Subject palladium complexes

Addition of several organomercury compounds (methyl, aryl, and benzyl) to conjugated dienes in the presence of Pd(II) salts generates the ir-allylpalladium complex 422, which is subjected to further transformations. A secondary amine reacts to give the tertiary allylic amine 423 in a modest yield along with diene 424 and reduced product 425[382,383]. Even the unconjugated diene 426 is converted into the 7r-allyllic palladium complex 427 by the reaction of PhHgCI via the elimination and reverse readdition of H—Pd—Cl[383]. 

Nucleophilic Substitution of xi-Allyl Palladium Complexes. TT-Allyl palladium species are subject to a number of useful reactions that result in allylation of nucleophiles.114 The reaction can be applied to carbon-carbon bond formation using relatively stable carbanions, such as those derived from malonate esters and (3-sulfonyl esters.115 The TT-allyl complexes are usually generated in situ by reaction of an allylic acetate with a catalytic amount of fefrafcz s-(triphenylphosphine)palladium... 

The transition metal catalysed formation of five membered heterocycles through the insertion of a triple bond has also been explored. o-Halophenyl-alkynylamines, propargylamines and propargyl-ethers have been subjected to ring closure reactions. These processes, however also require the presence of a second, anionic reagent, which converts the palladium complex formed in the insertion step to the product. 

Asymmetric hydrocarbalkoxylation of alkenes has been studied since the early 1970s, but the number of papers published on this subject is much less than that of asymmetric hydroformylation. This difference is mainly due to the fact that these reactions catalyzed by palladium complexes with chiral phosphine ligands usually require a very high pressure of carbon... 

It is very well known that jr-allyl palladium complex 1, which is a key intermediate for the Tsuji-Trost type allylation, has an electrophilic character and reacts with nucleophiles to afford the corresponding allylation products. We discovered that bis 7r-allyl palladium complex 2 is nucleophilic and reacts with electophiles such as aldehydes [27] and imines [28-32] (Scheme 2, Structure 2). We have also shown that bis 7r-allyl palladium complex 2 can act as an amphiphilic catalytic allylating agent it reacts with both nucleophilic and electrophilic carbons at once to produce double allylation products [33]. These complexes incorporate two allyl moieties that can bind with different hapticity to palladium (Scheme 3). The different complexes may interconvert by ligand coordination. The complexes 2a, 2b and 2c are called as r]3,r]3-bisallypalladium complex (also called bis-jr-allylpalladium complex), r)l,r)3-bis(allyl)palladium complex, -bis(allyl)palladium complex, respectively. Bis zr-allyl palladium complex 2 can easily be generated by reaction of mono-allylpalladium complex 1 and allylmetal species 3 (Scheme 4) [33-36]. Because of the unique catalytic activities of the bis zr-allyl palladium complex 2, a number of interesting cascade reactions appeared in the literature. The subject of the present chapter is to review some recent synthetic and mechanistic aspects of the interesting palladium catalyzed cascade reactions which in-... 

Palladium complexes were shown to open the cyclopropane ring and form 7t-complexes. This ring-opening reaction by palladium was subject of theoretical studies in which the activation via corner versus edge palladation was discussed. When bicyclopropyl was added to di- -... 

It was presumed from molecular models that the 3,6-substituents of quinox-aline units may play an important role in the stabilization of optically active helical structures. 1,2-Diisocyanobenzene 86 (4 equiv) bearing p-tolyl groups at the 3- and 6-positions was subjected to oligomerization in the presence of the chiral palladium complex 84 (Scheme 54) [96]. The resulting mixture of oligomers was separated by preparative GPC, leading to the isola-... 

Among a numerous number of chiral palladium complexes, those applied to organic synthesis, either catalytically or stoichiometrically, will be a central subject of this section. This section will cover only the chiral palladium complexes whose X-ray crystal structures and/or NMR data have been reported. Thus, chiral palladium catalysts that are generated in situ in the reaction media are excluded from discussion. Because of recent progress of the X-ray crystallographic and NMR techniques/instruments, examples of well-characterized chiral palladium species are growing rapidly. 

In the series of complexes with twelve chains ((55) M = Cu, Pd, VO R = OC H2 +i, = 6, 8, 10, 12, 14), an unusual phase sequence was observed (Table 34). The copper and palladium complexes displayed enantiotropic, disordered Coh and Coin phases, identified by their optical texture, and by X-ray diffraction. Quite uniquely, the Coin phase was systematically the lower-temperature mesophase, observed below the Coh phase. For the copper complexes, a Coir phase was seen for short-chain compounds with a transition to a Colh phase for n > 10. The intermediate octyloxy derivative displayed an unusual, but reproducible, I-Coh-Colh-Colr-Colh-Colh phase sequence on cooling from the isotropic liquid, several of these transitions being weakly first order. The decyloxy analog displayed a Colh-Colh-Colh-Colh phase sequence, and the two next homologous compounds showed a single Coin phase. To have, supposedly, so many phases of apparently the same symmetry in a single material is most unusual and no explanation was offered to help understand the phenomenon. It is to be hoped that at some stage they may be subject to re-examination so that this exotic behavior may be properly understood. 

A variety of 2- or 3-substituted thiophenes, as well as benzothiophenes, have been subjected to the catalytic direct arylation [3, 9, 10]. As expected, 2,2 -bithio-phene can be diarylated at the 5,5 -positions (Equation 10.47) [72], although the use of a bulky phosphine is of key importance for this reaction. 2,2 -Bithiophene protected by benzophenone at the 5-position reacts with aryl bromides, initially with liberation of the ketone (see Scheme 10.6, to give 5-aryl-2,2 -bithiophene, which is then arylated at the 5 -position (Equation 10.48) [72]. 5-Bromo-2,2 -bithio-phenes undergo oxidative homocoupling in the presence of a palladium complex and a silver salt (Equation 10.49) [73]. 

Pd-catalyzed allylic substitution reactions can also be performed using water-soluble phosphine ligands, including TPPTS 132, as shown by the reaction of nitroester 48 with allyl acetate 133 to give the substitution product 134 (Scheme 24). The use of water-soluble palladium catalysts has been the subject of a review.t Water-soluble catalysts have also been applied to supported Uquid phase reactions. A silica bead supports a thin film of polar solvent in which the palladium complex resides.t The substrates and product reside in the bulk organic phase and can be decanted from the glass bead catalyst at the end of the reaction. 

Conditions for obtaining unsaturated esters rather than the bicarboxylic ones were the subject of much work, most of which was a matter of patents see, for example. Ref. [12]. Cinnamic methyl ester, previously prepared in low yield from styrenef was obtained preferentially when methanol was added to Moiseev s clusters, a tetrameric palladium complex, previously treated with styrene under carbon monoxide atmosphere at 25 °C (Scheme 9). 

The metal-catalyzed cross-coupling of Grignard reagents with organylhalides is mostly referred as "Kumada reaction". In most cases. Nickel catalysts have been employed, but they are not subject of this chapter. However, there are many cases based on the pioneering works of Sekiya and Ishikawa, Kumada and Hayashi, where palladium complexes are used with success " (Scheme 5-102, Scheme 5-103, Experimental Procedure below ). The POPd2 system (see also Figure 5-12) delivers... 

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