Synthesis and characterization of platinum(ii) di-ynes and poly-ynes incorporating ethylenedioxythiophene (EDOT) spacers in the backbone

Abstract

A series of trimethylsilyl-protected di-alkynes incorporating 3,4-ethylenedioxythiophene (EDOT) linker groups Me₃Si–CC–R–CC–SiMe₃ (R = ethylenedioxythiophene-3,4-diyl 1a, 2,2′-bis-3,4-ethylenedioxythiophene-5,5′-diyl 2a, 2,2′,5′,2′′-ter-3,4-ethylenedioxythiophene-5,5′′-diyl 3a) and the corresponding terminal di-alkynes, H–CC–R–CC–H 1b–2b has been synthesized and characterized and the single crystal X-ray structure of 1a has been determined. CuI-catalyzed dehydrohalogenation reaction between trans-[(Ph)(Et₃P)₂PtCl] and the terminal di-alkynes 1b–2b in ⁱPr₂NH/CH₂Cl₂ (2 : 1 mole ratio) gives the Pt(II) di-ynes trans-[(Et₃P)₂(Ph)Pt–CC–R–CC–Pt(Ph)(Et₃P)₂] 1M–2M while the dehydrohalogenation polycondensation reaction between trans-[(ⁿBu₃P)₂PtCl₂] and 1b–2b (1 : 1 mole ratio) under similar reaction conditions affords the Pt(II) poly-ynes trans-[Pt(PⁿBu₃)₂–CC–R–CC-]_n1P–2P. The di-ynes and poly-ynes have been characterized spectroscopically and, for 1M and 2M, by single-crystal X-ray which confirms the “rigid rod” di-yne backbone. The materials possess excellent thermal stability, are soluble in common organic solvents and readily cast into thin films. Optical absorption spectroscopic measurements reveal that the EDOT spacers create stronger donor-acceptor interactions between the platinum(II) centres and conjugated ligands along the rigid backbone of the organometallic polymers compared to the related non-fused and fused oligothiophene spacers.