Nickel(II) Complexes with Tritopic Nimine CNHC Namine Pincer Ligands.
Tritopic NCNHC N' ligands containing a central N-heterocyclic carbene (NHC) donor flanked by two chemically-different nitrogen donors (Nimine and Namine ) were evaluated as potential tridentate pincer-type ligands in NiII complexes. The imidazolium chloride [(ImH){C(Me)=NDipp}(C2 NMe2 )]Cl (1) and the ammonium-imidazolium dichlorides [(ImH){C(Me)=NDipp}(C2 NHMe2 )]Cl2 (4) and [(ImH){C(Me)=NDipp}(C3 NHMe2 )]Cl2 (5), differing by the length (C2 or C3 ) of the alkyl spacer were used as precursors. Oxidative addition of 1 to [Ni(cod)2 ] afforded the dinuclear bis-NHC NiII complex [Ni2 Cl2 {μ-C(Me)=NDipp-κ2 Nimine ,C}{μ-Im(C2 NMe2 )-κ3 Namine ,CNHC ,Nimid }{Im[C(Me)=NDipp](C2 NMe2 )-κ1 CNHC }] (2) resulting from partial ligand rearrangement. A dinuclear byproduct 3 was also isolated. The salt [NiCl{Im[C(Me)=NDipp](C2 NMe2 )-κ3 Nimine ,CNHC ,Namine }]2 [NiCl4 ] (6) containing two Nimine CNHC Namine pincer NiII complex cations was obtained from 4. In contrast, the reaction of closely related 5 yielded [NiCl{Im[C(Me)=NDipp](C3 NMe2 )-κ2 Nimine ,CNHC }{μ-Im[C(Me)=NDipp](C3 NMe2 NiCl3 }-κ2 Namine ,CNHC }] (7 a), a dinickel(II) complex that contains a Nimine ,CNHC -chelating and a bridging κ2 Namine ,CNHC ligand. The molecular structures of 2, 3, 6, 7 a⋅THF, 7 b, an isomer of 7 a, and 8⋅CH2 Cl2 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.