Monooxo molybdenum(VI) complexes with catecholate and 2,2′-thiobis(phenolate) ligands: preparation and electrochemical and spectroscopic properties

Preparation, spectroscopic characterization and electrochemical behavior are reported for the six-coordinate monooxo Mo(VI) complexes, MoOL(cat), where L2−=2,2′-thiobis(4-methyl-6-tert-butylphenolate) or 2,2′-thiobis(4,6-di-tert-butylphenolate) and cat2−=catecholate (Cat2−), 4-methylcatecholate (Mecat2−), 4-nitrocatecholate (NO2cat2−), or 3,5-di-tert-butylcatecholate (DTBcat2−). The compounds are prepared by reaction of catechol with Mo2O3L2, the μ-oxo Mo(V) dimer produced by reaction of MoO2(acac)2 with H2L. MoOL(cat) complexes exhibit a MoO stretching vibration (νMoO) at 949–961 cm−1 and a reversible Mo(VI/V) reduction at −0.3 to −0.6 V versus Fc+/0. These features are characteristic of a mononuclear MoO4+ center. The kinetics of the metal-centered electrode reaction is sensitive to the catechol substituent. Under identical experimental conditions, the apparent electron-transfer rate indicated by the voltammetric peak potential separation (ΔEp) increases in the following sequence: DTBcat2−