Sulfuranes are relatively specialized functional group that feature tetravalent sulfur, with the formula SR Likewise, persulfuranes feature hexavalent SR.
One of the few all-carbon persulfuranes has two methyl and two biphenylene ligands:
It is prepared from the corresponding sulfurane 1 with xenon difluoride / boron trifluoride in acetonitrile to the sulfuranyl dication 2 followed by reaction with methyllithium in tetrahydrofuran to (a stable) persulfurane 3 as the cis isomer. X-ray diffraction shows C−S bond lengths ranging between 189 and 193 pm (longer than the standard bond length) with the central sulfur atom in a distorted octahedral molecular geometry.