Ligand-coupling through δ-sulfurane formed on treatment of sulfilimines with hydride anion

Abstract

The tetracoordinated hypervalent species named as $\sigma$- sulfurane 1 are relatively unstable and hence tend to transform, by extruding a ligand or two with a pair of electron, to stable compounds in which the central atom resumes a normal valency. It is best explained by a new ligand-coupling concept 2. Since the ligand-coupling is clean-out reaction, it is also promising for the reduction of sulfilimines to the sulfides. In order to elucidate the intermediate sulfurane derived from the reaction of N-(p-tolylsulfonyl) sulfilimines with lithium aluminum hydride, the reductions of various N-(p-tolylsulfonyl) sulfilimines with lithium aluminum hydride were carried out. In order to see the relative reduction rate of S-(p-substitutedphenyl)-S-methyl-N-(p-tolylsulfonyl) sulfilimine, competitative reaction between various S-(p-substitutedphenyl)-S-methyl-N-(p-tolylsulfonyl) and S-methyl-S-phenyl-N-(p-tolylsulfonyl)sulfilimine with lithium aluminum hydride was carried out. The obtained $\rho$-value was +1.5. The reaction appears apparently to be initiated via nucleophilic attack of the hydride on the trivalent sulfur. The initial back attack by hydride anion may form the $\sigma$-sulfurane contaning axial hydride ligand and then interconversion of the ligand takes place by pseudorotation to form the preferred sulfurane in which the hydride is replaced at an equatorial position and the apicophilic 3 benzyl group becomes an axial ligand in the incipient $\sigma$-sulfurance.