Catalytic Production of Isothiocyanates via a Mo(II)/Mo(IV) Cycle for the “Soft” Sulfur Oxidation of Isonitriles

Abstract

In the presence of excess amounts of elemental sulfur, the dimolybdenum dinitrogen complex {Cp*Mo­[N­(iPr)­C­(Ph)­N­(iPr)]}2(μ-N2) (4; Cp* = η5-C5Me5) serves as a precatalyst for the production of isothiocyanates from isonitriles via highly efficient and atom-economical metal-mediated sulfur atom transfer (SAT) under mild conditions. Mechanistic and structural studies support a catalytic cycle for SAT involving initial formation of a Mo­(II) bis­(isonitrile) complex that then undergoes sulfination to generate a formal “side-bound” Mo­(IV) κ2-(C,S)-isothiocyanate as the key intermediate. This metal-catalyzed SAT process has further been employed for the “on-demand” production of isothiocyanates that are trapped in situ by benzhydrazides to provide thiosemicarbazides, which are useful precursors to biologically active thiadiazoles.

Chromatography‐Free Multicomponent Synthesis of Thioureas Enabled by Aqueous Solution of Elemental Sulfur

“…Recently a couple of innovative, multicomponent and one‐pot procedures have been published for the use of elemental sulfur in synthetic procedures [20–26] . Numerous methods rely on the known transformation of isocyanides to isothiocyanates with elemental sulfur in the presence of base or various metal catalysts, [19,27–35] which is utilized in particular for the synthesis of thioureas (Scheme 1). Zhou et al .…”

“…[17] Recently a couple of innovative, multicomponent and one-pot procedures have been published for the use of elemental sulfur in synthetic procedures. [20][21][22][23][24][25][26] Numerous methods rely on the known transformation of isocyanides to isothiocyanates with elemental sulfur in the presence of base or various metal catalysts, [19,[27][28][29][30][31][32][33][34][35] which is utilized in particular for the synthesis of thioureas (Scheme 1). Zhou et al developed a cobalt-catalyzed method for the synthesis of thioureas starting from isocyanides, elemental sulfur, aliphatic and aromatic amines under oxidative conditions.…”

Recent Advances in the Synthesis of Isothiocyanates Using Elemental Sulfur

“…The application of chalcogens or transition metal catalysts, such as selenium [67], tellurium [68], molybdenum [69,70] or rhodium [71], greatly facilitates the generation of ITCs offering excellent yields. These results have already been discussed in previous excellent reviews; thus, we provide only a focused overview of this field [72,73].…”

Recent Advances in Organic Reactions Involving Elemental Sulfur

“…The molybdenum dinitrogen complex 250 serves as a precatalyst for the production of isothiocyanates from isonitriles via sulfur atom transfer using elemental sulfur under mild conditions (Scheme ) . Mechanistic and structural studies revealed that an initially formed Mo(II) bis(isonitrile) complex 251 underwent sulfuration to generate a formal “side‐bound” Mo(IV) κ 2 ‐(C,S)‐isothiocyanate 252 as the key intermediate.…”