Monitoring hydrosilylation reaction

In recent years a variety of spectroscopic and other techniques have been employed to investigate and monitor hydrosilylation reactions. The techniques include multinuclear NMR, transmission electron microscopy, extended X-ray absorption fine structure (EXAFS), etc. Results from these experiments indicate that depending on the precatalyst, colloids and/or mononuclear complexes take part as catalytic intermediates. 

Summary The use of the on-line FT-Raman spectroscopy for monitoring a multi-step hydrosilylation reaction combines all the advantages of an on-line analytical tool (like real time measuring results, a direct view into the reaction, and no off-line sample collection) with the requirements for the application of technology in production plants, e. g., low calibration effort within a wide temperature range, stable calibration, simple system handling for the operator, small sized equipment at the reaction vessel, and no contact with the reaction media. 

The progress of the reaction can be monitored by IR spectroscopy by removing a small quantity of the reaction mixture using a syringe and needle (via the septum), and examining the IR spectrum in the region 2000-2200 cm The disappearance of the band at 2155 cm (Si-H absorption band) indicates completion ofthe hydrosilylation reaction. 

Thus, the hydrosilylation reaction was carried out using either purified DAM or DAF with TCS in the presence of Karstedt s catalyst , and was monitored by gas chromatography (GC). The GC analysis was accomplished by a capillary column (DBS 30 m X 0,32 mm) with injection port at 250 °C and FID at 300 °C program started at 80 °C for 2 , then ramp at 25 °C/min. to 280 °C. The DAF was found to be a slightly faster reaction with all detectable DAF being consumed in -100 minutes, whereas DAM consumption required -150 minutes. Both reactions were run at a peak temperature of 90 C. The fumarate isomer was detected in the synthesis initiated with DAM as a result of trace amounts of water in the reaction. This allows for the... 

Methyl-( -ferrocenylethyl)- and methyl-[ -(r,3 -dimethylferrocenyl)ethyl]siloxane polymers 53 and 54, respectively were prepared by the hydrosilylation of vinyl-ferrocene and l,T-dimethylferrocene-3-vinylferrocene with methyl hydrosiloxane (molecular weight was originally reported to be 2270) or methylhydrosiloxane-dimethylsiloxane copolymer (molecular weight was originally reported to be 2000 — 2100) in the presence of chloroplatinic acid as a catalyst. The synthetic route is given in Seheme 10-25 [62], The reaction was monitored by IR spectroscopy until the complete disappearance of the Si-H absorption at 2161 cm". ... 

To further probe the reactivity of complex 25, its reaction with 10 equivalents of 1-octene (2) in hot [dsj-toluene was monitored by NMR spectroscopy (Scheme 5.9) [16]. After 4h, complete conversion of 25 into (ICy)Pt(l-octene)228 was observed, along with the hydrosilylated product 29. Unfortunately, compound 28 is too unstable to be isolated from the reaction... 

However, Hollis showed that the Rh(III) complex 36 bearing a monoanionic pincer ligand was a suitable catalyst precursor for the hydrosilylation of acetylenes (Figure 9.6). At 80 °C, full conversion was monitored after 1 hfor most internal and terminal acetylenes. The reaction proceeded much more slowly at room temperature (87% conversion, 12 h). The kinetic Z-product was preferred for terminal alkynes and the ratio of 10 90 (E Z) did not change over the reaction time, while sterically demanding groups or internal alkynes led to the thermodynamically favored -product ( 85 15). The catalyst precursor 36 has to be very pure, as additives can have a dramatic influence on the selectivity of this reaction. Addition of 1 equiv of LiCl or (n-Bu) NBr leads predominantly to the formation of the -product together with an increase of the a-hydrosilylated acetylenes, whose content can be further increased by the addition of water. 

The coupling of CO2 with epoxides was applied to imidazolimn-based ionic liquids. Using NHC-CO2 adducts as pre-catalysts was elfective for efficient CO2 fixation reactions. Lu tracked the reaction progress by in situ IR monitoring with various epoxides. In 2009, Ikariya and Tommassi extended the substrate scopes widely under milder conditions (Scheme 14.26). Ying discovered the NHC-induced hydrosilylation of CO2 to methanol via the NHC-CO2 adducts. ... 

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