Carborane carbosilanes prepared
Synthetic methods to incorporate carborane moieties into
organosilicon scaffolds to make dendrimers have been
reported for the first time by Rosario Núñez and Francesc
Teixidor of the Barcelona Institute of Materials Science, in
Spain, and their colleagues [Org. Lett., 7, 231 (2005)].
Carboranes are carbon-boron polyhedral clusters, such as
C2B10H12, that are readily derivatized. Their applications
include boron neutron-capture cancer therapy, selective
extraction of radionuclides, and catalysis. The research
team used two approaches to make the first-generation
dendrimer shown (Si = purple, C = blue, B = orange, H =
white). One method involves reacting a carbosilane,
Si[CH2CH2Si(CH3)2Cl]4, with four equivalents of the lithium
salt of a phenyl-substituted C2B10 carborane; the
carbosilane becomes the core of the dendrimer structure.
The second method involves forming a silyl-substituted
carborane followed by its reaction with tetravinylsilane,
Si(CH=CH2)4.