Ionic palladium complexes, catalyze

Palladium catalyzed reactions in ionic liquids, 251-284 Palladium complexes, 39 13 [PdBr2(C4mimy)2], 261 PhMeSiD2, 28... 

Ionic liquids can be used as replacements for many volatile conventional solvents in chemical processes see Table A-14 in the Appendix. Because of their extraordinary properties, room temperature ionic liquids have already found application as solvents for many synthetic and catalytic reactions, for example nucleophilic substitution reactions [899], Diels-Alder cycloaddition reactions [900, 901], Friedel-Crafts alkylation and acylation reactions [902, 903], as well as palladium-catalyzed Heck vinylations of haloarenes [904]. They are also solvents of choice for homogeneous transition metal complex catalyzed hydrogenation, isomerization, and hydroformylation [905], as well as dimerization and oligomerization reactions of alkenes [906, 907]. The ions of liquid salts are often poorly coordinating, which prevents deactivation of the catalysts. 

Wang, R.H., Zeng, Z., Twamley, B. et al. (2007) Synthesis and characterization of pyrazolyl-functionalized imidazolium-based ionic Uquids and hemilabile (carbene )palladium(II) complex catalyzed Heck reaction. Eur. J. Org. Chem., 655-61. 

Kim SM, Kang YK, Lee KS, Mang JY, Kim DY. Asymmetric electrophilic iluorination of 3-keto phosphonates in ionic liquid media catalyzed by chiral palladium complexes. Bull. Korean Chetn. Soc. 2006 27 423-425. 

The reaction of alcohols with CO was catalyzed by Pd compounds, iodides and/or bromides, and amides (or thioamides). Thus, MeOH was carbonylated in the presence of Pd acetate, NiCl2, tV-methylpyrrolidone, Mel, and Lil to give HOAc. AcOH is prepared by the reaction of MeOH with CO in the presence of a catalyst system comprising a Pd compound, an ionic Br or I compound other than HBr or HI, a sulfone or sulfoxide, and, in some cases, a Ni compound and a phosphine oxide or a phosphinic acid.60 Palladium(II) salts catalyze the carbonylation of methyl iodide in methanol to methyl acetate in the presence of an excess of iodide, even without amine or phosphine co-ligands platinum(II) salts are less effective.61 A novel Pd11 complex (13) is a highly efficient catalyst for the carbonylation of organic alcohols and alkenes to carboxylic acids/esters.62... 

My last comment concerns the reaction of palladium olefin complexes with carbon monoxide discovered by Tsuji. I agree that this is most likely to proceed by an insertion rather than an ionic mechanism. Chloride attack on coordinated olefin is rare however. Chloride ion is an inhibitor, for example in the palladous chloride catalyzed hydration of ethylene (0). I, therefore, wondered whether carbon monoxide was affecting the ease with which chloride attacks olefin. One can postulate that carbon monoxide participates in this insertion either as a gas phase reactant or by first forming a carbonyl olefin complex. Such complexes of the noble metals were unknown, but examining the reaction between carbon monoxide and the halogen bridged olefin complexes of platinum revealed that they are formed very readily... 

In a related transformation, a palladium-benzothiazole carbene complex has been reported to efficiently catalyze the arylation of allylic alcohols [79]. Carrying the reaction in an ionic liquid, the authors could couple aryl bromides and activated aryl chlorides with terminal allylic alcohols with remarkable regioselectivity (Scheme 10). The interest of this methodology was also highlighted by its application to the synthesis of three intermediates in the synthesis of medicinal products [80-82],... 

Another important reaction, the Heck reaction catalyzed by palladium salts and complexes, has been studied as well via EXAFS [191]. The authors of the study highlight the importance of correlating structural data with reaction kinetics. Among others the authors showed that in chloride-based ionic liquids the Heck reaction shows poor reactivity until, at some point during the reaction, Pd nanoparticles form, which initiates the reaction. They pointed out that the correlation between the induction period and the nanoparticle formation was strong, and although the metal may not be the active site for the catalysis [91], the presence of Pd(0) is clearly important. 

In none of the above cases has a reaction been performed whilst taking the EXAFS data. HamUl et al. [66] have investigated the Heck reaction, catalyzed by palladium salts and complexes, in room-temperature ionic liquids. On dissolution of palladium ethanoate in [BMIM]" " and N-butylpyridinium ([BPy]+)... 

An immobilized version of a Heck reaction catalyzed by Pd nanoparticles has been very recently described by Kaiimi and Enders [289]. The nanoparticles were obtained as a result of the covalent anchoring of a N-heterocyclic carbene palladium/ionic liquid matrix on a silica surfece and their nature was confirmed by TEM coupled with EDX analysis. The catalyst showed high thermal stability (up to 280 °C) and could be recycled four times for the reaction of bromobenzene with methylacrylate achieving a total turnover number of 36600. After carrying out a hot filtration process, the authors could not detect any Pd in the filtrate. The filtrate also showed no further reaction progress. Erom these findings the authors concluded that the reaction was, in their case, indeed catalyzed by the heterogeneous Pd particles and not from monomolecular Pd-complexes leached from the sur ce. 

Polyketones formed by the palladium-catalyzed alternating copolymerization of styrene and CO have become the subject of a great deal of attention [43]. Almost concurrently, two papers appeared describing this reaction in ionic liquids [44,45]. Seddon et al. used [Pd(bipy)2][PFs] in a variety ofionic liquids (Scheme 7-1) [44]. The complex was active in methanol [ca. 17.4 kg (g Pd) ], but the product polyketone was contaminated with palladium. In the ionic liquids the activity of the catalyst was dependent on the nature of the anion, decreasing in the order [N(S02CFj)2]"... 

The Suzuki-Miyaura cross-coupling reaction is a standard method for carbon-carbon bond formation between an aryl halide or triflate and a boronic acid derivative, catalyzed by a palladium-metal complex. As with the Mizoroki-Heck reaction, this cross-coupling reaction has been developed in ionic liquids in order to recycle and reuse the catalyst. In 2000, the first cross-coupling of a halide derivative with phenylboronic acid in [bmim] [BF4] was described. As expected, the reaction proceeded much faster with bromobenzene and iodobenzene, whereas almost no biphenyl 91 was obtained using the chloride derivative (Scheme 36). The ionic liquid allowed the reactivity to be increased, with a turnover number between 72 and 78. Furthermore, the catalyst could be reused repeatedly without loss of activity, even when the reaction was performed under air. Cross-coupling with chlorobenzene was later achieved - although with only a moderate yield (42%) - using ultrasound activation. 

Wang, R., Xiao, J., Twamley, B. and Shreeve, J.M. (2007) Efficient Heck reactions catalyzed by a highly recyclable palladium(II) complex of a pyridyl-functionalized imidazolium-based ionic liquid. Org. Biomol. Chem., 5, 671-8. 

Imamoto and coworkers described phosphine-borane complexes as a coupling partner for the synthesis of aryl phosphines with aryl electrophiles using Pd(PPh3),j at room temperature (Scheme 20.68) [228,229], The borane moiety can be easily removed ljy excess use of diethyl amine or morpholine. Gaumont and coworkers demonstrated the palladium-catalyzed C—P cross-coupling in imidazolium-based ionic liquid and that the catalyst can be recycled up to six cycles [230]. 

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