First controlled cyclopolymerization of diethyl dipropargylmalonate by MoCl5-n-Bu4Sn-EtOH-quinuclidine and MoOCl4-n-Bu4Sn-EtOH-quinuclidine to give highly regular polyenes consisting exclusively of 1,2-(cyclopent-1-enylene)-vinylene units

Diethyl dipropargylmalonate (DEDPM) was cyclopolymerized by MoCl5-n-Bu4Sn-EtOH-quinuclidine (1:1:5:1) and MoOCl4-n-Bu4Sn-EtOH-quinuclidine (1:1:2:1), respectively, to produce poly(DEDPM) exclusively based on 1,2-(cyclopent-1-enylene)vinylene units (EtOH = ethanol). The exact ratio of five- to six-membered rings was determined by quantitative C-13 NMR measurements. The initiator efficiency of MoOCl4-n-Bu4Sn-EtOH-quinuclidine (1:1:2:1) was as high as 91%, the highest value ever reported for such systems, whereas the efficiency for the corresponding MoCl5-based initiator was less than or equal to 67%. The absorption maximum lambda(max) for poly(DEDPM) was 587 nm. A maximum effective conjugation length (N-eff) of 49 was estimated therefrom. Molecular weights and polydispersity indices (PDIs) of the polymers were determined in CHCl3 by size exclusion chromatography (SEC) vs polystyrene (PS). Additionally, light-scattering (LS) data were collected lambda = 690 nm in order to calculate absolute molecular weights. Polydispersities less than or equal to 1.9 were obtained. A plot of number of monomers (N) added vs molecular weights as determined by LS shows a linear dependence for both initiators. Multistage polymerizations of DEDPM indicated for both initiator systems that the catalytic species were active for at least 6 h in the presence of monomer yet do not fulfill the criteria of a truly living polymerization. The H-1 NMR spectrum of the in situ prepared MoCl5-based initiator showed two triplet carbene resonances at delta = 11.27 and 11.02 ppm, indicating the presence of more than one butylidene species. Accordingly, the C-13 NMR spectrum of the MoCl5-based initiator showed carbene resonances at delta = 276.0, 275.9, 272.4, 271.3, 262.7, and 261.6 ppm. Identical triplet resonances were observed for the MoOCl4-based initiator at delta = 11.27 and 11.07. The corresponding C-13 NMR spectrum revealed carbene resonances at delta = 276.1, 262.7, and 261.6 ppm.