Investigation of Isomerization Rates and Mechanism of Some 17- and 18-Electron Substituted Carbonyl Complexes of Chromium, Molybdenum, and Tungsten Using Double Potential Step Chronoamperometry

Chemical and electrochemical oxidation and reduction of a series of [M(CO)2(P-P)2]0,+ complexes (M=Cr, Mo, or W and P-P=DPM [bis(diphenylphosphino)methane], DPE [l,2-bis(diphenylphosphino)ethane], and DPP [l,3-bis(diphenylphosphino)propane]) have shown that cis and trans isomers occur in both the 18- and 17-electron configurations. Using the reaction scheme [formula omitted] and a computerized version of double potential step chronoamperometry permits the measurement of k1 and k2 over a wide temperature range and in a variety of solvents and the calculation of the activation parameters ΔH⧧ and ΔS⧧. The results indicate that the rate of isomerization depends on the electronic configuration of the metal and the size of the bidentate ligand but not on the solvent. Isomerization in both the 18-electron trans-M(CO)2(P-P)2 and 17-electron cis-M(CO)2(P-P2)+ complexes is believed to occur via a twist mechanism.