Oxidative addition Subject

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)... 

Since Chatt and Davidson13 observed the first clear example of simple oxidative addition of a C—H bond of naphthalene to a ruthenium metal center, Ru(dmpe)2 (dmpe = Me2PCH2CH2PMe2), hydrocarbon activation has been the subject of many transition metal studies.11 c Sometimes, the efforts in this field have ended in findings different from the initial objectives, which have been the starting point for the development of novel organometallic chemistry. 

Transition metal centered bond activation reactions for obvious reasons require metal complexes ML, with an electron count below 18 ("electronic unsaturation") and with at least one open coordination site. Reactive 16-electron intermediates are often formed in situ by some form of (thermal, photochemical, electrochemical, etc.) ligand dissociation process, allowing a potential substrate to enter the coordination sphere and to become subject to a metal mediated transformation. The term "bond activation" as often here simply refers to an oxidative addition of a C-X bond to the metal atom as displayed for I and 2 in Scheme 1. 

Carbonylation is an exceedingly broad subject, but the main reaction patterns can be easily rationalized by recalling the classification used earlier for coupling reactions involving (a) metallacycles (b) hydride-promoted reactions and (c) oxidative addition of organic halides to zero-valent nickel. In fact, one or other of these steps is necessary to form a species able to undergo carbonylation. 

The group R1 can be allyl, acyl, or alkynyl, and arynes can also act as the acceptors. The catalysts are usually Ni(cod)2, or ligated palladium. The mechanisms are not understood in detail, but a catalytic cycle involving the product of oxidative addition, Sn-M-R1, is thought to be involved. The stannylalkenes that are formed can then be subjected to reaction with electrophiles (e.g., AczO or RCH=0), or to coupling reactions in the presence of transition metals (e.g., the Stille reaction). 

Toniolo reported the carbonylation of aromatic aldehydes containing electron-donating substituents with a Pd/PPh3 catalyst system in the presence of HC1 to give phenylacetic acid derivatives [64]. No activity was observed in the absence of PPI13 or HC1, and high yields could be achieved with alkanols as solvent (e.g., EtOH). It is believed that the mechanism involves HC1 addition to the aldehyde, with the resultant chlorohydrin being subject to oxidative addition to Pd, CO insertion, and alcoholysis. Upon Cl -o- OR substitution with the formed mandelic acid derivative, a second carbonylation takes place,... 

In later experiments 2)9 beans were subjected to a milder, longer exposure to ozone (25 pphm for 3 hr). This treatment did not diminish the sulfhydryl content appreciably, even though the ozonated leaves showed injury 18 hr later. However, we were able to detect newly produced disulfides (Table III). We concluded that ozonation changes proteins sufficiently to expose and oxidize additional sulfhydryl groups. 

Compared with the variety of existing carbon or nitrogen nucleophiles that were subjected to nucleophilic addition to there are few examples for phosphorus nucleophiles. Neutral trialkylphosphines turn out to be to less reactive for an effective addihon to Cjq even at elevated temperatures [114], Trialkylphosphine oxides show an increased reactivity. They form stable fullerene-substituted phosphine oxides [115] it is not yet clear if the reaction proceeds via a nucleophilic mechanism or a cycloaddition mechanism. Phosphine oxide addition takes place in refluxing toluene [115], At room temperature the charge-transfer complexes of with phosphine oxides such as tri-n-octylphosphine oxide or tri-n-butylphosphine oxide are verifiable and stable in soluhon [116],... 

Mention has already been made of the uciion of oxygen and oxidants on metal. It should be noted that metals react with sulfides, such as hydrogen sulfide, and are subsequently subject to additional slow attack by oxygen and oxidants. Thus, copper reacts to form sulfide and then the basic copper sulfate. 

Halpern et al. had already stressed the importance of radical mechanisms in the oxidative addition and insertion reactions of both [Rh(OEP)]2 and Rh(OEP) [338]. Thus, [Rh(OEP)]2 reacted with trimethylphosphite according to sequence (37), forming a rhodiophosphonate Rh(PO OMe 2) (OEP) and methyl radicals which were subject to further reactions [339]. In the presence of excess P(OMe)3, they were trapped by formation of MePO(OMe)2 in more than stoichiometric quantities, indicating a radical chain process. 

Vaska s complex trans-IrCl(CO)(PPh ) has served as an important model for mechanistic investigation of catalytically relevant reactions such as the oxidative addition and reductive elimination of small molecules(15). The latter processes have also been the subject of some photochemical investigation. For example, the reductive elimination of H2 depicted in Equation 5, which is a relatively slow thermally activated process (k = 3.8 x 10- s l in 25° benzene solution (15)), has been shown to occur readily when the dihydride complex was subjected to continuous photolysis with 366 nm light(16). However, Vaska s compound itself was reported to be... 

This chapter describes studies of an important class of organometallic reactions — oxidative addition reactions — utilizing femtosecond infrared spectroscopy. Since numerous excellent reviews have been published on this subject, only a brief account is presented below. 

As noted above, <7-carbon complexes derived from HCo(CO)4 are of low thermal stability and most of the isolated examples contain phosphine and phosphite ligands. Thus Co(PMe3)4 is readily alkylated by Mel to MeCo(PMc3)4. With excess Mel, oxidative addition with loss of one phosphine to Me2CoI(PMe3)3 is found. Higher alkyls are subject to /3-elimination (see -Elimination). 

A second important reaction of L-AuR species is the oxidative addition (see Oxidative Addition) of halogen or alkyl halides, which leads, at least in a first step, to organo(dihalo)gold(IIl) or diorgano(halo)gold(III) products. The structures are transformed from linear to square planar, and therefore cis and trans isomers are possible. The products may undergo secondary reactions and/or become subject to a reductive elimination (see Reductive Elimination) of other substituent combinations (equations 41 and 42). ... 

There are quite a number of routes available for the production of iridium(ni) alkyl compounds. In addition to the halide displacement and olefin insertion pathways noted above for iridium(l) compounds, oxidative addition of C-H bonds to iridium(l) to form iridium(in) hydrido alkyl complexes is also a possibihty. This subject will be covered in detail in Section 9 and will not be discussed here. However, there are other oxidative addition routes that lead to the formation of iridium(lll) alkyls. First, oxidative addition of O2 or HCl to some alkyl and aryl iridium(l) complexes can produce iridium(lll) alkyl or aryl compounds. In some cases, HgCl2 can add, but this appears to lead to tractable products only for the very stable pentafluorophenyl complex. Of course, oxidative addition see Oxidative Addition) of alkyl halides such as H3CI will also yield alkyl iridium(lll) compounds. Addition of Mel to Vaska s compound yields a stable iridium(III) complex, but addition of Etl does not produce a stable compound, presumably due to subsequent /J-hydride elimination see fi-Hydride Elimination). A number of mechanistic studies have been done on the oxidative addition of alkyl halides to iridium(l), especially Vaska s complex see Vaska s Complex). 

The corresponding ferrilactams (156), which have also been the subject of much attention, are available by the nucleophilic substitution of (155) by amines in the presence of a Lewis acid, usually ZnCb. The substitution occurs with allylic transposition,that is, attack at C-3 of (155). In selected cases, compounds of the type (156) have been prepared by oxidative addition of vinylaziridines or m-4-amino-l-butenols with (2). A bridged ferrilactam bonded through C-2 of the allyl (157) unit has been reported recently and was prepared by way of oxidative addition of a cyclic allylic... 

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