Neutral and Cationic Aluminum Complexes Supported by Sterically Bulky Amidinate Ligands

Aluminum complexes supported by sterically bulky amidinate ligands containing terphenyl substituents on the backbone carbon atoms are described. Three amidinate ligands featuring differing substituents at the ortho positions of the 2,6-phenyl rings have been employed:  [2,6-(2,4,6-Me₃Ph)₂Ph]C(NH-i-Pr)N-i-Pr (L_MeH), [2,6-(2,4,6-i-Pr₃Ph)₂Ph]C(NH-i-Pr)N-i-Pr (L_PrH), and [2,6-(4-t-BuPh)₂Ph]C(NH-i-Pr)N-i-Pr (L_BuH)]. Monoamidinate dialkyl complexes were generated (L_RAlMe₂), and their reactions with methide abstraction reagents to yield cationic aluminum alkyl species were studied. Additionally, an amidinate aluminum dichloride was synthesized (L_MeAlCl₂), with concomitant formation of an unexpected amidinium salt, [L_MeH₂][EtAlCl₃]. The crystal structures of representative dimethyl and dichloro species, as well as the latter salt, are presented.