Organometallic compounds with unsaturated halides

First, coordinatively unsaturated active palladium catalyst, PdL2, is produced via dissociation of the ligands, which then reacts with acyl halide to give the acylpalladium intermediate. Since deinsertion of CO of the acylpalladium derivatives may occur simul-taneously, the next step, transmetallation (so-called metathesis), is the most crucial for the efficiency of the overall reaction. A variety of organometallic compounds, such as boron, aluminum, copper, zinc, mercury, silicon, tin, lead, zirconium, and bismuth, are used as the partner in this coupling reaction without loss of CO. In this section, the important features of the cross-coupling reactions of a variety of organometallic compounds with acyl halides and related electrophiles are discussed. 

The same authors also used ESI-MS/MS to study an air-promoted oxidative Heck reaction between arylboronic acids and enamides as electron-rich olefins (Scheme 7.13) [29]. In addition to the conventional Mizoroki-Heck reaction of unsaturated compounds with organic halides or triflates as electrophiles, the use of nucleophilic organometallic reagents, such as organoboron compounds, has... 

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. 

Organosodium compounds are prepared from sodium and other organometallic compounds or active methylene compounds by reaction with organic halides, cleavage of ethers, or addition to unsaturated compounds. Some aromatic vinyl compounds and allyhc compounds also give sodium derivatives. 

Pd-catalyzed cross-coupling reactions of organozinc compounds with alkenyl and aryl halides can be carried out under mild conditions and are the fastest among all reactions using various organometallics. The reaction with acyl hahdes is not an exception. Usually, the reaction is completed at lower than room temperature within a couple of hours [38,251 - 25 3]. As organozinc compounds are coordinatively unsaturated and sterically less bulky, the transmetallation step is facilitated [29] ... 

CAS 102-54-5. The first organometallic sandwich compound (synthesized in 1951), which served as a prototype for metallocenes. Such compounds are based on cyclic unsaturates combined with a transition metal or its halide. 

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