Multinuclear Copper Triethanolamine Complexes as Selective Catalysts for the Peroxidative Oxidation of Alkanes under Mild Conditions

Abstract

Copper species are widely found in nature and are present in many enzymes as di-, tri-or polynuclear Cu centers that catalyze selectively various oxidation reactions.[1] These reactions include the poorly characterized particulate methane monooxygenase (pMMO), which is present in methanotrophs, wherein a tri-or multinuclear Cu cluster catalyzes alkane hydroxylation and alkene epoxidation.[1f-i] Although increasing attention has been paid to the design of Cu complexes with polydentate ligands as models of copper oxidases [1a,b, 2] and some mononuclear compounds have been

Mild Peroxidative Oxidation of Cyclohexane Catalyzed by Mono‐, Di‐, Tri‐, Tetra‐ and Polynuclear Copper Triethanolamine Complexes

“…The Cu À O3A bond length of 1.9420 (14) does not differ from the standard values for m-O À Cu bonds and agrees with the lengths (ca. 1.91 À 1.95 ) found in related compounds, [35,40,41] whereas the Cu À O1 and Cu À O2 distances [2.5640(18) and 2.4445 (18) , respectively] are remarkably longer than the normal Cu À O amino alcohol bond distances. Nevertheless, they lie in the 2.43 -2.56 range reported for 2a, 5 [35] and other triethanolaminate complexes.…”

“…1.91 À 1.95 ) found in related compounds, [35,40,41] whereas the Cu À O1 and Cu À O2 distances [2.5640(18) and 2.4445 (18) , respectively] are remarkably longer than the normal Cu À O amino alcohol bond distances. Nevertheless, they lie in the 2.43 -2.56 range reported for 2a, 5 [35] and other triethanolaminate complexes. [41,42] The Cu1 À O3 À Cu1A À O3A bridging mode is planar.…”

“…The Cu À Cu separation of 2.9222(5) and most of other bonding parameters agree with those found in related dinuclear complexes. [35,40,41] (1) …”

“…Nevertheless, most of these catalysts still provide very low yields (relative to cyclohexane) [26 -29,32 -34] and low selectivity, [26,30,31] require rather expensive [31,33] and environmentally unfriendly components, [34] are active only in the presence of various additives, [27,33,34] and/or involve complicated syntheses, [25,26,28,31 -33] thus being inaccessible on a large scale. Recently we have preliminary reported [35] a simple and convenient synthesis of several new multinuclear copper triethanolamine (H 3 tea) complexes using cheap, commercially available and environmentally tolerable reagents and opened up their potential application as highly active and selective catalysts or catalyst precursors for the mild peroxidative oxidation of alkanes to the corresponding alcohols and ketones. Hence, the main purpose of this work is to provide a detailed investigation of cyclohexane oxidation catalyzed by known [35] and newly synthesized copper triethanolamine complexes of diverse nuclearity (Scheme 1), thus extending the catalytic activity studies to a variety of experimental conditions, e.g., the oxidant-to-catalyst and substrate-tocatalyst molar ratios, reaction time, amount of solvent, multiple recycling of catalyst and the influence of various types of radical traps, aiming at the optimization of this process and the identification of the general type of mechanism in the search for an efficient way for cyclohexane oxidation.…”

C-Homoscorpionate Oxidation Catalysts—Electrochemical and Catalytic Activity

“…Indeed, oxidation of alkanes has been the object of considerable research [69][70][71][72][73][74][75][76][77][78], but still constitutes a serious challenge to modern chemistry, owing to the high inertness of these substrates. Currently, alkanes are mainly applied as fuels but it would be desirable to direct their application to the synthesis of organic products of a high added value.…”