ELECTROCHEMICAL AND IR SPECTROELECTROCHEMICAL INVESTIGATIONS OF THE SERIES MO(CO)(6-N)(CNR)(N) (N=1-6) (R=2,8-DIMETHYLPHENYL) - IN-SITU OBSERVATION OF FAC-MER AND CIS-TRANS ISOMERIZATIONS

Cyclic voltammetry and IR spectroelectrochemistry on the series of com pounds Mo(CO)(6-n)(dmpi)(n), where dmpi = 2,6-dimethylphenyl isocyanid e and n = 1-6, have determined the E(1/2) values for the first oxidati on of the molybdenum isocyanides and the identity of the cation formed . The Mo(CO)(6-n)(dmpi)(n) complexes undergo one-electron oxidation re actions at progressively less positive values as the substitution of i socyanides is increased. Mo(CO)(5)(dmpi) is oxidized at 1.18 V vs NHE while at the other extreme Mo(dmpi)(6), is oxidized at -0.34 V vs NHE. An electrochemical ligand parameter, E(L), Of 0.43 V has been calcula ted for the dmpi ligand. Stability of the oxidized products, [Mo(CO)(6 -n)(dmpi)(n)](+), also varies with substitution. Oxidation of the n = 5 and 6 compounds is chemically reversible, and IR spectroelectrochemi stry indicates a stable Mo(I) species is formed. Two members of the se ries, fac-Mo(CO)(3)(dmpi)(3) land cis-Mo(CO)(2)(dmpi)(4), undergo elec tron transfer induced isomerizations upon oxidation by one electron. T he isomerization reactions were confirmed by digital simulation of the cyclic voltammograms and IR spectroelectrochemical studies, which sho w clear conversion of the isomers upon electrolysis. The rare constant s for the isomerization reactions range from 7.0 s(-1) for the fac-[Mo (CO)(3)(dmpi)(3)](+) --> mer-[Mo(CO)(3)(dmpi)(3)](+) isomerization to 0.093 s(-1) for the cis-[Mo(CO)(2)(dmpi)(4)](+) --> trans-[Mo(CO)(2)(d mpi)(4)](+) reaction. The n = 1 and 2 cations are short-lived and deco mpose to free ligands.