Hydrosilylation-ethynylation

A combination of hydrosilylation-ethynylation and hydrosilylation-reduction is successfully applied to the syntheses of carbosilane dendrimers bearing 4, 8 and 12 end-ethynyl groups as well as their Co2(CO)6 complexes263. The synthesis of a second generation dendrimer 268 possessing twelve Co2(CO)6(HC=C—) units is shown in Scheme 29 as an example. The structure of 268 is confirmed by X-ray crystallographic analysis263. 

The utilization of allyl alcohol as the nucleophilic reagent to prepare dendritic carbo-siloxanes was also reported by Lang and Brilning134,135. Using a second generation allyl-terminated carbosiloxane dendrimer, they were able to attach titanium moieties via a simple hydrosilylation reaction (equation 12)134. Lang and coworkers were also successful in binding cobalt moieties to ethynyl-terminated carbosiloxane dendrimers (e.g. equation 13)136,137. 

Catalytic hydrosilylation provides a convenient route to silicon-containing den-drimers. Combinations of hydrosilylation with alkenylation (usually allylation and vinylation) and ethynylation give powerful protocols for the rapid and efficient synthesis of silicon-containing dendrimers (mostly carbosilanes and carbosilox-anes) [4]. This topic has recently been reviewed by Majoral [31] and Schlenk and Frey [32], At present carbosilane dendrimers are the most important class of Si-based dendrimers (cf. also Section 3.2.2). 

Rh catalyses the hydrosilylation of alkenes and the dehydrogenative silylation of 1,5-dienes and alkynes, and the silylcarbonylation of alkynes to give p-silylacrylaldehydes with exceptional stereocontrol , ketones and enones give silyl enol ethers, 1,3-cyclobutane dione gives 3-hydroxycyclobutanone, and assists in the silylformylation of ethynyl pyirolidone derivatives to give pyrrolizidine alkaloids, and epoxides to give p-siloxy aldehydes, and... 

Crosslinked films were prepared from these PDMS-b-PEO copolymers by hydrosilylation reaction between the terminal vinyl groups and multi hydride functional poly(dimethyl-co-methylhydride siloxane) (9), which was a commercial sample from Bayer (CA 730). A Si-H/vinyl ratio of 3 was used. Again Pt(0) was used as a catalyst and ethynyl cyclohexanol as an inhibitor, which prohibited curing before raising the temperature to 115 °C. 

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