Synthesis and characterization of asymmetric [Mo2O2(μ-S)2(S2)(L)] complexes (L = bipy, en, dien) and their heterogeneous reaction with propylene sulfide

Abstract

Crystalline and amorphous molybdenum sulfide “MoSx” catalysts are well established in sulfur removal from petrochemicals in heterogeneous reactions. Accessibility of sulfido ligands on the catalyst surface is generally accepted as pre-requisite for catalytic initiation. Interest in study of discrete molecules with similar active sites for sulfur transfer reactions in organic reactions prompted synthesis of the asymmetric dinuclear complexes, [Mo2O2(μ-S)2(S2)(L)] (1, L = bipyridine (bipy); 2, L = ethylene diamine (en), 3, L = diethylenediamine (dien)) in facile ligand exchange reaction. A single crystal of 1 was obtained from DMF/ether solution as dark red plates and analyzed by X-ray diffraction. The complexes remove sulfur from propylene sulfide in a heterogeneous reaction at ambient temperature on the NMR scale. Reactivity expected to reflect the donation properties of L with the largest LMCT contribution rendering the most reactive sulfido ligand yielded surprising results. DFT calculations of the optimized minimal energy structures of all three complexes were performed and several possible isomeric structures evaluated. The optimal energy form of 1 compared well with its crystal structure and results from calculated structures of 2 and 3 agree with spectroscopic observations. The modest reactivity is in agreement with poor access to the disulfide as inferred by DFT structures of the complexes and the crystal structure of 1 where strong SS interactions were found along its b-axis.