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

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 iPr 2NH/CH2Cl2 (2:1 mole ratio) gives the Pt(ii) di-ynes trans-[(Et3P)2(Ph)Pt-CC-R-CC-Pt(Ph)(Et 3P)2] 1M-2M while the dehydrohalogenation polycondensation reaction between trans-[(nBu3P)2PtCl 2] 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.