Dendrimer removal models

A working model for dendrimer thermolysis during calcination involves the PA-MAM dendrimer backbone initially reacting with oxygen (which may or may not be activated by a nanoparticle) in a relatively facile process to generate carboxylates and other surface species. Removal of carbonaceous species closely associated with the nanoparticle is required for complete activation of the catalyst. For Pt DENs, the surface carboxylates may be strongly adsorbed to the nanoparticle surface and extended O2 treatments are required for deep oxidation of the hydrocarbon to reach reasonably volatile species. Once formed, however, it appears that they can be removed more readily with a hydrogen treatment than with further oxidation. 

First generation dendrimer 82 was obtained in 64% yield after purification by HPLC to remove the monofunctionalised compound, formed in 18% yield. This dendrimer was also prepared in optically inactive form, starting from rac-t-Bu-BisP (BH3)2, in 82% yield. Second generation dendrimer 83 was then prepared similarly in 70% yield after HPLC purification. The diphosphine borane 84 was also prepared in 42% yield to be used as a model." " The optically active dendrimers were analysed by CD measurements and it was found that they exhibited the Cotton effect, induced by the stereogenic phosphorus atoms, in the 280 nm ti-ti absorption band of the aromatic rings. Unexpectedly, compound 84 did not display any Cotton effect." ... 

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