Stereoselective Olefin Polymerization Catalysts Generated by the Transfer-Epimetalation of Olefins or Acetylenes with Dialkyltitanium(IV) Complexes: Three-Membered Metallocycles as Proposed Chiral Sites1
摘要:
Efficient transfer-epimetalations of simple olefins and acetylenes by R2TiL2 reagents (R = Bu-n, Bu-t; L = X) are readily achieved in THF at - 78 degreesC to generate titanacyclopropa(e)ne intermediates, readily capable of inserting various unsaturated addends (olefin, acetylene, nitrile). Analogous epimetalations conducted in hydrocarbons lead to the stereoselective polymerization of 1-alkenes and the cyclotrimerizations of acetylenes. The 2-substituted-1-halotitanacyclopropyl cation is proposed as the active site for stereoselective olefin polymerization.
Stereoselective Olefin Polymerization Catalysts Generated by the Transfer-Epimetalation of Olefins or Acetylenes with Dialkyltitanium(IV) Complexes: Three-Membered Metallocycles as Proposed Chiral Sites<sup>1</sup>
作者:John J. Eisch、John N. Gitua
DOI:10.1021/om0303092
日期:2003.10.1
Efficient transfer-epimetalations of simple olefins and acetylenes by R2TiL2 reagents (R = Bu-n, Bu-t; L = X) are readily achieved in THF at - 78 degreesC to generate titanacyclopropa(e)ne intermediates, readily capable of inserting various unsaturated addends (olefin, acetylene, nitrile). Analogous epimetalations conducted in hydrocarbons lead to the stereoselective polymerization of 1-alkenes and the cyclotrimerizations of acetylenes. The 2-substituted-1-halotitanacyclopropyl cation is proposed as the active site for stereoselective olefin polymerization.
New syntheses of ansa-metallocenes or unbridged substituted metallocenes by the respective reductive dimerization of fulvenes with Group 4 metal divalent halides or with Group 4 metal dichloride dihydrides
作者:John J. Eisch、Fredrick A. Owuor、Xian Shi
DOI:10.1016/j.poly.2005.03.020
日期:2005.8
the attainment and the stereochemistry of the formation of ansa-bridged complexes or metallocenes with acetophenone, benzylideneaniline and 6-arylfulvenes, a mechanistic model is developed involving either a three-membered metallocycle formed from MCl2 or an “open-face sandwich” complex of the fulvene and MCl2. Such intermediates offer a rational steric explanation for the observed stereochemistry of