Reaction with organometallic species

The great majority of o-acetylide transition metal complexes are prepared by interaction of a metal halide with acetylide, RC C , or the formal oxidative addition of terminal alkynes or alkynyl stannanes to the metal center. As amply demonstrated in the previous section, alkynyliodonium salts may serve as electrophilic acetylene equivalents. In other words, transition metal complexes may act as nucleophiles in reactions with alkynyliodonium species. Indeed, the reaction [81] of the square planar Vaska s complex, 106, and its Rh analog, 107, with a variety of alkynyliodonium triflates in toluene results in 89-96% isolated yield of the hexa-coordinate o-acetylide complexes, 108 and 109 [Eq. (58)]. Reaction is essentially instantaneous and occurs with retention of stereochemistry around the metal center. 

Recent studies have shown that o-acetylide metal complexes exhibit very encouraging third-order nonlinear optical (NLO) properties [85,86]. Hence, there is considerable current interest in o-acetylide complexes and conjugated, bridging, bimetallic systems. 

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The electrophilic amination reaction of organometallic species using mono-, di- and trihaloamines has attracted a lot of attention for the synthesis of amines. Only a few cases have been reported using alkylchloroamines as precursors for the synthesis of tertiary amines One example is the reaction of functionalized aryhnagnesium compounds with benzyl-V-chloroamines 252 providing polyfunctional tertiary amines 253 (equation 164) °. The procedure was also applied for the preparation of chiral V-chloro-amines with retention of chirahty at the a-carbon. However, the amination process is limited to benzyl-V-chloroamines. 

Over the past few years, there has been great interest in the reactions of organometallic species with dihydrogen, H2. The product of such a reaction may take one of two forms. Usually, irradiation by UV light causes loss of a CO ligand from the metal to be replaced by two individual M-H bonds. Thus, dihydrogen is added oxidatively to the metal, the H-H bond is broken, and a classical dihydride species results. 

Fig. 3 Catalytic manifolds in iron-catalyzed cross-coupling reactions of alkyl halides 1 with organometallic species 2...

In the reviewed period of 1995-2007, no synthetic work on the reactivity of substituents attached to ring heteroatoms was published. Oxidation at ring sulfur atoms is reviewed in Section 4.12.6.2.5. Cleavage reactions with formation of the intermediate sulfonium species (dedithioacetalization process) and reactions with organometallic reagents occurring at ring sulfur atoms of 1,3-dithiolanes are described in Section 4.12.6.2.1. 

In conunon with much of the foregoing chemistry, some of the most flexible and versatile methods in this area are based on nickel- or palladium-catalyzed coupling reactions between organometallic species... 

So far, we have only reported oxidation type reactions. However, reduction type reactions have also been reported in the case of TCNQ-based materials associated with organometallic species.24,25 Moreover, in these examples, it was shown that different stoichiometries were reached and were controlled by the electrochemical conditions. 

The reaction of alkenyl epoxides with organometallic species (lithium, magnesium, copper, and boron) affords allylic alcohols, following an Sn and/or Sn mechanism. These processes can accommodate only little organic functionality and exhibit low regio- and/or stereoselectivity. Under smooth conditions, C—C bond formation proceeds by nucleophilic alkylation of vinyl epoxides in the presence of catalytic amounts of zerovalent palladium. Regio- and stereoselectivity can be achieved via the formation of a Tr-allylpal-ladium complex. Trost and Molander and Tsuji and co-workers simultaneously reported the first studies in 1981. Since then, numerous papers have dealt with this subject. Essentially, after chelation and oxidative addition of the palladium onto the vinyl epoxide, the zwitterionic 7r-allylpalladium complex deprotonates the nucleophile, which can in principle attack either carbon 2 (proximal attack) or 4 (distal attack) (Scheme 1). 

In an effort to discover new enolonium ion equivalents, it has been shown that allylically-substituted enolates react with organometallic species (mainly cuprates) in one of two ways, either 5n2 or 5n2 depending on the reaction conditions (Scheme 21). ... 

In Grignard reactions, Mg(0) metal reacts with organic halides of. sp carbons (alkyl halides) more easily than halides of sp carbons (aryl and alkenyl halides). On the other hand. Pd(0) complexes react more easily with halides of carbons. In other words, alkenyl and aryl halides undergo facile oxidative additions to Pd(0) to form complexes 1 which have a Pd—C tr-bond as an initial step. Then mainly two transformations of these intermediate complexes are possible insertion and transmetallation. Unsaturated compounds such as alkenes. conjugated dienes, alkynes, and CO insert into the Pd—C bond. The final step of the reactions is reductive elimination or elimination of /J-hydro-gen. At the same time, the Pd(0) catalytic species is regenerated to start a new catalytic cycle. The transmetallation takes place with organometallic compounds of Li, Mg, Zn, B, Al, Sn, Si, Hg, etc., and the reaction terminates by reductive elimination. 

Chain reactions such as those described above, in which atomic species or radicals play a rate-determining part in a series of sequential reactions, are nearly always present in processes for the preparation of thin films by die decomposition of gaseous molecules. This may be achieved by thermal dissociation, by radiation decomposition (photochemical decomposition), or by electron bombardment, either by beams of elecuons or in plasmas. The molecules involved cover a wide range from simple diatomic molecules which dissociate to atoms, to organometallic species with complex dissociation patterns. The... 

Mechanistically the reaction can be divided into two steps. Initially the alkyl halide 1 reacts with sodium to give an organometallic species 3, that can be isolated in many cases. In a second step the carbanionic R of the organometallic compound 3 acts as nucleophile in a substitution reaction with alkyl halide 1 to replace the halide ... 

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