Nickel(II) Complexes with Tritopic N C N Pincer Ligands.

Tritopic NC N' ligands containing a central N-heterocyclic carbene (NHC) donor flanked by two chemically-different nitrogen donors (N and N ) were evaluated as potential tridentate pincer-type ligands in Ni complexes. The imidazolium chloride [(ImH){C(Me)=NDipp}(C NMe )]Cl (1) and the ammonium-imidazolium dichlorides [(ImH){C(Me)=NDipp}(C NHMe )]Cl (4) and [(ImH){C(Me)=NDipp}(C NHMe )]Cl (5), differing by the length (C or C ) of the alkyl spacer were used as precursors. Oxidative addition of 1 to [Ni(cod) ] afforded the dinuclear bis-NHC Ni complex [Ni Cl {μ-C(Me)=NDipp-κ N ,C}{μ-Im(C NMe )-κ N ,C ,N }{Im[C(Me)=NDipp](C NMe )-κ C }] (2) resulting from partial ligand rearrangement. A dinuclear byproduct 3 was also isolated. The salt [NiCl{Im[C(Me)=NDipp](C NMe )-κ N ,C ,N }] [NiCl ] (6) containing two N C N pincer Ni complex cations was obtained from 4. In contrast, the reaction of closely related 5 yielded [NiCl{Im[C(Me)=NDipp](C NMe )-κ N ,C }{μ-Im[C(Me)=NDipp](C NMe NiCl }-κ N ,C }] (7 a), a dinickel(II) complex that contains a N ,C -chelating and a bridging κ N ,C ligand. The molecular structures of 2, 3, 6, 7 a⋅THF, 7 b, an isomer of 7 a, and 8⋅CH Cl have been determined by single-crystal X-ray diffraction. Our results emphasize the often-underestimated importance of seemingly minor changes in the length of the spacers connecting a NHC donor group to its N-bound lateral functionalities.