Structural variation in cobalt halide complexes supported by m-terphenyl isocyanides

Detailed herein are synthetic, spectroscopic and structural studies on trisisocyanide cobalt halide complexes featuring the encumbering m-terphenyl isocyanide CNArMes2 (Mes = 2,4,6-Me3C6H3). Addition of CNArMes2 to CoI2 in a 3:1 molar ratio provides the mononuclear complex, CoI2(CNArMes2)3, which can be oxidized to six-coordinate CoI3(CNArMes2)3 upon treatment with 0.5 equivalents of I2. Contrastingly, addition of CNArMes2 to CoBr2 provided the dinuclear complex Br2Co(μ2-Br)2Co(CNArMes2)3 irrespective of the molar ratios employed. FTIR analysis on these Co(II) and Co(III) complexes is used to assess the relative π-basicities of the cobalt centers toward the CNArMes2 ligands. Treatment of CoX2 (X = Cl, Br and I) with three CNArMes2 ligands followed by the addition of granulated Zn provides the pseudo-tetrahedral complexes XCo(CNArMes2)3. FTIR, magnetic and X-ray crystallographic studies are used to determine both the ground state electronic structure and relative π-basicities of these complexes.

Despite encumbering steric properties, the m-terphenyl isocyanide CNArMes2 stabilizes four-, five- and six-coordinate cobalt halide complexes. A range of formal oxidation states is also accommodated by a tris-CNArMes2 structural motif. Such variations in coordination number and oxidation state are used to rationalize the electronic structure and π-basicity properties of the central cobalt atom.Figure optionsDownload as PowerPoint slide