38339-47-8Relevant academic research and scientific papers
Self-immobilizing precatalysts: Norbornene-bridged zirconium ansa-metallocenes
Polo, Eleonora,Forlini, Fabrizio,Bertolasi, Valerio,Boccia, Antonella Caterina,Sacchi, Maria Carmela
experimental part, p. 1544 - 1556 (2009/07/30)
We report here the synthesis of new tethered biscyclopentadienyl and bisindenyl zirconocenes, bearing one unsaturation on the interannular bridge, and their use as self-immobilizing catalysts. They proved to be active catalysts towards ethylene polymerization in solution, with activities comparable to those displayed by commercial rac-Et-(Ind)2ZrCl2. When tested as self-polymerization catalysts under suitable experimental conditions, they gave colored precipitates that, once reactivated with MAO, were significantly active in ethylene polymerization, although lower than those of the corresponding catalytic systems in solution. The molecular weights of the produced polymers were similar to those obtained with the same catalysts in solution, but their distribution resulted to be broader, with values typical of heterogeneous catalytic systems. From 13C NMR studies we had the first spectroscopic evidence of the actual incorporation of a metallocene of this type into a polymeric chain.
Degenerate Thermal Rearrangement of 1,3-Dimethylenecyclopentane. Evidence for Partially Stereospecific Biradical Formation and Closure in 1,3 Shift
Gajewski, Joseph J.,Salazar, Jose Del C.
, p. 4145 - 4154 (2007/10/02)
Parolysis of 1,3-bis(dideuteriomethylene)cyclopentane at 370 deg C resulted in a first-order degenerate rearrangement in which the 1,3- and 3,3-shift products were formed in a 2:1 ratio, respectively, indicating the intermediacy of an effectively orthogonal 2,2'-bis(allylmethane) biradical.Pyrolysis of trans- and cis-4,5-dimethyl-1,3-dimethylenecyclopentane (T and C) gave 1,3- and 3,3-shift products with stereochemistry consistent with predominant conrotatory-bevel ring opening to produce the orthogonal diradical directly.Pyrolysis of optically active T gave the 1,3-shift products with 20.8percent inversion of configuration of the migrating carbon indicative of partial stereospecific closure of the biradical.Comparative pyrolysis of optically active T and its bis(dideuteriomethylene) derivative revealed no secondary kinetic deuterium isotop effect, but an alternation in the extent of racemization of starting material and amounts of 1,3- and 3,3-shift products indicates a product-determining isotope effect.These data provide further evidence for an intermediate.
