, unsubstituted C6-C24 aralkyl, substituted C6-C24 aralkyl, unsubstituted C6-C24 heteroaralkyl or substituted C6-C24 heteroaralkyl;R.15 is methyl, ethyl, n-propyl, or phenyl; or together with R.16 can form a five to ten membered cycloalkyl or heterocyclic ring, with the carbon atom to which they are attached; andR.16 is methyl, ethyl, n-propyl, or phenyl; or together with R15 can form a five- to ten- membered cycloalkyl or heterocyclic ring, with the carbon atom to which they are attached;R17 is adamantyl, 2,4,6-trimethylphenyl, 2,6-di- / so-propylphenyl, 2- methyl-6-tert-butylphenyl, 2- / so-propyl-6-methylphenyl, 2- / so-propyl-phe- nyl, 2,6-di-ethylphenyl, 2-ethyl-6-methylphenyl or 2-methyl-phenyl.In another embodiment, L2 can be represented by the structure of Formula (7) or Formula (8)Formula (7) Formula (8) wherein:Rll, R.12, R.13 and R.14 are independently Ci-Ce alkyl or hydrogen;R.15 is 2,4,6-trimethylphenyl, 2,6-di- / so-propylphenyl, 2-methyl-6- tert-butylphenyl, 2- / so-propyl-6-methylphenyl, 2- / so-propyl-phenyl, 2,6-di- ethylphenyl, 2-ethyl-6-methylphenyl, 2,4,6-trifluorophenyl, 2,6-difluoro- phenyl, 3,5-di-tert-butylphenyl, 2,4-dimethylphenyl or 2-methyl-phenyl;R.16 is adamantyl, 2,4,6-trimethylphenyl, 2,6-di- / so-propylphenyl, 2- methyl-6-tert-butylphenyl, 2- / so-propyl-6-methylphenyl, 2- / so-propyl-phe- nyl, 2,6-di-ethylphenyl, 2-ethyl-6-methylphenyl, 2,4,6-trifluorophenyl, 2,6- difluorophenyl, 3, 5-di -tert- butyl phenyl, 2,4-dimethylphenyl or 2-methyl- phenyl.The zinc dithiolate in this method for making a ruthenium catalyst can be provided by a method as described above. In this context, the step of providing the zinc dithiolate compound may be carried out in situ in the same reactor and is used in the following steps in the method for making the ruthenium catalyst described above, which is carried out as a one pot reaction.In one embodiment the method for making the ruthenium catalyst described above as a one pot reaction is carried out wherein the step of providing the zinc dithiolate compound is carried out in the same reactor used in the following steps and once completed, the missing educts for making the ruthenium catalyst (such as e.g. the ruthenium compound of formula 3) are added lateron once the zinc dithiolate has been made.In another embodiment the method for making the ruthenium catalyst described above as a one-pot reaction is carried out wherein the step of providing the zinc dithiolate compound is carried out in the same reactor used inthe following steps and the educts for making the ruthenium catalyst (such as e.g. the ruthenium compound of formula 3) are added before the step of providing the zinc dithiolate compound is completed, so that all these steps are carried out in one reaction mixture. In this context, the step of providing the zinc dithiolate compound can be carried out in situ in the reaction mixture with the ruthenium compound of formula 3 and the method is carried out as a one pot reaction.The subject patent application also relates to a compound of the following formulawherein R1 to R4 are defined as above and Y is nil or a neutral electron donor ligand that is not a base, in particular not a nitrogen containing ligand and more specifically that is not an amine, but it may be a solvent, for example DMSO (dimethyl sulfoxide). Such zinc dithiolate compounds exhibit nitrogen contents of less than 0.2 weight percent.More specifically, the Invention also relates to compounds of the structuresexhibiting a nitrogen content of less than 0.2 weight percent determined by elemental analysis.Examples Example A: Preparation of 4,7-dichloro-l,3-benzodithiole-2-thioneAn aqueous solution of sodium trithiocarbonate (40%, 411.4g, 1.07 mol, 1.5 equivalents) was diluted with dimethyl formamide (2000 mL). The resulting solution was heated at reflux (125°C) for 2 hours with nitrogen bubbling through the solution. About 5% of the solvent was distilled off and the mixture allowed to cool to 100°C. At this temperature, 1,2,3,4-tetrachlorobezene (160g, 711.5 mmol, 1.0 equivalents) was added and the mixture was heated at 100°C during 24 hours before being allowed to cool to 22°C. Water (2000 mL) was added and the precipitate was filtered over a sinter. The filter residue was successively washed with water (3 times with 1000 mL) and finally dried under reduced pressure leading to 4,7-dichloro-l,3-benzodithiole-2-thione (71.2 g, purity (NMR): 95.8%, yield: 40%) as yellow solid.Example B: Preparation of 3,6-dichlorobenzene-l,2-dithiolA reactor was charged with sodium hydroxide (56-2 g, 1.41 mol, 5.0 equivalents) and absolute ethanol (1000 mL) under stirring. The reactor was evacuated and flushed with nitrogen for three times and nitrogen was bubbled through the mixture for 30 minutes. 4,7-dichloro-l,3-benzodithiole-2-thione (95.8%, 71.2 g, 281.2 mmol, 1 equivalent) was added under a stream of nitrogen. The mixture was heated under reflux for 1 hour. The mixture was allowed to cool to 22°C and washed under nitrogen atmosphere with dichloromethane (3 times with 1000 mL). After cooling to 5°C, concentrated hydrochloric acid (125 mL) was added in order to lower the pH to 1. The mixture then was evaporated under reduced pressure and the residue was taken up in tert.-butyl-methylether (2000 mL). The organic phase was washed with water (2 times with 1500 mL) and brine (500 mL), dried over sodium sulfate and evaporated under reduced pressure. The residue was recrystallized from methanol (300 mL) to obtain 3,6-dichlorobenzene-l,2-dithiol (44.6 g, purity (NMR): 98.4%, yield: 75%) as a pale orange solid.Example 1 : Preparation of Zinc dithiolate according to the inventionAn inert 10L reaction vessel is charged with acetone (3,5 L) and the dithiol (781 g, 2.61 mol, 70.70 wt%). Zinc acetate (609 g, 2.75 mol) and acetone (3 L) are added subsequently to the obtained solution. The suspension is stirred for 24 h at ambient temperature. The formation of an off-white solid is observed. The material is isolated by filtration and washed with aceton(3x1 L) and petrol ether (1 L). The isolated material is dried overnight at 25 °C in-vacuo. Zinc dithiolate was obtained as an off-white solid (713 g, 79.5% corrected yield).A broad spectrum of analysis was done to characterize the obtained materials and to draw a comparison between zinc dithiolate and the reported zinc dithiolate ethylene diamine complex.XH NMR. (600 MHz, DMSO-d6) : 6.80 (s, 2H, product), 3.38 (s, water), 2.08 (s, acetone).13C NMR. (600 MHz, DMSO-d6) : 206.96, 147.34, 133.22, 122.01, 31.16.Zn : 20.30 wt%, C: 29.1 wt%, H : 1.9 wt%, N : <0.2 wt%, S: 21.0 wt% DSC: endothermal effect at ca. 219 °CTGA: 14% weight loss (acetone and water)It can be concluded that isolation of zinc dithiolate proves to be a reproducible purification method to achieve excellent ligand quality without the need of toxic additives. The isolated material consists of approx. 80 wt% dithiolate, 10 wt% water and 10 wt% acetone. No other signal from impurities are detected by NMR.. The composition was determined by elemental analysis, qNMR. and TGA. We therefore propose the existence of a zinc dithiolate-hydrate- acetone complex. R.esidual solvent can be removed by drying at higher temperature in-vacuo. The downside of dried material is a significantly lower solubility in solvents other than DMSO.Comparative Example 2: Preparation of (3,6-dichlorobenzene-l,2-dithio- lato)(ethylenediamine)zinc(II)Under ambient atmosphere, a 250 mL round bottom flask equipped with a magnetic stir bar is charged with 3,6-dichlorobenzene-l,2-dithiol (2.00 g, 9.47 mmol), zinc acetate dihydrate (8.32 g, 37.9 mmol), ethylenediamine (3.80 mL, 56.8 mmol), and isopropanol (100 mL). The suspension is rapidlystirred for 24 h at room temperature. The resulting precipitate is isolated by filtration, washed with methanol (50 mL), hot chloroform (50 mL), then dried in vacuo overnight affording (3,6-dichlorobenzene-l,2-dithiolato) (ethylenediamine) zinc(II) as an off-white to light yellow solid (2.78 g, 87.9%).XH NMR. (400 MHz, DMSO-de) 5 ppm : 6.78 (br s, 2H), 4.06 (br s, 4H), 2.65 (br s, 4H).XH NMR. (600 MHz, DMSO-d6): 6.80 (br s, 2H), 4.06 (br s, 4H), 2.67 (br s, 4H).13C NMR. (600 MHz, DMSO-d6): 147.94, 132.23, 121.97, 40.90.Zn: 19.94 wt%, C: 28.9 wt%, H : 2.9 wt%, N : 8.4 wt%, S: 19.10 wt%DSC: endothermal effect at 344.44 °CExample 3: One-Pot Synthesis M2102 in AcetonM722 M2102An inert 10L reaction vessel is charged with acetone (4L) and dithiol (316.7 g, 1.5 mol, 1.3 eq.). Zinc acetate (329.3 g, 1.5 mol, 1.3 eq.), M722 (824.5 g, 1.16 mol) and 650 mL Acetone are added subsequently to the obtained solution. The suspension is heated to 55 °C for 5 h - during that time, the formation of a dark yellow solid is observed. The reaction mixture is brought to 20 °C before the desired product is isolated by filtration. The isolated material is washed with Acetone (2x1,4 L) and Methanol (5x1,25 L) and afterwards dried at 40 °C overnight in-vacuo. M2102 is obtained as a dark yellow, crystalline solid (668.6g, 73% yield).XH NMR. (600 MHz, CD2CI2) 5 ppm: 14.52 (s, 1H), 7.38 - 7.46 (m, 2H), 7.32 - 7.38 (m, 2H), 7.30 (br d, 1H), 7.19 (br d, 1H), 6.94 (d, 1H), 6.89 (br d, 1H), 6.77 - 6.83 (m, 2H), 6.73 (br d, 1H), 6.54 (d, 1 H), 4.88 - 5.05 (m, 1H), 4.29 - 4.42 (m, 1H), 4.10 - 4.23 (m, 1H), 4.00 (br d, 1H), 3.82 - 3.90 (m,1H), 3.78 - 3.97 (m, 3H), 3.09 (br s, 1H), 2.44 (br d, 1H), 1.90 (br d, 3H), 1.42 (br d, 3H), 1.36 (br d, 3H), 1.23 - 1.32 (m, 7H), 1.07 (br d, 3H),1.00 - 1.01 (m, 1H), 0.93 (br d, 2H), 0.90 - 0.97 (m, 1H), 0.53 (br d, 3H), 0.04 (br d, 3H). Ru: 11.94 wt%, Zn: 0.48 wt%, insoluble components: 0.74 wt%.Examples 4: Synthesis of M2102 in various solventsM722 M2102An inert 10 L reaction vessel is charged with THF (5 L) and Zinc dithiolate (1,15 kg, 1,88 mol, 1.1 eq.). M722 (1,22 kg, 1,71 mol) and THF (4,5 L) are added subsequently to the suspension. Afterwards, the reaction mixture is heated to 55 °C for 5 h. The formation of a dark yellow solid is observed. The solid is isolated by filtration and washed with Acetone (1.5 L), Methanol (5x1.2 L) and Petrol ether (1.5 L). The isolated material is dried overnight at 40 °C in-vacuo. M2102 is obtained as a dark yellow, micro-crystalline solid (1.24 kg, 85% yield).XH NMR (600 MHz, CD2CI2) 5 ppm: 14.52 (s, 1H), 7.38 - 7.46 (m, 2H), 7.32 - 7.38 (m, 2H), 7.30 (br d, 1H), 7.19 (br d, 1H), 6.94 (d, 1H), 6.89 (br d, 1H), 6.77 - 6.83 (m, 2H), 6.73 (br d, 1H), 6.54 (d, 1 H), 4.88 - 5.05 (m, 1H), 4.29 - 4.42 (m, 1H), 4.10 - 4.23 (m, 1H), 4.00 (br d, 1H), 3.82 - 3.90 (m, 1H), 3.78 - 3.97 (m, 3H), 3.09 (br s, 1H), 2.44 (br d, 1H), 1.90 (br d, 3H), 1.42 (br d, 3H), 1.36 (br d, 3H), 1.23 - 1.32 (m, 7H), 1.07 (br d, 3H),1.00 - 1.01 (m, 1H), 0.93 (br d, 2H), 0.90 - 0.97 (m, 1H), 0.53 (br d, 3H), 0.04 (br d, 3H). Ru: 11.53 wt%, Zn: 280 ppm, insoluble components: 0.17 wt%.The synthesis was repeated, employing Acetone, Methyl-tert. -butyl ether (MTBE), Ethyl acetate, 2-Methyl-THF or cyclopentylmethylether (CPME) as solvent, which all showed to be suitable solvents.Example 5: M3002 One-Pot ProcedureM206 M3002An inert 250 mL flask is charged with Methanol (40 mL) and Dithiole (1.3 g, 5.89 mmol, 1.1 eq.). Zinc acetate (1.3 g, 5.89 mmol, 1.1 eq.) is added and the reaction mixture is stirred at ambient temperature for 1 h. M206 (5 g, 5.36 mmol) and DMSO (2,1 g, 26.79 mmol, 5 eq.) are added subsequently to the suspension. The reaction mixture is stirred overnight at ambient temperature. Formation of a dark yellow solid was observed. The reaction mixture was brought to 0 °C before the desired product was isolated by filtration. The isolated material was washed with Methanol (3x10 mL) and afterwards dried at 40 °C overnight in-vacuo. M3002 is obtained as a dark green, crystalline solid (3.9 g, 84% yield). M3002 can be also prepared in high yield (>90%) and very good purity using isolated Zn dithiolate.Example 6: X-ray diffraction analysisSingle crystals (colourless plates) of suitable quality for X-ray diffraction analysis were grown by dissolving 3 mg of the zinc dithiolate obtained in Example 1 in the minimum amount of DMSO, layering with ethyl acetate (1 mL), and allowing the solution to stand at room temperature overnight.A structural determination by was carried out with these crystals. Figure 1 shows a structure refinement for the compound. The crystal data is listed below:Empirical formula Cio H14 CI2 O2 S4 ZnFormula weight 430.79Temperature 100.15 KWavelength 1.54184 ACrystal system, space group Monoclinic, P 1 21 / n 1 Unit cell dimensions a = 9.5563(2) A alpha = 90 deg. b = 8.0105(2) A beta = 90.546(2) deg. c = 21.1229(4) A gamma = 90 deg.Volume 1616.90(6) A3

Claims

Claims1. Method for making a ruthenium catalyst comprising the steps of- Providing an aromatic dithiol substituted on adjacent aromatic carbon atoms with thiol groups, wherein in a first step an aromatic compound substituted with two leaving groups on adjacent aromatic carbon atoms are reacted with alkali trithiocarbonate to obtain an aromatic benzodithiole-thione, which in a subsequent step is reacted / hydrolysed with a base;- providing a zinc dithiolate compound by reacting the aromatic dithiol with a zinc carboxylate in an organic solvent;- Reacting the zinc dithiolate compound with a ruthenium compound of formula 3Formula 3 wherein XI and X2 are, independently of each other, are anionic ligands and are the same or different; L and L2 are, independently of each other, neutral electron donor ligands and are the same or different; Ar is an aromatic group which may be substituted and that can be bridged with L, if L is an alkoxy group;- Obtaining a ruthenium catalyst of formula 4 or 4a, wherein the anionic ligands are a bridging dithiolate forming a ring via its sulfur at- omswherein R.1 to R4 are, independently of each other, are selected from hydrogen, halogen, alkyl, aryl, or R.1 with R3, R3 with R4 or R2 with R4 are forming together an aliphatic or aromatic ring.

2. Method of claim 1, wherein the aromatic dithiol is an aromatic dithiol of formula 2 or 2a,or u a awherein R.1 to R4 are, independently of each other, are selected from hydrogen, halogen, alkyl, aryl, or R.1 with R3, R3 with R4 or R2 with R4 are forming together an aliphatic or aromatic ring.

3. Method for the preparation of aromatic dithiols substituted on adjacent aromatic carbon atoms with thiol groups, wherein in a first step an aromatic compound substituted with two leaving groups on adjacent aromatic carbon atoms are reacted with alkali trithiocarbonate to obtain an aromatic benzodithiole-thione, which in a subsequent step is reacted / hydrolysed with a base.

4. Method of claim 1 or 3, wherein the leaving groups are selected from the group consisting of halogens or pseudohalogens, or are selected from the group consisting of Cl, Br, I, -OCN and combinations thereof.

5. Method of any of claims 1, 3 or 4, wherein the aromatic dithiols and the aromatic compounds are comprising an aromatic or heteroaromatic ring or ring system exhibiting 5 to 26 carbon atoms, or 6 to 22 carbon atoms, or 6 to 16, or 6 to 8 carbon atoms.

6. Method of any of claims 1 or 3 to 5, wherein the aromatic dithiols and the aromatic compound can be further substituted with halogen, more specifically with F, Cl, Br or I or alkyl groups having 1 to 5 carbon atoms.

7. Method of any of claims 1 or 3 to 6, wherein alkali is selected from lithium, sodium, potassium and combinations thereof, or wherein alkali is sodium or potassium.

8. Method of any of claims 1 or 3 to 6, wherein the aromatic dithiols are 1,2-dithiols or, if substituted, 2,3-dithiols.

9. Method of any of claims 1 or 3 to 8, wherein the aromatic compound is a dihalobenzene, a tetrahalobenzene, a pentahalobenzene or a hexa- halobenzene.

10. Method of any of claims 1 or 3 to 9, wherein the aromatic compound is a heteroaromatic compound.

11. Method of any of claims 1 or 3 to 9, wherein the aromatic compound is a quinoxaline, particular selected form the group consisting of 2,3- difluoroquinoxaline, 2,3-dichloroquinoxaline and 2,3-dibromoquinoxa- line.

12. Method of any of claims 1 or 3 to 9, wherein the aromatic compound is selected from the group consisting of hexahalobenzene, pentahaloben- zene and 1,2,3,4-tetrahalobenzene, in particular selected from the group consisting of hexafluorobenzene, hexachlorobenzene, hexabromobenzene, 2,3-dichloro-l,4,5,6-tetrafluorobenzene, 2,3-dibromo- 1,4,5,6-tetrafluorobenzene, pentafluorobenzene, 2,3-dichloro-l,4,5- trifluorobenzene, 2,3-dibromo-l,4,5-trifluorobenzene, pentachlorobenzene, pentabromobenzene, 1,2,3,4-tetrafluorobenzene, 2,3-dichloro- 1,4-difluorobenzene, 2,3-dibromo-l,4-difluorobenzene, 1,2,3,4-tetra- chlorobenzene, 1,2,3,4-tetrabromobenzene, 1,2,3,6-tetrafluoroben- zene, 2,3-dichloro-l,4-difluorobenzene, 2,3-dibromo-l,4-difluoroben- zene, 1,2,3,4-tetrachlorobenzene, 1,2,3,4-tetrabromobenzene.

13. Method of any of claims 1 or 3 to 12, wherein the alkali trithiocarbonate is employed in a molar excess over the aromatic compound, in particular in an excess of 1.1 to 2, in particular 1.2 to 1.9 or 1.3 to 1.5 equivalents.

14. Method of any of claims 1 or 3 to 13, wherein the reaction of alkali trithiocarbonate with the aromatic compound is carried out at a temperature of about 80°C to 120°C, in particular 90°C to 110°C or 95°C to 105°C.

15. Method of any of claims 1 or 3 to 14, wherein the reaction of alkali trithiocarbonate with the aromatic compound is carried out in a polar solvent, in particular water, dimethyl formamide or combinations thereof.

16. Method of any of claims 1 or 3 to 15, wherein the base is a solution of an alkaline hydroxide in an alcohol, in particular ethanol.

17. Method of any of claims 1 or 3 to 16, wherein the base is employed at an excess of 3 to 8, in particular 4 to 6 or about 5 equivalents versus the aromatic benzodithiole-thione.

18. Method of any of claims 1 or 3 to 17, wherein the reaction of the base with the aromatic benzodithiole-thione is carried out in an alcohol, in particular ethanol.

19. Method of any of claims 1 or 3 to 18, wherein the reaction of the base with the aromatic benzodithiole-thione is carried out at a temperature of from about 70°C to about 100°C.

20. Method for making a zinc dithiolate compound by reacting a compound of formula 2 or 2a,or u a a wherein R.1 to R4 are, independently of each other, are selected from hydrogen, halogen, alkyl, aryl, or R.1 with R3, R3 with R4 or R2 with R4 are forming together an aliphatic or aromatic ring, with a zinc carboxylate in an organic solvent.

21. Method of claim 1 or 20, wherein R1 to R4 are, independently of each other, are selected from hydrogen, F, Cl, Br, I, Cl to C8 alkyl, or C5 to C14 aryl, optionally substituted with one or more substituents selected from the group consisting of F, Cl, Br, I, Cl to C8 alkyl, or C5 to C14 Aryl or combinations thereof.

22. Method of claim 1 or 20 to 22, wherein R.1 with R3, R3 with R4 or R2 with R4, taken together, are forming an aromatic ring or an aromatic ring system exhibiting 5 to 14 carbon atoms.

23. Method of any of claims 1 or 20 to 22, wherein R1 and R2 are hydrogen, halogen, methyl, ethyl or phenyl, R3 and R4 are hydrogen, halogen, methyl, ethyl or phenyl or R3 und R4, taken together, are forming an aromatic ring or ring system with 6 to 10 carbon atoms.

24. Method of any of claims 1 or 20 to 23, wherein the zinc carboxylate is zinc acetate (Zn(OAc)2) or zinc pivalate.

25. Method of claim 24, wherein the organic solvent is selected from the group consisting of alkohols, ethers, ketones, esters and combinations thereof.

26. Method of claim 24 or 25, wherein the organic solvent is selected from the group consisting of methanol, ethanol, isopropanol, tetrahydrofuran, acetone, ethyl acetate and combinations thereof.

27. Method of any of claims 1 or 20 to 26, wherein the reaction temperature is from 10°C to 40°C.

28. Method of any of claims 1 or 20 to 27, wherein the reaction time is from 2 hours to about 48 hours, in particular 4 to 36 hours or 6 to 24 hours.

29. A zinc dithiolate compound with a nitrogen content of less than 1 weight percent, obtainable by the method of any of claims 1 to 9.

30. A zinc dithiolate compound, in particular according to claim 29, of the formulawherein R.1 to R.4 are as defined in claims 1 to 4, Y is nil or an electron donor ligand that is not a nitrogen compound and the zinc dithiolate compound is exhibiting a nitrogen content of less than 0.2 weight percent.

31. Method for making a ruthenium catalyst of claim 1, comprising the steps of- Providing an aromatic dithiol with a method for the preparation of aromatic dithiols of formula 2 or formula 2a,Formula 2,Formula 2a, wherein R.1 to R4 are, independently of each other, are selected from hydrogen, halogen, alkyl, aryl, or R.1 with R3, R3 with R4 or R2 with R4 are forming together an aliphatic or aromatic ring; comprising the steps of: a) Reaction of an alkali trithiocarbonate with an aromatic compound of formula 2b or 2cwherein Rl, R2, R3 and R4 as defined above and wherein substituent A is a leaving group and can be the same or different, and wherein A can be selected from the group consisting of Cl, Br, I, -OCN and combinations thereof, so as to obtain a benzodithiole-thione, and- Hydrolysis of the benzodithiole-thione obtained in step a) with an alkali hydroxide dissolved in an alcohol to obtain the aromatic dithiols of formula 2 or 2a.;- providing a zinc dithiolate compound by reacting the aromatic di- thiol with a zinc carboxylate such as zinc acetate or zinc pivalate in an organic solvent selected from the group of alkohols, ethers, ketones, esters and combinations thereof;- Reacting the zinc dithiolate compound with a ruthenium compound of formula 3Formula 3 wherein XI and X2 are, independently of each other, are anionic ligands and are the same or different; L and L2 are, independently of each other, neutral electron donor ligands and are the same or different; Ar is an aromatic group which may be substituted and that can be bridged with L, if L is an alkoxy group;- Obtaining a ruthenium catalyst of formula 4 or 4a, wherein the anionic ligands are a bridging dithiolate forming a ring via its sulfur atomsFormula 4Formula 4a wherein R.1 to R4 are, independently of each other, are selected from hydrogen, halogen, alkyl, aryl, or R.1 with R3, R3 with R4 or R2 with R4 are forming together an aliphatic or aromatic ring.

32. A zinc dithiolate compound of claim 30 of the structure

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