Polymerization of Substituted Acetylenes

Synthesis and Structural Analysis of Four Coordinate (Arylimido)niobium(V) Dimethyl Complexes Containing Phenoxide Ligand: MAO-Free Ethylene Polymerization by the Cationic Nb(V)–Methyl Complex

“…Synthesis and reaction chemistry of the high oxidation state group 5 organometallic complexes have been considered as an important subject in organometallic chemistry as well as in catalysis . The study should be helpful not only for better understanding of the organometallic chemistry but also for design of efficient and unique molecular catalysts, because of their potentials as promising reactivity demonstrated in classical Ziegler type vanadium catalyst systems for olefin polymerization , and as reports in polymerization of disubstituted acetylenes mostly demonstrated by niobium and tantalum catalyst systems or niobium–, tantalum–alkylidene complex catalysts. − Although the metal–alkyl complex plays an important role in olefin coordination polymerization that has been known as the key reaction in production of polyolefins [linear low density (or high density) polyethylene, isotactic polypropylene], ,,, however, the reported examples by the niobium complex catalysts (exemplified in Chart A–K) − have been less compared to those by the vanadium complex catalysts , as well as the group 4 transition metal complex catalysts. , On the basis of reported results, niobium complexes should have certain potentials, because Cp*NbCl 2 (η 4 -diene) (A) and Cp*Nb­(η 4 -diene) 2 enable living ethylene polymerization in the presence of methylaluminoxane (MAO) to proceed . Moreover, the complexes containing chelate imino ligands (G, H) exhibited high catalytic activities for ethylene polymerization upon addition of halogenated Al alkyls and chlorinated reoxidant (ethyl trichloroacetate); the dichloride complex containing amine triphenolate ligand, NbCl 2 [(O-2,4- t Bu 2 C 6 H 2 -6-CH 2 ) 3 N] (K), exhibited high activities in the presence of MAO at 100, 120 °C .…”

Substituted Polyacetylenes: Synthesis, Properties, and Functions

“…Though substituted polyacetylenes also possess alternating carboncarbon double bonds along the main chain, their properties are fairly different from those of polyacetylene. [4][5][6][16][17][18][19] For instance, many of the substituted polyacetylenes are organo-soluble, more or less stable in air, variously colored, and electrically semiconducting or insulating. When polymers from mono-and disubstituted acetylenes are compared to each other, disubstituted acetylene polymers are usually more stable in air, less conjugated, and more lightly colored and they have stiffer polymer chains than monosubstituted acetylene polymers.…”

“…Their features as compared to Rh catalysts include high activity towards various acetylene monomers including sterically demanding disubstituted acetylenes and ortho-substituted PAs, although they are ineffective to highly polar or protic monomers due to decomposition. 4,5 Schrock et al succeeded in the living polymerization of several substituted acetylenes by using well defined Mo carbene catalysts (e.g., 3 in Chart 1), manifesting the validity of metathesis mechanism for acetylene polymerization with group 6 transition metal catalysts. 46,47 Recently it is reported that N-heterocyclic Mo carbene complex, [Mo(N-2,6-Me 2 C 6 H 3 ) (IMesH 2 )(CHCMe 2 Ph)(CF 3 SO 3 ) 2 ] (IMesH 2 D 1,3-dimesitylimidazolidin-2-ylidene) polymerizes a,v-diynes having protic groups.…”

“…39 Thereafter, a variety of group 6 and 5 transition metal catalysts were developed to achieve synthesis of various mono-and disubstituted acetylene polymers, and the metathesis-type polymerization mechanism was speculated for these catalysts. [3][4][5][6] The Rh catalysts most frequently employed at present are [(nbd)RhCl] 2 and (nbd)Rh C BPh 4 ¡ . Rh catalysts are useful to various monosubstituted acetylenes including polar monomers (e.g., PA, N-propargylamides), and feature formation of cis-stereoregular polymers.…”

“…In the areas of polymer design and synthesis, polymerization catalysts and novel monomers were investigated widely in the beginning, but recently the focus has shifted to more advanced areas including living polymerization, synthesis of helical polymers, incorporation of functional groups by either polymerization or polymer reactions, and construction of unique polymer structures such as polymer brushes and star polymers. [3][4][5][6][7][8][9][10][11][12][13][14][15] Substituted polyacetylenes belong to a category of conjugated polymers with stiff polymer chain, and hence studies of their properties and functions may lead to potential applications to organic optoelectronic and stimuli-responsive materials, [16][17][18][19][20][21][22] and further gas separation membranes. [23][24][25][26][27][28] 2.…”