Dioxygen activation by Fe II thiolate complexes is relatively rare in biological and chemical systems because the sulfur site is at least as vulnerable as the iron site to oxidative modification. O 2 activation by Fe II -SR complexes with thiolate bound trans to the O 2 binding site generally affords the Fe IV ═O intermediate and oxidized thiolate. On the other hand, O 2 activation by Fe(ii)-SR complexes with thiolate bound cis to the O 2 binding site generates Fe III -O-Fe III or S-oxygenated complexes. The postulated Fe IV ═O intermediate has only been identified in isopenicillin N synthase recently. We demonstrated here that O 2 activation by a dinuclear Fe II thiolate-rich complex produces a mononuclear Fe III complex and water with a supply of electron donors. The thiolate is bound cis to the postulated dioxygen binding site, and no Fe III -O-Fe III or S-oxygenated complex was observed. Although we have not detected the transient intermediate by spectroscopic measurements, the Fe IV ═O intermediate is suggested to exist by theoretical calculation, and P-oxidation and hydride-transfer experiments. In addition, an unprecedented Fe III -O 2 -Fe III complex supported by thiolates was observed during the reaction by using a coldspray ionization time-of-flight mass (CSI-TOF MS) instrument. This is also supported by low-temperature UV-vis measurements. The intramolecular NHO═Fe IV hydrogen bonding, calculated by DFT, probably fine tunes the O 2 -activation process for intramolecular hydrogen abstraction, avoiding the S-oxygenation at cis-thiolate.
All Science Journal Classification (ASJC) codes
- Inorganic Chemistry