Influence of Temperature
and Pressure on Cyclic Carbonate
Synthesis Catalyzed by Bimetallic Aluminum Complexes and Application
to Overall <i>syn</i>-Bis-hydroxylation of Alkenes
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Abstract
The effect of moderate temperatures (22–100 °C)
and
pressures (1–10 bar) on the synthesis of cyclic carbonates
from epoxides and carbon dioxide catalyzed by a combination of bimetallic
aluminum complexes and tetrabutylammonium bromide is investigated.
The combined bimetallic complex and tetrabutylammonium bromide catalyst
system is shown to be an order of magnitude more active than the use
of tetrabutylammonium bromide alone at all temperatures and pressures
studied. At the higher temperatures and pressures used, disubstituted
epoxides become substrates for the reaction and it is shown that reactions
proceed with retention of the epoxide stereochemistry. This allowed
a route for the overall <i>syn-</i>bis-hydroxylation of
alkenes to be developed without the use of hazardous metal based reagents.
At higher pressures it is also possible to use compressed air as the
carbon dioxide source