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

摘要

Cyclic voltammetry and IR spectroelectrochemistry on the series of compounds Mo(CO)(6-n)(dmpi)(n), where dmpi = 2,6-dimethylphenyl isocyanide and n = 1-6, have determined the E(1/2) values for the first oxidation of the molybdenum isocyanides and the identity of the cation formed. The Mo(CO)(6-n)(dmpi)(n) complexes undergo one-electron oxidation reactions at progressively less positive values as the substitution of isocyanides 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 calculated 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 spectroelectrochemistry indicates a stable Mo(I) species is formed. Two members of the series, fac-Mo(CO)(3)(dmpi)(3) land cis-Mo(CO)(2)(dmpi)(4), undergo electron transfer induced isomerizations upon oxidation by one electron. The isomerization reactions were confirmed by digital simulation of the cyclic voltammograms and IR spectroelectrochemical studies, which show clear conversion of the isomers upon electrolysis. The rare constants 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)(dmpi)(4)](+) reaction. The n = 1 and 2 cations are short-lived and decompose to free ligands. [References: 35]