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 iPrS 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.