BASE-PROMOTED CLEAVAGE OF A P-C BOND IN [PTCL2(PH2PCH2PPH2-PP')] UNDER MILD CONDITIONS

The complex [PtCl2(dppm-PP′)](4)(dppm = Ph2PCH2PPh2) reacts with NaOH under mild conditions in dmso, MeCN, or water to give cis- and trans-[Pt2(µ-OH)2(POPh2)2(PMePh2)2](3a) and (3b). The same products can be obtained from [Ptl2(dppm-PP′)] under similar conditions, or by base hydrolysis of [PtCl2(PClPh2)(PMePh2)]. The products (3a) and (3b) have been characterised by a combination of molecular weight measurements and i.r., 31P-{1H}, and particularly, 1H n.m.r. spectroscopy; the 1H signals for the µ-OH protons are high-field (0 to –2 p.p.m.) 1:8:18:8:1 multiplets due to coupling to two equivalent 195Pt nuclei. The OH bridges are surprisingly stable but may be cleaved by aqueous HCl to give [PtCl2(PPh2OH)(PMePh2)](6), or by acetylacetone (Hacac) to give [Pt(acac)(POPh2)(PMePh2)](8). Two mechanisms for the reaction of OH– with the chelate (4) are considered: µ-OH formation followed by OH– attack at P or OH–attack at P followed by µ-OH formation. No intermediates have been identified but the feasibility of the latter mechanism is shown by the hydrolysis of [PtMe2(dppm-PP′)](12) to give [PtMe2(PPh2OH)(PPh2Me)](13).