ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
In a theoretical investigation on Ziegler-Natta catalysis, the influence of the coordination number and ligand type of model compounds in relevant reaction steps were studied. Thus, by using the MEHT method, insertion reactions of ethylene into Zr-CH3 and Zr-H bonds were analyzed in systems of the type [Zr(C2H4)R4R′]-[Zr(Cp)(C2H4)R2R′], and [Zr(Cp)(C2H4)R3R′]-(R=R′=CH3, R=CH3, R′=H). It was found that all processes do not have significant kinetic barriers, whereas the reverse reactions in particular the β-hydride elimination have relatively high ones. The influence of coordination geometry and number on these transformations was found to be insignificant. While studying related conversions starting from [Zr(L)(C2H4)R3R′], [Zr(Cp)(C2H4)RR′(L)]+, and [Zr(Cp)(C2H4)R2R′(L)] (L = π-donor, R=R′=CH3 or R=CH3, R′=H) compounds a pronounced π-donor effect was observed. Methyl insertions in these cases showed a higher computed activation barrier than hydride migrations. An orbital basis for this phenomenon was provided and conclusions concerning chain-length control in Ziegler-Natta catalysis were drawn.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19930760325
