Ethynyl porphyrins bridging bis(phosphine)platinum(II) centers: molecular models for conjugated organometallic porphyrin polymers

Abstract

Linear ethynylporphyrin-bridged platinum(II) complexes, [X(R₃P)₂Pt–CC–Zn(por)–CC–Pt(PR₃)₂Y] [Zn(por) is a non-ethynylated porphyrin 1a] and related oligomers have been synthesized. Di- and tri-nuclear platinum centers are linked to different porphyrin arrays; the end groups Pt(PR₃)₂X and Pt(PR₃)₂Y (R = n-Bu or Ph; X = Y = Cl or I; X = Cl, Y = I) show that a ligand exchange Cl → I also occurs. The compounds containing PBu₃ as the ligand are more stable than the corresponding PPh₃ ones. The dinuclear platinum dimers containing one bridging porphyrin have been isolated and characterized by IR, UV/VIS, ¹H NMR and MALDI (matrix assisted laser desorption/ionization) mass spectroscopies. The mixture of longer oligomers was separated from the crude reaction products and could be identified by MALDI. The cis–trans isomerization of the porphyrin complexes with respect to the platinum precursor complexes, i.e. trans-[PtCl₂(PBu₃)₂], cis-[PtCl₂(PPh₃)₂] and trans-[PtH(Cl)(PPh₃)₂], was observed. The dimers and oligomers are expected to be model molecules for long chain organometallic polymers.