Iron Complex Catalyzed Selective C–H Bond Oxidation with Broad Substrate Scope

Abstract

The use of a peroxidase-mimicking Fe complex has been reported on the basis of the biuret-modified TAML macrocyclic ligand framework (Fe-bTAML) as a catalyst to perform selective oxidation of unactivated 3° C-H bonds and activated 2° C-H bonds with low catalyst loading (1 mol %) and high product yield (excellent mass balance) under near-neutral conditions and broad substrate scope (18 substrates which includes arenes, heteroaromatics, and polar functional groups). Aliphatic C-H oxidation of 3° and 2° sites of complex substrates was achieved with predictable selectivity using steric, electronic, and stereoelectronic rules that govern site selectivity, which included oxidation of (+)-artemisinin to (+)-10β-hydroxyartemisinin. Mechanistic studies indicate Fe(O) to be the active oxidant during these reactions.

Selective photocatalytic hydroxylation and epoxidation reactions by an iron complex using water as the oxygen source

“…This result is consistent with a similar oxidation reported by us using complex 1 and mCPBA as the oxidant. 19 Furthermore, the regioselective oxidation of 3° C–H bonds in the natural product derivative of cedrol, cedryl acetate, was performed. Cedrol is a sesquiterpene alcohol found in essential oil, having a very rigid structure with five 3° C–H positions.…”

“…However, the photochemical hydroxylation of unactivated C–H bonds using the [Fe II (MePy 2 tacn)] 2+ complex described above has not been reported. Mechanistic studies on iron-catalysed hydroxylation reactions have revealed that in both chemical and biological systems, efficient and selective hydroxylation of unactivated C–H bonds has been mostly catalysed by reactive intermediates such as oxoiron( v ) (synthetic systems), 14 , 15 , 19 the isoelectronic oxoiron( iv ) radical cation (heme enzymes) 4a , 11c , d and [(μ-O) 2 Fe IV 2 ] (methane monooxygenase 11a , b ). None of these intermediates have been formed in the photochemical systems reported to date using [Fe II (N 4 Py)] 2+ and [Fe II (MePy 2 tacn)] 2+ complexes, which explains the absence of iron catalysts being used to catalyse photochemical C–H bond oxidation in the literature.…”

“… 15 Moreover, complex 1 in combination with chemical oxidants catalyses the oxidation of unactivated alkanes, alkenes and alcohols selectively. 15b , 17b , 18 , 19 The high selectivity obtained has been attributed to the presence of oxoiron( v ) and [{(bTAML)Fe IV } 2 (μ-O)] 2– ( 2 ) as active intermediates in these reactions. We have also shown that the oxidant [Ru III (bpy) 3 ] 3+ , generated either chemically or photochemically, is a competent oxidant to oxidize the [(bTAML)Fe III (OH 2 )] – ( 1 ) complex in solution to the catalytically active [{(bTAML)Fe IV } 2 (μ-O)] 2– dimer ( 2 ).…”

Recent Advances in Iron Catalyzed Oxidation Reactions of Organic Compounds

“…Gupta demonstrated that a TAML ligand also can be employed in site‐selective oxidation reactions (Scheme ) . The polyfunctional compound 7 gave the tertiary alcohol a the oxidation product despite the presence of several other oxidizable CH groups present in the molecule.…”

Oxoiron(V) Complexes of Relevance in Oxidation Catalysis of Organic Substrates

“…Oxidation of CÀ H bonds catalyzed by [Fe III ( NO2 bTAML)(Cl)] 2À . [38] Figure 4. TPA, TPA-derivatives, PyTACN, 6-Me-PyTACN and BPMEN ligands [41,43] along with a schematic representation of their coordination around the iron(II) center.…”