Bi- and Trinuclear Ruthenium Alkylidene Triggered Cyclopolymerization of 1,6-Heptadiynes:  Access to An−X−An Block and (An)3X Tristar Copolymers

Benzoic acid (4-(2-propoxy)-3-vinylphenyl) ester (1), the divinyl compounds terephthalic acid bis(4-(2-propoxy)-3-vinylphenyl) ester (2) and bis(4-(2-propoxy)-3-vinylphenoxy)diphenylsilane (3), and the trivinyl compound benzene-1,3,5-tricarboxylic acid tris(4-(2-propoxy)-3-vinylphenyl) ester (4) were used for the synthesis of a series of ruthenium-based mono-, bi-, and trinuclear metathesis catalysts, i.e., RuX2(IMesH2)(CH-2-(2-PrO)-C6H3-5-OOCC6H5) (X = Cl, I1a; X = OOCCF3, I1b), 1,4-[RuX2(IMesH2)(CH-2-(2-PrO)-C6H3-5-OOC)]2C6H4 (X = Cl, I2a; X = OOCCF3, I2b), [RuX2(IMesH2)(CH-2-(2-PrO)-C6H3-5-O)]2SiPh2 (X = Cl, I3a; X = OOCCF3, I3b), and 1,3,5-[RuX2(IMesH2)(CH-2-(2-PrO)-C6H3-5-OOC)]3C6H3 (X = Cl, I4a; X = OOCCF3, I4b) (IMesH2 = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene), where the corresponding trifluoroacetate-derived systems were prepared from the parent dichloro-substituted initiators via reaction with CF3COOAg. Initiators I1aI4a and I1bI4b were used for the cyclopolymerization of a series of 1,6-heptadiynes, i.e., dimethyl dipropargylmalonate (M1), diethyl dipropargylmalonate (M2), di-tert-butyl dipropargylmalonate (M3), 4-(ethoxycarbonyl)-1,6-heptadiyne (M4), 4,4-(bishydroxymethyl)-1,6-heptadiyne (M5), and 4-(hydroxymethyl)-1,6-heptadiyne (M6), to yield the corresponding An−X−An type block and (An)3X type tristar copolymers. Cleavage of the An−X−An type block copolymer M225−CH-[2-(2-PrO)-1,5-C6H3]-O-SiPh2-O-[2-(2-PrO)-1,5-C6H3]-CH-M225 with tetrabutylammonium fluoride resulted in the formation of the low-PDI telechelic homopolymer M225-CH-[2-(2-PrO)-1,5-C6H3]-OH with half the molecular weight of the parent block copolymer, indicative for an equal activity of both initiator sites in I3b. An interesting finding was the fact that monomers with reduced steric demands in the 4-position (M1, M4, M5, and M6) could even be polymerized with chlorine-based initiators; however, values for Mn were in general lower than the calculated ones. In contrast to Mo-based initiators, no influence of monomer size on the structure of the final polymer in terms of the ratio of 1,2-(cyclopent-1-ene)vinylene and 1,3-(cyclohex-1-ene)methylidene units, respectively, was observed.