Reaction with palladium compounds stable

Both 1,4- and 1,5-dienes form stable complexes with Pd. For most 1,3-dienes, such as 1,3-butadiene, reaction with Pd° compounds leads to 7r-allyl formation. These reactions are described in Section 7. The coordinated double bonds in palladium diene complexes are reactive toward attack by many nucleophiles, and the resulting chelating alkene palladium alkyls are easily isolated. Many useful reactions of dienes were discovered by Jiro Tsuji in the 1960s and 1970s. These have been recently reviewed in a historical memoir. ... 

Oxidative addition [1, 38] of 1-alkenyl, i-alkynyl, allyl, benzyl, and aiyl halides to a palladium(O) complex affords a stable rra .s-<7-palladium(II) complex (11). The reaction proceeds with complete retention of configuration for alkenyl halides and with inversion for allylic and benzylic halides. Alkyl halides having /3-hydrogens are rarely useful because the oxidative addition step is very slow and may compete with /3-hydride elimination from the a-organopalladium(II) species. However, it has been recently shown that iodoalkanes undergo the cross-coupling reaction with organoboron compounds (Section 2.4.5). 

Transition metals such as Mn, Fe, Ru, Co, Rh, Ni and their metal compounds easily react with carbon monoxide to afford their metal carbonyl compounds (M ,(CO) ). But no correspond palladium compound (Pd (CO) ) is isolated. However, if the palladium is coordinated by an electron-donating compound such as phosphine and SO3F, the palladium atom is able to form stable compounds with carbon monoxide [36-49]. For example, palladium carbonyl compounds are prepared by the reaction of palladium phosphine with carbon monoxide or by the reaction of palladium compounds with phosphine in the presence of carbon monoxide as shown in eqs. (20.18) and (20.19) [39]. 

A novel chiral dissymmetric chelating Hgand, the non-stabiUzed phosphonium ylide of (R)-BINAP 44, allowed in presence of [Rh(cod)Cl]2 the synthesis of a new type of eight-membered metallacycle, the stable rhodium(I) complex 45, interesting for its potential catalytic properties (Scheme 19) [81]. In contrast to the reactions of stabihzed ylides with cyclooctadienyl palladium or platinum complexes (see Scheme 20), the cyclooctadiene is not attacked by the carbanionic center. Notice that the reactions of ester-stabilized phosphonium ylides of BINAP with rhodium(I) (and also with palladium(II)) complexes lead to the formation of the corresponding chelated compounds but this time with an equilibrium be-... 

Substantially more work has been done on reactions of square-planar nickel, palladium, and platinum alkyl and aryl complexes with isocyanides. A communication by Otsuka et al. (108) described the initial work in this area. These workers carried out oxidative addition reactions with Ni(CNBu )4 and with [Pd(CNBu )2] (. In a reaction of the latter compound with methyl iodide the complex, Pd(CNBu )2(CH3)I, stable as a solid but unstable in solution, was obtained. This complex when dissolved in toluene proceeds through an intermediate believed to be dimeric, which then reacts with an additional ligand L (CNBu or PPh3) to give PdL(CNBu )- C(CH3)=NBu I [Eq. (7)]. 

Next to the cyclopropane formation, elimination represents the simplest type of a carbon-carbon bond formation in the homoenolates. Transition metal homoenolates readily eliminate a metal hydride unit to give a,p-unsaturated carbonyl compounds. Treatment of a mercurio ketone with palladium (II) chloride results in the formation of the enone presumably via a 3-palladio ketone (Eq. (24), Table 3) [8], The reaction can be carried out with catalytic amounts of palladium (II) by using CuCl2 as an oxidant. Isomerization of the initial exomethylene derivative to the more stable endo-olefin can efficiently be retarded by addition of triethylamine to the reaction mixture. 

The reaction of Pd complexes (such as Pd(PhsP)4) with organic halides and related compounds has been used to prepare a number of stable Pd alkyl and vinyl compounds. This reaction with alkyl halides has the characteristics of an Sn2 reaction. Primary halides react faster than secondary halides. Also, when a chiral halide is used, such as (X)-(-F)-benzyl-o -D chloride, the benzyl palladium product is formed with inversion of configuration at the benzylic carbon (equation 8). With vinylic halides, retention of configuration at the double bond is observed... 

The most effective palladium catalysts are those in which a PdFe bimetallic compound carries a bridging diphosphine ligand, when the reaction is thought to occur at the palladium centre with the iron playing an important role.25 Optically active methyl-phenylneophyltin hydride, [a] +28.9°, reacts with palladium on charcoal to give the optically active distannane, [a] +13.2°, which is optically stable for several weeks.28... 

The less stable trifluoromethyl zinc compounds [48] can be used as a source of nucleophilic trifluoromethyl fragments either in the isolated form or generated in situ by sonication of perfluoroalkyl iodides with zinc in DMF or THF. Zinc perfluoroorganyls find application in Barbier-type reactions [49], palladium-catalyzed cross-coupling reactions [50], or hydroperfluoroalkylations of acetylenes or olefins [51] (Scheme 2.119). 

Like other cyclic compounds having a cis-azo linkage, benzo[c]cinnoline forms fairly stable complexes with many transition metal salts.These all have a 1 1 ligand metal ratio except in the case of palladium(II) chloride, where a 2 1 complex has been isolated.Benzo[c]cinnoline 5-oxide also gives 2 1 complexes with palladium(ll) chloride and with silver nitrate. " A nickel(O) complex, Ni(PEt3)2(benzo[c]cinnoline)2, has been obtained by reaction with biscyclooctadiene nickel and triethylphosphine in hexane. " ... 

Boron has a high affinity for fluoride, and boronic acids can be converted, via reaction with KHF2, into trifluoroborates (RBF3K), the fluorine analogues of the boronate anion. These compounds are very stable, but can be reactive under the appropriate conditions and are very useful in palladium-catalysed couplings. 

This reaction is catalyzed by nickel or palladium complexes. However, the selectivity and activity of nickel catalysts are lower than those of palladium catalysts. Palladium-catalyzed reactions give linear dimers selectively and no cydization takes place. Not only the zerovalent palladium complexes but also certain bivalent ones can be used as active catalysts in combination with excess PPh3. However, the zerovalent palladium complexes are somewhat tedious to prepare and unstable in oxygen, so easily available and stable bivalent palladium compounds such as Pd(OAc)2 are generally used with PPh3. A proposed mechanism is given in Figure 1 [1 f]. 

On the other hand, the palladium and platinum complexes of pyridine-2-aldoxime, when treated with acetyl chloride in hot chloroform, gave stable chelates containing the acylated ligand. A monoacetylated palladium chelate was isolated in which 1 mole of pyridine-2-aldoxime was replaced by two chloride ions (see reaction XXIV). This compound was identified by its infrared spectrum, which had a strong carbonyl absorption band near 1790 cm-1. The platinum complex of pyridine-2-aldoxime gave a... 

---