DFT studies on the mechanism of the conversion of thiols into disulfides and dihydrogen catalyzed by CpMn(CO)3 complex

A mechanism for conversion of thiols into disulfides and dihydrogen catalyzed by CpMn(CO)3 was studied in detail with the aid of density functional theory computations. Four major steps are involved in both of the two possible pathways (path1 and path2): (1) a ligand substitution process (dissociation of one carbonyl ligand and subsequent addition of RSH to the metal center); (2) intermolecular hydride migration; (3) addition of RSH and release of dihydrogen; (4) production of S2R2 and regeneration of the catalyst. Migration of the hydrogen from RSH to Cp ring can not be completed in one step, but need to form the key intermediate CpMnH(CO)2SR first. Ligand substitution process is the rate-determined reaction step. Path1 is the dominant pathway compared with path2, which mainly results from difficult formation of the five-member transition state in path2.

Thiols can be photo-converted into disulfides and dihydrogen using CpMn(CO)3 complex as catalyst.Figure optionsDownload as PowerPoint slideHighlights
► Photoconversion involves ligand exchange, H migration, H2 release and S2R2 formation.
► Large steric repulsion makes Int6 a 16-electron complex, not an 18-electron one.
► CpMn(CO)2HSR is an essential intermediate in hydrogen migration process.
► Release of dihydrogen is the rate-determined reaction step.
► Path1 is dominant over path2.