Complexation of Co(DBF2)2 by N-methylimidazole in acetonitrile: formation constants and 1H NMR shifts and relaxation times.

The complexation of Co(DBF2)2 by N-methylimidazole (MeIm) in acetonitrile has been studied by spectrophotometric titration at 0, 19, and 35 °C. The equilibrium constants K1 and K2 and their thermodynamic parameters have been determined. NMR studies of the chemical shifts and relaxation rates of the C−H protons of MeIm from −35 °C to 35 °C indicate that MeIm ligand exchange is in the fast-exchange limit. The relevance of these measurements to previous studies on related vitamin B12 models is discussed.