Nonsymmetrical Benzene–Pyridine-Based Nickel Pincer Complexes Featuring Borohydride, Formate, Ethyl, and Nitrosyl Ligands

Nonsymmetrical nickel PCN pincer complexes [Ni­( iPrPCNX)­Cl] (X = NMe, CH2) are obtained by metalation of the benzene–pyridine-based pincer ligand iPrPCNX (X = NMe, CH2) with [Ni­(dme)­Cl2] (dme = 1,2-dimethoxyethane). These nickel species afforded the respective borohydride and ethyl complexes [Ni­( iPrPCNX)­L] (L = BH4, Et) upon treatment with NaBH4 and EtMgBr (or Et2Mg), respectively. Reacting [Ni­( iPrPCNX)­(κ2-BH4)] with CO2 gave the formate complexes [Ni­( iPrPCNX)­(OCHO)]. Treatment of [Ni­( iPrPCNX)­Cl] with the nitrosyl salt NOBF4 led to the formation of the unusual cationic square-pyramidal nickel nitrosyl pincer complexes [Ni­( iPrPCNX)­(NO)­Cl]+ featuring a strongly bent NO ligand (∠Ni–N–O 128.5°). These systems can be described as {NiNO}10 according to the Enemark–Feltham convention. Despite of the bent nature of the NO ligand the νNO is observed at 1849 cm–1 which is more typical for a linear Ni–N–O arrangement. The structure of these complexes is rationalized by means of DFT calculations. The molecular structures of representative complexes are presented.