Nickel as a Lewis Base in a T-Shaped Nickel(0) Germylene Complex Incorporating a Flexible Bis(NHC) Ligand.

Flexible, chelating bis(NHC) ligand 2, able to accommodate both cis- and trans-coordination modes, was used to synthesize (2)Ni(η2 -cod), 3. In reaction with GeCl2 , it produced (2)NiGeCl2 , 4, featuring a T-shaped Ni0 and a pyramidal Ge center. Complex 4 could also be prepared from [(2)GeCl]Cl, 5, and Ni(cod)2 , in a reaction that formally involved Ni-Ge transmetalation, followed by coordination of the extruded GeCl2 moiety to Ni. A computational analysis showed that 4 possesses considerable multiconfigurational character and the Ni→Ge bond is formed through σ-donation from the Ni 4s, 4p, and 3d orbitals to Ge. (NHC)2 Ni(cod) complexes 9 and 10, as well as (NHC)2 GeCl2 derivative 11, incorporating ligands that cannot accommodate a wide bite angle, failed to produce isolable Ni-Ge complexes. The isolation of (2)Ni(η2 -Py), 12, provides further evidence for the reluctance of the (2)Ni0 fragment to act as a σ-Lewis acid.