Reactions Involving Oxidative Steps

Rhodium(I) complexes are effective reagents and/or catalysts for the decarbonylation of acyl halides and aldehydes 9 11,34,195,230,231,236). The compound Rh(PPh3)3Cl, especially, has received considerable attention. The first step in such reactions involves oxidative addition to Rh(I) of the organic molecule, exemplified by the following ... 

A possible mechanism for the P-alkylation of secondary alcohols with primary alcohols catalyzed by a 1/base system is illustrated in Scheme 5.28. The first step of the reaction involves oxidation of the primary and secondary alcohols to aldehydes and ketones, accompanied by the transitory generation of a hydrido iridium species. A base-mediated cross-aldol condensation then occurs to give an a,P-unsaturated ketone. Finally, successive transfer hydrogenation of the C=C and C=0 double bonds of the a,P-unsaturated ketone by the hydrido iridium species occurs to give the product. 

As discussed earlier, the generally accepted mechanism for the Heck reaction involves the steps of oxidative addition, coordination of the alkene, migratory insertion, and P-hydride elimination [2,3], With the intramolecular Heck reaction emerging as an important synthetic reaction over the past decade, the individual steps of this mechanism have come under closer scrutiny, and attention is beginning to be directed at determining the identity of the enantioselective step [41],... 

Reactions of chlorine or bromine and ReX(CO)3 (diars) compounds (X = Cl, Br) in chloroform give the rhenium(IV) complexes, ReX4 (diars). The initial step in these reactions involves oxidative addition to give an intermediate, which is further oxidized in a subsequent step. 

The mechanisms and catalysts used in this Buchwald-Hartwig chemistry mirror those of coupling reactions involving oxidative addition, transmetallation, and reductive elirruna-tion. The first step, as usual, is oxidative insertion of Pd(0) into the aryl-halogen bond. The Pd(ll) complex now adds the amine so that both coupling partners find themselves bonded to the same palladium atom. The base eliminates H—1 from the complex and reductive elimination forms the Ar—N bond. 

The fact that sometimes a type of saturation kinetics and sometimes pseudo first-order kinetics were observed indicates that the reaction involves two steps (1) formation of the catalyst-substrate complex and (2) dissociation of the product from the intermediate complex with the associated formation of either the now oxidized or reduced complex form (Scheme 4.4). Actually, The reaction between a reduced molybdenum centre and an oxygen-donating substrate has been proposed to proceed via a transition state where the substrate oxygen atom binds directly to the molybdenum atom . It has to be considered that the initial condition [S]o [E]o together with the circumstance that the en me will not be recycled but consumed are both responsible for the deviating behaviour. 

The three basic steps in the palladium-catalysed Suzuki-Miyaura reaction involve oxidative addition, transmetalation, and reductive elimination. A systematic study of the transmetalation step has found that the major process involves the reaction of a palladium hydroxo complex with boronic acid, path B in Scheme 3, rather than the reaction of a palladium halide complex with trihydroxyborate, path A. A kinetic study using electrochemical techniques of Suzuki—Miyaura reactions in DMF has also emphasized the important function of hydroxide ions. These ions favour reaction by forming the reactive palladium hydroxo complex and also by promoting reductive elimination. However, their role is a compromise as they disfavour reaction by forming of unreactive anionic trihydroxyborate. A method for coupling arylboronic acids with aryl sulfonates or halides has been developed using a nickel-naphthyl complex as a pre-catalyst. It works at room temperature in toluene solvent in the presence of water and potassium carbonate. ... 

In its native state, the iron-III species is coordinated equatorially by a heme unit and axially by a histidine residue and is therefore very similar to cytochrome P 450 [1311]. The first step in the reaction involves oxidation of the Fe" to form an iron-oxo derivative called Compound I. The latter contains a Fe =0 moiety and... 

Growth of the linear oligomer has been monitored by an NMR study of the reaction, involving oxidative addition as the rate-determining step (Scheme 118). The polymer formed is insoluble in solvents. l,2,4,5-Tetra(bromomethyl)-benzene can be used to generate the Pt(iv) complex 960, and this reagent can also be employed to generate star-shaped polymers.Thus, the trinuclear complex 961, prepared from the reaction of 4,4 -di(bro-... 

This reaction involves three steps (1) the jump of a metal atom from the metal towards the oxide lattice (2) its ionization to occupy a cation vacancy, and (3) the simultaneous displacement of the scale/substrate interface. Indeed, in its present form, reaction [2.3] implicitly assumes that all the cation vacancies created at the external gas/scale interface and arriving at the internal scale/ substrate interface are annihilated at the internal interface. Therefore, reaction... 

Herm/es/Djnamit JS obe/Process. On a worldwide basis, the Hercules Inc./Dynamit Nobel AG process is the dorninant technology for the production of dimethyl terephthalate the chemistry was patented in the 1950s (67—69). Modifications in commercial practice have occurred over the years, with several variations being practiced commercially (70—72). The reaction to dimethyl terephthalate involves four steps, which alternate between liquid-phase oxidation and liquid-phase esterification. Two reactors are used. Eirst, -xylene is oxidized with air to -toluic acid in the oxidation reactor, and the contents are then sent to the second reactor for esterification with methanol to methyl -toluate. The toluate is isolated by distillation and returned to the first reactor where it is further oxidized to monomethyl terephthalate, which is then esterified in the second reactor to dimethyl terephthalate. 

A chain mechanism is proposed for this reaction. The first step is oxidation of a carboxylate ion coordinated to Pb(IV), with formation of alkyl radical, carbon dioxide, and Pb(III). The alkyl radical then abstracts halogen from a Pb(IV) complex, generating a Pb(IIl) species that decomposes to Pb(II) and an alkyl radical. This alkyl radical can continue the chain process. The step involving abstraction of halide from a complex with a change in metal-ion oxidation state is a ligand-transfer type reaction. 

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