Preparation of Biscarboxylato Imido Alkylidene Complexes of Molybdenum and Cyclopolymerization of Diethyldipropargylmalonate To Give a Polyene Containing only Six-Membered Rings

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We wanted to prepare a catalyst that would yield polymers having exclusively one ring size and therefore began a search for new initiators containing `ancillary` ligands other than alkoxides. We report here that a new class of catalysts containing bulky carboxylate ligands can be prepared which encourage regioselective addition of the first triple bond to an alkylidene to give only a {beta}-subsituted metallacyclobutene and therefore polyenes that contain only six-membered rings in the polymer backbone as a consequence of specific head-to-tail cyclopolymerization. 14 refs., 1 fig., 2 tabs.