Abstract
Two “Mo2O2S2”-based complexes with phosphinoyldithioformate ligands were synthesized from the metathesis reaction of [R2P(O)CS2]− with (Me4N)2[Mo2O2(µ-S)2(Cl)4] to give [Mo2O2(µ-S)2{R2P(O)CS2}2] (1; R = Ph, 2; R = Bn). The complexes were fully characterized, including the X-ray crystal structure for 1. Variable temperatures 31P NMR of 1 and 2 exhibit non-rigid behavior in solution where three and two coordination isomers were present, respectively. The organic substituent on the P atom greatly impacts the complex non-rigid properties and behavior. The catalytic activity of 1 and 2 towards sulfur atom transfer (SAT) using propylene sulfide and cyclohexene sulfide was explored, employing homogeneous reaction conditions at an ambient temperature on the NMR scale. The complexes showed distinctly different properties along with high conversions in short reaction times. A catalytic cycle consistent with the results is proposed.
Highlights
Each molybdenum is located slightly above the plane formed by the bridging sulfur atoms and the equatorial atom is in an overall distorted octahedral coordination geometry
Catalytic cyclohexene sulfide propylene sulfide as sulfur source.source
Treatment of thiiranes with a catalytic amount of the Re complex in the presence of H2 S showed increased catalytic activity compared to PPh3 [49], where complete conversion of cyclohexene sulfide to cyclohexene was observed after 5 min, and 100% conversion of propylene sulfide to propylene was achieved after 3 h
Summary
The catalytic transfer of sulfur atoms by transition metal complexes has received extensive attention due to its many industrial applications [1,2,3,4,5,6,7,8,9]. Sulfur atom transfer from a thiirane to a metal may proceed through either an oxidative addition reaction to the metal or in an insertion reaction into M-S bond accompanied by an internal redox of the ligand (Scheme 1) [5,6,9,25]. Dinuclear molybdenum complexes have a natural ability to coordinate sulfur and add sulfur atoms into the Mo-S bond to form sulfur ligand rings with several sulfur atoms [30]. These sulfur ligand rings undergo internal redox where elemental sulfur is expelled when the ring size becomes sterically crowded [30]. Metal center and (b) sulfur atom insertion into a metal-sulfur bond
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