Unsymmetrical diphosphoramidite ligands for flexible hydroformylation reactions

Abstract

Disclosed is a compound having the structure of formula (I): The unsymmetrical diphosphoramidite compound is particularly useful as a ligand for a transition metal in a catalyst composition. The catalyst composition can advantageously be used in the hydroformylation of olefins to form aldehydes.

Description

UNSYMMETRICAL DIPHOSPHORAMIDITE LIGANDS FOR FLEXIBLE HYDROFORMYLATION REACTIONSCROSS-REFERENCE TO RELATED APPLICATIONThis application claims priority to U.S. Provisional Patent Application No. 63 / 683,079 filed on August 14, 2024; the entire content of which is hereby incorporated by reference.FIELD OF TECHNOLOGYThe invention generally relates to unsymmetrical diphosphoramidite compounds, catalyst compositions and catalyst solutions containing the compounds, and processes for preparing aldehydes using the catalyst solutions.BACKGROUNDThe hydroformylation reaction, also known as the oxo reaction, is used extensively in commercial processes for the preparation of aldehydes by reacting one mole of an olefin with one mole each of hydrogen and carbon monoxide. The most extensive use of the reaction is in the preparation of normal- and iso-butyraldehyde from propylene. The ratio of the amount of the normal-aldehyde product to the amount of the iso-aldehyde product is typically referred to as the normal to iso (N:I) or the normal to branched (N:B) ratio.In the case of propylene, both products (the normal- and the iso-butyraldehydes) are key building blocks for the synthesis of many chemical intermediates. For example, these aldehydes may be used to make solvents (such as alcohols, carboxylic acids, and esters), plasticizers, glycols, essential amino acids, flavorings, fragrances, polymers, insecticides, hydraulic fluids, and lubricants.The hydroformylation of higher α-olefins (such as 1-hexene, 1-octene, and 1-tetradecene) yield aldehyde products that are useful feedstocks for the preparation of detergent alcohols and plasticizer alcohols.A few Rh-based catalyst systems are employed industrially. However, in propylene hydroformylation, these systems provide higher normal-butyraldehyde selectivity. Higher iso-selectivity remains challenging. There is no known industrial process that provides greater than 50% yield of iso-butyraldehyde from propylene hydroformylation.Recently, ligand systems capable of producing 64.7% of iso-butyraldehyde at 90°C have been disclosed (see, e.g., US 10,144,751; US 10,183,961; US10,351,583; and Angew Chem. Int. Ed. 2019, 58, 2120). This is a significant advance. Unfortunately, the new ligand systems show thermal degradation at higher temperatures.Moreover, although different hydroformylation catalyst systems produce different nominal N:I ratios, it would be advantageous to be able to vary the N:I ratio during normal process operation without changing the catalyst system.Thus, despite the substantial progress that has been made in this area, there still exists a need for more thermally stable and more flexible hydroformylation catalyst systems.The present invention addresses this need as well as others, which will become apparent from the following description and the appended claims.SUMMARYThe invention is as set forth in the appended claims.Briefly, in one aspect, the present invention provides a compound having the structure of formula (I):(I)whereinR1 and R2 are each independently selected from H, and alkyl and cycloalkyl groups containing from 1 to 15 carbon atoms; andR3, R4, and R5 are each independently selected from H, F, CI, Br, and alkyl, aryl, alkoxy, trialkylsilyl, triarylsilyl, aryldialkylsilyl, diarylalkylsilyl, and cycloalkyl groups containing from 1 to 20 carbon atoms, wherein the silicon atom of the alkylsilyl or triarylsilyl is directly bonded to the position of substitution.In a second aspect, the invention provides a catalyst composition comprising:(a) a transition metal; and(b) a ligand having the structure of formula (I).In a third aspect, the invention provides a catalyst solution, which comprises the catalyst composition according to the invention and a solvent.In a fourth aspect, the invention provides a process for preparing an aldehyde. The process comprises the step of contacting an olefin with hydrogen and carbon monoxide in the catalyst solution according to the invention at conditions effective to form the aldehyde.A particularly preferred transition metal for use in the catalyst composition of the invention is rhodium.DETAILED DESCRIPTIONIt has been surprisingly discovered that certain unsymmetrical diphosphoramidite compounds in combination with a transition metal, particularly rhodium, can provide a flexible and thermally stable hydroformylation catalyst. For example, the inventive catalyst composition can provide different N:l product ratios simply by making modest changes in the process conditions as well as can operate at higher temperatures (e.g., ≥ 90°C) without thermal degradation.CompoundThus, in a first aspect, the present invention provides a compound having the structure of formula (I):(I)whereinR1 and R2 are each independently selected from H, and alkyl and cycloalkyl groups containing from 1 to 15 carbon atoms; andR3, R4, and R5 are each independently selected from H, F, CI, Br, and alkyl, aryl, alkoxy, trialkylsilyl, triarylsilyl, aryldialkylsilyl, diarylalkylsilyl, and cycloalkyl groupscontaining from 1 to 20 carbon atoms, wherein the silicon atom of the alkylsilyl or triarylsilyl is directly bonded to the position of substitution.The alkyl groups represented by R₁ and R2 may be the same or different, separate or combined, and contain from 1 to 15 carbon atoms. In various embodiments, the alkyl groups may contain from 1 to 10 carbon atoms, from 1 to 8 carbon atoms, from 1 to 6 carbon atoms, or from 1 to 4 carbon atoms.Examples of the alkyl groups that R₁ and R2 can individually represent include methyl, ethyl, butyl, pentyl, hexyl, 2-ethylhexyl, octyl, decyl, dodecyl, octadecyl, and various isomers thereof.In various embodiments, R₁ and R2 are each methyl or linear alkyl containing up to 15 carbon atoms.In various embodiments, R₁ and R2 are each methyl.The cycloalkyl groups represented by R₁ and R2 may be the same or different, and contain from 3 to 15 carbon atoms. In various embodiments, the cycloalkyl groups may contain from 3 to 12 carbon atoms, from 3 to 10 carbon atoms, from 3 to 8 carbon atoms, from 3 to 7 carbon atoms, from 3 to 6 carbon atoms, or from 3 to 5 carbon atoms.Examples of the cycloalkyl groups that R₁ and R2 can individually represent include cyclopentyl, cyclohexyl, and cycloheptyl.The alkyl groups represented by R3, R4, and R5 may be the same or different, separate or combined, and contain from 1 to 20 carbon atoms. In various embodiments, the alkyl groups may contain from 1 to 15 carbon atoms, from 1 to 10 carbon atoms, from 1 to 8 carbon atoms, from 1 to 6 carbon atoms, or from 1 to 4 carbon atoms.Examples of the alkyl groups that R3, R4, and R5 can individually represent include methyl, ethyl, butyl, pentyl, hexyl, 2-ethylhexyl, octyl, decyl, dodecyl, octadecyl, and various isomers thereof.The cycloalkyl groups represented by R3, R4, and R5 may be the same or different, and contain from 3 to 20 carbon atoms. In various embodiments, thecycloalkyl groups may contain from 3 to 18 carbon atoms, from 3 to 15 carbon atoms, from 3 to 12 carbon atoms, from 3 to 10 carbon atoms, from 3 to 8 carbon atoms, from 3 to 7 carbon atoms, from 3 to 6 carbon atoms, or from 3 to 5 carbon atoms.Examples of the cycloalkyl groups that R3, R4, and R5 can individually represent include cyclopentyl, cyclohexyl, and cycloheptyl.Examples of the aryl groups that R3, R4, and R5 can individually represent include phenyl, naphthyl, anthracenyl, and substituted derivatives thereof.Examples of the alkoxy groups that R3, R4, and R5 can individually represent include methoxy, ethoxy, butoxy, pentoxy, hexoxy, 2-ethylhexoxy, octoxy, decoxy, dodecoxy, and octadecoxy.Examples of the trialkylsilyl groups that R3, R4, and R5 can individually represent include trimethylsilyl, triethylsilyl, tripropylsilyl, tributylsilyl, and isomers thereof.Examples of the triarylsilyl groups that R3, R4, and R5 can individually represent include triphenylsilyl, tri(methoxyphenyl)silyl, tri(ethoxyphenly)silyl, and isomers thereof.Examples of the aryldialkylsilyl groups that R3, R4, and R5 can individually represent include dimethylphenylsilyl, diethylphenylsilyl, dipropylphenylsilyl, dibutylphenylsilyl, and isomers thereof.Examples of the diarylalkylsilyl groups that R3, R4, and R5 can individually represent include diphenylmethylsilyl, diphenylethylsilyl, diphenylpropylsilyl, and isomers thereof.In various embodiments, R3, R4, and R5 are each independently selected from H, F, CI, Br, trimethylsilyl, and alkyl, alkoxy, and cycloalkyl groups containing from 1 to 20 carbon atoms, wherein the silicon atom of the trimethylsilyl is directly bonded to the position of substitution.In various embodiments, R3, R4, and R5 are each independently selected from F, CI, Br, methyl, tert-butyl, (2-phenylpropan-2-yl), adamantyl, trimethylsilyl, and methoxy.In various embodiments, at least one R3 is tert-butyl.In various embodiments, at least one R4 is methoxy.In various embodiments, at least one R5 is hydrogen.In various embodiments, the compound of formula (I) has the following structure:This compound may be referred to as 1-(4,8-di-tert-butyl-2,10-dimethoxydibenzo[d,f][1,3,2]dioxaphosphepin-6-yl)-1,2-dimethyl-2-(2,4,8,10-tetra-tert-butyl-12-methyl-12H-dibenzo[d,g][1,3,2]dioxaphosphocin-6-yl)hydrazine.The compounds of formula (I) may be prepared using the procedures described in the Examples section hereinbelow.Catalyst CompositionIn a second aspect, the present invention provides a catalyst composition comprising (a) a transition metal and (b) a ligand comprising the compound having the structure of formula (1) as described herein.Among the transition metals, Group VIIIB metals (such as Fe, Co, Ni, Ru, Rh, Pd, Pt, etc.) are particularly useful. A preferred transition metal is rhodium.The transition metal may be provided in the form of various metal compounds, such as carboxylate salts of the transition metal. For example, rhodium compounds that may be used as a source of rhodium for the active catalyst include rhodium (II) orrhodium (III) salts of carboxylic acids. Examples of such salts include di-rhodium tetraacetate dihydrate, rhodium(II) acetate, rhodium(II) isobutyrate, rhodium(II) 2-ethylhexanoate, rhodium(II) benzoate, and rhodium(II) octanoate. Also, rhodium carbonyl species, such as Rh4(CO)12, Rh6 (CO)16, and rhodium(I) acetylacetonate dicarbonyl, may be suitable rhodium feeds. Additionally, rhodium organophosphine complexes, such as tris(triphenylphosphine) rhodium carbonyl hydride, may be used when the phosphine moieties of the complex feed are easily displaced by the diphosphoramidite ligands of the present invention. Less desirable rhodium sources are rhodium salts of strong mineral acids, such as chlorides, bromides, nitrates, sulfates, phosphates, and the like.In various embodiments, the catalyst composition may be formed in situ from a transition metal compound (such as [Rh(acac)(CO)2]) and a ligand. It is appreciated by those skilled in the art that a wide variety of Rh species may form the same active catalyst when contacted with ligand, hydrogen, and carbon monoxide; thus, there is no limitation on the choice of the Rh pre-catalyst.The molar ratio of the diphosphoramidite ligand to the transition metal can vary over a wide range, e.g., from 1:1 to 300:1. For rhodium-containing catalyst systems, the molar ratio of the diphosphoramidite ligand to rhodium can range from 1:1 to 200:1 or from 1:1 to 75:1.In various embodiments, the molar ratio of the ligand to the transition metal is at least 1:1, at least 2:1, at least 3:1, at least 4:1, at least 5:1, at least 6:1, at least 7:1, at least 8:1, at least 9:1, or at least 10:1.In various embodiments, the catalyst composition of the invention can provide a normal-aldehyde product to iso-aldehyde product (N:I) ratio ranging from 0.80:1 to 1.47:1. These hydroformylation N:I product ratios can be obtained by changing the CO / H2 partial pressure, the reaction temperature, or both. For example, the CO / H2 partial pressure may be changed from 1 to 20 bars absolute (about 14.5 to 290 psia), or from 5 to 15 bars absolute (about 72.5 to 218 psia). Likewise, the reaction temperaturemay be changed from 20 to 200°C, from 50 to 135°C, from 75 to 125°C, or from 80 to 110°C.In various embodiments, the catalyst composition of the invention is thermally stable. For example, the catalyst composition can be effective for converting an olefin to an aldehyde in the presence of hydrogen and carbon monoxide for at least 5 hours at 50°C, for at least 1 hour at 80°C, for at least 1 hour at 95°C, or for at least 1 hour at 110°C.Catalyst SolutionIn a third aspect, the invention provides a catalyst solution. The catalyst solution comprises the catalyst composition according to the invention and a solvent.The catalyst compositions and solutions of the invention may be used in a wide variety of transition metal-catalyzed processes, such as hydroformylation. The catalyst compositions / solutions comprising rhodium as the transition metal are especially useful for the hydroformylation of olefins to produce aldehydes.The solvent in the catalyst solution may be selected from a wide variety of compounds (or mixture of compounds). The main criteria for the solvent are that (1) it is a liquid under reaction conditions, (2) it can solubilize the catalyst and the reactants under reaction conditions, and (3) it is not a catalyst poison. General examples of solvents include alkanes, cycloalkanes, alkenes, cycloalkenes, carbocyclic aromatic compounds, alcohols, esters, ketones, acetals, ethers, and water. Specific examples of solvents include alkane and cycloalkanes, such as dodecane, decalin, n-octane, iso-octane, cyclohexane, cyclooctane, cyclododecane, and methylcyclohexane; aromatic hydrocarbons, such as benzene, toluene, xylene isomers, tetralin, and cumene; alkyl-substituted aromatic compounds, such as the isomers of diisopropylbenzene, triisopropylbenzene, and tert-butylbenzene; alkenes and cycloalkenes, such as 1,7-octadiene, dicyclopentadiene, 1,5-cyclooctadiene, octene-1, octene-2, 4-vinylcyclohexene, cyclohexene, 1,5,9-cyclododecatriene, and 1-pentene; crude hydrocarbon mixtures, such as naphtha, mineral oils, and kerosene; high-boiling esters,such as 2,2,4-trimethyl-1,3-pentanediol diisobutyrate; ethers, such as di-n-butyl ether; and ester-alcohols, such as 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate.The aldehyde product of a hydroformylation reaction may also be used as the solvent. In various embodiments, the solvent includes the higher boiling by-products that are formed during the hydroformylation reaction, or during subsequent separation or purification steps. Suitable solvents for the production of volatile aldehydes (e.g., propionaldehyde and butyraldehydes) include those that are sufficiently high boiling to remain, for the most part, in a gas-sparged reactor. Suitable solvents for the production of less volatile or non-volatile aldehydes include 1-methyl-2-pyrrolidinone; dimethyl-formamide; perfluorinated solvents, such as perfluoro-kerosene; sulfolane; water; and high-boiling hydrocarbon liquids. Mixtures of solvents may also be used. Non-hydroxylic compounds, in general, and hydrocarbons and esters, in particular, may also advantageously be used as the hydroformylation solvent, since their use can minimize decomposition of the ligand.The concentration of the transition metal (e.g., rhodium) and ligand in the solvent or reaction mixture is not critical. As mentioned above, a molar ratio of ligand to transition metal of at least 1:1 in the reaction mixture is typically sufficient (e.g., from 1:1 to 300:1, from 1:1 to 200:1, from 1:1 to 100:1, or from 1:1 to 10:1).The absolute concentration of transition metal in the reaction mixture or solution may vary from 1 mg / L up to 5000 mg / L or more. In various embodiments, the concentration of transition metal in the reaction solution is in the range of 20 to 300 mg / L. Concentrations lower than these ranges may not yield acceptable reaction rates with most olefin reactants and / or would require temperatures that are so high as to be detrimental to catalyst stability. Higher rhodium concentrations are less attractive because of the high cost of rhodium.No special or unusual techniques are required to prepare the catalyst compositions or solutions of the present invention. Nonetheless, to obtain a catalyst with high activity, the transition metal and the ligand may be mixed in an inert atmosphere, e.g., nitrogen, argon, and the like. The desired quantities of a suitabletransition metal compound and ligand may be charged to the reactor in a suitable solvent and thoroughly mixed. Typical mixing conditions include 10 to 150°C and 1 to 150 bars absolute for 1 minute to 12 hours.The catalyst compositions or solutions may be activated before use in hydroformylation. The activation can be accomplished by contacting the catalyst compositions or solutions with CO and hydrogen before introduction of the olefin. The contacting step may be carried out at hydroformylation reaction conditions or close to it, for, e.g., 1 minute to 12 hours.Hydroformylation ProcessIn a fourth aspect, the invention provides a process for preparing an aldehyde. The process comprises the step of contacting an olefin with hydrogen and carbon monoxide in the catalyst solution according to the invention at conditions effective to form the aldehyde.The process may be practiced with a wide range of olefin feeds, such as aliphatic (including ethylenically-unsaturated, low molecular weight polymers), alicyclic, aromatic, and heterocyclic mono-, di-, and tri-olefins containing 2 to 40 carbon atoms.Examples of aliphatic, mono-olefins include straight- and branched-chain, unsubstituted and substituted, a-olefins containing 2 to 20 carbon atoms. Examples of the groups that may be present on the substituted a-olefins include hydroxyl; alkoxy including ethers and acetals; alkanoyloxy, such as acetoxy; amino including substituted amino; carboxyl; alkoxycarbonyl; carboxamido; keto; cyano; and the like.Specific examples of a-olefins include ethylene, propylene, 1-butene, 1-octene, vinyl acetate, vinyl isobutyl ether, allyl alcohol, and 3-acetoxy-1-propene.Aliphatic, di-olefins may also be used in the inventive process, particularly those containing up to 20 carbon atoms.Cyclic olefins that may be used in the hydroformylation process include cycloalkenes (e.g., cyclohexene, 1,5-cyclooctadiene, and cyclodecatriene), vinyl-substituted cycloalkanes, heterocyclics, and aromatic compounds. Examples of suchcyclic olefins include 4-vinylcyclohexene, 1,4-cyclohexadiene, 4-cyclohexene-carboxylic acid, methyl 4-cyclohexene-carboxylic acid, 1,4-cyclooctadiene, and 1,5,9-cyclododecatriene.In various embodiments, the olefin reactants include a-olefins with 2 to 10 carbon atoms, especially propylene.In various embodiments, the olefin comprises propylene, and the aldehyde comprises normal- and iso-butyaldehyde.In various embodiments, the hydroformylation process provides a normal-butyraldehyde to iso-butyraldehyde (N:I) ratio ranging from 0.80:1 to 1.47:1.Mixtures of olefins can also be used in the practice of this invention. The mixtures may be of the same carbon number, such as mixtures of octene isomers, or may represent refinery distillation cuts, which can contain a mixture of olefins with a range of carbon numbers.The amount of olefin present in the reaction mixture is not critical. For example, relatively high-boiling olefins (such as 1-octene) may function both as the olefin reactant and the process solvent. In the hydroformylation of a gaseous olefin feedstock (such as propylene), the olefin partial pressures in the reactor typically can range from 0.07 to 35 bars absolute (about 1 to 508 psia). In practice, the rate of reaction can be favored by higher concentrations of olefin in the reactor. In the hydroformylation of propylene, for example, the partial pressure of propylene can be at least 1.4 bars (about 20 psia), e.g., from 1.4 to 10 bars absolute (about 20 to 145 psia). In the case of ethylene hydroformylation, the partial pressure of ethylene in the reactor can be at least 0.14 bars absolute (about 2 psia).The hydrogen to carbon monoxide molar ratio introduced into the reactor may vary considerably, ranging from 10:1 to 1:10, and the sum of the absolute partial pressures of hydrogen and carbon monoxide may range from 0.3 to 36 bars absolute. The molar ratio of hydrogen to carbon monoxide can be varied widely within these partial pressure ranges.In various embodiments, the partial pressures of hydrogen and carbon monoxide in the reactor are in the range of 1.4 to 13.8 bars absolute (about 20 to 200 psia) for each gas.Synthesis gas (also known as syngas) may be a source of the hydrogen and carbon monoxide. The molar ratio of hydrogen to carbon monoxide and the partial pressure of each in the syngas can be readily changed by adding either hydrogen or carbon monoxide to the syngas stream.The reaction conditions are not critical for the operation of the hydroformylation process. Conventional hydroformylation conditions can be used. The process may be carried out at temperatures in the range of 20 to 200°C, of 50 to 135°C, of 75 to 125°C, or of 80 to 110°C. Higher reaction temperatures can increase the rate of catalyst decomposition, while lower reaction temperatures may result in relatively slow reaction rates. The total reaction pressure may range from ambient or atmospheric to 70 bars absolute (about 1000 psig), or from 8 to 40 bars absolute (about 100 to 600 psig).While not critical for the operation of the hydroformylation process, the reaction conditions can be varied to effect a change in the N:l product ratio. As noted above, the N:I product ratio can be varied from 0.80:1 to 1.47:1, or more, by changing the CO / H2 partial pressure, the reaction temperature, or both. For example, the CO / H2 partial pressure may be changed from 1 to 20 bars absolute (about 14.5 to 290 psia), or from 5 to 15 bars absolute (about 72.5 to 218 psia). Likewise, the reaction temperature may be changed from 20 to 200°C, from 50 to 135°C, from 75 to 125°C, or from 80 to 110°C.Any of the known hydroformylation reactor designs or configurations may be used in carrying out the process of the present invention. In various embodiments, a gas-sparged, vapor take-off reactor can be used. In this mode of operation, the catalyst composition can be dissolved in a high-boiling organic solvent and may not leave the reaction zone with the aldehyde product, which is taken overhead by the unreacted gases. The overhead gases can then be chilled in a vapor / liquid separator to condense the aldehyde product, and the gases can be recycled to the reactor. The liquid productcan be let down to atmospheric pressure for separation and purification by conventional techniques.The process may also be practiced in a batchwise manner by contacting the olefin, hydrogen, and carbon monoxide with the catalyst composition or solution in an autoclave as illustrated in the working examples.A reactor design where catalyst and feedstock are pumped into a reactor and allowed to overflow with product aldehyde (i.e., a liquid overflow reactor design) is also suitable. For example, high-boiling aldehyde products, such as nonyl aldehydes, may be prepared in a continuous manner with the aldehyde product being removed from the reaction zone as a liquid in combination with the catalyst. The aldehyde product may be separated from the catalyst by conventional means, such as by distillation or extraction, and the catalyst may be recycled back to the reactor. Water-soluble aldehyde products can be separated from the catalyst by extraction techniques.A trickle-bed reactor design also is suitable for this process. It will be apparent to those skilled in the art that other reactor schemes may be used with this invention.General ProvisionsTo remove any doubt, the present invention includes and expressly contemplates and discloses any and all combinations of embodiments, features, characteristics, parameters, and / or ranges mentioned herein. That is, the subject matter of the present invention may be defined by any combination of embodiments, features, characteristics, parameters, and / or ranges mentioned herein.It is contemplated that any ingredient, component, or step that is not specifically named or identified as part of the present invention may be explicitly excluded.Any process / method, apparatus, compound, composition, embodiment, or component of the present invention may be modified by the transitional terms "comprising," "consisting essentially of," or "consisting of," or variations of those terms.As used herein, the indefinite articles “a” and “an” mean one or more, unless the context clearly suggests otherwise. Similarly, the singular form of nouns includes their plural form, and vice versa, unless the context clearly suggests otherwise.As used herein, the term "and / or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself, or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and / or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.While attempts have been made to be precise, the numerical values and ranges described herein should be considered to be approximations (even when not qualified by the term "about"). These values and ranges may vary from their stated numbers depending upon the desired properties sought to be obtained by the present invention as well as the variations resulting from the standard deviation found in the measuring techniques. Moreover, the ranges described herein are intended and specifically contemplated to include all sub-ranges and values within the stated ranges. For example, a range of 50 to 100 is intended to describe and include all values within the range including sub-ranges such as 60 to 90, 70 to 80, etc.Any two numbers of the same property or parameter reported in the working examples may define a range. Those numbers may be rounded off to the nearest thousandth, hundredth, tenth, whole number, ten, hundred, or thousand to define the range.The content of all documents cited herein, including patents as well as non-patent literature, is hereby incorporated by reference in their entirety. To the extent that any incorporated subject matter contradicts or conflicts with any disclosure herein, the disclosure herein shall take precedence over the incorporated content.This invention can be further illustrated by the following examples, although it will be understood that these examples are included merely for purposes of illustration and are not intended to limit the scope of the invention.EXAMPLESGeneral ProceduresAll reactions were performed under an inert atmosphere of nitrogen or argon using standard Schlenk techniques, unless otherwise stated. All glassware used were flame-dried. Dry and degassed solvents were obtained from a solvent still or SPS solvent purification system.Commercially purchased anhydrous solvents were degassed before use by the freeze-pump-thaw method or purging with inert gas. Triethylamine was degassed before use. All chemicals, unless specified, were purchased commercially and used as received. CO / H2 (1:1) and propylene / CO / H2 (10 / 45 / 45%) were obtained pre-mixed from BOC.Analytical MethodsNuclear magnetic resonance (NMR) spectra were recorded on a Bruker Avance 300, 400, or 500 MHz instrument. Proton chemical shifts were referenced to internal residual solvent protons. Carbon chemical shifts were referenced to the carbon signal of the deuterated solvent. Signal multiplicities were given as s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet), or a combination of the above, br (broad), vbr (very broad), ap (apparent). Where appropriate, coupling constants (J) were quoted in Hz and were reported to the nearest 0.1 Hz. All spectra were recorded at r.t. (unless otherwise stated), and the solvent for a particular spectrum is given in parentheses. NMR of compounds containing phosphorus were recorded under an inert atmosphere in dry and degassed solvent unless otherwise stated.Gas chromatography was performed on an Agilent Technologies 7820A machine.Mass spectrometry was performed on a Micromass GCT spectrometer, Micromass LCT spectrometer, Waters ZQ4000, Thermofisher LTQ Orbitrap XL, or Finnigan MAT 900 XLT instruments.Flash column chromatography was performed using Merck Geduran Si 60 (40-63 µm) silica gel.Thin layer chromatographic (TLC) analyses were carried out using POLYGRAM SIL G / UV254 or POLYGRAM ALOX N / UV254 plastic plates. TLC plates were visualized using a UV visualizer or stained using potassium permanganate dip followed by gentle heating.Example 1Preparation of Ligand (A): 1-(4,8-di-tert-butyl-2,10-dimethoxydibenzo[d,f][1,3,2]dioxaphosphepin-6-yl)-1,2-dimethyl-2-(2,4,8,10-tetra-tert-butyl-12-methyl-12H-dibenzo[d,g][1,3,2]dioxaphosphocin-6-yl)hydrazineThe structural formula of Ligand (A) is shown below.Ligand (A)To a stirred solution of 3,3'-di-tert-butyl-5,5'-dimethoxy-[1,1'-biphenyl]-2,2'-diol (0.226 g, 0.630 mmol) in THF (4 mL) at -78°C was added in one portion a solution of 1,2-bis(dichlorophosphaneyl)-1,2-dimethylhydrazine (0.165 g, 0.630 mmol) in THF (2 mL). This was followed by Et3N (0.220 mL, 1.575 mmol) addition via syringe. The reaction mixture was then allowed to warm to -50°C while stirring for 1 h. The solution was taken out of the cold bath and stirred for a further 60 minutes at room temperature. The reaction mixture was cooled down again to -78°C and, using a syringe, a solution ofthe second diol, 6,6'-(ethane-1,1-diyl)bis(2,4-di-tert-butylphenol) (0.276 g, 0.630 mmol) in THF (3 mL) was added in one portion, followed by Et3N (0.220 mL, 1.575 mmol). The reaction mixture was then allowed to warm up slowly for 1 h and then stirred at room temperature for another 60 minutes. The reaction mixture was filtered under an argon atmosphere and concentrated in vacuo.The resulting solid was purified under air by flash chromatography on silica gel (15:1 Hexane:Et2O) affording the desired product (0.289 g, 0.316 mmol, 50%) as an off-white solid (isomeric mixture in a 1:1.2 ratio as determined by 31P{H} NMR).The off-white solid product was analyzed by NMR spectroscopy and high-resolution mass spectroscopy (HRMS). The results are shown below.1H NMR (C6D6, 500 MHz) 8 7.44-7.35 (2 x 4H, br m, ArCH), 7.20 (2 x 2H, app br d, J = 10.1 Hz, ArCH), 6.74 (2 x 2H, app br d, J = 10.9 Hz, ArCH), 5.48 (1H, vbr s, CH), 4.17 (1H, vbr s, CH), 3.36 (2 x 9H, br s, 2 x OCH3, NCH3), 2.82 (2 x 3H, s, NCH3), 2.10-1.26 (2 x 57H, br m, CH3-CH, 6 x C(CH3)3).13C NMR (C6D6, 126 MHz) δ 155.84-128.20 (2 x 16 x ArC), 127.99 (2 x 2 x ArCH), 122.58 (2 x 2 x ArCH), 114.64 (2 x 2 x ArCH), 112.86 (2 x 2 x ArCH), 54.75 (2 x 2 x OCH3), 35.38 (2 x 2 x C(CH3)3), 35.25 (2 x 2 x C(CH3)3), 34.25 (2 x 2 x C(CH3)3), 31.33-30.72 (2 x 2 NCH3, 2 x 6 C(CH3)3).31P{H} NMR (C6D6, 202 MHz) δ 147.6 (brs), 144.4 (brs), 139.3 (brs), 131.5 (br s).HRMS (ES+) [MH]+ m / z: 913.5391 found; C54H79O6N2P2 requires 913.5408.Example 2Propylene HydroformylationPropylene hydroformylation reactions were conducted using [Rh(acac)(CO)2], as the Rh source, and Ligand (A).The hydroformylation reactions of propene were performed in a Parr 4590 Micro Reactor fitted with a gas entrainment stirrer, which contained holes to give better gas dispersion throughout the reaction mixture. The vessel had a volume capacity of0.1 L, an overhead stirrer with gas entrainment head (set to 1000 r.p.m.), temperature controls, a pressure gauge, and the ability to be connected to a gas cylinder.The catalyst was preformed from [Rh(acac)(CO)2] (5.12 x 10-3 mmol) and the ligand (10.24 x 10-3 mmol (L:Rh 2:1)) by stirring under 20 bar of CO / H2 at the activation temperature reported in Table 1 for 15 minutes in DOTP (90%) (18 mL + 2 mL toluene).In particular, the ligand (10.24 μmol (Rh:L 1:2)) was added to a Schlenk tube, which was then purged with nitrogen (or argon). The internal standard 1-methylnaphthalene (0.1 mL) was then added. The mixture was dissolved in a stock solution of [Rh(acac)(CO)2] in toluene (2 mg / mL, 0.65 mL, 5.12 µmol of [Rh(acac)(CO)2]), followed by the addition of toluene (1.35 mL) and dioctyl terephthalate (DOTP) (18 mL). The solution was transferred via syringe to the pressure vessel (which had been purged with CO / H2) through the injection port. A CO / H2 mixture (1:1) (20 bar) was added and the heating system was set to the desired temperature while stirring. Once the desired temperature was reached, the reaction mixture was stirred for the required time to fully activate the catalyst. Then, the pressure was slowly released and repressurized with a mixture of propene / CO / H2 in a 1:4.5:4.5 ratio. The reaction was then run for the time specified in Table 1. After this time, stirring was stopped and the reaction mixture was cooled by placing the vessel in a basin of cold water. The pressure was released, and the crude sample was analysed immediately by GC (using toluene as eluent).The GC method was run on a HP-5 Agilent column with a length of 30 m, a diameter of 0.250 mm, and a film thickness of 0.25 µm. The oven was initially held at 25°C for 6 minutes, and then increased to 60°C at a rate of 10°C per minute. The ramp was then increased to 20°C per minute until the temperature reached 300°C. The products could be identified with the following retention times: iso-butyraldehyde (1.02 min); n-butyraldehyde (1.15 min); and 1-methylnaphthalene (13.50 min). The GC was calibrated for propene hydroformylation using (1-methylnaphthalene) as an internal standard. Both the linear (n-butyraldehyde) and branched (iso-butyraldehyde) products were calibrated against the internal standard and against each other.From the GC results, the amount of both products from each reaction was calculated to give the iso-selectivity (which is the percentage of iso-butyraldehyde to total butyraldehyde products), the n-to-iso ratio, and the productivity of the catalyst based on the turnover number (TON). TON refers to the relationship between the metal catalyst loading and the amount of product formed using the equation: TON = (iso- + n-aldehyde) (mmol) / [Rh(acac)(CO)2] (mmol).The results of the hydroformylation of propylene for Ligand (A) are reported in Table 1.TABLE 1Effect of Reaction Conditions on Selectivity of Propylene Hydroformylation Using Ligand (A)Run Ligand L:R Molar Ratio Solvent Solvent Pressure (bar) Total partial Pressure (bar) Catalyst Activation Temp. (°C) Reemion Temp. (°C) Reaction Time (hr) Catalyst TON Selectivity iso (%) n:iso Ratio1 A 2:1 DOTP (90%) 20 0 105 80 1 205 41.0 1.45:12 A 10:1 DOTP (90%) 20 0 105 80 1 163 42.6 1.35:13 A 2:1 DOTP (90%) 20 10 105 80 1 192 40.5 1.47:14 A 2:1 DOTP (90%) 20 D 105 95 1 690 43.1 1.31:15 A 2:1 DOTP (90%) 20 10 105 95 1 469 50.8 0.97:18 A 2:1 DOTP (90%) 20 0 105 110 1197 49.2 1.03:17 A 10:1 DOTP (90%) 20 0 105 110 1 788 49.4. 1.02:18 A 2:1 DOTP (90%) 20 10 105 110 1 651 51.0 0.96:19 A 2:1 DOTP (90%) 20 15 105 110 1 290 55.6 0.80:1As seen from Table 1, for a given reaction temperature (particularly at 95°C and 110°C), the iso-selectivity can increase by decreasing the CO / H2 partial pressure (via increasing the N2 partial pressure while maintaining the same total pressure) (compare Run 4 with Run 5, and Run 6 with Runs 8 and 9). Similarly, for a given CO / H2 partial pressure (i.e., N2 partial pressure), the iso-selectivity can increase by increasing the reaction temperature (compare Run 1 with Runs 4 and 6, Run 3 with Runs 5 and 8, and Run 2 with Run 7). Additionally, the highest iso-selectivity was achieved when the reaction temperature was increased and the CO / H2 partial pressure was decreased (Run 9).The invention has been described in detail with particular reference to specific embodiments thereof, but it will be understood that variations and modifications can be made within the spirit and scope of the invention.

Claims

1. A compound having the structure of formula (l):(I)whereinR1 and R2 are each independently selected from H, and alkyl and cycloalkyl groups containing from 1 to 15 carbon atoms; andR3, R4, and R5 are each independently selected from H, F, CI, Br, and alkyl, aryl, alkoxy, trialkylsilyl, triarylsilyl, aryldialkylsilyl, diarylalkylsilyl, and cycloalkyl groups containing from 1 to 20 carbon atoms, wherein the silicon atom of the alkylsilyl or triarylsilyl is directly bonded to the position of substitution.

2. The compound of claim 1, wherein R₁ and R2 are each methyl or linear alkyl containing 15 carbon atoms or less.

3. The compound of any one of claims 1-2, wherein R₁ and R2 are each methyl.

4. The compound of any one of claims 1-3, wherein R3, R4, and R5 are each independently selected from H, F, CI, Br, trimethylsilyl, and alkyl, alkoxy, and cycloalkyl groups containing from 1 to 20 carbon atoms, andwherein the silicon atom of the trimethylsilyl is directly bonded to the position of substitution.

5. The compound of any one of claims 1-4, wherein R3, R4, and R5 are each independently selected from F, Cl, Br, methyl, tert-butyl, (2-phenylpropan-2-yl), adamantyl, trimethylsilyl, and methoxy.

6. The compound of any one of claims 1-5, wherein at least one R3 is tert-butyl.

7. The compound of any one of claims 1-6, wherein at least one R4 is methoxy.

8. The compound of any one of claims 1-7, wherein at least one R5 is hydrogen.

9. The compound of any one of claims 1-8, which has the structure:

10. A catalyst composition comprising:(a) a transition metal; and(b) a ligand comprising the compound of any one of claims 1-9.

11. The catalyst composition of claim 10, wherein the transition metal is a Group VIIIB metal.

12. The catalyst composition of any one of claims 10-11, wherein the transition metal comprises rhodium.

13. The catalyst composition of claim 12, wherein the rhodium is sourced from di-rhodium tetraacetate dihydrate, rhodium(II) acetate, rhodium(II) isobutyrate, rhodium(II) 2-ethylhexanoate, rhodium(II) benzoate, rhodium(II) octanoate, Rh4(CO)12, Rh6(CO)16, rhodium(I) acetylacetonate dicarbonyl, tris(triphenylphosphine) rhodium carbonyl hydride, or combinations thereof.

14. The catalyst composition of any one of claims 10-13, which provides a normal-aldehyde product to iso-aldehyde product (N:I) ratio ranging from 0.80:1 to 1.47:1.

15. The catalyst composition of any one of claims 10-14, which is effective for converting an olefin to an aldehyde in the presence of hydrogen and carbon monoxide for at least 5 hours at 50°C.

16. The catalyst composition of any one of claims 10-15, wherein the molar ratio of the ligand to the transition metal is at least 1:1, at least 2:1, at least 3:1, at least 4:1, at least 5:1, at least 6:1, at least 7:1, at least 8:1, at least 9:1, or at least 10:1.

17. A catalyst solution comprising:(a) the catalyst composition of any one of claims 10-16; and(b) a solvent.

18. The catalyst solution of claim 17, wherein the solvent comprises dodecane, decalin, n-octane, iso-octane, cyclohexane, cyclooctane, cyclododecane, methylcyclohexane, 1,7-octadiene, dicyclopentadiene, 1,5-cyclooctadiene, octene-1, octene-2, 4-vinylcyclohexene, cyclohexene, 1,5,9-cyclododecatriene, 1-pentene, benzene, toluene, xylene isomers, tetralin, cumene, diisopropylbenzene, triisopropylbenzene, tert-butylbenzene, naphtha, mineral oils, kerosene, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, bis(2-ethylhexyl) terephthalate, octafluorotolulene, 1-methyl-2-pyrrolidinone, dimethyl-formamide, perfluoro-kerosene, sulfolane, higher boiling by-products formed during a hydroformylation reaction, water, or combinations thereof.

19. A process for preparing an aldehyde, the process comprising contacting an olefin with hydrogen and carbon monoxide in the catalyst solution of any one of claims 17-18, at conditions effective to form an aldehyde.

20. The process of claim 19, wherein the olefin comprises ethylene, propylene, 1-butene, 1-octene, vinyl acetate, vinyl isobutyl ether, allyl alcohol, 3-acetoxy-1-propene, cyclohexene, 1,5-cyclooctadiene, cyclodecatriene, 4-vinylcyclohexene, 1,3-cyclohexadiene, 4-cyclohexene-carboxylic acid, methyl 4-cyclohexene-carboxylic acid, 1,4-cyclooctadiene, or 1,5,9-cyclododecatriene.

21. The process of claim 20, wherein the olefin comprises propylene, and the aldehyde comprises normal- and iso-butyraldehyde.

22. The process of claim 21, which provides a normal-butyraldehyde to iso-butyraldehyde (N:I) ratio ranging from 0.80:1 to 1.47:1.

23. The process of any one of claims 19-22, wherein the contacting step is carried out at a temperature of 50 to 135°C, of 75 to 125°C, or of 80 to 110°C.

24. The process of any one of claims 19-23, wherein the contacting step is carried out at a total pressure of 8 to 40 bars absolute.

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