Palladium chloride complex

Scheme 78) [89]. Aryl chlorides with activating as well as deactivating substituents could also be coupled under the same conditions in high yields, ranging from 60% to 95%, within 30-60 min of microwave irradiation. The process does not require an inert atmosphere. The increased conversion observed with the addition of the ionic liquid reveals that it might have an additional function besides simply acting as a molecular irradiator . It cannot be excluded for instance that carbene palladium complexes are formed in situ and implicated in the catalytic cycle. 

Palladium(II) chloride forms colored complexes with many aromatic and sulfur-containing compounds [27]. 

In 2003, Sigman et al. reported the use of a chiral carbene ligand in conjunction with the chiral base (-)-sparteine in the palladium(II) catalyzed oxidative kinetic resolution of secondary alcohols [26]. The dimeric palladium complexes 51a-b used in this reaction were obtained in two steps from N,N -diaryl chiral imidazolinium salts derived from (S, S) or (R,R) diphenylethane diamine (Scheme 28). The carbenes were generated by deprotonation of the salts with t-BuOK in THF and reacted in situ with dimeric palladium al-lyl chloride. The intermediate NHC - Pd(allyl)Cl complexes 52 are air-stable and were isolated in 92-95% yield after silica gel chromatography. Two diaster corners in a ratio of approximately 2 1 are present in solution (CDCI3). 

Very recently, well-defined complexes with general formula [PdCl(T -Cp) (NHC)] were synthesised and tested for the homocoupling of non-electrodeficient arylboronic acids at room temperature with good results (Scheme 7.7) [51]- This new class of catalysts were synthesised from commercially available NHC palladium(II) chloride dimers and are air-stable. 

Fagnou and co-workers reported on the use of a palladium source in the presence of different phosphine ligands for the intramolecular direct arylation reaction of arenes with bromides [56]. Later, they discovered that new conditions employing palladium complex 27 promoted the direct arylation of a broad range of aryl chlorides to form six- and five-membered ring biaryls including different functionalities as ether, amine, amide and alkyl (Scheme 7.11) [57]. 

A palladium catalyst with a less electron-rich ligand, 2,2-dipyridyl-methylamine-based palladium complexes (4.2), is effective for coupling of aryl iodides or bromides with terminal alkynes in the presence of pyrrolidine and tetrabutylammonium acetate (TBAB) at 100°C in water.37 However, the reactions were shown to be faster in NMP solvent than in water under the reaction conditions. Palladium-phosphinous acid (POPd) was also reported as an effective catalyst for the Sonogashira cross-coupling reaction of aryl alkynes with aryl iodides, bromides, or chlorides in water (Eq. 4.18).38... 

The allylation of aldehydes can be carried out using stannous chloride and catalytic cupric chloride or copper in aqueous media." In-situ probing provides indirect (NMR, CV) and direct (MS) evidence for the copper(I)-catalyzed formation of an allyltrihalostannane intermediate in very high concentration in water (Scheme 8.6). Hydrophilic palladium complex also efficiently catalyzes the allylation of carbonyl compounds with allyl chlorides or allyl alcohols with SnCl2 under aqueous-organic... 

In the ligand l,2-bis-(2-pyridylethynyl)benzene the pyridyl N atoms easily attain the appropriate separation for trans-chelation of metal cations. The 1 1 complex of the ligand with palladium(II) chloride has been structurally characterized.171,182... 

In summary, these results demonstrate that air-stable POPd, POPdl and POPd2 complexes can be directly employed to mediate the rate-limiting oxidative addition of unactivated aryl chlorides in the presence of bases, and that such processes can be incorporated into efficient catalytic cycles for a variety of cross-coupling reactions. Noteworthy are the efficiency for unactivated aryl chlorides simplicity of use, low cost, air- and moisture-stability, and ready accessibility of these complexes. Additional applications of these air-stable palladium complexes for catalysis are currently under investigation. 

However, some binuclear -jr-allyl palladium complexes have been obtained by facile decarboxylations from palladium chloride and some... 

A variety of triazole-based monophosphines (ClickPhos) 141 have been prepared via efficient 1,3-dipolar cycloaddition of readily available azides and acetylenes and their palladium complexes provided excellent yields in the amination reactions and Suzuki-Miyaura coupling reactions of unactivated aryl chlorides <06JOC3928>. A novel P,N-type ligand family (ClickPhine) is easily accessible using the Cu(I)-catalyzed azide-alkyne cycloaddition reaction and was tested in palladium-catalyzed allylic alkylation reactions <06OL3227>. Novel chiral ligands, (S)-(+)-l-substituted aryl-4-(l-phenyl) ethylformamido-5-amino-1,2,3-triazoles 142,... 

When Knochel and his co-workers attempted to use [PdC CF CN ] and related palladium(n) complexes as catalysts in the reactions of dialkylzincs with alkyl iodides, they observed the formation of the halogen-zinc exchange405 or cyclization406 products only. A recent paper of Zhou and Fu demonstrated that palladium complexes can also be used in the coupling reactions of alkylzinc bromides with alkyl iodides, bromides, chlorides, and... 

The main path of the palladium-catalyzed reaction of butadiene is the dimerization. However, the trimerization to form /j-1, 3,6,10-dodeca-tetraene takes place with certain palladium complexes in the absence of a phosphine ligand. Medema and van Helden observed, while studying the insertion reaction of butadiene to 7r-allylpalladium chloride and acetate (32, 37), that the reaction of butadiene in benzene solution at 50°C using 7r-allylpalladium acetate as a catalyst yielded w-1,3,6,10-dodecatetraene (27) with a selectivity of 79% at a conversion of 30% based on butadiene in 22 hours. 

Not only do palladium complexes catalyze reactions of Eq. (58), but nickel complexes were also effective (51) and formed the same products. Complexes such as Fe(CO)5 and Fe2(CO)8 were ineffective. Cobalt carbonyl, and tris-triphenylphosphinerhodium chloride were effective even at room temperature, but no 2 1 adducts were made. With both palladium and nickel, the activity of the catalyst and the distribution of products between 1 1 and 2 1 adducts is greatly dependent on the nature of the donor ligands on the metal. 

Palladium complexes effectively catalyze the three-component coupling reactions of CC>2461 or isocyanates,462 462 allyltributyltin, and allyl chloride to afford allyl 3-butenoate or iV-tosyl-iV-allyl-3-butenamides, respectively (Equations (104) and (105)). 

Recently, the groups of Fu and Buchwald have coupled aryl chlorides with arylboronic acids [34, 35]. The methodology may be amenable to large-scale synthesis because organic chlorides are less expensive and more readily available than other organic halides. Under conventional Suzuki conditions, chlorobenzene is virtually inert because of its reluctance to oxidatively add to Pd(0). However, in the presence of sterically hindered, electron-rich phosphine ligands [e.g., P(f-Bu)3 or tricyclohexylphosphine], enhanced reactivity is acquired presumably because the oxidative addition of an aryl chloride is more facile with a more electron-rich palladium complex. For... 

Several groups intercepted the indole-palladium complex that is initially obtained on cyclization by a subsequent Heck reaction. As will be seen, this can be a powerful elaboration of indoles. In the first example of this concept, Utimoto and co-workers ambushed intermediate 354 with a series of allylic chlorides to give 355. Normal acid workup yields the corresponding C-3 unsubstituted indoles (52-83%) [310]. 

---