Of coordinated carbonyl

Answer. Three aspects of the scheme shown in Figure 13.2 may be examined by orbital interaction theory (a) the binding of CO compared to ethylene (b) the reactivity of coordinated carbonyl compared to ethylene with respect to reactivity toward intramolecular nucleophilic attack and (c) the migratory aptitude of alkyl versus carbonyl groups. 

For the equilibration processes to take place on the nmr time scale, the energetic barrier for interconversion of CO bonding modes cannot be great (usually <22 kcal/mol). While the fluxional properties of metal carbonyls will not be of concern to us here, they illustrate the facility for interconverting CO bonding modes, and suggest that if CO activation can be achieved beginning with a particular mode of coordination, carbonyls bound in other ways to metal atoms may also be activatable. ... 

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.,... 

It was recognized at an early stage in the development of silicon-transition-metal chemistry that silicon-oxygen compounds often appeared, either as by-products from preparations or as decomposition products on heating or even on storage. At first, adventitious hydrolysis or oxidation was blamed, but it soon became clear that attack on silicon by oxygen of coordinated carbonyl groups was responsible. Since metal carbonyls are known to form adducts with Lewis acids such as compound (XXXIII) (286),... 

Figure 4.15. Geometries and relative reactivities of coordinated carbonyls [64].

Although chemical activation of coordinated carbonyls is mostly used for synthetic purposes, some examples relevant for comparison with the reactivity on surfaces should be mentioned. CO activation can be achieved in several ways the best known are the use of Me3NO,l " of Na-benzophenone ketyl or of [PPN]X (PPN = bis(triphenylphosphino)iminium cation [N(PPh3)2]+ X = halogen) salts.I Metal complexes may also be effective these usually work via electron-transfer catalysis or radical mechanisms. ... 

The decarboxylation of the hydroxycarbonyl species HM-CO2H should be facile and has been proposed for other conversions of coordinated carbonyl to hydride, e.g.. Reaction 4 (16). Subsequent reductive elimination of dihydrogen from MH2 has precedence for a number of... 

In many cases, complexes containing bridging carbyne ligands are formed via electrophilic addition to the oxygen atom of coordinated carbonyl group or to the carbon atom of carbide clusters [reactions (3.71)-(3.83), Section 3.10]. 

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