Aluminum Borohydrides with Acenaphthene-1,2-diimine Ligands

The reactions of BH3·NHMe2 with hydrides [(dpp-Bian)Al(H)2Li(THF)3] (1·THF) and [(dpp-Bian)Al(H)2Li(Et2O)2] (1·Et2O) (dpp-Bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) proceed with the deprotonation of BH3·NHMe2 and result in bimetallic borohydrides [(dpp-Bian)Al(H)NMe2BH3Li(THF)2] (2) and [dpp-bianAl(H)NMe2BH3Li(Et2O)]2 (3), respectively. The hydrides 1·THF and 1·Et2O serve as catalysts for the dehydrocoupling of BH3·NHMe2. The reactions of 1·THF and 1·Et2O with two equivalents of BH3·SMe2 led to LiBH4 elimination and the formation of aluminum borohydrides [(dpp-Bian)Al(BH4)(solv)] (5·THF, solv = THF; 5·Et2O, solv = Et2O). The sterically hindered hydride [(ArBIG-Bian)AlH(THF)] (7) (ArBIG-Bian = 1,2-bis[(2,6-dibenzhydryl-4-methylphenyl)imino]acenaphthene) also reacts with BH3·SMe2 to give the aluminum borohydride [(ArBIG-Bian)Al(BH4)(THF)] (8), which in turn induces a reductive opening of the tetrahydrofuran molecule to give the compound [ArBIG-BianAl(OnBu)(THF)] (9). Complexes 2, 3, 5, 8, and 9 have been characterized by infrared and nuclear magnetic resonance spectroscopies, and molecular structures of 2, 3, 5·Et2O, and 9 were determined by single-crystal X-ray analysis.