Metal complexes of unsaturated tertiary phosphines and arsines. Part IX. Platinum complexes of tris-olefin-phosphine, -arsine, and -stibine chelate groups

Three new ligands, tris-(ortho-vinylphenyl) phosphine (tvpp) and its arsenic (tvpa) and antimony (tvps) analogues, have been prepared and their complexes with platinum(II) investigated: these derivatives have the general formula PtBr2(Ligand), and are monomeric in chloroform. l.r. and Raman spectral studies indicate that in the solid state there are two types of aliphatic C:C bond present. We conclude that one of the double bonds is co-ordinated and the other two are free. 1H n.m.r. data indicate that all three vinyl C:C bonds are equivalent in solution, indicating a rapid, bonded ⇌ non-bonded equilibrium for the ·CH:CH2 groups to the platinum atom. The complexes react with two moles of bromine with saturation of two double bonds to give a platinum(II) compound with one, co-ordinated double bond. A possible reaction mechanism is presented.