Base-induced coupling of acetylenes held proximate to a metal: structures of unsymmetrical diphosphine complexes of platinum(II) containing strong vinyl alcohol–amine hydrogen bonds

Abstract

The complexes cis-[Pt(Cl₂)Y]·L [where Y = diphosphine Ph₂P·CH:C(CF₃)·C(PPh₂):C(OH)·CF₃: L = Et₂NH, Et₃N, Me₃N, or Pr₃N] have been synthesised by base-promoted coupling of phosphinoacetylene ligands in the complex cis-[PtCl₂(Ph₂PC⋮CCF₃)₂], and characterised by microanalysis, i.r. spectroscopy, and a single-crystal X-ray diffraction study of the diethylamine derivative (II). Crystals of (II) are monoclinic, space group P2₁/n, a= 18.707(13), b= 11.102(18), c= 19.383(13)Å, β= 111.48(10)°, D_m= 1.60 g cm^–3, Z= 4, D_c= 1.618 g cm^–3. The structure was solved by conventional heavy-atom methods and refined to R 0.065 for 3 384 observed diffractometer intensity data. The molecule contains an unsymmetrical diphosphine ligand formed via dimerisation of two alkyne fragments. The molecule of diethylamine is strongly hydrogen bonded to the oxygen atom of a vinyl alcohol moiety in the diphosphine ligand [N ⋯ O 2.74(2)Å]. Relevant metal–ligand distances are: Pt–Cl(1) 2.367(5), Pt–Cl(2) 2.357(5), Pt–P(1) 2.248(4), and Pt-P(2) 2.202(5)Å. The i.r. spectra of all four complexes are similar and characteristic of hydrogen-bonded systems with predominantly ion-pair C–Ō⋯ H–[graphic omitted](H)Et₂ character.