769921-35-9

Downstream Products

• 203000-59-3 Rh(P(CH₃)(C(CH₃)3)CH₂)2(CH₂(CH)6)⁽¹⁺⁾*BF₄^(1-)=[Rh(P(CH₃)(C(CH₃)3)CH₂)2(CH₂(CH)6)][BF₄] 

Relevant academic research and scientific papers

Mechanism of asymmetric hydrogenation catalyzed by a rhodium complex of (S,S)-1,2-bis(tert-butylmethylphosphino)ethane. Dihydride mechanism of asymmetric hydrogenation

The mechanism of asymmetric hydrogenation catalyzed by a new effective catalyst, viz., a rhodium complex of (S,S)-1,2-bis(tert-butylmethylphosphino)ethane (BisP*), has been studied by multinuclear NMR. Hydrogenation of the precatalyst [Rh(BisP*)(nbd)]BF4 (8) at -20 °C in deuteriomethanol affords solvate complex [Rh(BisP*)(CD3OD)2]BF4 (9), which is, in turn, hydrogenated at -90 °C producing equilibrium amounts (20% at -95 °C) of [RhH2(BisP*)(CD3OD)2] (10) - the first observable dihydride of a Rh(I) complex with a diphosphine ligand. Dihydride 10 is in equilibrium with 9 and dihydrogen, which was studied in the temperature interval from -100 to -50 °C, yielding thermodynamic parameters ΔH = -6.3 ± 0.2 kcal M-1 and ΔS = -23.7 ± 0.7 cal M-1 K-1. The hydrogenation of 9 is stereoselective: two isomers 10a and 10b are produced in a ratio 10:1. Use of HD for the hydrogenation of 9 yields the isomers with deuterium cis and trans to the phosphine in a ratio 1.3 (±0.1):1. The thermodynamic parameters of the equilibrium between 9, 10d, and HD are ΔH = -10.0 ± 0.4 kcal M-1 and ΔS = -20.3 ± 1 cal M-1 K-1. Dihydride 10 reacts with the substrate 12 at -90 °C, yielding the monohydride intermediate 17a. The same product is obtained when 13 is hydrogenated at -80 °C. At temperatures above -50 °C monohydride intermediate 17a undergoes reductive elimination, affording the hydrogenation product 15 in equilibrium with the product-catalyst complex 16 in which the catalyst is η6-coordinated to the phenyl ring of the product. The experimental data require that the dihydride mechanism is operating in the case of asymmetric hydrogenation catalyzed by 9. This, in turn, suggests that the enantioselective step is the migratory insertion in a dihydride intermediate 18.

P-Chirogenic phosphonium salts: Preparation and use in Rh-catalyzed asymmetric hydrogenation of enamides

P-Chirogenic trialkylphosphonium salts were prepared from the corresponding free phosphines by treatment with a strong acid (HBF4 or HOTf). No racemization of the phosphonium salts occurred in methanol or water even at considerably high tempera

Asymmetric Hydrogenation Catalyzed by (S,S)-R-BisP*-Rh and (R,R)-R-MiniPHOS Complexes: Scope, Limitations, and Mechanism

A new class of chiral C2-symmetric bis(trialkyl)phosphine ligands has been prepared and used in Rh(I)-catalyzed asymmetric hydrogenation reactions. The ligands, 1,2-bis(alkylmethylphosphino)ethanes 1 a-g (abbreviated as BisP*, alkyl = t-butyl, 1-adamantyl, 1-methylcyclohexyl, 1,1-diethylpropyl, cyclopentyl, cyclohexyl, isopropyl) and 1,2-bis(alkylmethylphosphino)methanes 2 a-d (abbreviated as MiniPHOS, alkyl = t-butyl, cyclohexyl, isopropyl, phenyl) are prepared by a simple synthetic approach based on the air-stable phosphine-boranes. These new ligands give the corresponding Rh(I) complexes, which are effective catalytic precursors for the asymmetric hydrogenation of a representative series of dehydroamino acids and itaconic acid derivatives. Enantioselectivities observed in these hydrogenations are universally high and in many cases exceed 99%. X-Ray characterization of four precatalysts, study of the pressure effects, deuteration experiments, and characterization of the wide series of intermediates in the catalytic cycle are used for the discussion of the possible correlation between the structure of the catalysts and the outcome of the catalytic asymmetric hydrogenation.

Synthesis of P-chirogenic diphosphine oxides and their use in catalytic asymmetric Diels-Alder reaction

New P-chirogenic phosphine oxides, (R,R)-1,2-bis(alkylmethylphosphinyl)ethanes (alkyl = 1-adamantyl, tert-butyl) and (S,S)-1, 1-bis(tert-butylmethylphosphinyl)methane have been synthesized from PCl3 via four steps. Their iron(III) complexes are