Nickel(II) cis- and trans-dimethyl complexes of di-N-heterocyclic carbenes

Alkyl complexes of Ni(II) incorporating di-N-heterocyclic carbenes, (CCmeth)-C-tBU and (CCeth)-C-tBu (where (CCmeth)-C-tBu = 1,1'-methylene-3,3'-di-tert-butyl-diimidazole and (CCeth)-C-tBu = 1,2-ethylene-3,3'-di-tert-butyl-diimidazole-2,2'-diylidene have been prepared for the first time. The complexes [{trans-NiMe2(PMe3)}(2)(mu-tBuCCmeth)] (1) and [Ni((CCeth)-C-tBu)Me-2] (2) have been prepared and characterized by single-crystal X-ray diffraction, and the complex [Ni((CCmeth)-C-tBu)Me-2] (3) has been observed spectroscopically. Thermal decomposition studies show that 2 eliminates methane rapidly and quantitatively above 50 degreesC by a predominantly unimolecular dissociative pathway with activation parameters DeltaH(double dagger) = 24.0(6) kcal mol(-1) and DeltaS(double dagger) = -4.7(1) cal K-1 mol(-1).