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C-H Activation from Iron(II)-Nitroxido Complexes.

Authors :: Kleinlein C
Bendelsmith AJ
Zheng SL
Betley TA
Source :: Angewandte Chemie (International ed. in English) [Angew Chem Int Ed Engl] 2017 Sep 25; Vol. 56 (40), pp. 12197-12201. Date of Electronic Publication: 2017 Aug 25.
Publication Year :: 2017
Abstract: 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 ( <superscript>Ar</superscript> L)Fe(κ <superscript>1</superscript> -TEMPO) and ( <superscript>Ar</superscript> L)Fe(κ <superscript>2</superscript> -N,O-AZADO) ( <superscript>Ar</superscript> L=1,9-(2,4,6-Ph <subscript>3</subscript> C <subscript>6</subscript> H <subscript>2</subscript> ) <subscript>2</subscript> -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 ( <superscript>Ar</superscript> L)Fe(κ <superscript>1</superscript> -TEMPO) reacts to give a diferrous hydroxide [( <superscript>Ar</superscript> L)Fe] <subscript>2</subscript> (μ-OH) <subscript>2</subscript> , the reaction of four-coordinate ( <superscript>Ar</superscript> L)Fe(κ <superscript>2</superscript> -N,O-AZADO) with hydrogen atom donors yields ferric hydroxide ( <superscript>Ar</superscript> L)Fe(OH)(AZAD). Mechanistic experiments reveal saturation behavior in C-H substrate and are consistent with rate-determining hydrogen atom transfer.<br /> (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)