Carbosilane synthesis

Their advantage over other types of dendrimers is their straightforward synthesis and, most importantly, their chemical and thermal stabilities. Two distinct steps characterize their synthesis a) an alkenylation reaction of a chlorosilane compound with an alkenyl Grignard reagent, and b) a Pt-cata-lyzed hydrosilylation reaction of a peripheral alkenyl moiety with an appropriate hydrosilane species. Scheme 2 shows the synthesis of catalysts Go-1 and Gi-1 via this methodology. In this case, the carbosilane synthesis was followed by the introduction of diamino-bromo-aryl groupings as the precursor for the arylnickel catalysts at the dendrimer periphery. The nickel centers of the so-called NCN-pincer nickel complexes were introduced by multiple oxidative addition reactions with Ni(PPh3)4. 

Fritz, G. Matem, E. Carbosilanes Synthesis and Reactions Springer New York,... 

Mercury compounds prepared in this way (Table VIII) are strongly refractive liquids which crystallize in favorable cases. They dissolve readily in organic solvents and are stable to water. Since the mercury compounds can be obtained in a pure form (by distillation, recrystallization) they are actually isolated as an intermediate step in carbosilane synthesis. This results in the removal of all the impurities arising from the various steps in the synthesis, a factor which is particularly important in making carbosilanes of higher molecular weights, where purification becomes more difficult as the molecular weight increases and by-products tend to have an unfavorable effect on the synthesis. 

The catalytic Si—H addition of 1,3,5-trisilacyclohexanes to monosilylethynes discussed in this section occurs in polycyclic carbosilane synthesis. The scheme below illustrates the principles of synthesis, whereby only the 1,1-disilylolefme is shown as product, since the 1,2-disilylolefine does not lead to ring formation. 

G. Fritz, E. Matem, Carbosilanes. Synthesis and Reactions, Springer-Verlag, Berlin, 1986. 

ADMET is quite possibly the most flexible transition-metal-catalyzed polymerization route known to date. With the introduction of new, functionality-tolerant robust catalysts, the primary limitation of this chemistry involves the synthesis and cost of the diene monomer that is used. ADMET gives the chemist a powerful tool for the synthesis of polymers not easily accessible via other means, and in this chapter, we designate the key elements of ADMET. We detail the synthetic techniques required to perform this reaction and discuss the wide range of properties observed from the variety of polymers that can be synthesized. For example, branched and functionalized polymers produced by this route provide excellent models (after quantitative hydrogenation) for the study of many large-volume commercial copolymers, and the synthesis of reactive carbosilane polymers provides a flexible route to solvent-resistant elastomers with variable properties. Telechelic oligomers can also be made which offer an excellent means for polymer modification or incorporation into block copolymers. All of these examples illustrate the versatility of ADMET. 

Another example of the flexibility of ADMET is the demonstration of successful polymerization of o /v-telechelic diene carbosilane macromonomers.45 The synthesis of macromonomer 30 is achieved using catalyst 23 and copolymerized with a rigid small-molecule diene, 4,4/-di-trans-l-propenylbiphenyl (Fig. 8.17). 

Figure 4.15. Synthesis of phosphine-functionalized carbosilane dendrimers.[31]...

A stochiometric approach was applied by Van Koten and co-workers [29], who used chiral carbosilane dendrimers as soluble supports in the in situ ester enolate-imine condensation in the synthesis of /Mactams (e.g. 19, Scheme 20). The formation of the /Mactam products proceeded with high trans selectivity, and with the same level of stereoinduction as was earlier established in reactions without the dendritic supports, (i.e. the use of the enantiopure dendritic support did not affect the enantioselectivity of the C-C bond formation). After the reaction, the dendrimer species could be separated from the product by precipitation or GPC techniques and reused again. 

The different carbosilane dendrimer supports (generation 0, 1 R=H, Me) were then used for the synthesis of the / -lactam (13). As shown in Scheme 7.2, the first step was again an immobilization of a carboxylic acid via ester bond formation. Treatment with LDA and ZnCl2 yielded in situ the corresponding zinc ester enolate (11) which reacts with N-(trimethylsilyl)phenylimine (12) to form the final four membered lactam ring (13). The last reaction step includes several intermediates. The last one is a supported /9-amino ester which undergoes spontaneous... 

M. Shimizu, T. Hiyama, T. Matsubara and T. Yamabe, J. Organomet. Chem., 611, 12 (2000). After this chapter had been finished. Moss and coworkers reported on the synthesis of highly hthiated carbosilane dendtimers R. Meijboom, A. T. Hutton and J. R. Moss, Organometallics, 22, 1811 (2003). 

The synthesis of carbosilane dendrimers with peripheral acetylenedicobalt hexa-carbonyl substituents has been reported Seyferth, D. Kugita, T. Organometallics 1995,14,5362. 

Research Focus Synthesis of dental compositions containing carbosilane methacrylate oligomers that have low shrinkage upon crosslinking. 

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. 

Reports of carbosilane dendrimers were published from 1990 onwards by the working groups of van der Made, van Leeuwen [76], Roovers [77], Muzafarov [78], and Seyferth [79]. Synthesis was generally accomplished in two steps ... 

The Si-O-C sequence is the distinctive structural unit of carbosilanes. Like that of the carbosilanes, the scaffold of this dendrimer family can be constructed in a targeted manner by the choice of certain core units [88] (Table 4.4). Synthesis of carbosiloxanes generally proceeds by... 

ROP of cyclic carbosilanes is one of the most promising techniques for the synthesis of well-defined polycarbosilanes. ROP of four-membered ring compounds, 1,3-disilacyclobutanes, and monosilacyclobutanes, as well as copolymerizations of mixtures of monomers, have been widely investigated in the last decades <1996JOMl, B-1996MI7621, B-2000MI247>. 

The synthesis of dendritic carbosilanes functionalized with various diphenylphosphino carboxylic acid ester endgroups has also been reported by the Van Koten group in collaboration with Vogt et al. [40,41], The coupling of carbosilane supports containing benzylic alcohol moieties with phos-phinoxy carboxylic acid chlorides resulted in the formation of Go and Gi phosphine oxides, which subsequently were converted into the phosphino... 

The group of Van Leeuwen has reported the synthesis of a series of functionalized diphenylphosphines using carbosilane dendrimers as supports. These were applied as ligands for palladium-catalyzed allylic substitution and amination, as well as for rhodium-catalyzed hydroformylation reactions [20,21,44,45]. Carbosilane dendrimers containing two and three carbon atoms between the silicon branching points were used as models in order to investigate the effect of compactness and flexibility of the dendritic ligands on the catalytic performance of their metal complexes. Peripherally phosphine-functionalized carbosilane dendrimers (with both monodentate... 

Olefin metathesis has become a very important reaction in polymer chemistry and natural product synthesis [47-49]. Garber et al. have used the physical properties of dendrimers in order to improve the separation between the dendritic metathesis catalyst and products on silica gel column chromatography [50]. The Van Koten group has reported on the synthesis of different generations of carbosilane dendrimers functionalized with ruthenium metathesis catalysts [51]. 

Recently, Reek et al. published the synthesis of a 9H,9 H- [4,4 ]bicarbazole-3,3r-diol (BICOL)-based chiral monodentate phosphoramidite ligand, which was functionalized with two different third-generation carbosilane dendritic wedges (Fig. 26) [57]. As reference reaction in the catalytic study, the rhodium-catalyzed asymmetric hydrogenation of Z-methyl-a-acetamido-cinnamate was chosen. Using a ligand-to-rhodium ratio of 2.2 led to enantio-selectivities which were comparable to the results obtained using the parent BINOL-derived monodentate phosphoramidite MonoPhos. 

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