Through Oxidative Addition

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). 

As reported in Scheme 1 the process involves a series of steps. The alkylpalladium species 1 forms through oxidative addition of the aromatic iodide to palladium(O) followed by noibomene insertion (4-7). The ready generation of complex 2 (8-11) from 1 is due to the unfavourable stereochemistry preventing P-hydrogen elimination from 1 (12). Complex 2 further reacts with alkyl halides RX to form palladium(IV) complex 3 (13-15). Migration of the R group to the... 

The proposed mechanism starts with a methyl group abstraction on platinum complex 416 with the borane reagent in the presence of diyne 414 (Scheme 105). The square-planar cationic diyne-platinum(n) complex 417 is converted to the octahedral platinum(rv) hydride intermediate 418 through oxidative addition of the hydrosilane. This complex decomposes rapidly with methane release to form another tetracoordinated platinum(n) species 419, followed by platinasilylation of the triple bond. The resulting vinylplatinum 420 undergoes an intramolecular carboplatination to... 

The most plausible mechanism proceeds through oxidative addition of the aldehyde to an active Ru(0) species to form (acyl)(hydrido)ruthenium(ll) complex 155. Insertion of the less-substituted double bond of the 1,3-diene into the Ru-H bond occurs to generate an (acyl)( 73-allyl)ruthenmm(ll) intermediate of type 156. Successive regioselective reductive eliminations between the acyl and the 73-allyl ligands provide the desired product with regeneration of the... 

Iridium hydride complexes effectively catalyze addition of nitriles or 1,3-dicarbonyl compounds (pronucleophiles) to the C=N triple bonds of nitriles to afford enamines.42S,42Sa Highly chemoselective activation of both the a-C-H bonds and the C=N triple bonds of nitriles has been observed (Equation (72)). To activate simple alkane dinitriles, IrHs(P1Pr3)2 has proved to be more effective (Equation (73)). The reaction likely proceeds through oxidative addition of the a-C-H bonds of pronucleophiles to iridium followed by selective insertion of the CN triple bonds to the Ir-C bond. 

Amination Through Oxidative Addition, / -Elimination, and Hydroamination... 

Recently, the crystal structure of a nickel(II) complex with a tridentate silyl ligand has been reported [20]. The structure in the solid state shows an //2-(Si-H) binding to nickel, with a Ni-H distance of 1.47 A NMR spectra of the complex in solution at -80 °C suggest the formation of a nickel(IV) hydride species through oxidative addition of the silyl-hydrogen to nickel [20]. 

Furthermore, when trimethylsilylacetylene 40 was used as an alkyne in the [IrCl(cod)]2-catalyzed reaction, propargyUc amines (where the alkyne was added to the double bond of imine) were obtained (Equation 10.7) [21, 23]. It is probable that the reaction proceeds through oxidative addition of the terminal C—H bond of alkyne to the Ir complex, followed by the insertion of imine to the resulting Ir-H complex. The crosscoupling reachon of trimethylsilyl (TMS)-acetylene with aldimines took place by [IrCl(cod)]2, leading to the corresponding adducts (Equahon 10.8) [24]. 

Until now, for most of the systems described here it has been accepted that alkane activation occurred through oxidative addition to the 14-electron intermediate complexes. Yet, Belli and Jensen [26] showed, for the first time, evidence for an alternative reaction path for the catalytic dehydrogenation of COA with complex [lrClH2(P Pr3)2] (22) which invoked an Ir(V) species. Catalytic and labeling experiments led these authors to propose an active mechanism (Scheme 13.12), on the basis of which they concluded that the dehydrogenation of COA by compound 22 did not involve an intermediate 14-electron complex [17-21], but rather the association of COA to an intermediate alkyl-hydride complex (Scheme 13.12). 

We have explored two types of carbon-carbon bond forming reactions operated under almost neutral conditions. Both reactions are initiated by the formation of an H-Rh-Si species through oxidative addition of a hydrosilane to a low-valence rhodium complex. Aldol-type three-component couphngs are followed by the insertion of an a,yS-unsatu-rated carbonyl compound into a Rh-H bond, whereas silylformylation is accomplished by the insertion of an acetylenic moiety into a Rh-Si bond. 

Activation of hydrogen through oxidative addition is best exemplified by the Wilkinson catalyst. The hydrogenation mechanism characteristic of dihydride complexes was originally suggested by Wilkinson2,109 and was later further... 

The mechanism probably involves the formation of a Cu(III) species through oxidative addition of the aryl halide. Subsequent reductive elimination then leads to the product ... 

Acylpalladium complexes are readily prepared through oxidative addition of Pd° complexes to acid chlorides. PdL4 compounds, where L is a tertiary phosphine, react with acid chlorides at room temperature to give trani-L2Pd(COR)Cl complexes. Since carbon monoxide does not insert into palladium acyl bonds, Pd(C0C02R) complexes are made from oxidative addition of oxalyl chloride monoesters. 

Although formally considered Ru(II) species, an important class of organo-ruthenium complexes can be accessed through ring opening of cycloalkenes Such ruthenium carbene complexes have recently been synthesized through oxidative addition pathways. ... 

In Sect. 2.3, generation of silylene complexes of transition metals was discussed on the basis of the reactivity of disilanyl-transition-metal complexes. The formation of silylene species in the presence of a catalytic amount of transition metals is also involved in the reactions of hydrodisilanes, which may readily form disilanyl complexes through oxidative addition of the Si-H bond prior to the activation of the Si-Si bond. Platinum-catalyzed disproportionation of hydrodisilanes affords a mixture of oligosilanes 89 up to hexasilane (Eq.45) [83]. The involvement of silylene-platinum intermediate was proven by the formation of a l,4-disila-2,5-cyclohexadiene derivative in the reaction of the hydrodisilane in the presence of diphenylacetylene. 

Manners first proposed that the transition-metal-catalyzed ROP occurred via a homogenous mechanism.157 However, a heterogenous catalytic cycle has been reported.158 The proposed mechanism for the Pt(l,5-cod)2 (cod-cyclooctadiene) catalyzed reaction is shown in Scheme 2.24. The Pt(l,5-cod)2 forms a [2]platinasilaferrocenophane through oxidative addition to the zero-valent Pt complex via elimination of a 1,5-cod ligand. Platinum colloids are then formed by the elimination of the second 1,5-cod ligand these platinum colloids are proposed to be the active catalysts. The polymers are then formed by subsequent oxidative addition and reductive eliminations at the colloid surface. 

Most cyclometallated compounds of Pt and Pd contain the metals in the + 2 oxidation state (d8 configuration) with its strong tendency for planar coordination. Other oxidation states, notably +4, are also possible. A series of Pt(IV)-cyclometallated complexes have been obtained [55] from Pt(II) compounds through oxidative addition reactions. Details of the photochemical and photophysical properties of these systems are discussed later in this review. Here we restrict ourselves to the discussion of the structural aspects of the Pt(IV) and, as far as applicable, to Pd(IV) compounds. 

Cyclometallated Pt(IV) complexes have, so far always, been obtained through oxidative addition reactions to cyclometallated Pt(II) complexes. In most cases bis-cyclometallated compounds have been used. The general reaction scheme is ... 

A proposed mechanism for the rhodium-catalyzed alcoholysis is represented in Scheme 49 (77). In the first step, activation of the hydrosilane occurs through oxidative addition. Formation of the alkoxysilane then takes place by nucleophilic attack of a noncoordinated alcohol molecule. The dihydro-rhodium complex 143 thus obtained liberates a hydrogen molecule upon reductive elimination. Nucleophilic cleavage of the silicon-rhodium bond, without prior coordination of the alcohol at the rhodium is supported by results obtained in asymmetric alcoholysis (cf. Sect. II-D). Optical yields were shown to be little dependent on the catalyst ligands (in marked contrast with the asymmetric hydro-silylation), indicating but weak interaction between alcohol and catalyst during the reaction. Moreover, inversion of configuration at silicon, which occurs in the particular case of methanol as solvent, is not likely to occur in a reaction between coordinated silane and alcohol. 

Cooper et al. reported that the cascade reaction of the palladium-catalyzed cyclization and the Barbier-type allylation of the 1,3-diene-aryl iodide 514, the aldehydes 515, and indium gave the heterocycles 516 in good yields (Scheme 154).220b The reaction proceeds through oxidative addition of a C—I bond of 514 to Pd(0) and subsequent insertion of a double bond of 517 to give the jr-allylpalladium intermediate 518. Transmetalation of the jr-allylpalladium 518 with indium leads to the allylindium complex 519, and the following reaction with the aldehydes 515 gives 516. 

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