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

The 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. Nitroxylradikale reagieren mit dem Eisen(I)‐Synthon (ArL)Fe zu Eisen(II)‐Nitroxidokomplexen. Die High‐Spin‐Eisen(II)‐Verbindungen sind stabil in Abwesenheit von schwachen C‐H‐Bindungen, zersetzen sich aber in Gegenwart labiler C‐H‐Bindungen über N‐O‐Bindungshomolyse zu FeII/III‐Hydroxiden.