Double lithiation of 2,4,6-triphenylbromobenzene: synthesis of bis-amidines and an aluminium bis-amidinate complex

The substituted m-terphenyl 2,4,6-triphenylbromobenzene (2Br) reacts cleanly with two equivalents of n-butyllithium in diethyl ether/hexane solution to produce the dilithiated species 2Li2222. Treatment of 2Li2222 with dialkylcarbodiimides (RNCNR, R = isopropyl or cyclohexyl) followed by aqueous work-up of the reaction mixture results in the formation of sterically hindered bifunctional amidines 5H22 and 6H222. Two bis-amidine derivatives were crystallographically characterised. Compound 5H22 reacts readily with trimethylaluminium to form a novel dialkylaluminium bis-amidinate complex 5[AlMe22]22.