Selective hydrogenation of the carbonyl group of α,β-unsaturated aldehydes to alcohols with iridium(I) complexes

Article abstract of DOI:10.1016/0022-328X(90)87205-R

The hydrogenation of C6H5CH=CHCHO (1), C6H5CH=C(CH)3CHO (6) and C6H5CH=C(Cl)CHO (7) by Ir(ClO4)(CO)(PPh3)2 (2), IrCl(PPh3)3 (8), IrCl(CO)(PPh3)2 (9) and ClO4 (10) occurs primarily at the carbonyl group to give unsaturated alcohols, C6H5CH=CHCH2OH (5), C6H5CH=C(CH3)CH2OH (11) and C6H5CH=C(Cl)CH2OH (12) at 50 deg C under 9 atm of hydrogen.Compound 5 is isomerized to C6H5CH2CH2CHO (3) by 2, 8 and 9 but no 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.