Studies of C−S Bond Cleavage Reactions of Re(V) Dithiolates: Synthesis, Reactivity, and Mechanism

A series of rhenium(V) complexes, [(X)(ReO)(dt)(PPh3)] and [(o-SC6H4PPh2)(ReO)(mtp)], were
prepared to explore electronic effects on the C−S cleavage reaction that occurs upon reaction with PAr3
at ambient temperature [where X = S(C6H4-p-Z) (Z = OMe, Me, H, F, Cl), OPh, Cl, and SC2H5, and dt is
the chelating dithiolate ligand derived from 2-(mercaptomethyl)thiophenol, 1,2-ethanedithiol, 1,3-propanedithiol, 1,3-butanedithiol, and 2,4-pentanedithiol]. The scope and selectivity of the C−S activation were
examined. The C−S bond cleavage to form metallacyclic Re(V) complexes with a Re⋮S core occurs only
for the complexes with mtp and pdt frameworks and X = SAr and SC2H5. The difference in reactivity is due
to the different donating abilities of ancillary and dithiolate ligands, especially their π-donating ability, which
plays a critical role in C−S activation. The kinetics of the C−S activation process was determined;
nucleophilic attack of PPh3 on the oxo group of the ReVO core appears to be the rate-controlling step. The
reaction is accelerated by electron-poor ArS ligands, but is unaffected by the substituents on phosphines.
A detailed mechanistic study is presented. The results represent a rare example of migration of alkanethiolate
leading to the formation of alkylthiolato complexes.