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 = η5-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 ΔH‡ and ΔS‡, 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, ρ = 2.3 (25 °C) which indicates a single nonconcerted mechanism in which the rate determining step is the nucleophilic attack on the activated phosphinate.