Preparation of biscarboxylato imido alkylidene complexes of molybdenum and cyclopolymerization of diethyldipropargylmalonate to give a polyene containing only six-membered rings

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 β-subsituted metallacyclobutene and therefore polyenes that contain only six-membered rings in the polymer backbone as a consequence of specific head-to-tail cyclopolymerization.