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

A novel non-innocent ligand class, namely cationic single-centre ambiphiles, is reported in the phosphine-functionalised cationic tetrylene Ni complexes, [ DippENi(PPh ) ] (4 a/b (Ge) and 5 (Sn); Dipp={Ph PCH SiR N} ; R=Ph, Pr; Dipp=2,6- Pr C H ). 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 centres which readily bind nucleophiles, reversibly in the case of NH . Further, the Ge centre in 4 a/b readily abstracts the fluoride ion from [SbF ] to form the fluoro-germylene complex DippGe(F)Ni(PPh ) 9, despite this Ge centre simultaneously being a σ-donating ligand towards Ni . 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.