Enhancing Chemo- and Stereoselectivity in C–H Bond Oxygenation with H₂O₂ by Nonheme High-Spin Iron Catalysts: The Role of Lewis Acid and Multimetal Centers

Abstract

Spin states of iron often direct the selectivity in oxidation catalysis by iron complexes using hydrogen peroxide (H 2 O 2 ) on an oxidant. While low-spin iron(III) hydroperoxides display stereoselective C−H bond hydroxylation, the reactions are nonstereoselective with high-spin iron(II) catalysts. The catalytic studies with a series of high-spin iron(II) complexes of N4 ligands with H 2 O 2 and Sc 3+ reported here reveal that the Lewis acid promotes catalytic C−H bond hydroxylation with high chemo-and stereoselectivity. This reactivity pattern is observed with iron(II) complexes containing two cis-labile sites. The enhanced selectivity for C−H bond hydroxylation catalyzed by the high-spin iron(II) complexes in the presence of Sc 3+ parallels that of the low-spin iron catalysts. Furthermore, the introduction of multimetal centers enhances the activity and selectivity of the iron catalyst. The study provides insights into the development of peroxide-dependent bioinspired catalysts for the selective oxygenation of C−H bonds without the restriction of using iron complexes of strong-field ligands.

Promoted catalytic potential in sulfides oxidation and biological screening of green Pd (II) and Co (II) complexes of salicylidene isatin hydrazone ligand

“…The highest yields of dps were detected to be 57% at 30 C after 150 min with PdLn and 58% after 150 min with Co (Ln) 2 (Tables 2a and 2b, entries 11-15). At 50 C and 60 C, the selectivity of the oxidation process with both catalysts was dramatically reduced with the enhancement of the yielding percentages of dpn and mpn and other unknown side products (Scheme 2), considerably with prolongation of time (Tables 2a and 2b, entries [16][17][18][19][20][21][22][23][24][25]. This could be estimated with the TONs values.…”

“…[ 14,19 ] The influence of the electronic and steric aspects of the ligandated organic backbone in the metallated complex catalysts, as well as the type and charge of the central metal ion in such sulfide oxidation protocols, displayed a superior role in the catalytic cycles, which have been discussed in the literature. [ 20,21 ]…”

“…[14,19] The influence of the electronic and steric aspects of the ligandated organic backbone in the metallated complex catalysts, as well as the type and charge of the central metal ion in such sulfide oxidation protocols, displayed a superior role in the catalytic cycles, which have been discussed in the literature. [20,21] Metallation of the molecules based on organic backbones elucidated a wonderful role for a clear improvement in their function against microbial and cancer cell lines, as effective drugs over their free uncoordinated organic molecules. For that, variable transition metal of different oxidation states in their coordination compounds of alternative geometrical structures monitors their bio-potential with DNA and microorganisms.…”

Incorporation of Cation Affects the Redox Reactivity of Fe–NNN Complexes on C–H Oxidation

“…While 1-Fe generally demonstrated a preference to the HAT oxidation pathway, addition of di- and tri-cations increased the OAT/HAT product ratios from around 0.67 up to 4.4. The increased reactivity could be attributed to the addition of cationic charges, which promotes the OAT pathway. − Preliminary kinetic studies by UV–vis spectroscopy, conducted with 1-Fe and addition of K + , Ba 2+ , and La 3+ , showed faster formation of products when any cation was present, as shown by the faster increase in absorptions within the same time period. A direct observation of each product and calculation of rate constants could not be performed by UV–vis spectroscopy due to the convoluted spectra, with all three products, anthracene, anthrone, and anthraquinone all absorbing in the range of 340–380 nm (Figure S23).…”

New iron(iii) complex of bis-bidentate-anchored diacyl resorcinol on a Fe3O4 nanomagnet: C–H bond oxygenation, oxidative cleavage of alkenes and benzoxazole synthesis

“…The catalytic cycle begins in the presence of the bimetallic complex and TBHP and/or O 2 , which oxidize the iron(III) complex to produce high-valent metal-oxo species by binding to the iron(III) in the catalyst's structure. 76,77 This species in turn produces short-lived alkyl radicals in the C-H bond's oxidation (cycle I). In view of the products obtained from the C-H bond oxidation, the alcohol produced transforms to its corresponding aldehyde or ketone (cycle II).…”