A mesoionic carbene stabilized nickel() hydroxide complex: a facile precursor for C-H activation chemistry

We report the synthesis of a new nickel( ii ) hydroxide complex 2 supported by a rigid, tridentate triazolylidene-carbazolid ligand. The complex can be accessed in high yields following a simple and stepwise extraction protocol using dichloromethane and aqueous ammonium chloride followed by aqeous sodium hydroxide solution. We found that complex 2 is highly basic, undergoing various deprotonation/desilylation reactions with E-H and C-H acidic and silylated compounds. In this context we synthesized a variety of novel, functionalized nickel( ii ) complexes with trimethylsilylolate ( 3 ), trityl sulfide ( 4 ), tosyl amide ( 5 ), azido ( 6 ), pyridine ( 7 ), acetylide ( 8 , 9 ), fluoroarene ( 10 & 11 ) and enolate ( 12 ) ligands. We furthermore found that 2 reacts with malonic acid dimethyl ester in a knoevennagel-type condensation reaction, giving access to a new enolate ligand in complex 13 , consisting of two malonic acid units. Furthermore, complex 2 reacts with acetonitrile to form the cyanido complex 14 . The formation of complexes 13 and 14 is particularly interesting, as they underline the potential of complex 2 in both C-C bond formation and cleavage reactions. We report the synthesis of a nickel( ii ) hydroxide complex 2 supported by a rigid, tridentate triazolylidene-carbazolid ligand, acting as a versatile precursor to perform E-H (E = O, S, N) and C-H activation reactions.