ORGANORUTHENIUM DENDRIMERS

We describe the synthesis of a series of very large organometallic den drimers. These dendrimers have been prepared by the convergent-approac h and contain organometallic functional groups, namely Cp(CO)(2)RuCH2C H2CH2O- (Cp = eta(5)-C5H5), which lie exclusively at the periphery of the dendritic structure. The construction of these dendrimers starts b y the reaction of the (bromopropyl)ruthenium complex [CpRu(CO)(2){(CH2 )(3)Br}] with the building block 3,5-dihydroxybenzyl alcohol. This rea ction gives the first generation dendritic wedge with a benzyl alcohol functional group at the focal point. The benzyl alcohol functional gr oup can then be activated by the reaction with a PPh(3)/CBr4 mixture t o give the dendritic wedge with a benzyl bromide functional group. Thi s first generation dendritic wedge reacts with 3,5-dihydroxybenzyl alc ohol 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 re action cycles, we have prepared dendritic wedges up to the fourth gene ration. This fourth generation dendritic wedge reacts with 1,1,1-tris( 4'-hydroxyphenyl)ethane to give a fourth generation dendrimer, which c ontains 48 ruthenium metal atoms and has a nominal molecular weight of 18 438 amu. The characterization data and thermal properties of the d endrimers and the dendritic wedges are reported and discussed.