Six-coordinate monooxo molybdenum(VI) complexes with catecholate and salicylaldehyde thiosemicarbazone ligands

Preparation and electrochemical and spectroscopic properties are reported for two six-coordinate monooxo Mo(VI) complexes, MoO(Mecat)(PhTSCsal) and MoO(DTBcat)(PhTSCsal), where Mecat2−=4-methylcatecholate, DTBcat2−=3,5-di-tert-butylcatecholate and PhTSCsal2−=the dianion of salicylaldehyde 4-phenylthiosemicarbazone. Each complex exhibits reversible, one-electron reduction of the MoO4+ center at approximately −0.6 V versus Fc+/0 and irreversible, one-electron oxidations of the coordinated catecholate at approximately 0.8 and 1.1 V versus Fc+/0 in 1,2-dichloroethane. Two infrared absorptions are observed in the MoO stretching region for both complexes. These are thought to arise from geometric isomers produced by meridional coordination of tridentate PhTSCsal2− and bidentate coordination of an unsymmetrical catechol to MoO4+.