Oxidative addition reviews

Perfluoroalkyl or -aryl halides undergo oxidative addition with metal vapors to form nonsolvated fluonnated organometallic halides and this topic has been die subject of a review [289] Pentafluorophenyl halides react with Rieke nickel, cobalt, and iron to give bispentafluorophenylmetal compounds, which can be isolated in good yields as liquid complexes [290] Rieke nickel can also be used to promote the reaction of pentafluorophenyl halides with acid halides [297] (equation 193)... 

Recent advancements involving oxanickellacycles as common intermediates, which are formed by oxidative addition of a Ni(0) species upon dienes and aldehydes, is also reviewed very briefly. 

Cross-coupling to form carbon heteroatom bonds occurs by oxidative addition of an organic halide, generation of an aryl- or vinylpalladium amido, alkoxo, tholato, phosphido, silyl, stannyl, germyl, or boryl complex, and reductive elimination (Scheme 2). The relative rates and thermodynamics of the individual steps and the precise structure of the intermediates depend on the substrate and catalyst. A full discussion of the mechanism for each type of substrate and each catalyst is beyond the scope of this review. However, a series of reviews and primary literature has begun to provide information on the overall catalytic process.18,19,22,23,77,186... 

There are now a number of quite stable Pt(IV) alkyl hydride complexes known and the synthesis and characterization of many of these complexes were covered in a 2001 review on platinum(IV) hydride chemistry (69). These six-coordinate Pt(IV) complexes have one feature in common a ligand set wherein none of the ligands can easily dissociate from the metal. Thus it would appear that prevention of access to a five-coordinate Pt(IV) species contributes to the stability of Pt(IV) alkyl hydrides. The availability of Pt(IV) alkyl hydrides has recently allowed detailed studies of C-H reductive elimination from Pt(IV) to be carried out. These studies, as described below, also provide important insight into the mechanism of oxidative addition of C-H bonds to Pt(II). 

The classic platinum(O) approach to C-H activation, yielding platinum(II) alkyl hydrides as the oxidative addition products, contributed significantly to our understanding of C-H activation. However, the platinum(II)/(IV) approach has proven capable of achieving oxidative functionalization of hydrocarbons, and so this review focuses on the higher oxidation state. 

As briefly discussed in section 1.1, and shown in Figure 1, the accepted mechanism for the catalytic cycle of hydrogenation of C02 to formic add starts with the insertion of C02 into a metal-hydride bond. Then, there are two possible continuations. The first possibility is the reductive elimination of formic acid followed by the oxidative addition of dihydrogen molecule to the metal center. The second possible path goes through the a-bond metathesis of a metal formate complex with a dihydrogen molecule. In this section, we will review theoretical investigations on each of these elementary processes, with the exception of oxidative addition of H2 to the metal center, which has already been discussed in many reviews. 

The importance of transition-metal mediated decomposition of ligands has been reviewed by Garrou [30] with an emphasis on oxidative addition as the mechanism. 

A large number of NHC complexes tolerate moisture, air, and elevated temperatures [1, 2]. The stability of these compounds is, however, still limited. One of the most important decomposition route for these complexes is the reductive elimination of 2-aIkyl or 2-aryl substituted azolium salts from NHC complexes with alkyl or aryl groups in cA-position to the NHC ligand. This route can be considered as the reverse reaction of the previously discussed oxidative addition of C2-X bonds to transition metals and has been reviewed [94, 123]. 

The [2 + 3] cycloaddition reaction of nitrile oxides, easily accessible from corresponding aldoximes, with different alkenes is known as an excellent route to isoxazohne derivatives . The reactions of asymmetric addition ° or addition of unsaturated ger-manes and stannanes to nitrile oxides were reviewed in recent years. In this subsection only the main directions of the synthesis of isoxazole derivatives are briefly reported. 

Niunerous oxidative additions to organometalHc complexes occur with 100% yield in the solid state. A review is given in [68]. Well-guided combustion reactions of soHds proceed almost quantitatively and may be relevant despite the gaseous products. 

In certain cases palladium(II) complexes might undergo oxidative addition. For a review... 

The short-lived [MH2(Cp)2] and [TaH4(dmpe)2] have been obtained from the Mv hydrides using photogenerated r-butoxy radicals, and were characterized by low temperature ESR.575 On the other hand, thermally stable, well-defined dinuclear or mononuclear MIV hydrides have been prepared by oxidative addition of H2 to dinuclear Mm or mononuclear Mn halide phosphine adducts, respectively. They constitute attractive entries to lower oxidation state compounds, and will be reviewed in Sections 34.4.3.l.i and 34.6.1.2.i. 

Iridium complexes having oxygen ligands are not nearly as extensive as those having nitrogen. Examples include acetylacetonates [Ir(P(C(5H5)3)2 (acac)H2] [64625-61-2], aqua complexes Ir(OH2)6]3+ [61003-29-0], nitrato complexes [Ir(0N02)(NH3),J2 [42482 42-8], and peroxides IrCl(P(C6I fy)3)2(02-/-(>/ I I9)2(CO) [81624-11-5]. Unlike rhodium, very few Ir(II) carboxylate-bridged dimers have been claimed and [Ir,2(OOCCI I3)4 has not been reported. Some Ir(T) complexes exhibit reversible oxidative addition of 02 to form Ir(III) complexes. That chemistry has been reviewed (172). 

Reaction (78) regenerates Mel from methanol and HI. Using a high-pressure IR cell at 0.6 MPa, complex (95) was found to be the main species present under catalytic conditions, and the oxidative addition of Mel was therefore assumed to be the rate determining step. The water-gas shift reaction (equation 70) also occurs during the process, causing a limited loss of carbon monoxide. A review of the cobalt-, rhodium- and iridium-catalyzed carbonylation of methanol to acetic acid is available.415... 

The vinyl substitution reaction often may be achieved with catalytic amounts of palladium. Catalytic reactions are carried out in different ways depending on how the organopalladium compound is generated. Usually copper(II) chloride or p-benzoquinone is employed to reoxidize palladium(0) to palla-dium(II) in catalytic reactions when methods (i) or (ii) are used for making the organopalladium derivative. The procedures developed for making these reactions catalytic are not completely satisfactory, however. The best catalytic reactions are achieved when the organopalladium intermediates are obtained by the oxidative addition procedures (method iii), where the halide is both the reoxidant and a reactant. Reviews of some aspects of these reactions have been published.u-le... 

Recent development of the Heck reaction has also led to greater understanding of its mechanistic details. The general outlines of the mechanism of the Heck reaction have been appreciated since the 1970s and are discussed in numerous reviews [2,3]. More recently, two distinct pathways, termed the neutral and cationic pathways, have been recognized [2c-g,3,7,8,9]. The neutral pathway is followed for unsaturated halide substrates and is outlined in Scheme 8G. 1 for the Heck cyclization of an aryl halide. Thus, oxidative addition of the aryl halide 1.2 to a (bisphosphine)Pd(O) (1.1) catalyst generates intermediate 1.3. Coordination of... 

The products of oxidative addition of acyl chlorides and alkyl halides to various tertiary phosphine complexes of rhodium(I) and iridium(I) are discussed. Features of interest include (1) an equilibrium between a five-coordinate acetylrhodium(III) cation and its six-coordinate methyl(carbonyl) isomer which is established at an intermediate rate on the NMR time scale at room temperature, and (2) a solvent-dependent secondary- to normal-alkyl-group isomerization in octahedral al-kyliridium(III) complexes. The chemistry of monomeric, tertiary phosphine-stabilized hydroxoplatinum(II) complexes is reviewed, with emphasis on their conversion into hydrido -alkyl or -aryl complexes. Evidence for an electronic cis-PtP bond-weakening influence is presented. 

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