Olefins oxidative-addition reactions

One other point to note in regard to this study (141) is that any evidence of oxidative addition, particularly with the chloro-olefins, was absent. The similarity of the spectra, coupled with the nonobservation of any bands in the visible region, as well as the observation of vc-c in the region commonly associated with 7r-complexation of an olefin (141, 142), all argue in favor of normal ir-coordination, rather than oxidative insertion of the metal atom into, for example, a C-Cl bond. Oxidative, addition reactions of metal atoms will be discussed subsequently. 

In this chapter, theoretical studies on various transition metal catalyzed boration reactions have been summarized. The hydroboration of olefins catalyzed by the Wilkinson catalyst was studied most. The oxidative addition of borane to the Rh metal center is commonly believed to be the first step followed by the coordination of olefin. The extensive calculations on the experimentally proposed associative and dissociative reaction pathways do not yield a definitive conclusion on which pathway is preferred. Clearly, the reaction mechanism is a complicated one. It is believed that the properties of the substrate and the nature of ligands in the catalyst together with temperature and solvent affect the reaction pathways significantly. Early transition metal catalyzed hydroboration is believed to involve a G-bond metathesis process because of the difficulty in having an oxidative addition reaction due to less available metal d electrons. 

The reduced donor ability of the phosphinite complexes such as 5e and 5f has an impact beyond the catalyst activation stipulated above. Apparently, the decreased tendency to undergo oxidative addition reactions also disfavors catalyst deactivation via oxidative olefin addition. Accordingly, (vinyl) (hydride) complexes such as 3 are less relevant. Simultaneously, product oxidative addition is restricted and, as... 

The major route to -cyclopropenylium complexes L M(C3R3) (metallatetrahedranes) is by oxidative addition reactions of cyclopropenylium salts to transition metal complexes of groups 5 (V), 6 (Mo, W), 8 (Fe, Ru), 9 (Co, Rh, Ir) and 10 (Ni, Pd, Pt). The addition is frequently accompanied by loss of one or more carbonyl, olefin or halogen auxiliary ligand. Concurrent formation of oxocyclobutenyl complexes by carbonyl insertion into the cyclopropenyl ring is often observed in reactions with group 9 cobalt triad and early transition metal complexes. 

In a similar approach, naproxen is prepared from an olefin, the product of a Heck reaction (see Section 5.3.2.1). As described above, the reaction proceeds in the presence of water and HC1, additionally copper(n)chloride is added, possibly to prevent the formation of palladium black (Scheme 5.39). Addition of HC1 to the double bond and subsequent oxidative addition reaction of the benzylic chloride with the active Pd° species initiates the catalytic cycle, which proceeds similarly to the ibuprofen synthesis [70-73]. 

Pt(0), NVE 16/Pt(II), NVE 16). Oxidative additions generally occur most readily for low valent complexes, and for metals in the order 5d > Ad 3d. In addition to those that formally cleave C-X, H-X, and X-X (X = halide) bonds, oxidative addition reactions are also known where the metal is inserted into C-0, C-H, and some strained or activated C-C bonds. Another reaction which is effectively an oxidative addition is the formation of metallacycles from a low valent metal and an olefin (Equation 7). 

Olefin Process (SHOP). Although this Ni complex is prepared by oxidative addition reaction (Section II.B.4), most other phosphinoenolato complexes are prepared by deprotonation of the corresponding phosphines R3PCH(R )C(0)R" or by other methods, as discussed in Sections III.A and IV.A. 

Oxidative addition reactions of dihydrogen , iodine ", alkyl halides and Hg(CN)2 to carbonyl, olefin or phosphine substituted derivatives of rhodium(I) and iridium(I) have been described. In order to determine the effect on the rate of the reaction, the kinetics of the oxidative addition of Hg(CN)2 to Rh(dik)(P(OPh)3)2 has been studied . A second-order rate law coupled to large negative values of the activation entropy suggest an associative mechanism which probably proceeds via a cyclic three-centred transition state (equation 58). Analogous results were obtained with Ir(dik)(cod) . ... 

The preparation is based on a convenient starting compound that may be stored readily. The procedure can be used to prepare adducts of other olefins and acetylenes. The ethylene complex is of widespread use in the study of oxidative addition reactions of platinum(O). ... 

During the past decade, considerable progress has been made in the area of transition metal-catalyzed cleavage and functionalization of the inert C-Cl bond in nonactivated chloroaromatic compounds. This new and important field of chemistry is reviewed in the present chapter, which describes both mechanistic and synthetic aspects of C-Cl activation. Oxidative addition reactions of chloroarenes to complexes of catalytic metals are discussed, along with their applications in a wide variety of reductive dechlorination, nucleophilic displacement, olefin arylation, coupling, and carbonylation reactions. 

It is therefore not surprising that the reactivities of arenes and alkanes in electrophilic substitution reactions are very different, with the former being much more active. At the same time, the mechanism of the interaction (oxidative addition) of both saturated and aromatic hydrocarbons with complexes of metals in a low oxidation state is in principle the same. The reactivities of arenes and alkanes in oxidative addition reactions with respect to low-valent metal complexes therefore usually differ insignificantly. Furthermore, a metal complex via the oxidative addition mechanism can easily cleave the C-H bond in olefin or acetylene. 

Scheme IV. 11. Oxidative addition reactions followed by addition of hydride to olefin and by the formation of allyl complexes. Reference numbers are in brackets.

Rh(TTP) reacts with alkyl halides, acyl halides, aroyl halides, and sulfonyl halides, but it shows no evidence of reaction with molecular hydrogen. These observations further emphasize the fact that Rh(TTP) is essentially a nucleophile and it therefore reacts with those reagents RX that can oxidatively add by nucleophilic attack (34). Rh(TTP) does not react with H2, and H2 seems always to add to (P complexes via a concerted mechanism (35). It appears that Rh(TTP) has very little diradical character, i.e. it is not a good analog of a carbene (35). It is possible that this unreactivity may be associated with the stereochemistry of chelation by the macrocyclic ligand. Earlier studies on the oxidative addition reactions of Rh(I) complex with a tetraaza macrocycle revealed that the Rh(I) had strong nucleophilic properties but the activation of molecular H2 was not reported (36, 37). This possibility is supported by reports that dialkyl sulfide complexes of rhodium chloride catalyze the hydrogenation of olefins (38). 

The formation of q -allyl complexes can also be regarded as an oxidative addition reaction. Proton abstraction from an olefin leads to the formally anionic allyl group (Eq. 2-38). 

Ethylene can also coordinate through a C-H bond as a a-complex or as a more stable TT-complex. Ti -Complexes of ethylene are intermediates in C-H oxidative addition reactions in some cases but not in others. As depicted in Equation 6.39, the complex Cp Ir(PMe3)(ethylene) is more stable than the vinyl hydride isomer Cp Ir(PMe3)(vinyl)(H), but the vinyl hydride complex is the kinetically preferred product. Thus, the ethylene complex cannot be an intermediate in the oxidative addition of the C-H bond of ethylene in this case. However, the olefin complex may form prior to oxidative addition of the vinyl C-H bond in other cases. ... 

The chemistry of carbonyl compounds with transition metal compounds is very rich. The paper by J. Bryan and M. Mayer [22] deserves special attention. It reports on a new type of oxidative addition reaction in which a carbonyl double bond is cleaved to form divalent ligands. The final result is an oxoalkylidene complex (Sch. 6). Such complexes are discussed in a mechanistic study of OM mediated by high-valent group 6 catalysts [23]. Three bimolecular chain termination steps, resulting in olefin, carbonyl compound and singlet oxygen, are proposed. 

In the oxidative addition reaction of Pd(0)L with H2 shown in Scheme 1, Pd is oxidized from an FOS of 0 to +2, while H2, which serves, at least in this step, as an oxidant ( ), is reduced by two elections. Specifically, each H atom is reduced from an FOS of 0 to -1. In the hydropalladation step, an olefin is reduced by two electrons (0 to -2), which is counterbalanced by two-electron oxidation of one H atom. In the reductive elimination step, the other H is oxidized by 2 electrons, while Pd is reduced from an FOS of -i-2 to 0 (Scheme 1). 

The carbene mechanism of COER according to our hypothesis consists of forward (Z = O, X = Y = C) and backward (X = O, Y = Z = O) Wittig-like reactions. A transition metal-carbene complex reacts with a carbonyl compound generating an olefin and transition metal oxo-complex. Then the oxo-complex reacts with another olefin generating a new carbonyl compound and regenerating the transition metal-carbene complex. It is known that oxo-alkylidene complexes can be generated via oxidative addition reaction between some tungsten complexes with carbonyl compounds. 

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