“A posteriori” modification of carbosilane dendrimers and dendrons: their activation in core and branch positions

Abstract

The introduction of phenyl groups at different points on carbosilane dendrimers allows their acidolytic conversion to highly reactive triflato groups which in turn are readily substituted by anionic nucleophiles. Core phenylated first–fourth generation dendrimers were synthesized from tri(allyl)phenylsilane by an alternating sequence of hydrosilylation and allylation steps. Similarly, carbosilane dendrimers containing phenyl-Si groups at the branching points and in the periphery were prepared from tetraallylsilane which was hydrosilylated with PhHSiCl₂. Reaction of the phenylated dendrimers with triflic acid in toluene cleanly gave the silyl triflate derivatives, provided that the correct stoichiometry of the reagents was used. In the presence of a large excess of triflic acid the SiMe₃-end groups are slowly converted to SiMe₂(OTf)-units. The proof of concept was provided by the fixation of a {Ph₂PCH₂} group using the lithiated diphenylphosphinomethanide Ph₂PCH₂Li, obtained by cleavage of Ph₃SnCH₂PPh₂ with PhLi, as well as a lithiated ether-alcohol functionalized triphos derivative to the core of a third generation carbosilane dendrimer.