Synthesis of the Tantalum Hydride Complex (<i>R,R</i>)-[Ta(O₂C₂₀H₁₀{SiMe₃}₂-3,3‘)₂(H)] and Reactivity with Aldehydes, Ketones, Acetylenes, and Related Substrates:  A Reagent for the Asymmetric Hydrogenation of Prochiral Carbonyl Species^†

Abstract

The tantalum phenyl complex (R,R)-[Ta(O2C20H10{SiMe3}2-3,3‘)2(Ph)], (R,R)-1, has been prepared from [H2NEt2][Ta(O2C20H10{SiMe3}2-3,3‘)2Cl2] and has been employed for the synthesis of the hydride species (R,R)-[Ta(O2C20H10{SiMe3}2-3,3‘)2(H)], (R,R)-2, by reaction with diisobutylaluminum hydride (DIBAL-H). The reaction proceeds cleanly and in high yield. Compound (R,R)-2 undergoes clean reactions with acetophenone and benzaldehyde-d to give alkoxide complexes that are chiral at the α-carbon. The progress of these reactions was monitored by 13C NMR spectroscopy. An X-ray crystal structure of one of the products (R,R,R)/(R,R,S)-[Ta(O2C20H10{SiMe3}2-3,3‘)2(OCH{CH3}{Ph})(OC{CH3}{Ph})] was obtained, and the catalytic conversion of benzaldehyde-d to benzyl alcohol-d was carried out using (R,R)-2. The hydride complex also reacts with acetylenes to give vinyl metal complexes, with 2,6-dimethylphenyl isocyanide to give an iminoformyl complex, and with allene to yield a labile η3-π-allyl species