Metal carbonyls oxidative addition

The individual reaction steps of both Rh or Ir and Mel catalysed MeOH or MeOAc carbonylation oxidative addition of Mel to the metal center, migratory insertion to generate a metal acyl species and elimination from the metal acyl to generate the... 

Reactions Involving sp -CH Activation. The insertion of ruthenium complexes into alkane C—H bonds is quite limited most synthetic routes require an adjacent nitrile group to first coordinate to the metal center. Oxidative addition of the C—H bond to the ruthenium center gives the hydrido ruthenium intermediate. An aldehyde or an a.jS-unsaturated carbonyl acts as the electrophile, which after reductive elimination from the metal affords the corresponding alcohol. This reaction is typically catalyzed by either CpRuCl(PPh3)2 or RuH2(PPh3)4 (58). 

Ca.ta.lysis, Iridium compounds do not have industrial appHcations as catalysts. However, these compounds have been studied to model fundamental catalytic steps (174), such as substrate binding of unsaturated molecules and dioxygen oxidative addition of hydrogen, alkyl haHdes, and the carbon—hydrogen bond reductive elimination and important metal-centered transformations such as carbonylation, -elimination, CO reduction, and... 

Use of alcohol as a solvent for carbonylation with reduced Pd catalysts gives vinyl esters. A variety of acrylamides can be made through oxidative addition of carbon monoxide [630-08-0] CO, and various amines to vinyl chloride in the presence of phosphine complexes of Pd or other precious metals as catalyst (14). 

Besides dissociation of ligands, photoexcitation of transition metal complexes can facilitate (1) - oxidative addition to metal atoms of C-C, C-H, H-H, C-Hal, H-Si, C-0 and C-P moieties (2) - reductive elimination reactions, forming C-C, C-H, H-H, C-Hal, Hal-Hal and H-Hal moieties (3) - various rearrangements of atoms and chemical bonds in the coordination sphere of metal atoms, such as migratory insertion to C=C bonds, carbonyl and carbenes, ot- and P-elimination, a- and P-cleavage of C-C bonds, coupling of various moieties and bonds, isomerizations, etc. (see [11, 12] and refs, therein). 

We have reviewed experiments on two classes of systems, namely small metal particles and atoms on oxide surfaces, and Ziegler-Natta model catalysts. We have shown that metal carbonyls prepared in situ by reaction of deposited metal atoms with CO from the gas phase are suitable probes for the environment of the adsorbed metal atoms and thus for the properties of the nucleation site. In addition, examples of the distinct chemical and physical properties of low coordinated metal atoms as compared to regular metal adsorption sites were demonstrated. For the Ziegler-Natta model catalysts it was demonstrated how combination of different surface science methods can help to gain insight into a variety of microscopic properties of surface sites involved in the polymerization reaction. 

The most intensive development of the nanoparticle area concerns the synthesis of metal particles for applications in physics or in micro/nano-electronics generally. Besides the use of physical techniques such as atom evaporation, synthetic techniques based on salt reduction or compound precipitation (oxides, sulfides, selenides, etc.) have been developed, and associated, in general, to a kinetic control of the reaction using high temperatures, slow addition of reactants, or use of micelles as nanoreactors [15-20]. Organometallic compounds have also previously been used as material precursors in high temperature decomposition processes, for example in chemical vapor deposition [21]. Metal carbonyls have been widely used as precursors of metals either in the gas phase (OMCVD for the deposition of films or nanoparticles) or in solution for the synthesis after thermal treatment [22], UV irradiation or sonolysis [23,24] of fine powders or metal nanoparticles. 

The development of the Grignard-type addition to carbonyl compounds mediated by transition metals would be of interest as the compatibility with a variety of functionality would be expected under the reaction conditions employed. One example has been reported on the addition of allyl halides to aldehydes in the presence of cobalt or nickel metal however, yields were low (up to 22%). Benzylic nickel halides prepared in situ by the oxidative addition of benzyl halides to metallic nickel were found to add to benzil and give the corresponding 3-hydroxyketones in high yields(46). The reaction appears to be quite general and will tolerate a wide range of functionality. 

Base catalysis of ligand substitutional processes of metal carbonyl complexes in the presence of oxygen donor bases may be apportioned into two distinct classifications. The first category of reactions involves nucleophilic addition of oxygen bases at the carbon center in metal carbonyls with subsequent oxidation of CO to C02, eqns. 1 and 2 (l, 2). Secondly, there are... 

Since nucleophilic addition to a metal-coordinated alkene generates a cr-metal species bonded to an -hybridized carbon, facile 3-H elimination may then ensue. An important example of pertinence to this mechanism is the Wacker reaction, in which alkenes are converted into carbonyl compounds by the oxidative addition of water (Equation (108)), typically in the presence of a Pd(n) catalyst and a stoichiometric reoxidant.399 When an alcohol is employed as the nucleophile instead, the reaction produces a vinyl or allylic ether as the product, thus accomplishing an etherification process. 

Incorporation of CO into an organic substrate usually occurs by insertion of CO into a C-metal bond. The requisite Cl-metal bond is formed by oxidative addition of a Pd(0) species into the Cl-Br bond, the normal first step upon combining a Pd(0) compound and an aryl halide. Coordination and insertion of CO follows. Addition of N to the carbonyl and loss of Pd(0) gives an iminium ion, which is trapped by EtOH to give the product. 

The first reports on c-alkane metal complexes date back to the 1970s, the work of Perutz and Turner on photochemically generated unsaturated metal carbonyls of Group 6 [4], which is well before the C-H oxidative addition studies of alkanes. The enthalpy gain of formation of c-alkane metal complexes... 

The preparation of carbonyl-lr—NHC complexes (Scheme 3.1) and the study of their average CO-stretching frequencies [7], have provided some of the earliest experimental information on the electron-donor power of NHCs, quantified in terms of Tolman s electronic parameter [8]. The same method was later used to assess the electronic effects in a family of sterically demanding and rigid N-heterocyclic carbenes derived from bis-oxazolines [9]. The high electron-donor power of NHCs should favor oxidative addition involving the C—H bonds of their N-substituents, particularly because these substituents project towards the metal rather than away, as in phosphines. Indeed, NHCs have produced a number of unusual cyclometallation processes, some of which have led to electron-deficient... 

Vaska s complex catalyzed the transformahon of aUenylcyclopropane into 2-alkenylidenecyclohex-3-enone under conditions of pressurized CO (Scheme 11.25) [38]. In this reaction, the jr-coordination to internal oleflnic moiety of the aUene brings the metal closer to the cyclopropane ring. Release of the cyclopropane ring strain then facilitates the oxidative addition of vinylcyclopropane moiety along with C-C bond cleavage, such that metallacyclohexene is obtained a subsequent carbonyl insertion and reductive elimination then provides the product Hence, the reaction can be recognized as a [5+1] cycloaddition of vinylcyclopropane and CO. 

Recently, the oxidative addition of C2-S bond to Pd has been described. Methyl levamisolium triflate reacts with [Pd(dba)2] to give the cationic palladium complex 35 bearing a chiral bidentate imidazolidin-2-ylidene ligand [120]. The oxidative addition of the levamisolium cation to triruthenium or triosmium carbonyl compounds proceeds also readily to yield the carbene complexes [121], The oxidative addition of imidazolium salts is not limited to or d transition metals but has also been observed in main group chemistry. The reaction of a 1,3-dimesitylimidazolium salt with an anionic gallium(I) heterocycle proceeds under formation of the gaUium(III) hydrido complex 36 (Fig. 12) [122]. 

Our own group is also involved in the development of domino multicomponent reactions for the synthesis of heterocycles of both pharmacologic and synthetic interest [156]. In particular, we recently reported a totally regioselective and metal-free Michael addition-initiated three-component substrate directed route to polysubstituted pyridines from 1,3-dicarbonyls. Thus, the direct condensation of 1,3-diketones, (3-ketoesters, or p-ketoamides with a,p-unsaturated aldehydes or ketones with a synthetic equivalent of ammonia, under heterogeneous catalysis by 4 A molecular sieves, provided the desired heterocycles after in situ oxidation (Scheme 56) [157]. A mechanistic study demonstrated that the first step of the sequence was a molecular sieves-promoted Michael addition between the 1,3-dicarbonyl and the cx,p-unsaturated carbonyl compound. The corresponding 1,5-dicarbonyl adduct then reacts with the ammonia source leading to a DHP derivative, which is spontaneously converted to the aromatized product. 

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