Reactivity of [Pt(CH2X)2(Ph2PCH2PPh2-PP′)](X = Cl, Br, or I): four- to five-membered ring expansions. Crystal structure of [bis(diphenylphosphino)-methane-PP′]bis(chloromethyl)platinum(II)

Abstract
Addition of CH2N2 to the chelates [PtX2(dppm-PP′)](X = Cl, Br, or I; dppm = Ph2PCH2PPh2) gives the complexes [Pt(CH2X)2(dppm-PP′)](2a)–(2c) which have been fully characterised. The X-ray crystal structure of [Pt(CH2Cl)2(dppm-PP′)](2a) has been determined in confirmation of its chemical identity (orthorhombic, space group Pbca, R= 0.053 for 2 499 observed reflections [I/σ(I) 2.0]. Addition of HCl to complex (2a) gives [PtCl(CH2Cl)(dppm-PP′)](3). Treatment of (2a) with phosphines or pyridine leads to a ring-expansion reaction to give [PtL(CH2Cl)(CH2PPh2CH2PPh2)]Cl [L = pyridine (4a), PPh3(4b), or PPh2H (4c)]. With dppm, (2a) gives the bis chelate [Pt(CH2PPh2CH2PPh2)2]Cl2(5). The mechanism of these ligand-promoted ring expansions is discussed. The products have been fully characterised by a combination of elemental analysis, i.r., 1H, and 31P-{1H} n.m.r. spectroscopy.