Effect of chelate-ring size on spectroscopic and chemical properties of methylplatinum(II) complexes of the ditertiary phosphines Ph2P[CH2] n PPh2(n= 1,2, or 3)

The ditertiary phosphines Ph2P[CH2]nPPh2(n= 2 or 3, dppe and dppp respectively) displace cyclo-octa- 1,5-diene (cod) from [PtMe(cod)Cl] to give monomeric complexes [PtMe(Cl)(dppe)] and [PtMe(Cl)(dppp)]. A similar reaction using Ph2PCH2PPh2(dppm) gives predominantly an oligomer [{PtMe(Cl)(dppm)}n] containing bridging dppm groups, together with a small amount of monomeric [PtMe(Cl)(dppm)]. Molecular-weight measurements suggest that the oligomers [{PtMe(X)(dppm)}n](X = Cl or I) may be trimeric in solution (n= 3). Dimethyl complexes, [PtMe2(diphosphine)], have been obtained from [PtMe2(cod)] and dppe, dppp, or dppm, 31P N.m.r. parameters and oxidative-addition reaction of the complexes with iodine or methyl iodide are very dependent on the ditertiary phosphine.