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

Abstract

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

Palanquin-Like Cu4Na4 Silsesquioxane Synthesis (via Oxidation of 1,1-bis(Diphenylphosphino)methane), Structure and Catalytic Activity in Alkane or Alcohol Oxidation with Peroxides

“…The experiment shown in Figure 5 demonstrated that the reduction of the reaction solution with PPh 3 gave rise to a higher concentration of cyclohexanol and a decrease of cyclohexanone concentration (compare top and bottom graphs in Figure 5). These changes testify that the alkyl hydroperoxide was formed in the course of the oxidation (the so called Shul'pin method [51][52][53][54][55][56][57][58][59][60][61][62][63][64]). The following selectivity parameters were obtained for the oxidation of n-heptane: Figure 6), as well as the selectivity parameters measured here, indicate that the reaction occurred with the participation of hydroxyl radicals, and alkyl hydroperoxides were formed as the main primary products [65].…”

High Catalytic Activity of Heterometallic (Fe₆Na₇and Fe₆Na₆) Cage Silsesquioxanes in Oxidations with Peroxides

“…Moreover, cyclohexane gives minimum number of oxidation products which are easily identified by the GC method. As demonstrated previously in other oxidations [19,[59][60][61][62][63][64][65][66][67][68], if the direct injection of a reaction sample into the chromatograph gave comparable amounts of cyclohexanol and cyclohexanone, the reduction of the sample with PPh3 (or certain sulfides) prior to GC analysis in many cases led to the noticeable predominance of the alcohol (Figure 8). The comparison of the results obtained before and after the reduction clearly indicated that cyclohexyl hydroperoxide was formed as the main primary product.…”

“…In order to determine concentrations of all cyclohexane oxidation products the samples of reaction solutions after addition of nitromethane as a standard compound were in some cases analyzed twice (before and after their treatment with PPh3) by GC (LKhM-80-6 instrument, columns 2 m with 5% Carbowax 1500 on 0.25-0.315 mm Inerton AW-HMDS; carrier gas argon) to measure concentrations of cyclohexanol and cyclohexanone. This method (an excess of solid triphenylphosphine is added to the samples 10-15 min before the GC analysis) was proposed by one of us earlier [19,[59][60][61][62][63][64][65][66][67][68]. Attribution of peaks was made by comparison with chromatograms of authentic samples.…”

A comparative study on the catalytic performance of heme and non‐heme catalysts: Metal porphyrins versus metal Schiff bases

“…The epoxidation of alkenes catalyzed by metalloporphyrins can proceed through the intermediacy of high valent oxo‐metal intermediates analogue to the oxoiron(V) species involved in cytochrome P450‐mediated oxidations [1a]. On the other hand, high valent manganese and iron oxo species were prepared using their Schiff base complexes . In other words, both metal porphyrins and metal Schiff bases demonstrated ability to form high valent oxo metal species under oxidative conditions.…”