Addition reactions halide metalation

Neutral carboranes and boranes react with transition-metal complexes forming metallocarboranes or metalloboranes, respectively. However, most metallocarboranes and metalloboranes are prepared from transition-metal halides and anionic carborane and borane species ( 6.5.3.4) or by reacting metal atoms and neutral boranes and carboranes. These reactions are oxidative addition reactions ( 6.5.3.3). 

Reactions of alkyl halides with alkaU metal phosphides [39-41], addition reactions of olefins with PHj [42] or the pyrolytic cleavage of P-0 bonds in RPO2H2 [43] are also reported for the preparation of alkyl/aryl functionalized primary... 

Secondary bromides and tosylates react with inversion of stereochemistry, as in the classical SN2 substitution reaction.24 Alkyl iodides, however, lead to racemized product. Aryl and alkenyl halides are reactive, even though the direct displacement mechanism is not feasible. For these halides, the overall mechanism probably consists of two steps an oxidative addition to the metal, after which the oxidation state of the copper is +3, followed by combination of two of the groups from the copper. This process, which is very common for transition metal intermediates, is called reductive elimination. The [R 2Cu] species is linear and the oxidative addition takes place perpendicular to this moiety, generating a T-shaped structure. The reductive elimination occurs between adjacent R and R groups, accounting for the absence of R — R coupling product. 

Among all the nucleophilic addition reactions of carbonyl compounds, allylation reaction has been the most successful, partly due to the relatively high reactivity of allyl halides. Various metals have been found to be effective in mediating such a reaction (Scheme 8.4). Among them, indium has emerged as the most popular metal for such a reaction. 

Domino Michael/aldol processes, which are initiated by the addition of a halide to an enone or enal, have found wide attention. They are valuable building blocks, as they can be easily converted into a variety of extended aldols via subsequent SN2 reactions with nucleophiles or a halide/metal exchange. As an example, a-haloalkyl- 3-hy-droxy ketones such as 2-76 have been obtained in very good yields and selectivities by reaction of enones 2-71 with nBu4NX in the presence of an aldehyde 2-74 and TiCl4as described by the group of Shinokubo and Oshima (Scheme 2.16) [24]. 

The ionic P-P bond polarization renders P-phosphino-NHPs highly active reactants for various metathesis and addition reactions at exceedingly mild conditions. Metathesis is observed in reactions with alcohols, chloroalkanes, and complex transition metal halides (Schemes 11 and 12) [39, 73], Of particular interest are the reactions with chlorotrimethylstannane which yield equilibria that are driven by a subtle balance of P-X bond strengths to yield either diphosphines or P-chloro-NHPs as preferred product (Scheme 11). Chlorotrimethylsilane does not react with... 

Anionic complexes [R2Au] are present in salts with metal or large quaternary cations, but only a few compounds of this type have been isolated.1,2 Solutions of the lithium salts generated in situ are substrates for addition reactions with alkyl halides leading to alkylgold(m) compounds.26... 

Metallic zinc is typically covered with a zinc oxide layer that must be removed before the metal can engage in an oxidative addition reaction with organic halides. This activation can be done in one of several ways. 

In the reaction of group 13 element halides with metal carbonyl dianions, the analysis is more complex than observed for the reactions with metal monoanions. Upon addition of metal dianions to EX3 or REX3, either one or two halide ions may be eliminated. When only one halide ion is eliminated per added metal dianion, the complexes may still be viewed as E3+ derivatives (Equations (33)-(36)).19 This may be controlled to some extent by the stoichiometry of the reaction. Comparison of Equations (33)19 and (34)19 shows that the electron demand at the main group element can be satisfied by coordination either to an electron-rich metal center 26 or formation of a halide bridge 27. Ligand-stabilized forms may also be prepared in this fashion (Equation (36)).19... 

For the purpose of carrying out carbonyl addition reactions, allylstannanes can be prepared in situ from metallic tin and an allyl halide (Barbier conditions),259 for example, Equation (93).260... 

Electronic ligand effects are highly predictable in oxidative addition reactions a-donors strongly promote the formation of high-valence states and thus oxidative additions, e.g. alkylphosphines. Likewise, complexation of halides to palladium(O) increases the electron density and facilitates oxidative addition [11], Phosphites and carbon monoxide, on the other hand, reduce the electron density on the metal and thus the oxidative addition is slower or may not occur at all, because the equilibrium shifts from the high to the low oxidation state. In section 2.5 more details will be disclosed. 

The polymerization of olefins in the presence of halides such as aluminum chloride and boron fluoride but in the absence of hydrogen halide promoter may also be described in terms of the complex carbonium ion formed by addition of the metal halide (without hydrogen chloride or hydrogen fluoride) to the olefin (cf. p. 28). These carbonium ions are apparently more stable than those of the purely hydrocarbon type the reaction resulting in their formation is less readily reversed than is that of the addition of a proton to an olefin (Whitmore, 18). Polymerization in the presence of such a complex catalyst, may be indicated as follows (cf. Hunter and Yohe, 17) ... 

Metal-Halogen Compounds. An unusual example of the addition of a metal halide to a conjugated diene has been reported. The complex formed from palladium chloride and butadiene has been shown to be a dimer of 1-chloromethyl-7r-allylpalladium chloride, (85). Whether this is a true insertion reaction or some type of ionic reaction has not been determined, but its close analogy with the olefin-palladium chloride insertion reaction mentioned above would suggest an insertion mechanism for the diene reaction also. 

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