Palladium complexes reactivity

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... 

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. ... 

A series of new palladium complexes 26 bearing a phosphine-functionalised NHC ligand has been shown to be more efficient than typical catalytic systems (i.e. Pd(OAc), PPhj) for the reaction depicted in Scheme 7.10 [55], In fact, these conditions afforded the 9-benzylidene-97f-fluorene in higher yields when iodobenzene was used, whereas the reaction of the less reactive phenyl bromide with diphenylacetylene was achieved for the first time affording the desired product in moderate to good yields. 

Uson, R., Fomies, J., Laguna, A. and Valenzuela, J.I. (1982) Pseudohalo-bridged pentafiuorophenyl gold-palladium complexes. Synthesis and Reactivity in Inorganic and Metal-Organic Chemistry, 12(7), 935-946. 

Addition of disilanes to isocyanides is catalyzed by palladium complexes, giving A-substituted bis(silyl)imino-methanes (Equation (53)).132 A wide range of isocyanides including aryl isocyanides and alkyl isocyanides can take part in the reaction. However, it is important to note that tert-alkyl isocyanides hardly undergo the bis-silylation reaction. This low reactivity of / r/-alkyl isocyanides allows their use as spectator ligands in the catalytic bis-silylations. 

Addition of diphenyl disulfide (PhS)2 to terminal alkynes is catalyzed by palladium complexes to give l,2-bis(phe-nylthio)alkenes (Table 3)168-172 The reaction is stereoselective, affording the (Z)-adducts as the major isomer. A rhodium(i) catalyst system works well for less reactive aliphatic disulfides.173 Bis(triisopropylsilyl) disulfide adds to alkynes to give (Z)-l,2-bis(silylsulfanyl)alkenes, which allows further transformations of the silyl group to occur with various electrophiles.174,175 Diphenyl diselenide also undergoes the 1,2-addition to terminal alkynes in the presence of palladium catalysts.176... 

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... 

To summarize this part, various palladium complexes efficiently catalyze the lactonization of alkynols. Many mechanistic studies remain to be carried out to have a clear understanding of the mechanism in order to anticipate the reactivity of such substrates. Nevertheless, the implication of palladium-hydride intermediates should take a large place in this catalysis. 

Oxidative addition involving carbon-to-oxygen bonds is of relevance to the catalysis with palladium complexes. The most reactive carbon-oxygen bond is that between allylic fragments and carboxylates. The reaction starts with a palladium zero complex and the product is a ir-allylic palladium(II) carboxylate Figure 2.16. 

Addition of the H-P bond in secondary phosphine oxides (hydrophosphiny-lation) also proceeds in the presence of palladium complexes (Scheme 36) [32]. Secondary phosphine oxides appear more reactive than hydrogen... 

The slow addition of the arylzinc compound to a solution containing both an aryl hahde, Ar X, and the palladium complex furnished the biaryl in good to excellent yields. The very reactive Pd(0) complex was likely formed in situ by reduction of the starting palladium(II) complex by ArZnX. The reactions were very rapid (ca 1 or 2 h) compared to most usual Pd-catalyzed reactions involving ArZnX (ca 24 h). The reduction of Pd(II) could account for the formation of a small amount of Ar-Ar (2-5%) in the last non-electrochemical step while no homocoupling of Ar X occurred. 

Although in many respects relativistic effects and the lanthanide contraction serve to make the postlanlhanide elements less reactive than would otherwise be the case, in other respects their bonding ability is increased. For example, bis(phosphine)plati-num(0) complexes react with molecular hydrogen, but the analogous palladium complexes do not 3... 

The square planar palladium complexes which give values of m of ca. 0.4 (Table 1) are known to react via a mainly associative mechanism so that the values of m are taken to indicate that Pd—Cl bond cleavage and leaving Cl solvation were both important in determining the reactivity trend for these complexes, i.e. there is a greater degree of M—Cl bond breaking in the transition state of palladium compared with cobalt. 

In the previous sections, double silylation was facilitated by using more reactive substrates such as alkynes and dienes with activated and strained disilanes. However, the use of palladium complexes with certain ligands allows successful reaction with the unactivated disilanes. 

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