Kinetic and mechanistic studies on the reaction of (trithioperoxybenzoato)(dithiobenzoato)oxomolybdenum(IV), MoO(S3CC6H5)(S2CC6H 5), with tertiary phosphines

Article abstract of DOI:10.1021/ic00136a070

Kinetics of the reaction of (trithioperoxybenzoato)(dithiobenzoato)oxomolybdenum(IV), MoO(S₃CC₆H₅)(S₂CC₆H ₅), with tertiary phosphine, R₃P (R = H-Bu, C₆H₅), was investigated in 1,2-dichloroethane by the use of a stopped-flow spectrophotometer under pseudo-first-order conditions with excess R₃P. The result has revealed that MoO(S₃CC₆H₅)(S₂CC₆H ₅) undergoes sulfur abstraction by n-Bu₃P to give MoO(S₂CC₆H₅)₂, which further reacts with excess Bu₃P, affording an intermediate involving the charge-transfer interaction between the S₂CC₆H₅ moiety and n-Bu₃P. The subsequent rearrangement of the intermediate proceeds in a zero-order kinetics with respect to the phosphine concentration, yielding cis-MoO(S₂CC₆H₅)₂(n-Bu ₃P). The intermediate is stable below -40°C, and the structure is proposed on the basis of ¹³C and ¹H NMR spectra. A similar sulfur abstraction from the S₃CC₆H₅ moiety by Ph₃P occurs. The subsequent reaction of MoO(S₂CC₆H₅)₂ with excess Ph₃P, however, gives no charge-transfer complex between the S₂CC₆H₅ moiety and Ph₃P but an equilibrium mixture of trans- and cis-MoO(S₂CC₆H₅)₂(Ph₃P) and the dissociated species in solution. The difference in mechanisms between the reactions of Ph₃P and n-Bu₃P toward MoO(S₂CC₆H₅)₂ is interpreted in terms of the donor properties of these phosphines.