m-Terphenyl-Substituted Amidinates:  Useful Ligands in the Preparation of Robust Aluminum Alkyls

The syntheses of m-terphenyl-substituted amidines and their corresponding dialkylaluminum amidinate complexes are reported. The amidines are prepared in a one-pot reaction using 2,4,6-triphenylphenyllithium (formed in situ by the reaction of 2,4,6-triphenylphenylbromide with n-butyllithium) with dialkylcarbodiimides (RNCNR, R = cyclohexyl or isopropyl). An aqueous workup of the reaction mixtures results in the formation of sterically demanding amidines 2H and 3H. The amidines react readily with trimethylaluminum to form dialkylaluminum amidinate complexes. Two complexes have been prepared and comprehensively characterized in the solid state using single-crystal X-ray crystallography. In the crystalline state, dialkylaluminum amidinates are robust complexes that can be easily handled in air for short periods of time without noticeable decomposition.