Reactions oxidative-addition

Oxidative addition reactions are important in many areas of d block coordination/organometallic chemistry, although the term can be extended into other branches of inorganic (and organic) chemistry. We are dealing with reactions of the type  

The most typical oxidative addition occurs with square coplanar complexes where the central atom has the d8 configuration, especially Rh(I) or Ir(I). These conform to a 16-electron rule (Section 8.6) oxidative addition leads to an octahedral six-coordinate complex obeying the 18-electron rule, with a low-spin d6 central atom, e.g.  

The reverse process, reductive elimination, is also recognised as a common reaction in which the changes d6- d8 or d8- d10 occur. 

The central atom in a square planar d8 complex is sometimes described as coordinatively unsaturated. This term is best used to denote a tendency to take up additional ligands without change in oxidation state it does not necessarily follow that a coordinatively-unsaturated species will be susceptible to oxidative addition. However, square d8 complexes do have some tendency to take up a ligand to become trigonal bipyramidal, 18-electron species. Trigonal bipyramidal d8 complexes formed by Fe(0), 

Ru(0) and Os(O) are said to undergo oxidative addition in such reactions as  

Oxidative addition reactions usually involve a coordinatively unsaturated 16-electron metal complex or a five-coordinate 18-electron species, and take the following general form  

If the X and Y ligands in the product are considered to be formally -1, then the metal center has increased its formal oxidation state by +2, and diis is the origin of the name oxidative addition. The reverse reaction is called reductive elimination. The various mechanisms have been reviewed by Rendina and Puddephat, with special reference to Pt(II) systems. The following reactions are examples of various types of oxidative additions. The stereochemistry of the products can be controlled by subsequent isomerization reactions and is not always indicative of the immediate oxidative addition product. 

Oxidative addition reactions can also produce less obvious products, as shown in the following examples  

If (L) M—X and (L) M—Y are stable products, the implication is that (L) M is an odd-electron (e.g., 17-electron) organometallic complex. This mechanism is observed for bis(dimethylglyoxime)cobalt(II) and Co(CN)j reacting with organic halides, but only the products are true organometallic complexes. 

The above discussion refers to what are now called classical hydrides. In 1984, Kubas and co-workers reported the first noncl ical hydride complexes containing The first examples were W(CO)3(PR3)2(H2), 

Alkyl ligands have low electronegativity and therefore they enhance reactivity of the central atom in oxidative addition reactions (see Section 4.10.b). 

The phenyl compound of Cr(III)CrPh3 3THF undergoes rearrangement to an arene coordination compound (see Section 10.14.b). 

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C-Allyl Complex Formation. AHyl hahde, aHyl ester, and other aHyl compounds undergo oxidative addition reactions with low atomic valent metal complexes to form TT-aHyl complexes. This is a specific reaction of aHyl compounds. 

The oxidative addition reactions of Cp2M(CO)2 show some interesting differences between the Ti and Zr analogues. For Cp2Ti(CO)2, both... 

For many species the effective atomic number (FAN) or 18- electron rule is helpful. Low spin transition-metal complexes having the FAN of the next noble gas (Table 5), which have 18 valence electrons, are usually inert, and normally react by dissociation. Fach normal donor is considered to contribute two electrons the remainder are metal valence electrons. Sixteen-electron complexes are often inert, if these are low spin and square-planar, but can undergo associative substitution and oxidative-addition reactions. 

The heterocyclic telluride 32 is susceptible to oxidation-addition reactions and readily adds halogen atoms under a treatment with halogens or sulfuryl chloride (93MI1). Compounds 34 were obtained in almost quantitative yields. 

Oxidative addition reactions of platinum(II) complexes with N-heterocyclic ligands 97CRV1735. 

The mechanism of action of the cyanation reaction is considered to progress as follows an oxidative addition reaction occurs between the aryl halide and a palladium(O) species to form an arylpalladium halide complex which then undergoes a ligand exchange reaction with CuCN thus transforming to an arylpalladium cyanide. Reductive elimination of the arylpalladium cyanide then gives the aryl cyanide. 

Organometallic complexes of copper, silver, and gold are ideal precursors for carbene complexes along with some C- and N-coordinated species. Their reactivity pattern, in particular in oxidative addition reactions, was the most comprehensively studied. 

Oxidative addition—Reaction of the carbon electrophile with palladium-(0) complex 5 to give a palladium-(II) complex 6. 

Ru(NO)2(PPh3)2 has a similar electronic structure to the [M(NO)2(PPh3)2]+ (M = Rh, Ir) ions and like them has a pseudo tetrahedral structure with linear Ru-N—O [126]. It also resembles them in its oxidative addition reactions (Figure 1.47). 

RhCl(PPh3)3 is a very active homogenous hydrogenation catalyst, because of its readiness to engage in oxidative addition reactions with molecules like H2, forming Rh—H bonds of moderate strength that can subsequently be broken to allow hydride transfer to the alkene substrate. A further factor is the lability of the bulky triphenylphosphines that creates coordinative unsaturation necessary to bind the substrate molecules [44]. 

The cation has significant tetrahedral distortion from square planar geometry (P—Ir—P 150°) to minimize non-bonding interactions. It undergoes various oxidative addition reactions... 

Figure 2.72 Oxidative additive reactions of [Ir(PMe3)4]+ and bond lengths.

The similar species Ir(PMe3)4 likewise shows tetrahedral distortion from square planar geometry (P-Ir—P 152.6-158.9°). It undergoes some remarkable oxidative addition reactions with species like H2O and H2S (Figure 2.72). 

Carbonyl complexes infrared spectra oxidative additions reactions structures syntheses... 

Relatively few examples are known which utilize an oxidative addition reaction of metal hydrides to necessarily low valent silicon compounds. Seyfert s hexame-thylsilirane (31) could be used as a source of dimethylsilylene to perform an... 

This synthetic approach is known from the synthesis of L M(alkene)H compounds from LnM(CO)alkane precursors and can easily be applied to the analogous silyl complexes. The Si—H bond even shows an increased activity for oxidative addition reactions [42, 43]. 

Oxidative-addition reactions of transition metal complexes. J. Halpern, Acc. Chem. Res., 1970, 3, 386-392 (66). 

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