New Pyridine Dicarbene Pincer Ligands with Ring Expanded NHCs and their Nickel and Chromium Complexes.

The pincer complexes [NiBr(CNC)]Br (4), [CrBr(CNC)] (5 a) and [CrBrCl(CNC)] (5 b), where CNC=3,3'-(pyridine-2,6-diyl)bis(1-mesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene), were obtained from the novel ligand CNC, generated in situ from the precursor (CHNCH)Br and [NiBr(PPh)] or from [Cr{N(SiMe)}(THF)] and (CHNCH)Br by aminolysis, respectively. The tetrahedrally distorted square planar (τ≅0.30) geometry and the singlet ground state of Ni in 4 were attributed to steric constraints of the CNC backbone.