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

Abstract

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.