Development of Dynamic Multi-Functional Chiral Molecular Catalysts for Asymmetric Reduction and C-C Bond Formation

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A well-defined chiral transition metal amide complex with a M/NH bifunctional unit, Ru(Tsdpen)η^6-arene) or C_p^*M(Tsdpen), (M = Rh, Ir), has sufficient Bronsted basicity to deprotonate 2-propanol or formic acid and acidic organic compounds, leading to a hydrido amine complex and amine complexes bearing a metal bonded C- nucleophile, respectively. Thanks to a rapid and effective interconversion between the amide complex and the amine complex, the chiral amide complex has proven to effect asymmetric transfer hydrogenation of α-substituted aromatic ketones and asymmetric Michael addition to cyclic eneones in a highly stereoselctive manner. The dynamic M/NH bifunctional effect can be applied to the chiral Ru cluster-based catalyst systems generated in situ from Ru_3(CO)_<12> and chiral diiminodiphosphine tetradentate ligands. This chiral cluster effected asymmetric transfer hydrogenation of aromatic ketones in 2-propanol, leading to optically active alcohols with high ee. The dynamic mult … More i-functional effect of both the amide and the amine complexes is responsible for the excellent catalyst performance in terms of high reactivity, selectivity, and practicability.We have demonstrated that supercritical fluids are promising reaction media for molecular catalysis and the utilization of a particular fluid, scCO_2 caused a remarkable enhancement of reactivities and selectivities of molecular catalysts. In order to gain deeper understanding of the reaction mechanism of the molecular catalysis in this unique media, a supercritical fluid nuclear magnetic resonance (scNMR) spectroscopic method has been developed using a commercially available NMR spectrometer equipped with a high-pressure zirconia cell. We found that trialkylphosphite ligands are highly effective for increasing the solubility of dichloropalladium(II) and dichlororuthenium(II) complexes in scCO_2 and the Ru complex promoted rapid vinyl carbamate formation from phenylacetylene, diethylamine, and scCO_2. The scNMR investigation on a dynamic behavior of diethylamine in scCO_2 revealed that formation of N, N-diethylcarbamic acid was reversible and the concentration of the carbamic acid was highly influenced by the pressure and temperature. Less