Synthesis and ε-Caprolactone Polymerization Activity of Electron-Deficient Gallium and Aluminum Species Containing a Charged Redox-Active dpp-Bian Ligand.

Abstract

The synthesis of electron-deficient gallium- and aluminum-centered species containing a redox-active dpp-Bian ligand (dpp-Bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) is described. The reaction of digallane [(dpp-Bian)Ga-Ga(dpp-Bian)] with [Ph3C][PF6] or AgPF6 resulted in polyoxidized species [(dpp-Bian)GaF2]2 (1), [(dpp-Bian)H2][PF6] (2), and [(dpp-Bian)GaF(O2PF2)]2 (3). The reaction of digallane with B(C6F5)3 led to electron-deficient gallylene [(dpp-Bian)GaB(C6F5)3] 4 of a dpp-Bian radical anion. The soft oxidation of digallane with tosyl cyanide gave the trinuclear cationic species [(dpp-Bian)Ga(Tos)3Ga(Tos)3Ga(dpp-Bian)][Ga(CN)4] (5) containing dpp-Bian radical anions. The reaction of [(dpp-Bian)AlEt2] with 1 equiv of [Ph3C][B(C6F5)4] resulted in the cationic complex [(dpp-Bian)AlEt2][B(C6F5)4] (6) of neutral dpp-Bian, while the treatment of [(dpp-Bian)AlEt(Et2O)] with 1 equiv of [Ph3C][B(C6F5)4] resulted in the compound [(dpp-Bian)AlEt(Et2O)][B(C6F5)4] (7) of a dpp-Bian radical anion. The reaction of diethylaluminum derivative [(dpp-Bian)AlEt2] with 1 equiv of B(C6F5)3 gave the cationic complex [{(dpp-Bian)AlEt}2F][EtB(C6F5)3] (8) containing radical-anion dpp-Bian ligands. The paramagnetic compounds 1, 2, 4, 5, 7, and 8 were characterized by electron paramagnetic resonance spectroscopy, and the diamagnetic complex 6 was characterized by NMR spectroscopy. The molecular structures of 1-6 and 8 were established by single-crystal X-ray diffraction analysis. Compounds 4 and 6-8 were found to be active initiators for immortal ring-opening polymerization of ε-caprolactone.