A comparison of two convergent routes for the preparation of metalloporphyrin-core dendrimers: Direct condensation vs. chemical modification

Porphyrin-core dendrimers consisting of benzyl ether dendrons assembled around a porphyrin core have been prepared by two different convergent syntheses. The first involves the direct condensation of convergent dendrons having 3,5-disubstituted benzaldehyde focal points with an equivalent amount of pyrrole. This route which requires very mild conditions is especially useful for the rapid assembly of small dendrimers but suffers from steric limitations as the size of the dendrons increases above the fourth generation. The second route involves the attachment of pre-formed benzyl bromide dendrons to a functionalized porphyrin through a simple Williamson synthesis. This route is also very practical but it requires careful purification of the final product from the partially functionalized porphyrin dendrimers that are also obtained. MALDI mass spectrometry proved to be a very useful tool both for monitoring the formation of the dendritic porphyrins and for their characterization.