Abstract
The pentaaryl borole (Ph*C)4BXylF [Ph*=3,5‐tBu2(C6H3); XylF=3,5‐(CF3)2(C6H3)] 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)4BXylF] complex of AlIII revealed a strong, ionic bonding interaction. The formation of the heteroleptic borole‐cyclopentadienyl “aluminocene” leads to significant changes in the 13C NMR chemical shifts within the borole unit. In the case of the less‐reductive GaCp*, borole (Ph*C)4BXylF 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.
Highlights
The pentaaryl borole (Ph*C)4BXylF [Ph* = 3,5tBu2(C6H3); XylF = 3,5-(CF3)2(C6H3)] 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
Among a variety of intriguing reactivities, including the activation of hydrogen[3] or SiÀH bonds,[4] Diels–Alder reactions, and ring expansions,[1b,5] boroles can be readily reduced by two electrons to form Hückel-aromatic borolediides[6] or they can react as potent Lewis acids.[7]
Summary
Structural, spectroscopic, and computational analysis of the resulting unprecedented neutral h5-Cp*,h5-[(Ph*C)4BXylF] complex of AlIII revealed a strong, ionic bonding interaction. In the case of the less-reductive GaCp*, borole (Ph*C)4BXylF reacts as a Lewis acid to form a dynamic adduct with a dative 2-center-2-electron GaÀB bond.
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