Organoruthenium Dendrimers

Abstract

We describe the synthesis of a series of very large organometallic dendrimers. These dendrimers have been prepared by the convergent approach and contain organometallic functional groups, namely Cp(CO)2RuCH2CH2CH2O− (Cp = η5-C5H5), which lie exclusively at the periphery of the dendritic structure. The construction of these dendrimers starts by the reaction of the (bromopropyl)ruthenium complex [CpRu(CO)2{(CH2)3Br}] with the building block 3,5-dihydroxybenzyl alcohol. This reaction gives the first generation dendritic wedge with a benzyl alcohol functional group at the focal point. The benzyl alcohol functional group can then be activated by the reaction with a PPh3/CBr4 mixture to give the dendritic wedge with a benzyl bromide functional group. This first generation dendritic wedge reacts with 3,5-dihydroxybenzyl alcohol to give a dendritic wedge of the second generation; it will also react with the trifunctional core molecule 1,1,1-tris(4‘-hydroxyphenyl)ethane to give the first generation dendrimer. Through consecutive reaction cycles, we have prepared dendritic wedges up to the fourth generation. This fourth generation dendritic wedge reacts with 1,1,1-tris(4‘-hydroxyphenyl)ethane to give a fourth generation dendrimer, which contains 48 ruthenium metal atoms and has a nominal molecular weight of 18 438 amu. The characterization data and thermal properties of the dendrimers and the dendritic wedges are reported and discussed.