Homogeneous selective hydrogenation of dienes and styrene derivatives by use of palladium ferrocenyl amine sulfide complexes as catalysts

Abstract

Homogeneous hydrogenation of different conjugated dienes and styrene derivatives was performed at room temperature and low pressure by use of palladium ferrocenyl amine sulfide catalysts CpFeC5H3[CH2NMe2][SMe][PdCl2] (1) (Cp=C5H5), CpFeC5H3[CH2NMe2][S(4-tolyl)][PdCl2] (2), CpFeC5H3[CHMeNMe2][SMe][PdCl2] (3), [S(4-tolyl)]C5H4FeC5H3[CH2NMe2][S(4-tolyl)][PdCl2] (4) and [S(4-tolyl)]C5H4FeC5H3[CHMeNMe2] [S(4-tolyl)][PdCl2] (5). Hydrogenation of conjugated dienes was selective and monoenes were obtained as the main products. Trisubstituted double bonds were hydrogenated very slowly compared with mono- and disubstituted bonds, while tetrasubstituted double bonds were not hydrogenated. Hydrogenation of 2,3-dimethyl-1,3-butadiene was accompanied by isomerization and resulted in 2,3-dimethyl-2-butene as the major product. Styrene, 4-methylstyrene and α-methylstyrene were hydrogenated rapidly with almost quantitative yields, while β-methoxystyrene and β-methylstyrene were hydrogenated considerably more slowly and lower yields were obtained. Bulky styrene derivatives (i.e. β-bromostyrene or β,β-dimethylstyrene) were not hydrogenated under the reaction conditions. © 1991.