Bonding and ligand exchange in pentamethyldialane. An IR, NMR and ab initio study

Abstract

IR studies have shown that the major constitutent of a labile gas-phase equilibrium in mixtures of trimethylalane and dimethylalane is the heteroleptic pentamethyldialane, Me₂Al(µH)(µMe)AlMe₂. A partial normal coordinate analysis of the spectra of isotopic variants reveals that this predominance arises from a significant strengthening of the Al—H—Al bridging bond. The experimental observations are supported by ab initio calculations of model systems. IR and variable temperature ¹H NMR studies lead to similar conclusions for solutions of alane mixtures in toluene, and lend support for a ligand-exchange mechanism involving singly bridged species.