Simple synthesis of carbosiloxane dendrimers

The divergent synthesis of the second generation carbosiloxane dendrimer Si(OCH2CH2CH2SiMe(OCH2CH2CH2SiMe(OCH2CH=CH2)(2))(2))(4) (5) is described. Hydrosilation of Si(OCH2CH=CH2)(4) (1) with HSiMeCl2 in the presence of catalytic amounts of H2PtCl6 produces Si(OCH2CH2CH2SiMeCl2)(4) (2) in high yield. Treatment of 2 with HOCH2CH=CH2 and NEt3 affords Si(OCH2CH2CH2SiMe(OCH2CH=CH2)(2))(4) (3). The sequential reaction of the latter molecule with HSiMeCl2/H2PtCl6 and HOCH2CH=CH2/NEt3 affords the dendrimer 5, which can be further functionalized with organometallic building blocks via hydrosilation reactions.