Are intramolecularly stabilized compounds of aluminum suitable structural models of the S N2 transition state? Molecular structure of [( tBu) 2Al(μ-OC 6H 4-2-OMe)] 2

Abstract

The synthesis and crystallographic characterization of [( t Bu) 2Al(μ-OC 6H 4-2-OMe)] 2, when combined with the previously reported methyl, ethyl and iso-butyl analogs, allows for the structural comparison of the homologous series [R 2Al(μ-OC 6H 4-2-OMe)] 2 with the ideal structural changes that occur during the S N2-like cleavage of an aluminum alkoxide dimer with an intramolecular Lewis base. Ab initio calculations on the model system, [H 2Al(μ-OCH 2CH 2OH)] 2, confirm that in the absence of steric effects, intramolecularly stabilized compounds of aluminum are suitable structural models of the S N2 transition state. However, real compounds are not good models since the bond distances are controlled by the steric bulk of the alkyl substituents on adjacent aluminum centers rather than the extent of coordination of the fifth ligand.