Catalytic Asymmetric Hydrogenation Using Hydridorhodium(I) Diop Complexes [Diop = 2,3‐0‐Isopropylidene‐2,3‐Dihydroxy‐1,4‐Bis (Diphenylphosphino)Butane]

Abstract

The hydridorhodium(I) phosphine complex HRh[(+)‐diop]2, [(+)‐diop = (+)‐2,3,‐0‐isopropylidene‐2,3‐dihydroxy‐1,4‐bis(diphenylphosphino)butane] has been studied for catalytic hydrogenation of a number of olefinic substrates. Certain prochiral olefinic carboxylic acids have been reduced to products with up to about 60% enantiomeric excess. Rate data show the importance of the degree of substitution at the olefinic bond in terms of steric effects, and the ‐COOH function of the substrate likely plays a role. Kinetic and spectrophotometric studies on the hydrogenation of itaconic acid in n‐butanol‐toluene (2:1) solutions under mild conditions are best interpreted in terms of a mechanism involving formation of a metal alkyl via coordination of the olefinic substrate, followed by reaction with H2 to give saturated product and the starting catalyst complex. The actual catalyst is thought to be HRh(diop)(diop*), where diop* represents a monodentate diop with one dangling ‐CH2PPh2 moiety. The catalyst systems are somewhat complicated by the occurrence of slower side‐reactions, the extent of these varying from negligible for the more rapidly reducing substrates, to possibly of prime importance in the slow hydrogenations. The initial hydride catalyst, for example, is slowly decomposed to the cationic [Rh(diop)2]+ complex by protons from the olefinic substrate. Under H2, the cation reversibly forms a dihydride. The cation is also formed from a reaction that appears to involve an intermediate alkyl complex and the butanol.

Oxidation Kinetics of the Potent Insulin Mimetic Agent Bis(maltolato)oxovanadium(IV) (BMOV) in Water and in Methanol

“…The O 2:V stoichiometries for the oxidation reactions were measured by following the O 2-uptake in a thermostated constant pressure apparatus which has been described previously. 24 ESR and 51 V NMR spectra (78.86 MHz) were employed to confirm the purity of the vanadium(IV) and vanadium(V) species, respectively, and were recorded on Bruker ECS-106 ESR and Varian XL-300 spectrometers.…”

Catalytic asymmetric hydrogenation using ruthenium(II) complexes with chelating chiral sulfoxide ligands

“…We have named these ligands dios, bdios, and ddios, respectively, since they are patterned after the chelating phosphine derivative diop, developed by Kagan and Dang (4). Diop complexes of rhodium (1) and ruthenium(I1) are known to be highly effective as catalysts for stereoselective hydrogenations (5)(6)(7).…”