[Ni(iPr2Im)2Br2]: A Convenient Entry into NHC Nickel -Chemistry

The reaction of the NHC iPr2Im [NHC=N-heterocyclic carbene, iPr2Im = 1, 3-bis(isopropyl)imidazolin-2-ylidene] with freshly prepared NiBr2 in thf or dme results in the formation of the air stable nickel(II) complex trans-[Ni(iPr2Im)2Br2] (2). Complex 2 was structurally characterized. Thermal analysis (DTA/TG) reveals a very high decomposition temperature of 298 degrees C. Reduction of 2 with sodium or C8K in the presence of the olefins COD (cyclooctadiene) or COE (cyclooctene) affords the highly reactive compounds [Ni2(iPr2Im)4(COD)] (1) and [Ni(iPr2Im)2(COE)] (4). Alkylation of 2 with organolithiums leads to the formation of trans-[Ni(iPr2Im)2(R)2] [R = Me (5), CH2SiMe3 (6)], whereas the reaction of 2 with LiCp* [Cp* = (?5-C5(CH3)5)] at 80 degrees C causes the loss of one NHC ligand and affords [(?5-C5(CH3)5)Ni(iPr2Im)Br] (7).