Synthesis method and application of diboron alkene with stable phosphine ligand

Abstract

The invention provides a synthesis method of a diboron alkene structure with a stable phosphine ligand and CO2 activation application of the diboron alkene structure. The method is suitable for the fields of synthesis of novel small organic molecules and activation and conversion of CO2. A B = B structure is successfully synthesized through a linear synthesis method of boryl body synthesis-Lewis alkali coordination stabilization-reduction dehalogenation to alkene, two ends of a B = B unit are connected with different ligands, the electronic structure of diborane is effectively influenced by utilizing the electronic effect and steric effect differences of the ligands, the stability of the diborane and the reaction activity of the diborane and CO2 are differentially adjusted, and the stability of the diborane and the reaction activity of the diborane and CO2 are greatly improved. The design, synthesis and application of the compounds are expanded.

Description

Technical Field

[0001] The present invention belongs to novel organic small molecule synthesis and CO 2 The field of activation conversion, specifically relates to a method of synthesizing a diborene structure stabilized by a phosphine ligand and its CO using sodium naphthalene reduction 2 Activation application. Background Art

[0002] CO 2 The global environmental problems caused by excessive emissions have attracted great attention from the international community. Activation and conversion of CO2 into resources is an effective solution. At present, transition metal compounds can effectively activate CO2. 2 However, its high price, poor stability, and high heavy metal residues seriously restrict its practical application. 2 The precise activation and conversion of CO is a scientific frontier issue in this field. 2 There is an OCO delocalized π bond in the molecule, and the C=O bond has a very high bond energy, which makes its chemical properties very stable and difficult to be transformed and utilized. Based on the electronegativity difference between C atoms and O atoms, a method for activating CO by attacking the C / O center with nucleophilic / electrophilic reagents was developed. 2 Among them, efficient and stable organoboron reagents have become the key research direction in this field.

[0003] Diborene (containing B=B double bond) is a very active organic boron reagent, which can easily react with chemical bonds such as CH, C=O, C≡C, and can be used as an activated CO 2 It is an efficient reaction reagent with high research value and application prospects. However, at present, diborene compounds still have many problems such as poor environmental stability, single structure, and uncontrollable reaction. By connecting different substituents / ligands at both ends of the B=B unit and taking advantage of their electronic effect and steric effect differences, the electronic structure of diborene can be effectively influenced, and the stability of diborene and its reaction with CO can be differentially adjusted. 2 The reactivity of these compounds can be improved to expand the design, synthesis and application of these compounds.

[0004] Changing the ligands and substituents connected to the two ends of asymmetric diborene can adjust its steric hindrance and electronic structure, thereby regulating CO 2 The activation reaction process and product selectivity. However, the general synthesis still has problems such as harsh reaction conditions and unstable products. The linear synthesis method based on "borane base synthesis-Lewis base coordination stabilization-reduction dehalogenation to olefins" uses different reducing agents to react with halogenated diboranes stabilized by ligands such as nitrogen heterocyclic carbene (NHC) and alkyl-amino carbene (cAAC) to prepare a series of diborenes, and Lewis bases as ligands can effectively stabilize the B=B unit.

[0005] The present invention prepares a novel diborene structure stabilized by phosphine ligands based on the linear synthesis method of "borane base synthesis-Lewis base coordination stabilization-reduction dehalogenation to olefins", and applies it to CO 2 Activation aspect. Summary of the invention

[0006] The purpose of the present invention is to provide a diborene structure stabilized by a phosphine ligand and to apply the structure to CO 2 Activation areas.

[0007] The present invention is implemented by the following technical scheme: On the one hand, the present invention provides a method for synthesizing ligand-stabilized tetrabromodiborane and tetrabromodiborane phosphine ligand adduct by preliminarily using a phosphine ligand and a tetrabromodiborane bis(dimethyl sulfide) adduct for ligand exchange, and reducing the tetrabromodiborane phosphine ligand adduct to a phosphine ligand-stabilized diborene by a reducing agent, sodium naphthalene, comprising the following steps:

[0008] (1) Using a multi-step synthesis method, dimethyl sulfide, boron tribromide and tetrakis(dimethylamino)diboron are heated and stirred at 80°C to 100°C in a hexane solvent for 10 to 12 hours, and the solvent is vacuum-evacuated to synthesize tetrabromodiborane bis(dimethyl sulfide) adduct;

[0009] (2) The above tetrabromodiborane bis(dimethyl sulfide) adduct and the phosphine ligand are uniformly stirred in an organic solvent at room temperature to exchange ligands, and the solvent is vacuum-evacuated to obtain tetrabromodiborane stabilized with the phosphine ligand, which is expressed as B 2 Br 4 L 2 ;

[0010] (3) The obtained phosphine ligand-stabilized tetrabromodiborane is dissolved in a tetrahydrofuran organic solution, and a sodium naphthalene solution is added under low temperature conditions and stirred for 1 to 2 hours. The solvent is then vacuum-evacuated to obtain a phosphine ligand-stabilized diborene structure, which is expressed as B 2 Br 2 L 2 (L:PCy 3 , PCy 2 Ph).

[0011] In a preferred technical embodiment, the molar ratio of dimethyl sulfide, boron tribromide and tetrakis(dimethylamino)diboron in step (2) is 2-2.5:2:1.

[0012] In a preferred technical embodiment, the phosphine ligand is one of tricyclohexylphosphine and phenyldicyclohexylphosphine.

[0013] In a preferred technical embodiment, the molar ratio of the phosphine ligand to the tetrabromodiborane bis(dimethyl sulfide) adduct is 2 to 2.5:1.

[0014] In a preferred technical embodiment, the concentration of the sodium naphthalene tetrahydrofuran solution is 0.343 mol / L.

[0015] In a preferred technical embodiment, the molar ratio of tetrabromodiborane stabilized by the phosphine ligand to sodium naphthalene is 1:2 to 2.5.

[0016] The diborene structure stabilized by the phosphine ligand of the present invention is used for CO 2 activation.

[0017] The invention provides a method for using CO 2 Activated B 2 Br 2 L 2 (L:PCy 3 , PCy 2 Ph) structure, its preparation and application have the following advantages:

[0018] (1) The present invention utilizes a ligand exchange method to synthesize tetrabromodiborane stabilized with a phosphine ligand. Different ligands can be selectively connected to both ends of the B=B unit to thereby regulate its physicochemical properties, and the process is safe and controllable.

[0019] (2) The present invention reduces bromoborane to a borene structure by reducing and dehalogenating to olefins, thereby increasing its stability and CO 2 Reactivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0021] Figure 1 The synthetic route of the phosphine ligand-stabilized diborene and the activated CO 2 Reaction mechanism diagram;

[0022] Figure 2 The NMR spectrum of diborene stabilized by the phosphine ligand of the present invention;

[0023] Figure 3 The infrared spectrum of diborene stabilized by the phosphine ligand of the present invention;

[0024] Figure 4 is a high-resolution mass spectrum of diborene stabilized by the phosphine ligand of the present invention;

[0025] Figure 5 This is the nuclear magnetic spectrum of the activated product of the present invention;

[0026] Figure 6 is the infrared spectrum of the activated product of the present invention;

[0027] Figure 7 This is a high-resolution mass spectrum of the activation product of the present invention;

[0028] Figure 8 This is the Gibbs free energy diagram of the activation process of the present invention. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to these embodiments.

[0030] Example 1: Tricyclohexylphosphine-stabilized diborene B 2 Br 2 (PCy 3 ) 2 Preparation

[0031] This example is the preparation of tricyclohexylphosphine-stabilized diborene. Figure 1 As shown, the specific preparation method is: dimethyl sulfide, boron tribromide and tetrakis(dimethylamino)diboron are heated and stirred at 80°C to 100°C for 10 to 12 hours by a multi-step synthesis method, the solvent is vacuum-evacuated to synthesize tetrabromodiborane bis(dimethyl sulfide) adduct, and then the tetrabromodiborane bis(dimethyl sulfide) adduct is uniformly stirred with tricyclohexylphosphine in an organic solvent at room temperature for ligand exchange, and the solvent is vacuum-evacuated to synthesize tetrabromodiborane with tricyclohexylphosphine ligand, which is expressed as B 2 Br 4 (PCy 3 ) 2 The synthesized tricyclohexylphosphine-stabilized tetrabromodiborane was added to a 0.343 mol / L sodium naphthalene tetrahydrofuran solution, stirred at -78°C for 2-3 hours, and the solvent was vacuum-dried to obtain tricyclohexylphosphine-stabilized diborene, the expression of which is B 2 Br 2 (PCy 3 ) 2 .

[0032] Example 2: Phenyldicyclohexylphosphine-stabilized diborene B 2 Br 2 (PCy 2 Ph) 2 Preparation

[0033] This example is the preparation of diborene stabilized by phenyldicyclohexylphosphine. Figure 1As shown, the specific preparation method is: dimethyl sulfide, boron tribromide and tetrakis(dimethylamino)diboron are heated and stirred at 80°C to 100°C for 10 to 12 hours by a multi-step synthesis method, the solvent is vacuum-evacuated to synthesize tetrabromodiborane bis(dimethyl sulfide) adduct, and then the tetrabromodiborane bis(dimethyl sulfide) adduct is uniformly stirred with a phosphine ligand in an organic solvent at room temperature for ligand exchange, and the solvent is vacuum-evacuated to synthesize phenyldicyclohexylphosphine-stabilized tetrabromodiborane, which is expressed as B 2 Br 4 (PCy 2 Ph) 2 The synthesized tetrabromodiborane stabilized by phenyldicyclohexylphosphine was added to a 0.343 mol / L sodium naphthalene tetrahydrofuran solution, stirred at -78°C for 2-3 hours, and the solvent was vacuum-dried to obtain diborene stabilized by phenyldicyclohexylphosphine, the expression of which is B 2 Br 2 (PCy 2 Ph) 2 .

[0034] Figure 2 The phosphine ligand-stabilized diborene B prepared in Examples 1 and 2 2 Br 4 L 2 (L:PCy 3 , PCy 2 Ph). H NMR spectrum a: 1 H NMR (400 MHz, C 6 D 6 ): δ = 3.6 (s, 1H, P-CH), 3.38-3.32 (d, 2H, Cy-H), 2.03-1.21 (m, 8H, Cy-H), b: 1 H NMR (400MHz, C6D6): δ = 7.96-7.91 (m, H, Ph-H), 7.78-7.75 (m, 2H, Ph-H), 7.67-7.62 (m, 2H, Ph-H), 3.75 (s, 4H, P-CH), 3.51-3.45 (d, 2H, Cy-H), 1.95-1.21 (m, 16H, Cy-H), the integration of the high field position 1:2:8 proves the existence of cyclohexyl, and the peak integration of the aromatic region 1:2:2 proves the existence of benzene ring. 2 Br 2 (PCy 3 ) 2 With B 2 Br 2 (PCy 2 Ph) 2 11B NMR are 20.97 and 19.74 ppm respectively. It can be seen that as the electron donating ability of the ligand increases, the peak position moves to the high field. 31 P NMR were 9.82 and 9.01 ppm respectively, which were consistent with the boron spectrum.

[0035] Figure 3 The phosphine ligand-stabilized diborene B prepared in Examples 1 and 2 2 Br 4 L 2 (L:PCy 3 , PCy 2 Ph) Fourier transform infrared spectrum (FT-IR). -1 The characteristic absorption peaks at correspond to the stretching vibrations of the B=B bond and the BP bond, respectively, which proves the successful ligand exchange and the successful synthesis of the B=B double bond.

[0036] Figure 4 The phosphine ligand-stabilized diborene B prepared in Examples 1 and 2 2 Br 4 L 2 (L:PCy 3 , PCy 2 The high-resolution mass spectrum of Ph. The charge-to-mass ratios of 741.3726 and 729.2337 were obtained in the positive ion mode of the ESI ion source, which were consistent with the calculated results. This further proved the successful synthesis of diborene stabilized by phosphine ligands.

[0037] Figure 5 The phosphine ligand-stabilized diborene B prepared in Examples 1 and 2 2 Br 4 L 2 (L:PCy 3 , PCy 2 Ph) NMR spectrum of the activated product. a: 1 H NMR (400 MHz, C 6 D 6 ): δ = 2.65 (s, 1H, P-CH), 2.26-2.23 (d, 2H, Cy-H), 1.88-1.21 (m, 8H, Cy-H), b: 1 H NMR (400MHz, C6D6): δ=7.36-7.31 (m, H, Ph-H), 7.16-7.14 (m, 2H, Ph-H), 7.08-7.05 ( m, 2H, Ph-H), 3.84 (s, 2H, P-CH), 3.41-3.32 (d, 4H, Cy-H), 1.89-1.58 (m, 16H, Cy-H). e: 13 C{ 1H} NMR (400MHz, C6D6): δ = 31.77 (d, Cy-C), 31.38 (d, Cy-C), 27.73 (d, Cy-C), 26.61 (s, Cy-C), 21.06 (s, OC), f: 13 C{ 1 H}NMR (400MHz, C6D6): δ=134.74(d, Ph-C), 128.95(d, Ph-C), 125.32(s, Ph-C), 30.24(d, Cy-C), 28.93(d, Cy-C), 28.93(d, Cy-C), 26.40(s, Cy-C), 21.06(s, OC). It can be seen from the carbon nuclear magnetic spectrum that the product has a carbon atom inserted at 21.06ppm. 11 The BNMR values ​​were -18.66 and -21.40 ppm respectively, which were close to the peak positions of substances with similar structures.

[0038] Figure 6 The phosphine ligand-stabilized diborene B prepared in Examples 1 and 2 2 Br 4 L 2 (L:PCy 3 , PCy 2 Ph) activated product Fourier transform infrared spectrum (FT-IR). -1 The characteristic absorption peaks at the positions correspond to the C=O bond and the BO bond, respectively, proving the successful cleavage of CO 2 And insert C=O bond and BO bond.

[0039] Figure 7 The phosphine ligand-stabilized diborene B prepared in Examples 1 and 2 2 Br 4 L 2 (L:PCy 3 , PCy 2 The high-resolution mass spectra of the activated products of Ph were obtained in the positive ion mode of the ESI ion source, with charge-to-mass ratios of 785.3186 and 773.2243, respectively, proving that an equal mole of CO was inserted during the activation process. 2 molecular.

[0040] Figure 8 The phosphine ligand-stabilized diborene B prepared in Examples 1 and 2 2 Br 4 L 2 (L:PCy 3 , PCy 2 Ph) Gibbs free energy diagram of the activation process. The calculated reaction mechanism is basically consistent with the experimental results. 2When reacting with diborene, the B=B double bond and the C=O bond undergo a 2+2 cycloaddition reaction to form a COBB four-membered ring structure. This structure is not stable and will continue to crack and add upon heating to transform into a four-membered ring stable structure of CBOB. It has also been proven that LHB=O and LHB=CO are stable in the reaction between diborene and CO 2 Intermediate role in the reaction.

Claims

1. A synthesis of diborene stabilized by a phosphine ligand, characterized in that: The specific steps include: (1) Using a multi-step synthesis method, dimethyl sulfide, boron tribromide and tetrakis(dimethylamino)diboron are heated and stirred at 80°C to 100°C in a hexane solvent for 10 to 12 hours, and the solvent is vacuum-evacuated to synthesize tetrabromodiborane bis(dimethyl sulfide) adduct; (2) the above tetrabromodiborane bis(dimethyl sulfide) adduct and the phosphine ligand are uniformly stirred in an organic solvent at room temperature to perform ligand exchange, and the solvent is vacuum-evacuated to obtain tetrabromodiborane stabilized with the phosphine ligand, the expression being B2Br4L2; (3) The obtained phosphine ligand-stabilized tetrabromodiborane is dissolved in a tetrahydrofuran organic solution, and a sodium naphthalene solution is added under low temperature conditions and stirred for 1 to 2 hours. The solvent is then vacuum-evacuated to obtain a phosphine ligand-stabilized diborene, expressed as B2Br2L2(L:Pcy3,Pcy2Ph).

2. The preparation method according to claim 1, characterized in that: The molar ratio of dimethyl sulfide, boron tribromide and tetrakis(dimethylamino)diboron in step (1) is 2-2.5:2:

1.

3. The preparation method according to claim 1, characterized in that: The phosphine ligand in step (2) is one of tricyclohexylphosphine and phenyldicyclohexylphosphine.

4. The preparation method according to claim 1, characterized in that: The molar ratio of the phosphine ligand to the tetrabromodiborane bis(dimethyl sulfide) adduct in step (2) is 2 to 2.5:

1.

5. The preparation method according to claim 1, characterized in that: The concentration of the sodium naphthalene tetrahydrofuran solution described in step (3) is 0.343 mol / L.

6. The preparation method according to claim 1, characterized in that: The molar ratio of tetrabromodiborane stabilized by the phosphine ligand to sodium naphthalene in step (3) is 1:2 to 2.

5.

7. Use of diborene stabilized by any one of the phosphine ligands in claims 1 to 6 in CO2 activation.

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