Base-promoted cleavage of a P–C bond in [PtCl2(Ph2PCH2PPh2-PP′)] under mild conditions

Abstract

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).