Carbosilanes chemical

Van Koterfs group used a chemically inert, lipophilic carbosilane dendrimer scaffold as support material for fixation of up to 12 transition metal complex fragments. The covalently fixed fragments with nickel as catalytic site acceler-... 

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. 

Two papers from R. Nesper and M. Weiiunann cover various approaches to the preparation of functional silicon-based non-oxidic ceramics, especially those consisting of the Si—B-C-N moieties which exhibit an extraordinary high-temperature stability. Chapter VI ends by describing carbosilane elastomers as promising membrane materials (N. N. Ushakov) and investigations into the Chemical Functionalization of Titanium Surfaces with 1-trichlorosilylalkanes. 

Krukonis (1983c) reports on the fractionation of a perfluoroalkylpolyether, which is an example of a polymer with a chemical makeup very different in structure from that of the siloxanes and carbosilanes. The perfluoroalkylpolyether has the structure... 

Other stationary phase materials are also being investigated, such as coatings of dimethylpolysiloxane (PDMS) (with or without 5% the diphenyl doping), carbosilanes and Nanoglass, provided by Ohio Valley, SeacoastSciences, Dow Chemical and Honeywell SM (Nanoglass), respectively, which may or may not feature nanopores. 

Mass spectra of various groups of carbosilanes have been investigated to supplement the information gained from chemical studies 52). The first... 

Chemical Shifts of Linear Carbosilanes with Si—H Bonds (S7)°... 

In spite of the difficulties discussed above, the spectra of the cyclo-carbosilanes may be used in solving structural problems such as those associated with position isomerism in unsymmetrical methyl-substituted rings. This type of analytical application of nuclear magnetic resonance spectroscopy is particularly valuable for the carbosilanes, as the possibilities of establishing structures by chemical means are very restricted. The carbosilanes are not reactive and, unlike carbon compounds, undergo few reactions which yield information concerning their structures. In fact the structures of a number of compounds were first established with the aid of nuclear resonance. 

The carbosilane which is obtained from the Grignard reaction of the SiCl-containing cyclocarbosilane from the pyrolysis of MeSiCl3 (45) may, on chemical evidence, have either formula (e) or (/). 

With carbosilanes containing no SiH groups it is not always possible to determine the structure unambiguously from the PMR spectra because of the lack of characteristic spin-spin couplings. In such cases a solution of the structural problem may be possible by using nuclear resonance to follow the course of a chemical reaction of the compound in question. The small amount of substance required is a distinct advantage. For example,... 

Pd complexes of soluble P,0-fimctionalized carbosilane dendrimers (8) were used by Vogt and co-workers for the hydrovinylation reaction (codimerization of ethylene and styrene). This C-C coupling reaction is of great interest, because it opens an easy access to building blocks for fine chemicals as well as pharmaceuticals [Eq. (6)] [16]. 

Figure 13. Slices from the HCSi 3D NMR spectrum of carbosilane dendrimer using coherence transfer delays based on (a c) Jch Jcsu and (d f) Jqh and Jcsv (Reproducedfrom reference 14. Copyright 1999 American Chemical Society.)...

Entries (5)-(7) compare PCS (Dow Coming X9-6348, [-(Me)2Si-CH2-], oo[-(Me)2Si-CH2-]o.8l and poly-(ethynyl)carbosilane prepared by chemical modification of PCS to provide a precursor with high solubility and latent reactivity [81], The data in entry (5) are for the original PCS. Pyrolysis to 1,000 °C gave -SiC with small crystal-lites [by x-ray diffraction (XRD)] [81]. In entries (8) and (9), data for poly(vinylsilane) (=polysilylethylene) and poly(dimethylsi-lylethylene) are provided [82,83], The former was synthesized from ViSiHCl2 and the latter from ViSiHMe2 (Vi=vinyl). 

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