Synthesis and characterisation of new acetylide-functionalised oligothiophenes and their dinuclear platinum complexes

A series of rigid-rod alkynes with extended π conjugation through oligothiophene linkage units in the backbone, 2,5-bis(trimethylsilylethynyl)thiophene Ia, 2,5-diethynylthiophene Ib, 5,5′-bis(trimethylsilylethynyl)-2,2′-bithiophene IIa, 5,5′-diethynyl-2,2′-bithiophene IIb, 5,5″-bis(trimethylsilylethynyl)-2,2′ : 5′,2″-terthiophene IIIa and 5,5″-diethynyl-2,2′ : 5′,2″-terthiophene IIIb, has been prepared. Treatment of the complex trans-[PtPh(Cl)(PR₃)₂] (R = Et or Buⁿ) with half an equivalent of the diterminal alkynyl oligothiophene chromophores Ib-IIIb in CH₂Cl₂-NHPrⁱ₂, in the presence of CuI, at room temperature, afforded the platinum dimers trans-[(Et₃P) ₂PhPt-C≡CR′C≡C-PtPh(PEt₃)₂] (R′ = thiophenediyl 1a, bithiophenediyl 2 or terthiophenediyl 3) and trans-[(Buⁿ₃P) ₂PhPt-C≡CR′C≡C-PtPh(PBuⁿ ₃)₂] 1b (R′ = thiophenediyl) in good yields. All the new compounds have been characterised by analytical and spectroscopic methods, and the single-crystal structures of IIa, 1a and 2 have been established.