Observation of the first titanium alkyl/alkyl complexes: The key intermediate in the Ziegler-Natta mechanism for the polymerization of alkenes

The complexes trans-TiX$\sb2$(dmpe)$\sb2$ (X = BH$\sb4,$ Br, Cl, Me, and OPh) react with alkenes to give two diamagnetic products: the mononuclear and dinuclear complexes trans-TiX$\sb2$ (alkene)(dmpe)($\eta\sp1$-dmpe) and trans- (TiX$\sb2$(alkene)(dmpe)) \sb2(μ-dmpe). A crystallographic study of (TiCl$\sb2$(C$\sb2$H$\sb4)$(dmpe)) \sb2(μ-dmpe) confirms the trans geometry and shows that the ethylene ligand resides in the plane described by the phosphine ligands. The complexes TiMe$\sb2$(C$\sb2$H$\sb4)$(dmpe)($\eta\sp1$-dmpe) and (TiMe$\sb2$(C$\sb2$H$\sb4)$(dmpe)) \sb2(μ-dmpe) are the first structural models of the key titanium alkyl/alkene intermediate in the Cossee mechanism for Ziegler-Natta catalysis. Above $-$20$\sp\circ$C, the TiX$\sb2$(dmpe)$\sb2$ complexes catalyze the dimerization of ethylene to 1-butene with turnover rates of up to 440 hr$\sp{-1};$ the rates of ethylene dimerization vary according to the nature of the X group (Me $>$ BH$\sb4 >$ Cl $>$ OPh). Most of the evidence favors a mechanism involving the oxidative coupling of two coordinated ethylenes followed by β-hydrogen abstraction and reductive elimination. Interestingly, there is no insertion of ethylene into the Ti-CH$\sb3$ bonds. This behavior is probably a general feature of d$\sp2$ metal centers.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2011

Author dc:creator

• Spencer, Michael Donald

Contributors dc:contributor

• Girolami, Gregory S.

• Chemistry, Inorganic

Statement dc:rights

• Copyright 1993 Spencer, Michael Donald

Language dc:language

eng

Identifier

AAI9411788
(UMI)AAI9411788

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/20877