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

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.