On the σ-complex character of bis(gallyl)/digallane transition metal species.

σ-complexes of homoatomic E-E bonds are key intermediates in catalytically relevant oxidative addition reactions, but are as yet unknown for the group 13 elements. Here, stable species best described as σ-complexes of a 1,2-dichlorodigallane derivative with Ni and Pd are reported. They are readily accessed through the combination of a 1,2-dichlorodigallane derivative, which features chelating phosphine functionalities, with Ni0 and Pd0 synthons. In-depth computational analyses of these complexes importantly reveal considerable Ga-Ga bonding interactions in both Ni and Pd complexes, despite the expected elongation of the Ga-Ga bond upon complexation, suggestive of σ-complex character as opposed to more commonly described bis(gallyl) character. Finally, the well-defined disproportion of the Ni complex is described, leading to a unique GaI-nickel complex, with concomitant expulsion of uncomplexed GaIII species.

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.