Palladium complexes, as catalysts for

PAM sec polyacrylamide PAM see polyacrylonitrile palladium complexes, as catalysts for ATRP 492 Patterns of Reactivity scheme 11,26, 31 for prediction of reactivity ratios 365-6 lor prediction of iransfer constants 287 PB see polybutadieue PE see polyethylene... 

De Groot et al. (18) prepared phosphine-functionalized carbosilane dendrimers of different generations (4, 8, 24, and 36 phosphine end groups) and used their palladium complexes as catalysts for the allylic alkylation of allyl trifluoroacetate with diethyl sodio-2-methylmalonate. 

The increase of the catalyst turnover numbers is indeed one other major area where further improvements could be expected. Such improvements have recently been achieved for the standard Heck reaction by the use of high pressure conditions [86], the use of preformed palladacycles as catalysts [87], or by using a macrocyclic tetraphole as hgand [88].Dendritic diphosphine-palladium complexes as catalysts for Heck reactions have also been reported to possess superior stabihty compared to the monomeric parent compounds [89]. Transferring such iimovations to the AHR remains an important goal. 

The participation of cationic diphosphine/diphosphane palladium complexes as catalysts for the co-polymerization of CO with alkenes and in the alkoxycarbonylation of alkenes has been studied extensively. Quite recently, delineation of the initiation, propagation, and termination steps of the cycle has been reported. The systems are very complex to permit readily detailed kinetics experiments. However, the mechanistic steps and reactivity of those steps have been established, by principally, NMR spectroscopic methods. 

Five more papers reported on various modifications of PES involving introduction and substitution of chloro or bromoatoms. For instance, bromination of the bisphenol-A unit in a commercial PES yielded the dibromoproduct (23), which was treated with butyllithium. The lithiated PES was then reacted with methyliodide [39] or with tosylazide [40]. The resulting azide groups were finally reduced to amino groups (24). Another modification of brominated PESs utilized palladium complexes as catalysts for the... 

Mkoyi HD, et al. (Pyrazol-l-yl)carbonyl palladium complexes as catalysts for ethylene polymerization reaction. J Organomet Chem 2013 724 95-101. 

Kostic et al. reported the use of various palladium(II) aqua complexes as catalysts for the hydration and alcoholysis of nitriles,435,456 decomposition of urea to carbon dioxide and ammonia, and alcoholysis of urea to ammonia and various carbamate esters.457 Labile aqua or other solvent ligands can be displaced by a substrate. In many cases, the coordinated substrate thus becomes activated toward nucleophilic addition of water or alcohols. 

Kostic et al. recently reported the use of various palladium(II) aqua complexes as catalysts for the hydration of nitriles.456 crossrefil. 34 Reactivity of coordination These complexes, some of which are shown in Figure 36, also catalyze hydrolytic cleavage of peptides, decomposition of urea to carbon dioxide and ammonia, and alcoholysis of urea to ammonia and various carbamate esters.420-424, 427,429,456,457 Qggj-jy palladium(II) aqua complexes are versatile catalysts for hydrolytic reactions. Their catalytic properties arise from the presence of labile water or other solvent ligands which can be displaced by a substrate. In many cases the coordinated substrate becomes activated toward nucleophilic additions of water/hydroxide or alcohols. New palladium(II) complexes cis-[Pd(dtod)Cl2] and c - Pd(dtod)(sol)2]2+ contain the bidentate ligand 3,6-dithiaoctane-l,8-diol (dtod) and unidentate ligands, chloride anions, or the solvent (sol) molecules. The latter complex is an efficient catalyst for the hydration and methanolysis of nitriles, reactions shown in Equation (3) 435... 

Supported palladium catalysts for fine chemicals synthesis are generally based on metal particles. Nevertheless, a few examples are reported of the use of supported complexes as catalysts for the Heck reaction (see Chapter 9.6). Nearly all the possible immobilization methods have been tested for this reaction. 

Palladium-T riary lphosphine Complexes as Catalysts for Vinylic Halide Reactions... 

The Heck-type reaction. The Heck reaction135 (or some modified procedure of it) is certainly one of the most powerful tools used in the preparation of precursors with acetylenic and vinylic subunits. For instance, in the case of precursors 46-49 the synthesis is conveniently achieved by a cross-coupling reaction in the presence of palladium complexes as catalyst. Two pathways are possible, as represented by equations 9 and 10108. 

Bailar and co-workers have used several complexes as catalysts for reduction of linolenic ester to linoleic or oleic ester without any reduction to the saturated stearic ester. A considerable portion of this work was carried out using a mixed catalyst consisting of tin(II) chloride and a platinum(II) complex. However, catalytic work has also been carried out using palladium and nickel complexes, the former again being used along with tin(II) chloride J91). The experimental details have been recently reviewed (f90) so that this article is concerned with the conclusions and mechanistic aspects rather than with the direct results. 

In several cases, the in situ formation of hydrogen peroxide is the first step of the process. Thus, phenol can be obtained from benzene, carbon monoxide (5 atm) and oxygen (65 atm) at 70 °C in a benzene-water-methyl isobutyl ketone mixture, with TS-1 and a palladium complex as catalysts [26]. Despite a 91% selectivity to phenol, benzene conversion (3.2%) and productivity are still too low for industrial application. The palladium complex is required to promote hydrogen peroxide formation upon reaction of oxygen, carbon monoxide and water [27[. 

The arylation reaction of primary and secondary amines has been investigated using nickel or palladium complexes as catalysts, and bromo- or chloroarenes as arylating agents. Among the complexes tested, the more efficient catalyst is the bis (bipyridyl) nickel (II) bromide, bipy2NiBr2, which affords for example high yields in the arylation of allylamine with /n-bromotrifluoromethylbenzene. The reduction of the haloarene, sometimes observed with the nickel complexes, becomes predominant with palladium catalysts whatever the complex used. 

Unsymmetrical biaryh and diarylmethanes. Negishi et al have used a nickel-(0) complex or a palladium(0) complex as catalyst for the cross-coupling of aryl-or benzylzinc halides with aryl halides at room temperature to form biaryls or diarylmethanes. The zinc derivatives are prepared by reaction of aryl- or benzyl-lithium with zinc chloride or bromide. 

Another interesting hydroarylation reaction of alkynes with arenes using a dinuclear palladium complex as catalyst has been reported (Eq. 71) [161], although the precise mechanism is unclear. Trialkylboranes act as effective promoters for this reaction. 

Ozdemir, L, Yigit, M., Cetinkaya, E. and Cetinkaya, B. (2006) Synthesis of novel palladium IV-heterocyclic-carbene complexes as catalysts for Heck and Suzuki cross-coupling reactions. 

Much effort has been devoted to developing catalysts that control the enantioselectiv-ity of these substitution reactions, as well as the regioselectivity of reactions that proceed through unsymmetrical allylic intermediates. A majority of this effort has been spent on developing palladium complexes as catalysts. Increasingly, however, complexes of molybdenum, tungsten, ruthenium, rhodium, and iridium have been studied as catalysts for enantioselective and regioselective processes. In parallel with these studies of allylic substitution catalyzed by complexes of transition metals, studies on allylic substitution catalyzed by complexes of copper have been conducted. These reactions often occur to form products of Sj 2 substitution. As catalylic allylic substitution has been developed, this process has been applied in many different ways to the synthesis of natural products. ... 

Cobalt, nickel, iron, ruthenium, and rhodium carbonyls as well as palladium complexes are catalysts for hydrocarboxylation reactions and therefore reactions of olefins and acetylenes with CO and water, and also other carbonylation reactions. Analogously to hydroformylation reactions, better catalytic properties are shown by metal hydrido carbonyls having strong acidic properties. As in hydroformylation reactions, phosphine-carbonyl complexes of these metals are particularly active. Solvents for such reactions are alcohols, ketones, esters, pyridine, and acidic aqueous solutions. Stoichiometric carbonylation reaction by means of [Ni(CO)4] proceeds at atmospheric pressure at 308-353 K. In the presence of catalytic amounts of nickel carbonyl, this reaction is carried out at 390-490 K and 3 MPa. In the case of carbonylation which utilizes catalytic amounts of cobalt carbonyl, higher temperatures (up to 530 K) and higher pressures (3-90 MPa) are applied. Alkoxylcarbonylation reactions generally proceed under more drastic conditions than corresponding hydrocarboxylation reactions. 

R. F. Heck, Adv. Chem. Ser, 1982, 196, 213-230. Palladium-Triarylphosphine Complexes as Catalysts for Vinylic Halide Reactions. 

Zhang, C. Huang, J. TrudeU, M. L. Nolan, S. R 1999. Palladium-imidazol-2-ylidene complexes as catalysts for facile and efficient Suzuki cross-coupling reactions of aryl chlorides with arylboronic acids. J. Org. Chem. 64 3804-3805. 

A new procedure, for the electrochemical synthesis of methyl acetylenecarboxylates starting from alkynes, imder mild conditions, is reported using a palladium complex as catalyst, carbon monoxide (p CO=l atm) and methanol at room temperature. The process is outlined in the following reaction. 

Intramolecular hydroamination is an atom efficient cyclization reaction which finds use for the synthesis of pharmaceutically relevant intermediates such as N-heterocycles. Krogstad and co-workers [56] tested as series of Pd, Pt and Ir-PTA complexes as catalysts for the hydroamination of 4-pentyn-l-amine to 2-methyl-pyrroline and studied the reaction mechanism mainly by NMR techniques in solution using various deuterated solvents (Table 7.12). Palladium complexes cis-[PdCl2(PTA)2] (49) and cw-[PdBr2(PTA)2] (53) outperformed the Pt analogs cii-[PtCl2(PTA)2] H20 (54), cw-[PtBr2(PTA)2] (55),... 

An iinportanl advance in this synthesis of allylsilanes involved the use of optically active palladium ferrocenyl complexes as catalysts to provide optically active allylsilanes with good enantiomeric excesses being obtained for (/. (-allylsilanes and less good enantiomeric excesses for (Z)-allylsilanes26,27. 

Organotins. The organotin reagents have much lower nucleophilicity than that of the Grignard reagents, thus allowing the use of a variety of functionalized monomers for the polymerization. Aryl-alkenyl iodides, bromides and tosylates have been used as substrates. Palladium complexes are commonly employed as catalysts for the reaction. Because the catalysts can be destroyed... 

In 2004, Molander et al. developed another type of chiral sulfur-containing ligands for the intermolecular Heck reaction. Thus, their corresponding novel cyclopropane-based phosphorus/sulfur palladium complexes proved to be active as catalysts for the reaction between phenyltriflate and dihydrofuran, providing at high temperature a mixture of the expected product and its iso-merised analogue (Scheme 7.7). The major isomer C was obtained with a maximum enantioseleetivity of 63% ee. 

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