Preparation and reactions of tantalum alkylidene complexes containing bulky phenoxide or thiolate ligands. Controlling ring-opening metathesis polymerization activity and mechanism through choice of anionic ligand

Metathesis Polymerization of Substituted Acetylenes and Norbornene by M(CO)6-Ph2CCl2-hν (M=Mo, W) Catalysts

“…Ph 2 CC1 2 was distilled under reduced pressure and stored as toluene solution. W(CO) 6 and Mo(CO) 6 (Strem) were used as received. Toluene was purified by the standard method.…”

“…The catalyst solution was UV irradiated with a high-pressure Hg lamp (200 W) at a distance of 5 cm and kept in the dark. The colorless toluene solution of M(CO) 6 and Ph 2 CC1 2 turned green on UV irradiation. To this catalyst solution was added a monomer solution, and the polymerization solution was kept at a constant temperature.…”

“…Polymerization of phenylacetylene readily proceeds in the presence of metal chloride-based catalysts, but the molecular weight of the formed polymer is around 5000 at highest probably due to the Lewis acidity of the catalysts. 9 Group 6 transition metal hexacarbonyl-based catalysts, M(CO) 6 -CClchv (M = W, Mo), induce metathesis polymerization of both cycloolefins 12 · 13 and substituted acetylenes. 14 • 15 The Lewis acidity of these catalysts is lower than those of metal chlorides, and consequently the molecular weight of the poly(phenylacetylene) produced by the W(COkbased catalyst reaches almost a hundred thousand.…”

“…A requirement for the M(C0) 6 -based catalysts is that CC1 4 must be used as solvent; otherwise sufficient catalytic activity is not attained. It is assumed that a metal carbene, which serves as active species, is generated by CO elimination from M(CO) 6 by ultraviolet (UV) irradiation and subsequent reactions of M(CO) 5 with CC1 4 , and so forth. 16 Further, generation of tungsten diphenylcarbene as an intermediate in the W(CO) 6 -Ph 2 CC1 2 -hv system was suggested on the basis of a finding that the presence of 2-ethoxynorbornene in this system leads to the formation of a diphenylcarbene adduct.…”

“…16 Further, generation of tungsten diphenylcarbene as an intermediate in the W(CO) 6 -Ph 2 CC1 2 -hv system was suggested on the basis of a finding that the presence of 2-ethoxynorbornene in this system leads to the formation of a diphenylcarbene adduct. 17 Taking this into account, we examined Ph 2 CCl 2 in place of CC14 in the W(CO) 6 -CC1 4 -hv system to find that the W(CO) 6 -Ph2CC12-hv system polymerizes phenylacetylene. 18 In the present study, we investigated the polymerization of substituted acetylenes and norbornene by the M(CO)6-Ph2CC12-hv (M = W, Mo) systems in detail to clarify the effectiveness of Ph 2 CC1 2 as second catalyst component 1 To whom all correspondence should be addressed.…”