Factors relevant for the ruthenium-benzylidene-catalyzed cyclopolymerization of 1,6-heptadyines

Fourteen metathesis initiators that had been designed for use in the living polymerization of diethyl dipropargylmalonate (DEDPM), including the Hoveyda catalyst [RUCl(2-)(IMesH(2))(=CH-2-(2-PrO)_C(6)H(4))] (1a), as well as [Ru(CF(3)COO)(2)- (IMesH(2))(=CH-2-(2-PrO)-C(6)H(4))] (1b), [Ru(CF(3)CF(2)COO)(2)(IMesH(2))(=CH-2-(2-PrO)-C(6)H(4))] (1c), [Ru(CF(3)CF(2)CF(2)COO)(2)(lMesH(2))(=CH-2-(2-PrO)-C(6)H(4))] (1d), [RuCl(2)(IMesH(2))(=CH-2,4,5(MeO)(3)-C(6)H(2))] (2a), [Ru(CF(3)COO)(2)- (IMesH(2))(=CH-2,4,5-(MeO)(3) -C(6)H(2))] (2b), [Ru(CF(3)CF(2)COO)(2)(IMesH(2))(=CH-2,4,5-(MeO)(3)-C(6)H(2))] (2c), [Ru(CF(3)CF(2)- CF(2)COO)(2)(lMesH(2))(=CH-2,4,5-(MeO)(3)-C(6)H(2))] (2d), [RuCl(2)(IMes)(=CH-2-(2-PrO)-C(6)H(4))] (3a), [Ru(CF(3)COO)(2)(IMes)(=CH-2-(2-PrO)-C(6)H(4))] (3b), [RUCl(2)(IMesH(2))(=CH-2-(2-PrO)-5-NO(2)-C(6)H(3))] (4a), [Ru(CF(3)COO)(2)(I- MesH(2))(=CH-2-(2-PrO)-5-NO(2)-C(6)H(3))] (4b), [Ru(CF(3)CF(2)COO)(2)(IMesH(2))(=CH-2-(2-PrO)-5-NO(2)-C(6)H(3))] (4c), and [Ru(CF(3)CF(2)CF(2)COO)(2)(IMesH(2))(=CH-2-(2-PrO)-5-NO(2)-C(6)H)] (4d) (IMes = 1,3-dimesitylimidazol-2-ylidene; IMesH2 = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) were prepared. Living polymerization systems could be generated with DEDPM by careful tuning of the electronic nature and steric placement of the ligands. Although 1a, 2a, 3 a, 3b, and 4 a were inactive in the cyclopolymerization of DEDPM, and initiators 1b-d did not allow any control over molecular weight, initiators 2b-d and 4b-d offered access to class VI living polymerization systems. In particular, compounds 2b and 4d were superior. The livingness of the systems was demonstrated by linear plots of M. versus the number of equivalents of monomer added (N). For initiators 2b-d and 4b-d, values for K(p)/K(i) were in the range of 3-7, while 1b, 1c, and 1d showed a k(p)/k(i) ratio of > 1000, 80, and 40, respectively. The use of non-degassed solvents did not affect these measurements and underlined the high stability of these initiators. The effective conjugation length (N(eff)) was calculated from the UV/Vis absorption maximum (lambda(max)). The final ruthenium content in the polymers was determined to be 3 ppm.