H₂O₂activation with biomimetic non-haem iron complexes and AcOH: connecting the g = 2.7 EPR signal with a visible chromophore

Abstract

Mechanistic studies of H2O2 activation by complexes related to [(BPMEN)Fe(II)(CH3CN)2](2+) with electron-rich pyridines revealed that a new intermediate formed in the presence of acetic acid with a 465 nm visible band can be associated with an unusual g = 2.7 EPR signal. We postulate that this chromophore is an acylperoxoiron(III) intermediate.

Hydroxylation of Aromatics by H2O2 Catalyzed by Mononuclear Non‐heme Iron Complexes: Role of Triazole Hemilability in Substrate‐Induced Bifurcation of the H2O2 Activation Mechanism

“…[39] By contrast, complexes with L 4 2 or related ligands only show as ingle signal. [17,37] The EPR signature of [(mtL 4 2 )Fe III (OOH)] 2 + is very close to that of [(L 4 2 )Fe III (OOH)] 2 + . [17] This likely results from the decoordination of the labile triazole, leadingt oaL 4 2 -type coordination sphere( Scheme 2).…”

“…Such ac hromophore (520 nm) is typical of N x Fe III (OOH) species within this family of ligands. [11][12][13][14][34][35][36] Remarkably,s uch ac hromophore can also be generated in MeCN with [(L 4 2 )Fe(OTf) 2 ]( with am aximum at 560 nm, Figure S21) or otherF e II complexes with tetradentatel igands, [37,38] but cannotb ea ccumulatedi nM eCN with [TPENFe](PF 6 ) 2 , [(L 5 2 )Fe(OTf) 2 ]( FiguresS19, S20), and with mostF e II precursors with pentadentate ligands, for which MeOH has to be used instead. [32,[39][40][41] To confirm the nature of the transient species, an EPR sample was drawn from the solutiona tt he maximum of accumulationo ft he 520 nm chromophorea nd frozen in an EPR tube.…”

Biologically inspired non-heme iron-catalysts for asymmetric epoxidation; design principles and perspectives

“…Synthesis of acylperoxoiron(III) complexes from reaction of [Fe( DMM men)(CH 3 CN) 2 ](ClO 4 ) 2 (C17) and [Fe( DMM PDP)(CH 3 CN) 2 ](ClO 4 ) 2 (C12') with H 2 O 2 /AcOH or peracids 68. 69 Scheme 8.…”

NMR and EPR spectroscopy applied to homogeneous catalysis

“…The starting compounds for the synthesis of new dimeric iron(III) complexes 14 and 15 (Scheme 1)tris((3,5 dimethyl 4 methoxypyridine 2 yl)methyl) amine (TPA*) [4], (S,S) 1,1 bis((3,5 dimethyl 4 methoxypyridine 2 yl)methyl)2,2' bipyrrolidine (PDP*) [5], and iron(II) trifluoromethanesulfonate Fe II (OTf) 2 ⋅ 2CH 3 CN [6] (OTf = trifluoromethane sulfonate)-were synthesized using standard proce dures. 2 Fe III (TPA*)](OTf) 4 Complex (14) A solution of Fe II (OTf) 2 ⋅ 2CH 3 CN (252 mg) in CH 3 CN (1 mL) was slowly added to a stirred suspen sion of TPA* (270 mg) CH 3 CN (1 mL).…”

“…The mass fractions of elements (%) were calculated for the formula C 56 H 78 F 12 Fe 2 N 8 O 18 S 4 · CH 3 CN (the num bers in parentheses are experimental data): C, 41.96 (41.77); H, 4.92 (4.82); N, 7.59 (7.38); S, 7.73 (7.85). The structure of the bright orange dimeric complex [(PDP*)Fe III (μ OH) 2 Fe III (PDP*)](ClO 4 ) 4 has recently been determined by X ray diffraction [5]. This complex contains the perchlorate anion, while the anion in its analogue 15 synthesized in this study is trifluo romethanesulfonate.…”