C−H Activation from Iron(II)‐Nitroxido Complexes

Abstract

AbstractThe reaction of nitroxyl radicals TEMPO (2,2′,6,6′‐tetramethylpiperidinyloxyl) and AZADO (2‐azaadamantane‐N‐oxyl) with an iron(I) synthon affords iron(II)‐nitroxido complexes (ArL)Fe(κ1‐TEMPO) and (ArL)Fe(κ2‐N,O‐AZADO) (ArL=1,9‐(2,4,6‐Ph3C6H2)2‐5‐mesityldipyrromethene). Both high‐spin iron(II)‐nitroxido species are stable in the absence of weak C−H bonds, but decay via N−O bond homolysis to ferrous or ferric iron hydroxides in the presence of 1,4‐cyclohexadiene. Whereas (ArL)Fe(κ1‐TEMPO) reacts to give a diferrous hydroxide [(ArL)Fe]2(μ‐OH)2, the reaction of four‐coordinate (ArL)Fe(κ2‐N,O‐AZADO) with hydrogen atom donors yields ferric hydroxide (ArL)Fe(OH)(AZAD). Mechanistic experiments reveal saturation behavior in C−H substrate and are consistent with rate‐determining hydrogen atom transfer.