A stable carbonyl-pyrazine-metal(0) complex: Synthesis and characterization of cis-tetracarbonylpyrazinetrimethylphosphitetungsten(0)

The pentacarbonylpyrazinetungsten(0), (CO)5W(pyz), is soluble in polar solvents such as acetone or dichloromethane, however, exists at equilibrium with the bimetallic complex, (CO)5W(pyz)W(CO)5 plus free pyrazine (pyz) in solution. Using the quantitative 1H NMR spectroscopy, the equilibrium constant could be determined to be Keq = (5.9 ± 0.8) × 10−2 at 25 °C. Introducing trimethylphosphite as donor ligand into the molecule stabilizes the metal-pyrazine bond, so that cis-W(CO)4[P(OCH3)3](pyz), could be isolated and characterized.