Biologically inspired oxidation catalysis

Abstract

The development of processes for selective hydrocarbon oxidation is a goal that has long been pursued. An additional challenge is to make such processes environmentally friendly, for example by using non-toxic reagents and energy-efficient catalytic methods. Excellent examples are naturally occurring iron- or copper-containing metalloenzymes, and extensive studies have revealed the key chemical principles that underlie their efficacy as catalysts for aerobic oxidations. Important inroads have been made in applying this knowledge to the development of synthetic catalysts that model enzyme function. Such biologically inspired hydrocarbon oxidation catalysts hold great promise for wide-ranging synthetic applications.

Towards robust alkane oxidation catalysts: electronic variations in non-heme iron(ii) complexes and their effect in catalytic alkane oxidation

“…A number of different classes of alkane oxidation catalysts have been developed during the last 50 years, including the cobalt and manganese acetate catalyst systems used industrially, 5 the heme-based iron complexes containing porphyrin-type ligands used in nature, 6,7 polyoxometalates [8][9][10] and more recently, non-heme iron based catalyst systems. [11][12][13][14][15][16][17] The metal catalysts are typically combined with oxidants, which can have different oxo transfer abilities 18 , for example H 2 O 2 , O 2 , ClO -, PhIO, O 3 or N 2 O, whereby the first two oxidants are economically and environmentally the most attractive oxidants. 19,20 An appealing feature of non-heme iron catalysts is that ligand modifications and catalyst tuning are relatively straightforward, compared for example with porphyrintype ligand systems.…”

The Formazanate Ligand as an Electron Reservoir: Bis(Formazanate) Zinc Complexes Isolated in Three Redox States

“…Recently, there has been increased interest in redox processes that do not occur at the metal centre, but instead take place within the ancillary ligand framework (so-called 'redox-active' or 'non-innocent' ligands). [1] The use of organic ligands as redox equivalents is of key importance in biological (enzymatic) transformations, [2] and has been shown to open new reactivity pathways in catalysis. [1c] The most studied ligands of this class are dithiolenes and dioxolenes, while recent work has focussed on α-diimines [3] and bis(imino)pyridines.…”

Iron Catalyzed Highly Enantioselective Epoxidation of Cyclic Aliphatic Enones with Aqueous H2O2

“…[1][2][3][4] Catalytic epoxidation methodologies based on iron complexes and peroxides (especially H 2 O 2 ), which can be considered as biologically inspired, are interesting because of the availability and low environmental impact of these reagents. [5][6][7][8][9][10][11][12][13][14][15]16 Despite appealing, the approach is challenging because it requires the design of iron coordination complexes that can activate the O-O bond of peroxides to create selective metal based oxidants, and avoid the often facile production of hydroxyl radicals via the Fenton reaction. 10,11,17,18 Recent reports have disclosed successful examples where asymmetric epoxidation is accomplished, in some cases producing high levels of stereoselectivity ( Figure 1).…”

“…In general, substitutions at the olefinic side ( and β) decrease ee's, while substitutions at the opposite side (' and β') lead to important improvement. For example, alkyl substitution at the  position of 5 and 6-member ring enones caused a significant decrease in ee's (62-65% ee, entries [5][6], that could be partially rescued by employing 2 as catalyst (for S5 75% yield and 76 % ee, and for S6 81 % yield and 75% ee). Also, for tert-butyl group in  position the reaction didn't take place (entry 7, S7).Although the current ee values leave room for improvement, it should be stated that the current catalysts constitute the first ones that provide good enantioselectivities for these substrates.…”