SELECTIVE HYDROGENATION OF THE CARBONYL GROUP OF ALPHA,BETA-UNSATURATED ALDEHYDES TO ALCOHOLS WITH IRIDIUM(I) COMPLEXES

The hydrogenation of C6H5CHCHCHO (1), C6H5CHC(CH3)CHO (6) and C6H5CHC(Cl)CHO (7) by Ir(ClO4)(CO)(PPh3)2 (2), IrCl(PPh3)3 (8), IrCl(CO)(PPh3)2 (9) and [Ir(CO)(PPh3)3]ClO4 (10) occurs primarily at the carbonyl group to give unsaturated alcohols, C6H5CHCHCH2OH (5), C6H5CHC(CH3) CH2OH (11) and C6H5CH C(Cl)CH2OH (12) at 50°C under 9 atm of hydrogen. Compound 5 is isomerized to C6H5CH2CH2CHO (3) by 2, 8 and 9 but not by 10. The carbonyl group of 3 is further hydrogenated to produce the saturated alcohol, C6H5CH2CH2CH2OH (4) in the presence of 2, 8 and 9. The isomerizations: 5 → 3 by 10, and 11 → C6H5CH2CH(CH3)CHO and 12 → C6H5CH2CH(Cl)CHO by 8 and 9 probably do not occur for steric reasons; the interaction between the internal olefinic group and the iridium with bulky ligands is hindered. © 1990.