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Ketones insertion into metal hydrides

The reactivity of the cationic Zr complexes is a direct consequence of their Lewis acidity see Lewis Acids Bases) (i) various substitution reactions can occur into the Zr-solvent weak bond, (ii) unsatnrated substrates (CO, alkenes, alkynes, or ketones) insert into the Zr-C bond, potentially leading to polymerization reactions (see Section 8.2), (iii) new organic ligands obtained after reaction in the coordination sphere of the metal can be spontaneously released by /3-H elimination see -Hydride Elimination), or (iv) C-H bond activation of suitable ligands can occur. [Pg.5316]

Insertion of Ketones and Imines into Metal-Hydride Bonds... [Pg.370]

The insertions of ketones and imines into metal hydrides have also been studied, although they have been studied less extensively than the insertion of olefins into metal hydrides. This elementary reaction is relevant to one of the mechanisms for the hydroge nation of ketones and imines. An example of the insertion of a ketone into a ruthenium hydride is shown in Equation 9.55. Hie alkoxide product is stable toward reductive... [Pg.370]

Tributyltin hydride reduction of carbonyl compounds. The reduction of carbonyl compounds with metal hydrides can also proceed via an electron-transfer activation in analogy to the metal hydride insertion into TCNE.188 Such a notion is further supported by the following observations (a) the reaction rates are enhanced by light as well as heat 189 (b) the rate of the reduction depends strongly on the reduction potentials of ketones. For example, trifluoroacetophenone ( re<1 = —1.38 V versus SCE) is quantitatively reduced by Bu3SnH in propionitrile within 5 min, whereas the reduction of cyclohexanone (Erea — 2.4 V versus SCE) to cyclohexanol (under identical... [Pg.252]

One pervasive mechanistic feature of many of the hydrogenations described in other chapters of this handbook concerns the bonding of the unsaturated substrate to a metal center. As illustrated in generalized form in Eq. (1) for the hydrogenation of a ketone, a key step in the traditional mechanism of hydrogenation is migratory insertion of the bound substrate into a metal hydride bond (M-H). [Pg.154]

Several systems have been reported involving stoichiometric hydrogenation of ketones or aldehydes by metal hydrides in the presence of acids. An ionic hydrogenation mechanism accounts for most of these hydrogenations, though in some examples alternative mechanisms involving the insertion of a ketone into a M-H bond are also plausible. [Pg.168]

In transfer hydrogenation with 2-propanol, the chloride ion in a Wilkinson-type catalyst (18) is rapidly replaced by an alkoxide (Scheme 20.9). / -Elimination then yields the reactive 16-electron metal monohydride species (20). The ketone substrate (10) substitutes one of the ligands and coordinates to the catalytic center to give complex 21 upon which an insertion into the metal hydride bond takes place. The formed metal alkoxide (22) can undergo a ligand exchange with the hydride donor present in the reaction mixture, liberating the product (15). [Pg.590]

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 . ... [Pg.585]

The small number of examples of transition metal hydrides known to undergo addition across > C=0 is due to lack of study rather than lack of reactivity. There are numerous examples of catalytic hydrogenation and hydrosilation of ketones that involve insertions of >C=0 into M-H bonds The complex Cp2ZrH2 reacts readily with (CH3)2C = 0 to give Cp2Zr(OC3H7)2 . [Pg.585]

The presence of the hydride acyl intermediate in decarbonylation suggests the possibility of alkene insertion into the metal hydride bond and reductive elimination of a ketone. This was first observed in the intramolecular hydroacylation of 2,3-disubstituted 4-pcntcnals using stoichiometric amounts of Wilkinson s catalyst or in the presence of tin(IV) chloride to give substituted cyclopentanones and stereoisomeric cyclopropanes as side products27. [Pg.360]

Ligand-promoted reductive elimination of ketones is directly observed with alkyl-acyl rhodium complexes formed via oxidative addition of either Wilkinson s catalyst or [ethylene insertion into the metal hydride bond33-37. [Pg.362]

Outer Coordination Sphere Catalysts. In the classical hydrogenation catalysis shown previously, the substrate must be coordinated to the metal prior to its insertion into a metal-hydrogen bond. However, in recent years, it has been found that unsaturated polar bonds can be hydrogenated without coordination of the substrate to the metal (37). Two well-known, nonclassical possibilities for the hydrogenation of unsaturated polar bonds, such as ketones, are the metal-ligand bifunctional mechanism (38) and the ionic mechanism (39). In the metal-ligand bifunctional mechanism discovered by Noyori (recipient of the Nobel Prize in 2001) for highly efficient ruthenium amine complexes, the hydridic RuH and... [Pg.1181]

The organometallic products included recovered [(CO)5M(OAc)], along with M(CO)6 and the bimetallic bridging hydride complex [( -H)M2(CO)10]T It was proposed that, under the reaction conditions, [(CO)5MH] and HOAc were produced, and that insertion of the ketone into the M-H bond gave a metal alkox-ide that reacted with HOAc to produce the alcohol. [Pg.176]

Formation of M-H complexes by refluxing metal halides, or complex halides, with alcohols in the presence of stablizing hands occurs via formation of a metal alkoxide followed by j -hydride elimination . This reaction represents the reverse of insertion of an aldehyde or ketone into an M-H bond. [Pg.585]

The electrophile ftat modifies a coordinated ligand can be a proton, a strong Lewis acid, or an unsaturated electrophile. Examples of Lewis acids include tiityl cahon or per-fluoroarylboranes, and examples of unsaturated electrophiles include CO, SO, isocyanates, aldehydes, ketones, and related compoimds. Reactions of these electrophiles can lead to the formation of catioruc metal complexes by abstraction of a hydride or hydrocarbyl group by the Lewis acid, or they can lead to products from insertion of the unsaturated electrophile into the metal-carbon bond. These reactions are sho-wn generically in Equations 12.1-12.3. [Pg.453]


See other pages where Ketones insertion into metal hydrides is mentioned: [Pg.34]    [Pg.498]    [Pg.30]    [Pg.707]    [Pg.2523]    [Pg.468]    [Pg.2522]    [Pg.707]    [Pg.4161]    [Pg.176]    [Pg.381]    [Pg.599]    [Pg.1239]    [Pg.222]    [Pg.1112]    [Pg.98]    [Pg.157]    [Pg.333]    [Pg.43]    [Pg.94]    [Pg.169]    [Pg.178]    [Pg.303]    [Pg.135]    [Pg.364]    [Pg.176]    [Pg.381]    [Pg.941]    [Pg.64]    [Pg.298]   
See also in sourсe #XX -- [ Pg.370 ]




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Hydride ketones

Insertion into

Ketones insertion

Ketones metalation

Metal insertion

Metal inserts

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