Electrochemical Redox Behavior of the Hexakis-(Aryl Isocyanide) Complexes of Molybdenum(O) and Tungsten(O)

摘要

The hexakis(alkyl isocynanide) and hexakis(arylisocyanide) complexes of chromium, Cr(CNR)6(n+) and Cr(CNAr)6(n+), are noteworthy for their well-defined redox chemistry and the range of accessible stable oxidation states (n can be 3, 2, 1 or 0). In contrast to this situation, solutions of the hexakis(phenyl isocyanide) complexes Mo(CNPh)6 and W(CNPh)6 in 0.2 M tetra-n-butylammonium hexa-fluorophosphate(TBAH)-dichloromethane possess a reversible one-electron oxidation at E sub 1/2 = -0.2 V vs. SCE, and a second oxidation at E sub pa = +0.48 V (Mo), or +0.44 V (W) vs. SCE, that is chemically irreversible when the bulk electrolytes of solutions of Mo(CNPh)6 and W(CHPh)6 in 0.2 M TBAH-CH2Cl2 were carried out at a potential (+0.6 V) that was positive of the second (irreversible) oxidation then the corresponding seven coordinate dictation M(CNPH)7(2+) was the major product, implying that the very reactive 16-electron six-coordinate species M(CNPh)6(2+) can scavenge phenyl isocyanide. In an effort to explore the significance of these redox properties insofar as they pertain to other aryl isocyanide, complexes of the types Mo(CNAr)6 and W(CNAr)6, and to ascertain the mechanism whereby M(CNAr)7(2+) is formed by the electrochemical oxidation of M(CNAr)6, we have examined further the electrochemical redox properties of M(CNAr)6, with emphasis upon the more readily synthesized molybdenum complexes. Several key points emerging from these investigations are addressed herein.