Carbonyls, metal Oxygen-bonded

The reduction of a ketone by a metal hydride involves the formation of two bonds the linking of the carbonyl carbon to a hydride and the formation of a metal oxygen bond (4). 

Abstract This review is a summary of supported metal clusters with nearly molecular properties. These clusters are formed hy adsorption or sirnface-mediated synthesis of metal carbonyl clusters, some of which may he decarhonylated with the metal frame essentially intact. The decarhonylated clusters are bonded to oxide or zeolite supports by metal-oxygen bonds, typically with distances of 2.1-2.2 A they are typically not free of ligands other than the support, and on oxide surfaces they are preferentially bonded at defect sites. The catalytic activities of supported metal clusters incorporating only a few atoms are distinct from those of larger particles that may approximate bulk metals. 

Allyl silanes will also attack carbonyl compounds when they are activated by coordination of the carbonyl oxygen atom to a Lewis acid. The Lewis acid, usually a metal halide such as TiCLj or ZnCl2, activates the carbonyl compound by forming an oxonium ion with a metal-oxygen bond. The allyl silane attacks in the usual way and the (3-silyl cation is desilylated with the halide ion. Hydrolysis of the metal alkoxide gives a homoallylic alcohol. 

Examples of the insertion of carbonyl compounds into metal-oxygen bonds are shown in Table... 

Rather, a carbon-metallated strnctnre retaining a strong metal-oxygen bond, as in 11, seemed a more accurate description. The dative bond between the carbonyl oxygen and metal center resnlts in a lower bond order for the carbonyl, which is reflected in a carbonyl stretch at snbstantially lower wave numbers. 

Bis(triaryltin)oxides react with carbon disulfide and carbonyl sulfide in a similar manner to afford the corresponding sulfides in high yields. Similarly, Pb, Hg and As metal organic compounds with metal-oxygen bonds or metal-hydroxy bonds undergo this reaction. 

Metal carbonyl derivatives with metal-oxygen bonds are not common. Flash photolysis of oxygen-iron pentacarbonyl mixtures produces a substance believed to be [Fc202(C0)] 226). Sulfur trioxide and iron pentacarbonyl afford an unisolable material thought to be the pyrophosphate Fe[0(S03)2](C0)3 141). However, the reaction between sulfur dioxide and enneacarbonyldiiron gives a substance [Fe2(C0)gS02], for which... 

When a carbonyl group is bonded to a substituent group that can potentially depart as a Lewis base, addition of a nucleophile to the carbonyl carbon leads to elimination and the regeneration of a carbon-oxygen double bond. Esters undergo hydrolysis with alkali hydroxides to form alkali metal salts of carboxylic acids and alcohols. Amides undergo hydrolysis with mineral acids to form carboxylic acids and amine salts. Carbamates undergo alkaline hydrolysis to form amines, carbon dioxide, and alcohols. 

At the outset it is important to clarify the scope of this discussion by the elimination of areas which will not be considered. When one notes that the term "activation of carbon monoxide" may mean a process as little perturbative of the C-0 bond as its end-on attachment to a metal atom in carbonyls, or as strongly perturbative as its dissociation to atoms on a metal surface, the need for limits becomes obvious. In this discussion we will consider only the activation of carbon monoxide in the sense that isolable products are formed by the addition of hydrogen to the molecule without complete rupture of all carbon-oxygen bonds, oxygenates are formed. 

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