Sulfur versus Iron Oxidation in An Iron-Thiolate Model Complex

In the absence of base, the reaction of [FeII(TMCS)]PF6 (1, TMCS = 1-(2-mercaptoethyl)-4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane) with peracid in methanol at −20 °C did not yield the oxoiron(IV) complex (2, [FeIV(O)(TMCS)]PF6), as previously observed in the presence of strong base (KOtBu). Instead, the addition of 1 equiv of peracid resulted in 50% consumption of 1. The addition of a second equivalent of peracid resulted in the complete consumption of 1 and the formation of a new species 3, as monitored by UV−vis, ESI-MS, and Mossbauer spectroscopies. ESI-MS showed 3 to be formulated as [FeII(TMCS) + 2O]+, while EXAFS analysis suggested that 3 was an O-bound iron(II)−sulfinate complex (Fe−O = 1.95 A, Fe−S = 3.26 A). The addition of a third equivalent of peracid resulted in the formation of yet another compound, 4, which showed electronic absorption properties typical of an oxoiron(IV) species. Mossbauer spectroscopy confirmed 4 to be a novel iron(IV) compound, different from 2, and EXAFS (Fe═O = ...