Rhodium(I) catalyzed E/Z isomerization of dimethyl butenedioate

Abstract

Hydride complexes of Rh(I) represent highly effective homogeneous catalysts of the isomerization of (Z)-dimethyl butenedioate (I) yielding (E)-dimethyl butenedioate (II) in benzene at 25 °C. The reaction catalyzed by RhH(P(C6H5)3)4 is first order both in I and in the catalyst, k = 0.51 l mol-1 s-1, Ea = 48 kJ mol-1, ΔS≠ = -46 J mol-1 K-1. At high substrate-to-catalyst ratios the catalyst is inactivated, which consists mainly in deoxygenation and decarbonylation of the E- and Z-esters with formation of methyl 2-butenoate, triphenylphosphine oxide, and carbonylocomplexes of Rh(I). Statistical redistribution of deuterium during the isomerization of equimolar mixture of I and [2,3-2H2]-I and other experimental evidence are consistent with the addition-elimination hydride mechanism of the isomerization involving σ-alkyl rhodium complexes as the intermediates and RhH(P(C6H5)3)2 as the catalytically active species.