Synthesis of the tantalum hydride complex (R,R)-[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

The tantalum phenyl complex (R,R)-[Ta(O 2 C 2 0 H 1 0 {SiMe 3 } 2 -3,3')2(Ph)], (R,R)-1, has been prepared from [H 2 NEt 2 ][Ta(O 2 C 2 0 H 1 0 {SiMe 3 } 2 -3,3') 2 Cl 2 ] and has been employed for the synthesis of the hydride species (R,R)-[Ta(O 2 C 2 0 H 1 0 {SiMe 3 } 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 1 3 C NMR spectroscopy. An X-ray crystal structure of one of the products (R,R,R)'(R,R,S)-[Ta(O 2 C 2 0 H 1 0 {SiMe 3 } 2 -3,3')2(OCH{CH 3 }{Ph})(O=C{CH 3 }{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 η 3 -π-allyl species.