A Lewis Base Promoted Alkyl/Alkoxide Ligand Redistribution: Reaction of [Me2Al(μ-OCPh3)]2 with THF

Abstract

The reaction of [Me2Al(μ-OEPh3)]2 with pyridine yields the expected acid−base complexes AlMe2(OEPh3)(py) [E = C (1) and Si (2)]. In contrast, the reaction with THF yields AlMe(OEPh3)2(THF) [E = C (5) and Si (6)], although the dimethyl compounds, AlMe2(OEPh3)(THF) [E = C (3) and Si (4)], are observed in THF-d8 solution. The reaction of [Me2Al(μ-OCPh3)]2 with THF was followed by 1H NMR and found to occur by a two-step process. First, the Al2O2 core of [Me2Al(μ-OEPh3)]2 is cleaved by THF to form compound 3. Second, two molecules of AlMe2(OCPh3)(THF) react with each other, with prior dissociation of THF from at least one complex, resulting in the ligand redistribution and the formation of 5 and AlMe3(THF). The conversion of [Me2Al(μ-OCPh3)]2 into compound 3 is exothermic, and the subsequent formation of 5 and AlMe3(THF) is endothermic. The rate equations for the formation of 3 and its conversion to 5 have been determined. The observation of both alkoxide cleavage and alkyl/alkoxide exchange requires a fine ba...