Reactivity Modes of an Iron Bis(alkoxide) Complex with Aryl Azides: Catalytic Nitrene Coupling vs Formation of Iron(III) Imido Dimers

Abstract

The iron bis(alkoxide) complex Fe(OR) 2 (THF) 2 (R = C t Bu 2 Ph), 1, was found to have strikingly different reactivity with various aryl azides, ArN 3 . Azides with methyl or ethyl groups in the ortho positions of the phenyl ring react catalytically via nitrene coupling to give azoarenes, ArNNAr. Catalyst loading as low as 1 mol % yields clean, quantitative conversion of aryl azides to azoarenes at room temperature in as little as 4 h. A combination of two different aryl azides leads to the catalytic formation of all three possible azoarenes, including the asymmetric one. In contrast, reactions with aryl azides lacking ortho substituents yield stable dimeric iron imido complexes of the form (RO)(THF)Fe(μ-NAr) 2 Fe(THF)(OR) (Ar = 4-(trifluoromethyl)phenyl, 5; Ar = phenyl, 6; Ar = 3,5-dimethylphenyl, 7), which do not undergo catalytic nitrene coupling. The isocyanide adduct Fe(OR) 2 (CNR) 2 (4, R = 2,6-dimethylphenyl) was obtained from the reaction of Fe(OR) 2 (THF) 2 with two equivalents of isocyanide. No C−N bond formation was observed in the reaction of compound 4 with azides or in the reaction of compounds 5−7 with isocyanides.

Facile hydrogen atom transfer to iron(iii) imido radical complexes supported by a dianionic pentadentate ligand

“…Compound 4 likely forms through the rapid formation of an Fe( iv ) imido, 3·SO 2 Ar , which rapidly picks up a second equivalent of Fe( ii ) 1 to give the observed dinuclear species ( Scheme 1 ). 42 Attempts to observe 3·SO 2 Ar by using an “inverse addition” strategy, or by treating 4 with an excess of azide reagent met with failure and only 4 was produced. When isolated samples of 4 were treated with an excess of THF at room temperature, a 1 : 1 mixture of 2·SO 2 Ar and 1·THF was produced rapidly.…”

Nitrene Insertion into CC and CH Bonds of Diamide Diimine Ligands Ligated to Chromium and Iron

“…[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] For certain metals,nitrene-like activity is inferred by the products derived from inter-a nd intramolecular insertions into CÀH bonds, [20][21][22][23][24][25][26][27] aziridinations, [28][29][30][31] and related reactions. [32][33][34][35][36][37][38][39][40] In many instances,i mide radical character is inferred from the reactivity and supported by calculations, [41,42] and the chemistry can be related to biological transformations such as the oxygenations by cytochrome P450. [43][44][45][46][47][48][49] During the course of examining chromium and iron complexes chelated by adiamide diimine tetradentate ligand, unusual azide-dependent reactivity featuring CÀCa nd CÀH bond activations was discovered in conjunction with redox non-innocence (RNI).…”

Nitrene Insertion into CC and CH Bonds of Diamide Diimine Ligands Ligated to Chromium and Iron

“…[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] For certain metals,nitrene-like activity is inferred by the products derived from inter-a nd intramolecular insertions into CÀH bonds, [20][21][22][23][24][25][26][27] aziridinations, [28][29][30][31] and related reactions. [32][33][34][35][36][37][38][39][40] In many instances,i mide radical character is inferred from the reactivity and supported by calculations, [41,42] and the chemistry can be related to biological transformations such as the oxygenations by cytochrome P450. [43][44][45][46][47][48][49] During the course of examining chromium and iron complexes chelated by adiamide diimine tetradentate ligand, unusual azide-dependent reactivity featuring CÀCa nd CÀH bond activations was discovered in conjunction with redox non-innocence (RNI).…”