Silicon compounds carbonylation

The 13C-NMR spectra of 4-7, 9-11 show a close similarity to the spectral data of analogous carbene complexes. The shift differences between the metal carbonyls of the silylene complexes and the related carbon compounds are only small. These results underline the close analogy between the silicon compounds 4-7, 9-11 and Fischer carbene complexes. This view is also supported by the IR spectral data. On the basis of an analysis of the force constants of the vco stretching vibration,... 

Besides rhodium catalysts, palladium complex also can catalyze the addition of aryltrialkoxysilanes to a,(3-unsaturated carbonyl compounds (ketones, aldehydes) and nitroalkenes (Scheme 60).146 The addition of equimolar amounts of SbCl3 and tetrabutylammonium fluoride (TBAF) was necessary for this reaction to proceed smoothly. The arylpalladium complex, generated by the transmetallation from a putative hypercoordinate silicon compound, was considered to be the catalytically active species. 

Schiff base complex, 32 13 -selenium complex FejScj complexes, 32 348 Fc4Se3 complexes, 32 349-350 Fc4Se4 complexes, 32 348-349 -selenium-nitrosyl complexes, 32 348-350 selenocyanates, 17 295, 296 sequestration in apoferritin, 36 463-464 silicates, Mbssbauer effect of, 6 474-479 -silicon compounds, 3 250 silyl complexes anionic tetracarbonyl, 25 37 binuclear carbonyls, 25 3, 5, 16, 33, 44-45, 116... 

Because transition-metal anions can be prepared conveniently in tetrahydrofuran solution, this cyclic ether was often used in earlier attempts to prepare silicon-metal compounds. It is now generally realized, however, that tetrahydrofuran can frustrate these attempts in two ways. First, it promotes electrophilic attack by the silicon compound on oxygen atoms of coordinated carbonyl groups this leads to the formation of products with Si-0 bonds (54, 138, 262, 300, 306, 310, 336,337), e.g.,... 

While platinum and rhodium are predominantly used as efficient catalysts in the hydrosilylation and cobalt group complexes are used in the reactions of silicon compounds with carbon monooxide, in the last couple of years the chemistry of ruthenium complexes has progressed significantly and plays a crucial role in catalysis of these types of processes (e.g., dehydrogenative silylation, hydrosilylation and silylformylation of alkynes, carbonylation and carbocyclisation of silicon substrates). 

The other side of the coin is that the S 2 reaction at carbon is not much affected by partial positive [ charge (5+) on the carbon a tom. The Sn2 reaction at silicon is affected by the charge on silicon. The r most electrophilic silicon compounds are the silyl triflates and it is estimated that they react some 108-109 times faster with oxygen nucleophiles than do silyl chlorides. Trimethylsilyl triflate is, in fact, an excellent Lewis acid and can be used to form acetals or silyl enol ethers from carbonyl compounds, and to react these two together in aldol-style reactions. In all three reactions the triflate attacks an oxygen atom. 

The term Peterson alkenation has been used to describe the elimination of a functionalized organo-silicon compound with alkene formation for substrates synthesized by these methods. In accordance with the mechanistic definition outlined in the introduction to this cluq)ter, such topics are not considered in detail in this review. For the purpose of this discussion, the Peterson alkenation will be considered as the addition of an anion derivative to a carbonyl compound, followed by elimination to the alkene. 

Nucleophilic addition of the trifluoromethyl group to aldehydes, ketones and other carbonyl compounds leads primarily to the corresponding trimethylsilyl ether this must subsequently be hydrolyzed to the alcohol. Because typical reaction conditions are very mild, the method is widely applicable, even for sensitive substrates. In contrast with most other methods, fluoride-induced perfluoroalkylation via silicon compounds also works for enolizable carbonyl compounds. With c(, -un-saturated substrates 1,2-addition directly to the carbonyl group is strongly preferred [64b]. If the oxygen is coordinated to a bulky Lewis acid, for example aluminum tri(2,6-bis(tert-butyl)phenoxide (ATPH), the 1,4-addition products are obtained selectively [73f] (Scheme 2.128). 

In the previous section one of the two major aspects of silicon syntheses was described. A major problem for the organosilicon chemist is producing a silicon-carbon bond. A second synthetic area involves functional-group transformations. Most useful reactions at silicon centers are substitution processes. This is an important difference between the chemistry of silicon compounds and that of carbon compounds. The synthetic or reaction processes in organic compounds are increased enormously by the availability of double bonds present in olefins and carbonyl derivatives. In fact, substitution at sp3-carbon centers may represent the least interesting of organic reactions. 

It in and silicon compounds in from carbonylation of 4-bromo-Iphenoxides. ... 

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