New Selective Synthesis of Dithiaboroles as a Viable Pathway to Functionalized Benzenedithiolenes and Their Complexes

A synthetic protocol to synthesize 2-bromobenzo-1,3,2-dithiaboroles in one step from easily accessible benzene bis(isopropyl thioether)s has been developed. The reaction is remarkably specific in converting substrates with two adjacent (i)PrS moieties while leaving isolated thioether functions and other functional groups intact. On the basis of the spectroscopic detection or isolation of reaction intermediates, a mechanistic explanation involving a neighbor-group-assisted dealkylation as a key step is proposed. The resulting products featuring one or two dithiaborole units were isolated in good yields and fully characterized. Subsequent methanolysis, which was carried out either as a separate reaction step or in the manner of a one-pot reaction, gave rise to functionally substituted benzenedithiols. The feasibility of a methylphosphoryl-substituted benzenedithiol to act as a dianionic S,S-chelating ligand was demonstrated with the formation of paramagnetic Ni(III) and Co(III) complexes. Selective reduction of the phosphoryl group afforded a rare example of a phosphino dithiol which was shown to act as a monoanionic P,S-bidentate ligand toward Pd(II). All complexes were characterized by spectral data and X-ray diffraction studies, and the paramagnetic ones also by superconducting quantum interference device magnetometry.