Cis-trans isomerization of dimeric [Me(2)Al(mu-NH(t)Bu)](2)

Abstract

The trans (2a)-cis (2b) isomerization of [Me(2)Al(mu-NH'Bu)](2) (2) has been studied by 1(H) NMR spectroscopy The equilibrium has been observed to follow reversible first order kinetics with Delta H degrees = 2.22 +/- 0.07 KJmol(-1) and Delta S degrees = 2.85 +/- 0.07 JK(-1)mol(-1). The activation parameters for the conversion 2a-->2b are Delta H-1 = 49.7 +/- 2.3 kJmol(-1) and Delta S-1 = -126.3 +/- 0.2 JK(-1)mol(-1) and for the reverse reaction 2b-->2a are Delta H--1 = 47.5 +/- 2.3 kJmol(-1) and Delta S--1 = -129.1 +/- 0.5 JK(-1)mol(-1). The isomerization is markedly accelerated in the presence of Lewis bases. A crossover experiment indicates that the isomer interconversion is a unimolecular process. The large negative entropies of activation suggest either the existence of a sterically congested intermediate or theparticipation of solvent in the isomerization process.