A Synthetic Model of the Putative Fe(II)-Iminobenzosemiquinonate Intermediate in the Catalytic Cycle of <i>o</i>-Aminophenol Dioxygenases

The oxidative ring cleavage of aromatic substrates by nonheme Fe dioxygenases is thought to involve formation of a ferrous–(substrate radical) intermediate. Here we describe the synthesis of the trigonal-bipyramdial complex Fe­(^Ph2Tp)­(ISQ^tBu) (<b>2</b>), the first synthetic example of an iron­(II) center bound to an iminobenzosemiquinonate (ISQ) radical. The unique electronic structure of this <i>S</i> = 3/2 complex and its one-electron oxidized derivative ([<b>3</b>]⁺) have been established on the basis of crystallographic, spectroscopic, and computational analyses. These findings further demonstrate the viability of Fe²⁺–ISQ intermediates in the catalytic cycles of <i>o</i>-aminophenol dioxygenases