P-31 NMR INVESTIGATION OF THE COMPARATIVE HYDROLYTIC BREAKDOWN OF NICKEL(II) AND CADMIUM(II) VERSUS ZINC(II) BIS(O,O-DIETHYL DITHIOPHOSPHATES) IN AN AQUEOUS-MEDIUM

The hydrolytic breakdown of nickel(II) and cadmium(II) bis(O,O-diethyl dithiophosphates) 1b and c, respectively in aqueous dimethoxyethane a t 85 degrees C have been studied using P-31 NMR spectroscopy. The comp lexes are hydrolysed at different rates although in each case the proc ess leads to identical end-products, viz. phosphoric acid 7, O-ethyl O ,O-dihydrogen phosphorothioate 8, O,O-diethyl O-hydrogen phosphorothio ate 9, and ethyl dihydrogen phosphate 10. Comparison of the kinetic re sults obtained with those for the previously studied zinc(II) analogue 1a show that there is ca. one hundred-fold decrease in the rate of hy drolysis for the nickel(II) complex, this being ascribed to the interv ention of two hitherto unobserved hydrated species 11 and 12, both of which are sufficiently stable to be observed by P-31 NMR spectroscopy. Similar intermediates are not observed with the cadmium(II) complex 1 c which hydrolyses at a comparable rate to its zinc counterpart. These results are explained in terms of the respective metal-sulfur bond st rengths of the dithiophosphate complexes and further support the conte ntion that hydrolysis occurs by attack of water at the metal centre fo llowed by the loss of O,O-diethyl S-hydrogen phosphorodithioate 3, the primary hydrolysis product.