Transition metal–carbon bonds. Part XXIV. Alkenyl- and allenylplatinum(II) and alkenyl-palladium(II) complexes

Acetylene–platinum(0) complexes [Pt(ac)(PPh3)2] react with acids (HX)(X = Cl or OCOCF3) to give alkenyl–platinum(II) complexes of type trans-[PtX(alkenyl)(PPh3)2]. Other alkenyl complexes of this type (X = Br) were made from [Pt(PPh3)x] and vinylic bromides. Hydrazine reduction of cis-[MCl2(PMe2Ph)2](M = Pt or Pd) in the presence of β-bromostyrene gives trans-[MBr(CH:CHPh)(PMe2Ph)2] in poor yields. 1H N.m.r. studies show that in alkenyl complexes, prepared by protonation of acetylene complexes, the added proton and the platinum are cis on the alkenyl double-bond. Protonation also goes in the Markownikoff sense, i.e. [Pt(RC⋮CH)(PPh3)2] gives [PtX(RC:CH2)(PPh3)2]. Some allenyl complexes of the type trans-[PtCl(CH:C:CR1R2)(PPh3)2] were synthesized from Pt(PPh3)3 and prop-2-ynylic halides, HC⋮CC(Cl)R1R2(R1, R2= H, Me or Ph, etc.). Values of the coupling constants J(Pt–H), J(H–H), and J(P–H) are used to confirm the structures and assign the stereochemistry of these complexes. Other 1H and 31P n.m.r. data and also i.r. data are given and discussed.