Hydrosilylation nanoclusters

Though most of the catalysts discussed here are homogeneous, monoatomic species, it is possible to catalyze alkyne hydrosilylation by nanoparticles and polyatomic clusters.46 47 Recently, a report on this topic demonstrated the feasibility of using gold nanoclusters supported on alumina as a catalyst for alkyne hydrosilylation.48... 

Abstract In this chapter, nanocluster catalyzed modifications of organic and silicon based polymers are described. The tailoring of the polymeric tanplates was carried out under mild conditions and led to hybrid polymers in quantitative yields. Detailed characterization studies indicated that the integrity of the polymeric templates was not compromised during the functionalization process. The nanoparticle catalysis was found to be quite effective and highly selective, hi most cases exclusive 6-hydrosilylation products were obtained without any rearrangement or isomerization reactions. Detailed characterization and property profiling of the new hybrid polymers is also presented. 

In recent years, we have been investigating easy and economical functionalization of widely nsed carbon based polymers snch as polybntadienes. The preliminary results of these studies have led our group to discover a highly selective and mild synthetic route to silyl-functionalization of 1,2-polybutadienes (PBD) via Pt-nanocluster catalyzed hydrosilylation of olefin bonds. Unlike other catalytic systems, our system was found to be equally effective with all varieties of functional silanes such as halo-, alkyl-, aryl- and alkoxy- silanes affording high yields and selectivities. In addition, all the hydrosilylation reactions were found to be very clean with the ease of product separation and purifications (Scheme 2). 

Pt-nanocluster catalyzed hydrosilylation has also been explored with aromatic alkenes using PMHS. As shown in the results summarized in Table 3, substrate dependent (alkene) regioselectivity pattern was displayed for the hydrosilylation... 

Table 3 Pt-nanocluster catalyzed regioselective hydrosilylation of aromatic olefins...

Chauhan BPS, Rathore J S. (May 16-20, 2006) Synthesis of Isolable Nanocluster Catalysts and Their Applications in Macromolecular Hydrosilylation Catalysis. 39th Silicon Symposium, Frankenmuth, MI USA, Abs. No. 300... 

Using an alternative to Speier s catalyst, Chauhan and coworkers reported that recyclable platinum nanoclusters can function as catalysts in PBD hydrosilylation (Fig. 14). These nanoclusters, which were prepared via reduction of Me2Pt(COD) and recovered after the reaction by centrifugation, showed consistent activity up to five cycles of consecutive hydro-silylations. Complete conversion of 1,2-PBD was achieved with a variety of silane structures and yielded the hydrosilylation product via anti-Markovnikov addition at the terminal positions of 1,2-butadiene units. The retention of a narrow molecular weight (M /M =. 4—. 5) in the GPC analysis confirmed that no chain scission or cross-finking occurred in the polymer chains during hydrosilylation. 

Figure 14 Selective anti-Markovnikov hydrosilylation of 1,2-PBD with a variety of silane structures using recyclable platinum nanoclusters.

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