Living Cyclopolymerization of 1,6-Heptadiyne Derivatives Using Well-Defined Alkylidene Complexes: Polymerization Mechanism, Polymer Structure, and Polymer Properties

We report here the living cyclopolymerization of 1,6-heptadiyne derivatives (usually 4,4-disubstituted) using well-defined alkylidene complexes as initiators. Diethyl dipropargylmalonate (2a), di-tert-butyl dipropargylmalonate (2b), optically active di-(1R,2S,5R)-([minus])-menthyl dipropargylmalonate (2c([minus])), di-(1S,2R,5S)-(+)-menthyl dipropargylmalonate (2c(+)), di-(1R)-endo-(+)-fenchyl dipropargylmalonate (2d), 4,4-bis[[(p-tolylsulfonyl) oxy]methyl]-1,6-heptadiyne (3b), 4,4-bis[(trimethylsiloxy)methyl]-1,6-heptadiyne (3c), the cyclic silyl ether, PhEtSi(OCH[sub 2])[sub 2]C-(CH[sub 2]C[triple bond]CH)[sub 2] (3d), and N,N-dipropargyl-2,4,6-triisopropylbenzamide (5b) are polymerized to give soluble polymers in high yield using Mo(NAr)(CHCMe[sub 2]Ph)(OR[sub F6])[sub 2] (1a; Ar = 2,6-i-Pr[sub 2]C[sub 6]H[sub 3], OR[sub F6] = OCMe(CF[sub 3])[sub 2]) as the initiator in 1,2-dimethoxyethane (DME). The polymers show a high degree of conjugation ([lambda][sub max] > 500 nm) and have narrow molecular weight distributions. Poly(2a) is soluble in most organic solvents (THF, C[sub 6]H[sub 6], toluene, CH[sub 2]Cl[sub 2], CHCl[sub 3], DME, DMF, MeCN). The mechanism of the polymerization has been investigated by [sup 1]H NMR studies and by monomer, initiator, and solvent variations. Symmetric, diphenyl-capped polyenes, [open quotes]pull-pull[close quotes] polyenes containing p-cyanophenyl end groups, and [open quotes]push-push[close quotes] polyenes containing p-dimethylamino end groups have all been prepared. 93 refs., 12 figs., 11 tabs.