T‐shaped Ni0 Systems Featuring Cationic Tetrylenes: Direct Observation of L/Z‐type Ligand Duality, and Alkene Hydrogenation Catalysis.

We report a facile synthetic method for accessing rare T‐shaped Ni0 species, stabilised by low‐coordinate cationic germylene and stannylene ligands which behave as Z‐type ligands toward Ni0. An in‐depth computational analysis indicates significant Nid→Ep donation (E=Ge, Sn), with essentially no E→Ni donation. The tetrylene ligand's Lewis acidity can be modulated in situ through the addition of a donor ligand, which selectively binds at the Lewis acidic tetrylene site. This switches this binding centre from a Z‐type to a classical L‐type ligand, with a concomitant geometry switch at Ni0 from T‐shaped to trigonal planar. Exploring the effects of this geometry switch in catalysis, isolated T‐shaped complexes 3 a–c and 4 a–c are capable of the hydrogenation of alkenes under mild conditions, whilst the closely related trigonal planar and tetrahedral Ni0 complexes 5, D, and E, which feature L‐type chloro‐ or cationic‐tetrylene ligands, are inactive under these conditions. Further, addition of small amounts of N‐bases to the catalytic systems involving T‐shaped complexes significantly reduces turnover rates, giving evidence for the in situ modulation of ligand electronics for catalytic switching. [ABSTRACT FROM AUTHOR]