Stereoselective Alkane Oxidation with meta-Chloroperoxybenzoic Acid (MCPBA) Catalyzed by Organometallic Cobalt Complexes

Abstract

Cobalt pi-complexes, previously described in the literature and specially synthesized and characterized in this work, were used as catalysts in homogeneous oxidation of organic compounds with peroxides. These complexes contain pi-butadienyl and pi-cyclopentadienyl ligands: [(tetramethylcyclobutadiene (10). Complexes 1 and 2 catalyze very efficient and stereoselective oxygenation of tertiary C-H bonds in isomeric dimethylcyclohexanes with MCBA: cyclohexanols are produced in 39 and 53% yields and with the trans/cis ratio (of isomers with mutual trans-or cis-configuration of two methyl groups) 0.05 and 0.06, respectively. Addition of nitric acid as co-catalyst dramatically enhances both the yield of oxygenates and stereoselectivity parameter. In contrast to compounds 1 and 2, complexes 9 and 10 turned out to be very poor catalysts (the yields of oxygenates in the reaction with cis-1,2-dimethylcyclohexane were only 5%-7% and trans/cis ratio 0.8 indicated that the oxidation is not stereoselective). The chromatograms of the reaction mixture obtained before and after reduction with PPh 3 are very similar, which testifies that alkyl hydroperoxides are not formed in this oxidation. It can be thus concluded that the interaction of the alkanes with MCPBA occurs without the formation of free radicals. The complexes catalyze oxidation of alcohols with tert-butylhydroperoxide (TBHP). For example, tert-BuOOH efficiently oxidizes 1-phenylethanol to acetophenone in 98% yield if compound 1 is used as a catalyst.

Hexacoppergermsesquioxanes as complexes with N-ligands: Synthesis, structure and catalytic properties

“…It is important to note that catalyzed by 2 oxidation of cis-1,2-dimethylcyclohexane with meta-CPBA occurs stereoselectively (the trans/cis ratio was 0.3; (we found previously analogous effect; see, for example, ref. [108]).…”

Cobalt(II) Complexes with N,N,N-Scorpionates and Bidentate Ligands: Comparison of Hydrotris(3,5-dimethylpyrazol-1-yl)borate Tp* vs. Phenyltris(4,4-dimethyloxazolin-2-yl)borate ToM to Control the Structural Properties and Reactivities of Cobalt Centers

“…To date, some cobalt compounds, including Tp R [ 27 , 28 ] and To M [ 10 ] complexes, have been employed as catalysts for hydrocarbon oxygenation with organic peroxides (ROOH) such as tert -butyl hydroperoxide (TBHP) [ 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ] and meta -chloroperbenzoic acid ( m CPBA) [ 10 , 37 , 38 , 39 , 40 , 41 , 42 , 43 ]. Therefore, we explored catalysis of the entitled mixed ligand complexes toward alkene oxidation with TBHP and alkane oxidation with m CPBA as indicated below.…”

“…These trends suggested that the reactions proceeded through a radical mechanism. It is known that oxidations of aliphatic C–H groups with H 2 O 2 through radical mechanisms result in generation of the corresponding alkylhydroperoxides, and the resulting alkylhydroperoxides are converted to alcohols when the reaction mixtures are treated with PPh 3 quencher prior to analysis [ 43 ]. In our system, the absence of an increase of A suggested that cyclohexenylhydroperoxide did not form.…”

Copper(II) Complexes of Arylhydrazone of 1H-Indene-1,3(2H)-dione as Catalysts for the Oxidation of Cyclohexane in Ionic Liquids

“…When using H 2 O 2 as oxidant, a higher selectivity towards the alcohol is observed, while with TBHP, the amount of this product is lower than that of the ketone ( [13][14][15][16].…”