Reversible Intramolecular P–S Bond Formation Coupled with a Ni(0)/Ni(II) Redox Process

P–S
bond formation/cleavage mediated by a nickel ion supported
by a PPP ligand (PPP = P­[2-PiPr2-C6H4]2–) has
been investigated herein. To gain an entry into this chemistry, a
mononuclear thiolato nickel complex, (PPP)­Ni­(SAr) (1a,b) was prepared by treating the chloride starting material
with NaSPh. Upon carbonylation, this complex produces a nickel(0)
monocarbonyl species, (PPSArP)­Ni­(CO) (2a,b), in which the thiolate migrates onto the central P of the
ligand to give a P–S bond and two-electron reduction of a nickel­(II)
center. The reaction undergoes via a pseudo-first-order decay with
respect to consumption of a nickel­(II) thiolato species, suggesting
an intramolecular reaction under the excess CO­(g) conditions. The
reverse reaction involving P–S bond cleavage with concomitant
decarbonylation occurs to regenerate 1a,b in benzene. Reaction of 2a with trityl chloride results
in Ph3CSPh formation, whereas the reaction with MeI gives
methylation at a phosphide moiety or a thiolate group.