Exploration of Cocatalyst Effects on a Bimetallic Cobalt Catalyst System: Enhanced Activity and Enantioselectivity in Epoxide Polymerization
作者:Peter C. B. Widger、Syud M. Ahmed、Geoffrey W. Coates
DOI:10.1021/ma201078m
日期:2011.7.26
Organic ionic compounds were synthesized and investigated as cocatalysts with a bimetallic cobalt complex for enantioselective epoxide polymerization. The identities of both the cation and the anion were systematically varied, and the subsequent reactivity was studied. The nature of the ionic cocatalyst dramatically impacted the rate and enantioselectivity of the catalyst system. The ionic cocatalyst (CH2)(4))(3))(4)(+)] [(BuCO2-)-Bu-t] in combination with a bimetallic cobalt complex produced a catalyst system that exhibited the greatest activity and selectivity for a variety of monosubstituted and epoxides.
Anhydrous Phosphazenium Fluorides as Sources for Extremely Reactive Fluoride Ions in Solution
aprotic solvents like benzene or THF, one of them even at -30 degrees C. Such solutions probably represent the most basic metal-free and stable media known to date. Comparison of these fluorides with known F- sources demonstrates that they are of unprecedented reactivity and selectivity in E2 elimination reactions.
A series of peralkylated polyaminophosphazenium cations exhibiting extraordinary base resistance under phase-transfer conditions were efficiently synthesized from readily available starting materials. Their half lives under these conditions exceed those of the most stable conventional organiccations by factors of up to 3000.