A theoretical study of syndiospecific styrene polymerization with Cp-based and Cp-free titanium catalysts: 2. Mechanism of chain-end stereocontrol

Gianluca Minieri, Paolo Corradini, Gaetano Guerra, Adolfo Zambelli, Luigi Cavallo*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

62 Scopus citations

Abstract

A theoretical study of the mechanism of chain-end stereocontrol in the syndiospecific polymerization of styrene with models based on the CpTiIIICH(Ph)CH3+ species is presented. Independent of the chirality of styrene coordination, low-energy transition states are always characterized by interactions of the aromatic group of the last enchained unit with the metal atom. However, the most stable transition state leads to formation of a syndiotactic diad, and it is favored by 6 kJ mol-1 with respect to the most stable transition state which leads to an isotactic diad. According to our calculations, the transition state which leads to a syndiotactic diad is favored because the smallest substituent on the Cα atom of the chain, the H atom, can be pointed toward the Cp ligand. On the other hand, the transition state which leads to an isotactic diad is of higher energy because one group between the aromatic ring on the Cα atom of the growing chain, or the Cβ and following groups of the growing chain, must be oriented toward the Cp ring. In agreement with experiments, models of the type Cp*TiIIICH(Ph)CH3+ and (benzene)TiIICH(Ph)CH3+ are calculated to be more stereoselective than CpTiIIICH(Ph)CH3+, since the transition states leading to a syndiotactic diad are favored by 16 and 13 kJ mol-1 with respect to the transition states leading to an isotactic diad.

Original languageEnglish (US)
Pages (from-to)5379-5385
Number of pages7
JournalMacromolecules
Volume34
Issue number16
DOIs
StatePublished - Jul 31 2001

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

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