P-S Bond Scission by Bis(cyclopentadienyl)molybdenum(IV) Dichloride, Cp2MoCl2(aq): First Documented Example of an Organometallic Complex Hydrolyzing Thiophosphinates

Thiophosphinate hydrolysis involving P-S bond scission is desirable for the degradation of organophosphate neurotoxins, and we report the first case for such a hydrolytic process by an organometallic compound. The metallocene, bis(cyclopentadienyl)molybdenum(IV) dichloride, Cp2MoCl2 (Cp = (eta)^5-C5H5), hydrolyzes a variety of thioaryl diphenylphosphinates in an aqueous THF solution. P-S scission of p-methoxythiophenyl diphenylphosphinate has a 500-fold rate of acceleration in the presence of Cp2MoCl2(aq) with activation parameters of 20(3) kcal mol^-1 and -15(3) cal mol^-1 K^-1 for (delta)H(double dagger) and (delta)S(double dagger), respectively. These activation parameters and the rate acceleration are consistent with an intermolecular hydrolytic process in which the Cp2Mo serves as a Lewis acid to activate the phosphinate for nucleophilic attack. Furthermore, (rho)= 2.3 (25 °C) which indicates a single nonconcerted mechanism in which the rate determining step is the nucleophilic attack on the activated phosphinate.