Selective Oxidation of Nonrefractory and Refractory Sulfides by Cyclopentadienyl Molybdenum Acetylide Complexes as Efficient Catalysts Macchindra G. Chandgude • Ankush V. Biradar • Trupti V. Kotbagi • Vedavati G. Puranik • Mohan K. Dongare • Shubhangi B. Umbarkar Received: 31 May 2011 / Accepted: 23 August 2012 / Published online: 19 September 2012 Ó Springer Science+Business Media, LLC 2012 Abstract The synthesis and catalytic properties of molybdenum acetylide complexes CpMo(CO) 3 (–C:CR), R = Ph(1), C 6 H 4 –p-CF 3 (2) and C 6 H 4 –p-CH 3 (3) has been studied. The molybdenum acetylide complexes were syn- thesized from CpMo(CO) 3 Cl and aryl acetylenes via Ste- phens–Castro coupling reaction. These complexes were characterized by single crystal X-ray diffraction analysis, FTIR and 1 H NMR spectroscopy. These complexes on treatment with hydrogen peroxide, formed corresponding molybdenum oxo-peroxo species. These in situ formed oxo-peroxo species were found very active (up to 100 % conversion) and selective (up to 100 %) oxidation catalysts for various refractory and nonrefractory sulfides. Interest- ingly, even though the molybdenum acetylide complexes are homogeneous, they could be recycled very efficiently by extracting the catalytically active molybdenum oxo- peroxo species in aqueous phase. Keywords Homogeneous catalysis Á Molybdenum acetylide Á Refractory sulfide oxidation Á Oxo-peroxo species 1 Introduction Sulfur (S) is an essential element in the life processes of all living things including micro-organisms, higher plants, animals, and humans. Sulfur plays a major role in the formation of the proteins that are essential to sustain life in all biological organisms [1]. However, it is one of the major problems in fuel that causes air pollution leading to acid rains. Moreover, it poisons the catalyst in catalytic convertor [2]. In order to control the pollution, Environ- mental Protection Agency (EPA) has enforced stringent regulation for substantial reduction in the total sulfur content of gasoline and diesel fuel [3, 4]. Hence it is of great importance to develop effective ways to remove sulphur impurities from the fuel [5]. Commercially, these impurities are removed by hydrodesulfurization (HDS), which is a highly efficient process till date for removing nonrefractory sulfides, although not very effective for refractory sulfides [6]. An alternative route for removing refractory sulfides is oxidative desulfurization (ODS) pro- cess [7, 8]. Researchers worldwide have shown the use of heterogeneous Co–Mo or Co–Ni catalysts for HDS [9]. The refractory sulfides include dibenzothiophene (DBT) and especially 4,6-dimethyldibenzothiophene (DMDBT), which are difficult to remove by hydrodesulfurisation (HDS) process, owing to the steric hindrance of methyl groups of DMDBT that do not allow close contact with the catalyst surface [10]. In ODS process the organosulfur compounds are oxidized to their corresponding sulfones, and these products are removed by extraction, adsorption, distillation or decomposition [11, 12]. Though sulfur compounds in fuel are poison for catalytic converter, many sulphoxides and sulphones are used as intermediates in chemically and biologically active compounds, including therapeutic agents such as anti-ulcer (proton pump Electronic supplementary material The online version of this article (doi: 10.1007/s10562-012-0898-x) contains supplementary material, which is available to authorized users. M. G. Chandgude Á A. V. Biradar Á T. V. Kotbagi Á M. K. Dongare Á S. B. Umbarkar (&) Catalysis Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India e-mail: sb.umbarkar@ncl.res.in V. G. Puranik Centre for Material Characterization, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India 123 Catal Lett (2012) 142:1352–1360 DOI 10.1007/s10562-012-0898-x