Insertion, into metal-hydrogen bonds

Another general method is based on oxygen insertion into metal-hydrogen bonds (50,72,79-81) by any of several known mechanisms. Hydrogen abstraction by superoxo complexes followed by oxygenation of the reduced metal, as in the catalytic reaction of Eqs. (3)-(4) (50,72), works well but is limited by the low availability of water-soluble transition metal hydrides and slow hydrogen transfer (equivalent of reaction (3)) for sterically crowded complexes. 

Carbon Monoxide Insertions into Metal-Hydrogen Bonds. 

Carbon Monoxide Insertions Into Metal-Hydrogen Bonds. 

Carbon monoxide insertions into metal-hydrogen bonds have been elusive. The first direct formation of a metal-coordinated formyl group from a metal-hydride complex and carbon monoxide was observed with the hydride of octaethylporphyrinatorhodium(III), which reacts as follows with carbon monoxide at atmospheric pressure in benzene ... 

The reaction of transition metal hydrides and metal alkyls with CO2 frequently results in the formation of metal formates and carboxylates via an insertion of CO2 into a metal hydride or metal carbon bond. Step 2 of Scheme 1 (15-19). In some instances, the mechanism for this reaction has been investigated in detail. It has been found that the reaction can proceed by either a dissociative mechanism to produce a coordinatively unsaturated metal hydride as an intermediate, or it can occur by an associative mechanism (20-25). Thus, the metal hydride shown in Scheme 1 may or may not be required to be coordinatively unsaturated. Organometallic and metal phosphine complexes are again the two classes of complexes most commonly involved in CO2 insertions into metal hydrogen bonds (15-19). 

However, because of the difficulties involved in handling this reagent, other methods for preparing these compounds are generally preferred. Olefins and acetylenes insert into metal-hydrogen bonds to give alkyl and alkenyl complexes, respectively. Examples are... 

Another very interesting reaction involving insertion of dicyclopentadienyl-stannylene into metal-hydrogen bond with displacement of its ligands has been described by J. G. Noltes et al.16S). The resulting product was identified by X-ray structural analysis. 

Like carbene insertions into carbon-hydrogen bonds, metal nitrene insertions occur in both intermolecular and intramolecular reactions.For intermole-cular reactions, a manganese(III) meio-tetrakis(pentafluorophenyl)porphyrm complex gives high product yields and turnovers up to 2600 amidations could be effected directly with amides using PhI(OAc)2 (Eq. 51). The most exciting development in intramolecular C—H reactions thus far has been the oxidative cychzation of sulfamate esters (e.g., Eq. 52), as well as carbamates (to oxazolidin-2-ones), ° and one can expect further developments that are of synthetic... 

Much effort has been devoted to activate hydrocarbons, particularly saturated compounds, through the formation of organometallic compounds and transformation of the latter to substituted derivatives. A number of transition-metal complexes have been found to insert into carbon-hydrogen bonds leading to stable alkyl metal hydrides ... 

In certain early transition metal complexes and in metal clusters, organic nitriles can insert into metal-hydrogen or metal-carbon bonds (equations 92 and 93). Similarly, nucleophilic attack at coordinated nitrile can yield methyleneamido complexes (equation 94). 

In general, the insertion reaction of carbon dioxide into metal hydrogen bonds is formally much akin to the analogous process involving olefins (Scheme 1). This analogy is particularly appropriate since the binding of... 

By assuming insertion of alkene into metal-hydrogen bond to be the ratedetermining step, draw a hypothetical free energy diagram for the catalytic cycle of Fig. 2.10. How many catalytic intermediates and transition states are there ... 

Hydroperoxo complexes are prepared75 by protonation of peroxo complexes, by insertion of dioxygen into metal-hydrogen bonds, by hydrogen abstraction by metal dioxygen complexes, by reduction of superoxo complexes or by reaction of the metal ion with hydrogen peroxide. Well-defined stable species have been characterized for Cu,76 Ir, Pt, and other metals, for example, by syntheses of the type ... 

The following sections are organized by the group on the metal to which a molecule is inserting. Thus insertions into element-hydrogen bonds, insertions into element-carbon bonds, etc., are covered separately. 

Insertion of organic carbonyl compounds into metal-hydrogen bonds is important in organic synthesis. The reductions of esters, ketones, and aldehydes by main group hydrides and complex hydrides are of particular importance, but since the primary products of insertion are not characterized, they are not considered here . ... 

While insertion of carbon monoxide into metal-hydrogen bonds is an elusive reaction, the analogous insertion with isocyanides and Pt-H compounds occurs readily. For example, [tmns-Pt(CNR)(H)L2]Cl undergoes a retroionization reaction and is converted to the corresponding formamidoyl complexes ... 

Insertion of alkynes into metal-hydrogen bonds to produce cr-vinyl complexes is an important elementary step in catalytic hydrogenation. 

Olefin Insertion into Metal-Hydrogen and Metal-Alkyl Bonds 1.22.6 Databases... 

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