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.