Mixed Azido-N-Heterocyclic Carbene Complexes of Nickel(II) as a Template for New Organometallics Bearing Carbodiimido, Tetrazolato, and Abnormal Tetrazolin-5-ylidene Ligands

Salt metathesis reaction of the dihalo-bis(carbene) complex trans-[NiBr2(NHC)2] (1, NHC = 1,3-diisopropylbenzimidazolin-2-ylidene) with NaN3 in DMF at elevated temperature afforded the diazido-bis(carbene) complex trans-[Ni(N3)2(NHC)2] (2) as a red crystalline solid in a yield of 78%. Complex 2 served as a metal-template for the 1,3-dipolar cycloaddition of 2,6-dimethylphenylisocyanide (CN-Xyl) to the azido ligands to yield the mixed tetrazolato-carbodiimido complex trans-[Ni(CN4-Xyl)(NCN-Xyl)(NHC)2] (3) at ambient temperature and the dicarbodiimido complex trans-[Ni(NCN-Xyl)2(NHC)2] (4) at 70 °C. Reaction of alkyl isocyanides with 2 at ambient temperature gave the ditetrazolato complexes trans-[Ni(CN4-R)2(NHC)2] (5, R = tert-butyl; 6, R = cyclohexyl) in good yields. The novel cationic “abnormal” tetrazolin-5-ylidene complex trans-[Ni(CN4-tBu,Me)2(NHC)2](BF4)2 (7, tBu = tert-butyl) was synthesized by direct methylation of 5 with [Me3O]BF4. All compounds have been fully characterized by multinuclear NMR spectroscopies and ESI mass spectrometry. The solid state molecular structures of complexes 2, 4, 5, and 7·2CH2Cl2 have also been confirmed by X-ray diffraction studies.