Catalytic cyclopolymerization and copolymerization of 1,6-heptadiynes by Mo(CO)₆

The catalytic polymerization of a series of 1,6-heptadiynes (1-4) by Mo(CO)₆ under simple thermal conditions produces corresponding poly(1,6-heptadiyne)s with highly conjugated polyenes. The number-average molecular weights of the polymers range from 2400 to 110,000. The structures of the polymers depend on the types of monomers employed. Namely, diethyl dipropargylmalonate (DEDPM) and 1 result in a polyene backbone consisting of only five-membered rings, whereas the remaining monomers (2-4) result in a mixture of both five-membered and six-membered ring structures. The copolymerization of DEDPM and phenylacetylene (PA) can also be effected by the same catalysis to yield a polyene backbone consisting of only five-membered rings as well as PA. The relative molar ratio of the two monomers determines the yields and molecular weights of the copolymers. Comparative studies show that Mo(CO)₆ exhibits reactivity toward DEDPM alone, thus initially catalyzing metathesis cyclopolymerization of DEDPM followed by copolymerization with PA.