A Neutral “Aluminocene” Sandwich Complex: η(1)‐ versus η(5)‐Coordination Modes of a Pentaarylborole with ECp* (E=Al, Ga; Cp*=C(5)Me(5))

The pentaaryl borole (Ph*C)(4)BXyl(F) [Ph*=3,5‐tBu(2)(C(6)H(3)); Xyl(F)=3,5‐(CF(3))(2)(C(6)H(3))] reacts with low‐valent Group 13 precursors AlCp* and GaCp* by two divergent routes. In the case of [AlCp*](4), the borole reacts as an oxidising agent and accepts two electrons. Structural, spectroscopic, and computational analysis of the resulting unprecedented neutral η(5)‐Cp*,η(5)‐[(Ph*C)(4)BXyl(F)] complex of Al(III) revealed a strong, ionic bonding interaction. The formation of the heteroleptic borole‐cyclopentadienyl “aluminocene” leads to significant changes in the (13)C NMR chemical shifts within the borole unit. In the case of the less‐reductive GaCp*, borole (Ph*C)(4)BXyl(F) reacts as a Lewis acid to form a dynamic adduct with a dative 2‐center‐2‐electron Ga−B bond. The Lewis adduct was also studied structurally, spectroscopically, and computationally.