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 (LMeH), [2,6-(2,4,6-i-Pr3Ph)2Ph]C(NH-i-Pr)N-i-Pr
(LPrH), and [2,6-(4-t-BuPh)2Ph]C(NH-i-Pr)N-i-Pr (LBuH)]. Monoamidinate dialkyl complexes
were generated (LRAlMe2), and their reactions with methide abstraction reagents to yield
cationic aluminum alkyl species were studied. Additionally, an amidinate aluminum
dichloride was synthesized (LMeAlCl2), with concomitant formation of an unexpected
amidinium salt, [LMeH2][EtAlCl3]. The crystal structures of representative dimethyl and
dichloro species, as well as the latter salt, are presented.