Homo and Hetero Trinuclear Metal Clusters of Co, Mn and Co/Mn Hybrid Materials as Catalysts for Epoxidation of Cyclohexe
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RESEARCH PAPER
Homo and Hetero Trinuclear Metal Clusters of Co, Mn and Co/Mn Hybrid Materials as Catalysts for Epoxidation of Cyclohexene M. Moosavifar1
•
A. Navid Arbat1,2 • M. Ranjbar1 • S. F. Hojati3
Received: 21 February 2020 / Accepted: 9 August 2020 Shiraz University 2020
Abstract Trinuclear metal clusters of Co, Mn, and Co/Mn hybrid of [Mn3(O)(CH3COO)6-(py)3ClO4], [Co3(O)(CH3COO)6-(py)3ClO4], [Co2Mn(O)(CH3COO)6-(py)3ClO4], and [CoMn2(O)(CH3COO)6-(py)3ClO4] were prepared and characterized by FT-IR and UV–Vis spectroscopic techniques. These homogeneous catalysts were investigated in the epoxidation of cyclohexene in the presence of H2O2/O2 under mechanical stirring conditions. The effect of the oxidant, reaction temperature, kind of promoter, and solvent system were investigated on conversion and epoxide selectivity. In these systems, NaBr was selected as a promoter of oxidation based on standard potential (X = Cl-, Br-) toward Co3?, and Mn3?. These homogeneous catalytic systems can be the perfect choice for epoxidation of cyclohexene with good conversion and high epoxide selectivity over short periods. Keywords Metal cluster complexes Epoxidation Homogeneous catalyst H2O2/O2 system NaBr
1 Introduction Metalloproteinase enzymes are classified in the multinuclear metal cluster category. Clusters as biomimetic system are similar to metalloenzymes which catalyze the variety of reactions including electron transformations and energy generating reactions in biological systems (Chavan 2002). Clusters with unique structural features and unusual reactivity have been obtained using several atoms as bridging ligands. Figure 1 shows the general structure of the trinuclear metal cluster. Carboxylate anions as versatile ligands with metal ions are common which have played key roles in the conceptual development of coordination chemistry. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s40995-020-00964-7) contains supplementary material, which is available to authorized users. & M. Moosavifar [email protected]; [email protected] 1
Department of Chemistry, Faculty of Science, University of Maragheh, Maragheh, P.O. Box 55181-83111, Iran
2
Department of Chemistry, Payam Noor University, Tehran, P.O. Box 19395-3697, Iran
3
Department of Chemistry, University of Sabzevar, Sabzevar, P.O. Box 96179-76487, Iran
Trinuclear metal clusters [MM0 3O(RCOO)6(L)3]x (where M, M0 = metal atoms, RCOO: carboxylate; L = terminal ligand (usually H2O, Py, …) if M = M0 , is called homonuclear cluster and if M# M0 , is called heteronuclear (mixed valance) clusters (Vlachos et al. 2004; Boudalis et al. 2005). There is a mixed valance oxidation state in heteronuclear compounds. In addition, trinuclear l3-oxo-centered carboxylate-bridged complexes have been considered for several reasons, for example, they are used as precursors for preparation of higher nuclearity clusters (Tao et al. 2016) until creating new opportunities
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