Supercritical carbon dioxide dendrimers

Employing the same dendrimer-stabilized palladium colloids for Heck reactions in supercritical carbon dioxide, after 24 h reaction time and 55% conversion no further reaction was observed for reasons not clarified. Remarkably, methyl 2-phenylacrylate was formed exclusively instead of the expected methyl cinnamate (Scheme 1) [37]. 

Researchers van der Broeke and coworkers[" created perfluoro-functionalized poly(propyleneimine) dendrimers (23 Fig. 4) and demonstrated their potential as phase-transfer catalysts in supercritical carbon-dioxide-water mixtures and as anionic species extractants. The dendrimers were accessed via reaction of perfluorinated, linear alkyl acid chlorides with the terminal amines. Extraction of perinanganate or dichromate from aqueous to CO2 solution was described as rather low, whereas their use as phase-transfer catalysts in a halogen exchange reaction [benzyl chloride to benzyi bromide (24)] resulted in high rates of conversion. 

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