Cyclohexene as a substrate probe for the nature of the high-valent iron-oxo oxidant in Fe(TPA)-catalyzed oxidations

Oloo, Williamson N.; Feng, Yan; Iyer, Shyam R.; Parmelee, Sean R.; Xue, Genqiang; Que, Lawrence

doi:10.1039/c3nj00524k

Cited by 31 publications

(49 citation statements)

References 24 publications

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“…[83] Unlike other cyclic olefins (such as cyclooctene), cyclohexene hasamarked tendency to undergo allylic hydrogen atom abstraction in the presence of free radicals (see Scheme 10). Fort his reason, free radical-promotedo xidations generally yield allylic alcohols or unsaturated ketones,w hile metal-based oxidants usually givet he epoxides by oxygen atom transfer.…”

Section: Cyclohexene Oxidationmentioning

confidence: 99%

“…Fort his reason, free radical-promotedo xidations generally yield allylic alcohols or unsaturated ketones,w hile metal-based oxidants usually givet he epoxides by oxygen atom transfer. [83] However, the results of this test should be always cross-checkedw ith the ones of other tests, since even catalytic systems which usuallyo perate throughametal-based mechanismm ay giveacertain amount of allylic oxidation products. [84] 3I mine-Based Iron Complexes as Catalysts for Oxidation Reactions…”

Section: Cyclohexene Oxidationmentioning

confidence: 99%

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Non‐Heme Imine‐Based Iron Complexes as Catalysts for Oxidative Processes

2016

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Non-heme iron complexes are emerging as powerful and versatile catalysts in several oxidative transformations. Them ost investigated iron complex structures are based on aminopyridine ligands,b ut an umber of imine-based ligands have been also tested. In this review ac ollection of recent results obtained in oxidation catalysisw ith non-heme iminebased iron complexes is presented. Theirc atalytic performances in C À H, C=Ca nd À S À oxidation are spread over aw ide range of efficiency,g oing from very low to quite high.S uch performances are discussed, whenever possible,i nl ight of the operating reactionm echanismsa nd of catalyst stability.I n order to facilitate the discussion,a ni nitial survey of the most useful mechanistic tools widelya pplied to distinguish am etal-based oxidation from ar adicalchain process is also reported. Imine-basedc atalysts are divided into twoc lasses:( i) salen-Fec omplexes, and (ii)i mine-Fe complexes.I ns ome cases clues for free-radical oxidation mechanisms have been reported whilei no ther casese vidence for metal-based mechanisms has been collected. Thep referredm echanisticp athway is shown to be af unction of catalyst structure and features

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Section: Cyclohexene Oxidationmentioning

confidence: 99%

Section: Cyclohexene Oxidationmentioning

confidence: 99%

Non‐Heme Imine‐Based Iron Complexes as Catalysts for Oxidative Processes

2016

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“…Theoretical studies on the H atom abstraction capabilities of Cpd I and Cpd II mimics have also found sluggish oxidative properties for the latter, with H atom abstraction barriers of 2−5 kcal/mol higher than those computed for the former. 6 For nonheme systems, the geometric and electronic structures as well as reactivities of oxoiron(IV) and oxoiron(V) species having the same ancillary nonheme ligand have, to date, not been experimentally compared, primarily due to the paucity of systems with reasonably stable oxoiron(V) species. However, note that computational investigations on hypothetical iron-oxo models have been performed by Neese et al to correlate the electronic properties and reactivity of these high-valent iron-oxo complexes.…”

Section: Introductionmentioning

confidence: 99%

“…However, note that computational investigations on hypothetical iron-oxo models have been performed by Neese et al to correlate the electronic properties and reactivity of these high-valent iron-oxo complexes. 6d,e In their study, the superior reactivity of the hypothetical [Fe V (O)(NH 3 ) 4 (OH) axial ] 2+ over its one-electron reduced species [Fe IV (O)(NH 3 ) 4 (OH) axial ] 4+ in the oxidation of ethane was established based on the H atom abstraction barrier, the radical character of the iron-oxo bond, and the approach of C− H bond. Experimentally, the reactivities of two pairs of nonheme oxoiron(V) and oxoiron(IV) complexes have been compared in the literature, but no rate measurements have been reported.…”

Section: Introductionmentioning

confidence: 99%

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Spectroscopic and Reactivity Comparisons of a Pair of bTAML Complexes with Fe^V═O and Fe^IV═O Units

et al. 2017

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In this report we compare the geometric and electronic structures and reactivities of [FeV(O)]− and [FeIV(O)]2− species supported by the same ancillary nonheme biuret tetraamido macrocyclic ligand (bTAML). Resonance Raman studies show that the Fe=O vibration of the [FeIV(O)]2− complex 2 is at 798 cm−1, compared to 862 cm−1 for the corresponding [FeV(O)]− species 3, a 64 cm−1 frequency difference reasonably reproduced by density functional theory calculations. These values are, respectively, the lowest and the highest frequencies observed thus far for nonheme high-valent Fe=O complexes. Extended X-ray absorption fine structure analysis of 3 reveals an Fe=O bond length of 1.59 Å, which is 0.05 Å shorter than that found in complex 2. The redox potentials of 2 and 3 are 0.44 V (measured at pH 12) and 1.19 V (measured at pH 7) versus normal hydrogen electrode, respectively, corresponding to the [FeIV(O)]2−/[FeIII(OH)]2− and [FeV(O)]−/[FeIV(O)]2− couples. Consistent with its higher potential (even after correcting for the pH difference), 3 oxidizes benzyl alcohol at pH 7 with a second-order rate constant that is 2500-fold bigger than that for 2 at pH 12. Furthermore, 2 exhibits a classical kinteic isotope effect (KIE) of 3 in the oxidation of benzyl alcohol to benzaldehyde versus a nonclassical KIE of 12 for 3, emphasizing the reactivity differences between 2 and 3.

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Catalytic Electrophilic Halogenations and Haloalkoxylations by Non‐Heme Iron Halides

2014

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Synthetic non-heme iron halides promote sub-stoichiometric aliphatic halogenation reactions via a radical mechanism. Complementary to such activity, we have developed an electrophilic halogenation of arenes employing non-heme iron halides. A catalytic version of these reactions has also been developed using potassium halide as the source of halogen atom for arenes at room temperature. Efforts towards understanding the mechanism of these catalytic halogenation reactions led to the discovery of the haloalkoxylation of olefins by a non-heme iron complex. Implications of these findings with respect to natural transformations are also discussed.

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Cyclohexene as a substrate probe for the nature of the high-valent iron-oxo oxidant in Fe(TPA)-catalyzed oxidations

Cited by 31 publications

References 24 publications

Non‐Heme Imine‐Based Iron Complexes as Catalysts for Oxidative Processes

Non‐Heme Imine‐Based Iron Complexes as Catalysts for Oxidative Processes

Spectroscopic and Reactivity Comparisons of a Pair of bTAML Complexes with Fe^V═O and Fe^IV═O Units

Catalytic Electrophilic Halogenations and Haloalkoxylations by Non‐Heme Iron Halides

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Cyclohexene as a substrate probe for the nature of the high-valent iron-oxo oxidant in Fe(TPA)-catalyzed oxidations

Cited by 31 publications

References 24 publications

Non‐Heme Imine‐Based Iron Complexes as Catalysts for Oxidative Processes

Non‐Heme Imine‐Based Iron Complexes as Catalysts for Oxidative Processes

Spectroscopic and Reactivity Comparisons of a Pair of bTAML Complexes with FeV═O and FeIV═O Units

Catalytic Electrophilic Halogenations and Haloalkoxylations by Non‐Heme Iron Halides

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Spectroscopic and Reactivity Comparisons of a Pair of bTAML Complexes with Fe^V═O and Fe^IV═O Units