Marked stabilization of redox states and enhanced catalytic activity in galactose oxidase models based on transition metal S-methylisothiosemicarbazonates with -SR group in ortho position to the phenolic oxygen.

Reactions of 5-tert-butyl-2-hydroxy-3-methylsulfanylbenzaldehyde S-methylisothiosemicarbazone and 5-tert-butyl-2-hydroxy-3-phenylsulfanylbenzaldehyde S-methylisothiosemicarbazone with pentane-2,4-dione (Hacac) and triethyl orthoformate in the presence of M(acac)2 as template source at 107 °C afforded metal complexes of the type MIIL1 and MIIL2, where M = Ni and Cu, with a new Schiff base ligand with thiomethyl (H2L1) and/or thiophenyl (H2L2) group in the ortho position of the phenolic moiety. Demetalation of NiL1 in CHCl3 with HCl(g) afforded H2L1. The latter reacts with Zn(OAc)2·2H2O with formation of ZnL1. The effect of −SR groups and metal ion identity on stabilization of phenoxyl radicals generated electrochemically was studied in detail. A marked stabilization of phenoxyl radical was observed in one-electron-oxidized complexes [ML2]+ (M = Ni, Cu) at room temperature, as demonstrated by cyclic voltammetry, EPR spectroscopy, and UV–vis–NIR measurements. In solution, the oxidized CuL2 and NiL2 display i...