Insertion of H<sub>2</sub>CCHX (X = F, Cl, Br, O<sup>i</sup>Pr) into (<sup>t</sup>Bu<sub>3</sub>SiO)<sub>3</sub>TaH<sub>2</sub> and β-X-Elimination from (<sup>t</sup>Bu<sub>3</sub>SiO)<sub>3</sub>HTaCH<sub>2</sub>CH<sub>2</sub>X (X = OR): Relevance to Ziegler−Natta Copolymerizations
作者:Stephanie A. Strazisar、Peter T. Wolczanski
DOI:10.1021/ja003315n
日期:2001.5.1
The insertion of H2C=CHX (X = OR; R = Me, Et, Pr-n,Pr-1, CH=CH2, Ph) into ((Bu3SiO)-Bu-t)(3)TaH2 (1) afforded ((Bu3SiO)-Bu-t)(3)HTaCH2CH2X (2-CH2CH2X), which beta -X-eliminated to give ethylene and ((Bu3SiO)-Bu-t)(3)- HTaX (3-X). beta -X-elimination rates were inversely proportional to the size of R. An X-ray crystallographic study of ((Bu3SiO)-Bu-t)(3)(HTaCH2CH2OBu)-Bu-t (2-(CH2CH2OBu)-Bu-t) revealed a distorted trigonal bipyramidal structure with an equatorial plane containing be hydride and a -(CH2CH2OBu)-Bu-t ligand with a staggered disposition. erythro and threo-((Bu3SiO)-Bu-t)(3)HTaCHDCHDOEt (2-CHDCHDOEt) are staggered in solution, according to H-1 NMR spectroscopic studies, and eliminated cis- and trans-HDC=CHD, respectively, helping verify the four-centered transition state for beta -OEt-elimination. When X = F, Cl, or Br, 2-CH2CH2X was not observed en route to 3-X, signifying that olefin insertion was rate-determining. Insertion rates suggested that substantial positive charge on the substituted carbon was incurred. The reactivity of other H2C=CHX with 1, and a discussion of the observations and their ramifications on the incorporation of functionalized monomers in Ziegler-Natta copolymerizations, are presented.