Cobalt-mediated vinyl hydrogen activation in coordinated trienes

• Main Author: Pelter, Libbie S. W
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1996
• Subjects: Chemistry; Inorganic chemistry; Organic chemistry
• ISBN: 9780591322002; 0591322005

This report presents experimental investigations conducted to better define the mechanism of the bimolecular thermal reaction of (trans-$\eta\sp4$-1,3,5-hexatriene)$(\eta\sp5$-cyclopentadienyl)cobalt (1) to form a metal-metal bonded complex 2 bridged by a single, six-carbon ligand. The structure of the latter is the product of a (1,6) hydrogen transfer implying the occurrence of a unique activation of a vinyl carbon-hydrogen bond in the complexed triene. The kinetics of this process are presented including measurement of the dependence of the reaction rate on the concentration of 1 and the uncomplexed triene. The palladium-catalyzed coupling of two equivalents of trimethylsilylethyne and cis- or trans-1,2-dichloroethene provide cis- and trans-1,6-bis-(trimethylsilyl)hex-3-en-1,5-diyne respectively. The alkynes were then successfully reduced to give either 1,6-bis-(trimethylsilyl)-1,3,5-hexatriene or 1,6-bis-(trimethylsilyl)-1,6-dideutero-1,3,5-hexatriene depending on the reagents. The attempted synthesis of 1,1,6,6-tetradeutero-1,3,5-hexatriene is discussed. It is concluded that the formation of 2 from 1 follows a complex reaction pathway involving an equilibrium prior to vinyl hydrogen activation. The overall rate of reaction is accelerated by an increase in the concentration of 1. Addition of 1,3,5-hexatriene slows the formation of 2, but results in an increase in the consumption of 1 due to the production of $(\eta\sp4$-1,3-cyclohexadiene)$(\eta \sp5$-cyclopentadienyl)cobalt (1a).