Turning a New Leaf on Metal-TMC Chemistry: Ni(II)(TMC) Acetylides

Novel [Ni(TMC)C≡CY](+)-type compounds 1-4 [TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane; Y = SiMe3 (1), Si(i)Pr3 (2), Ph (3), and C2H (4)] have been synthesized and characterized. Single-crystal X-ray diffraction studies revealed that these compounds adopt a distorted square-pyramidal geometry, with the acetylide ligand occupying the apical position and a RSRS isomer for the TMC ligand. The room temperature magnetic properties of 1-4 are consistent with an S = 1 ground state, as corroborated by CASSCF and density functional theory calculations, which indicate that the singly occupied molecular orbitals are d(z(2)) and d(x(2)-y(2)).