A Neutral “Aluminocene” Sandwich Complex: η1 - versus η5-Coordination Modes of a Pentaarylborole with ECp (E=Al, Ga; Cp =C5 Me5)

Abstract

The pentaaryl borole (Ph C)4 BXylF [Ph =3,5-tBu2 (C6 H3 ); XylF =3,5-(CF3 )2 (C6 H3 )] 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 η5 -Cp ,η5 -[(Ph C)4 BXylF ] complex of AlIII 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 BXylF 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.