OXIDATION OF CPM(CO)3-CENTER-DOT AND CPM(CO)3(NCME)CENTER-DOT (M=CR, MO, W) - KINETIC AND THERMODYNAMIC CONSIDERATIONS OF THEIR POSSIBLE INVOLVEMENT AS REDUCING AGENTS - RELATIVE ACETONITRILE AFFINITIES OF CPM(CO)3-CENTER-DOT( AND CPM(CO)3)

The electrochemistry of the anions, radicals, and cations CpM(CO)3-/./ + (M = Cr, Mo, W) in acetonitrile has been reinvestigated by cyclic vo ltammetry and digital simulation techniques. For M = Cr, oxidation of the persistent radical to the cation is directly observed at a potenti al ca. 1.0 V more positive than the anion oxidation potential. For M = Mo and W, oxidation of the 17-electron radicals cannot be directly ob served due to the rapid follow-up dimerization reactions. Thermochemic al considerations establish that the generation of the cationic produc ts CpM-(CO)3(NCMe)+ (M = Mo, W) even at the anion oxidation potentials cannot be due to the direct oxidation of the radicals CPM(CO)3.. Digi tal simulation results demonstrate that the 19-electron radicals CpM(C O)3(NCMe)., which are stronger reducing agents than CpM(CO)3. by about 1.4 V, are kinetically and thermodynamically competent intermediates for the production of the cations by heterogeneous and homogeneous ele ctron transfer. Thermochemical cycle shows that acetonitrile binds mor e strongly to the 16-electron cations CpM(CO)3+ than to the 17-electro n radicals CpM(CO)3. by ca. 135 kJ/mol.