Electrochemistry and photoelectron spectroscopy of oxomolybdenum(V) complexes with phenoxide ligands: effect of para substituents on redox potentials, heterogeneous electron transfer rates, and ionization energies.
Complexes of the form (Tp*)MoOCl(p-OC(6)H(4)X) and (Tp*)MoO(p-OC(6)H(4)X)(2) (Tp* = hydrotris(3,5-dimethyl-1-pyrazolyl)borate and X = OEt, OMe, Et, Me, H, F, Cl, Br, I, and CN) were examined by electrochemical techniques and gas-phase photoelectron spectroscopy to probe the effect of the remote substituent (X) on electron-transfer reactions at the oxomolybdenum core. Cyclic voltammetry revealed that all of these neutral Mo(V) compounds undergo a quasireversible one-electron oxidation (Mo(VI)/Mo(V)) and a quasireversible one-electron reduction (Mo(V)/Mo(IV)) at potentials that linearly depend on the electronic influence (Hammett sigma(p) parameter) of X. The first ionization energies for (Tp*)MoO(p-OC(6)H(4)X)(2) (X = OEt, OMe, H, F, and CN) were determined by photoelectron spectroscopy. A nearly linear correlation was found for the Mo(VI)/Mo(V) oxidation potentials in solution and the gas-phase ionization energies. Calculated heterogeneous electron-transfer rate constants show a slight systematic dependence on the substituent.
Graff
Julie N
JN
Department of Chemistry, The University of Arizona, Tucson, Arizona 85721-0041, USA.
McElhaney
Anne E
AE
Basu
Partha
P
Gruhn
Nadine E
NE
Chang
Chaung-Sheng J
CS
Enemark
John H
JH
D004563:Electrochemistry; D013058:Mass Spectrometry; D015394:Molecular Structure; D008982:Molybdenum / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*
D009942:Organometallic Compounds; D010087:Oxides; D008982:Molybdenum