Triflates palladium complexes

The original Sonogashira reaction uses copper(l) iodide as a co-catalyst, which converts the alkyne in situ into a copper acetylide. In a subsequent transmeta-lation reaction, the copper is replaced by the palladium complex. The reaction mechanism, with respect to the catalytic cycle, largely corresponds to the Heck reaction.Besides the usual aryl and vinyl halides, i.e. bromides and iodides, trifluoromethanesulfonates (triflates) may be employed. The Sonogashira reaction is well-suited for the synthesis of unsymmetrical bis-2xy ethynes, e.g. 23, which can be prepared as outlined in the following scheme, in a one-pot reaction by applying the so-called sila-Sonogashira reaction ... 

Palladium complexes also catalyze the carbonylation of halides. Aryl (see 13-13), vinylic, benzylic, and allylic halides (especially iodides) can be converted to carboxylic esters with CO, an alcohol or alkoxide, and a palladium complex. Similar reactivity was reported with vinyl triflates. Use of an amine instead of the alcohol or alkoxide leads to an amide. Reaction with an amine, AJBN, CO, and a tetraalkyltin catalyst also leads to an amide. Similar reaction with an alcohol, under Xe irradiation, leads to the ester. Benzylic and allylic halides were converted to carboxylic acids electrocatalytically, with CO and a cobalt imine complex. Vinylic halides were similarly converted with CO and nickel cyanide, under phase-transfer conditions. ... 

Lehn has also reported the hydrogen-bonding templated assembly of receptors based on bipyridine copper and palladium complexes [102]. A mixture of substituted bipyridines (76, 77) (see Scheme 39) with copper(I) triflate generates a mixture of tetrahedral complexes and uncoordinated ligands. 

Recently, the oxidative addition of C2-S bond to Pd has been described. Methyl levamisolium triflate reacts with [Pd(dba)2] to give the cationic palladium complex 35 bearing a chiral bidentate imidazolidin-2-ylidene ligand [120]. The oxidative addition of the levamisolium cation to triruthenium or triosmium carbonyl compounds proceeds also readily to yield the carbene complexes [121], The oxidative addition of imidazolium salts is not limited to or d transition metals but has also been observed in main group chemistry. The reaction of a 1,3-dimesitylimidazolium salt with an anionic gallium(I) heterocycle proceeds under formation of the gaUium(III) hydrido complex 36 (Fig. 12) [122]. 

Organozinc reagents, including the Reformatsky reagents, are extensively used in transition metal catalysed coupling reactions with aryl halides or triflates, vinyl halides, and allylic halides or acetates, as reviewed by Erdik156. Nickel and palladium complexes are... 

Extensive studies by Amatore, Jutand, and co-workers have shed light on the structure and oxidative addition chemistry of a number of synthetically important palladium complexes [42], In particular, these workers have shown that the major species in a solution of Pd(dba)2 and BINAP is Pd(dba)BINAP and that oxidative addition of Phi to this complex generates (Bl-NAP)Pd(Ph)I [42d,43], In addition, it has been demonstrated that palladium halide complexes such as (PhjP jaryljPdCl do not dissociate the halide ligand in DMF solution [44], whereas the corresponding triflate complex is completely dissociated [44,45], As noted earlier, the nature of the oxidative addition intermediates defines two mechanistic pathways for the Heck reaction the neutral pathway for unsaturated halide substrates and the cationic pathway for unsaturated triflate substrates [2c-g,3,7-9]. Further, it is possible for halide substrates to be diverted to the cationic pathway by addition of Ag(I) orTh(I) salts [3], and it is possible to divert some triflate substrates to the neutral pathway by addition of halide additives [38]. Individual steps of these two pathways have recently received some scrutiny. 

Cross-coupling reactions of alkenylsilicates 114 with aryl or vinyl halides or triflates are catalyzed by a palladium complex to give the corresponding alkenes (equation 92)173. 

Abstraction of chloride from a vinylpalladium complex by silver acetate has been reported,45 as well as halide abstraction by silver triflate from arylpalladium halides.46 More interestingly in the context of creating C-C bonds, silver perchlorate was able to promote the reaction of (r -aryl)palladium bromide with dienes. Silver-promoted bromide abstraction led to the formation of (r 1-r 2-enyl)palladium complexes, which evolved further through the regioselective formation of a C-C bond between the aryl group and the former diene. Reactions with nonconjugated dienes suggested that the reaction proceeds via carbometallation of the less crowded double bond. Isomerization and (3 elimination led to a (ri3-allyl)palladium complex (Scheme 10.26).47... 

The palladium-catalyzed arylation and alkenylation of olefins, which were first discovered in the 1970 s by Heck (7,2) and Mizoroki (3) and have been often called the "Heck reaction", are versatile synthetic means for making a carbon-carbon bond. These reactions have been extensively used for organic synthesis during the past two decades (4-7). However, no reports on the "asymmetric Heck reaction" have been appeared until very recently. Shibasaki reported an asymmetric intramolecular cyclization of alkenyl iodides to give c/j-decalin derivatives of 80-91% ee (8-10). Overman reported an intramolecular cyclization of alkenyl triflate, giving a chiral quaternary carbon center of 45% ee (77). We report herein the first example of intermolecular asymmetric Heck-type arylation of cyclic olefins catalyzed by (7 )-BINAP-coordinated palladium complexes (Scheme 1) (12,13). 

Palladium(O) complexes containing P(o-C6H4Me)3 as ligand show low reactivity toward aryl triflates [95,96]. Thus, the original catalyst is not effective for the ami-nation of aryl triflates. However, palladium complexes with the chelating phosphines DPPF and BINAP are effective [97,98]. Selected animations of aryl triflates by aniline are shown in Eq. (9), and selected animations of aryl triflates by alkylamines in Eq. (10). 

The amination of aryl halides and triflates catalyzed by palladium complexes is suitable for use in complex synthetic problems. Many substrates will produce high yields of mixed arylamines with one of the existing catalyst systems. Nevertheless, there are many combinations of substrates for which the amination chemistry may be substantially improved. For the most part, these reactions involve nitrogen centers, such as those in pyrroles, indoles, amides, imidazoles and other heterocyclic groups that are less basic than those in standard alkylamines. Although mild reaction conditions have been developed for many substrates, the harsh conditions used in many of the applications indicate that continued studies on developing mild condi-... 

The neutral palladium(II) compound 43 is transformed by addition of AgOTf into the cationic complex 44. In the presence of water an exchange of the triflate anion to hydroxide occurs (44 — 45). Finally, the palladium enolate 46 is formed from the palladium complex and the silyl enol ether. 

For the palladium dibenzylideneacetone complex (1), NMR data to support the proposition that the bis-phosphine acts as a bidentate ligand has been reported. A triflate salt of the TT-allyl palladium complex has been isolated and is stable in the solid state. However, no crystals suitable for X-ray analysis were obtained. An X-ray crystal structure of the ligand and a bis-palladium complex has been reported. The palladium complexes are generated just before use under an inert atmosphere exposure to air affords a catalytically inactive tetra-coordinated palladium(II) species. ... 

Different conditions (including additives and solvent) for the reaction have been reported,often focusing on the palladium catalyst itself," or the ligand." Catalysts have been developed for deactivated aryl chlorides," and nickel catalysts have been used." Modifications to the basic procedure include tethering the aryl triflate or the boronic acid to a polymer, allowing a polymer-supported Suzuki reaction. Polymer-bound palladium complexes have also been used." " The reaction has been done neat on alumina," and on alumina with microwave irradiation." Suzuki coupling has also been done in ionic liquids," in supercritical... 

The palladium-catalyzed amination of aryl halides has recently emerged as a powerful alternative to other methods for the synthesis of aryl amines.5 This method allows for the cross-coupling of aryl halides arrd triflates with amines in the presence of a stoichiometric amount of a base and catalytic amounts of palladium complexes bearing tertiary phosphine ligands. As shown in Tables I and II, the Pd/BlNAP catalyst is highly effective for reactions of aryl bromides and triflates with primary and cyclic... 

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