Geometrically Constrained Cationic Low-Coordinate Tetrylenes: Highly Lewis Acidic σ-Donor Ligands in Catalytic...

A novel non-innocent ligand class, namely cationic single-centre ambiphiles, is reported in the phosphine-functionalised cationic tetrylene Ni⁰ complexes, [^PhR DippENi(PPh₃ )₃ ]⁺ (4 a/b (Ge) and 5 (Sn); ^PhR Dipp={[Ph₂ PCH₂ SiR₂ ](Dipp)N}^- ; R=Ph, ⁱ Pr; Dipp=2,6-ⁱ Pr₂ C₆ H₃ ). The inherent electronic nature of low-coordinate tetryliumylidenes, combined with the geometrically constrained [N-E-Ni] bending angle enforced by the chelating phosphine arm in these complexes, leads to strongly electrophilic E^II centres which readily bind nucleophiles, reversibly in the case of NH₃ . Further, the Ge^II centre in 4 a/b readily abstracts the fluoride ion from [SbF₆ ]^- to form the fluoro-germylene complex ^PhR DippGe(F)Ni(PPh₃ )₃ 9, despite this Ge^II centre simultaneously being a σ-donating ligand towards Ni⁰ . Alongside the observed catalytic ability of 4 and 5 in the hydrosilylation of alkynes and alkenes, this forms an exciting introduction to a multi-talented ligand class in cationic single-centre ambiphiles.