Electrochemical, chemical, and spectroscopic characterization of the trans-[tetracarbonylbis(triphenylphosphine)chromium]+/0 redox couple

Article abstract of DOI:10.1021/om00079a002

Electrochemical oxidation of trans-Cr(CO)₄(PPh₃)₂ at mercury, silver, or platinum electrodes or chemical oxidation with AgClO₄, NOPF₆ or NOBF₄ produces trans-[Cr(CO)₄(PPh₃)₂]⁺. The 17-electron monomeric cation has been characterized by analysis and a wide variety of electrochemical (polarographic, voltammetric, and controlled potential electrolysis) and spectroscopic (infrared, electron spin resonance) techniques. trans-[Cr(CO)₄(PPh₃)₂]⁺ is light and moisture sensitive and unlike trans-Cr(CO)₄(PPh₃)₂ reacts relatively rapidly with acetonitrile, acetone, iodide, and bromide as well as water. All reactions studied produce trans-Cr(CO)₄(PPh₃)₂ as a product, in some cases (bromide and iodide) by redox reactions and in others by disproportionation. Electron-transfer catalysis reactions initiated via the ligand, L, substitution reaction trans-[Cr(CO)₄(PPh₃)₂]⁺ + L → trans-[Cr(CO)₄PPh₃L]⁺ + PPh₃ do not appear to be favored, although the observation of Cr(CO)₅PPh₃ as a reaction product with CO in the presence of light suggests that this step may be light catalyzed. This reaction, if it occurs, is a slow step relative to other pathways, and the [Cr(CO)₄(PPh₃)2]^+/0 redox couple is not a good candidate for electron-transfer catalysis.