Bipyridine-Palladium acetate

It is remarkable that the palladium(O) complexes are inactive in the absence of chloroform.236 Palladium acetate-bipyridine complex has been reported to catalyse conjugate addition of arylboronic acids to a -unsaturated carbonyl compounds in aqueous media with high yields.237... 

A few recent examples of related C-C bond-forming reactions, all involving a palladium-catalyzed C-H activation step at arenes, will be mentioned. Salts are produced in these reactions, or acetic acid, as in the first example. Allylation of indoles at the 3-position was achieved by using palladium acetate, and bipyridine and allylic acetates as the reactants (Scheme 5) [19]. 

Oxidative addition of aryl halides to [Pd(dba)2] in the presence of tetramethylethylenediamine or 2,2 -bipyridine to produce cis- [Pd(N-N)(Ph)X] proceeds easily when iodides are used but with more difficulty with bromides. Methyllithium reacts with the iodo complexes to give the mixed dialkyls. Cross coupling of alkenylboronic and arylboronic acids with alkenes is catalysed by palladium acetate in acetic acid. The reaction is believed to occur by oxidative addition of the carbon-boron bond across an in situ Pd(0) centre. 35... 

Helquist et al. [129] have reported molecular mechanics calculations to predict the suitability of a number of chiral-substituted phenanthrolines and their corresponding palladium-complexes for use in asymmetric nucleophilic substitutions of allylic acetates. Good correlation was obtained with experimental results, the highest levels of asymmetric induction being predicted and obtained with a readily available 2-(2-bornyl)-phenanthroline ligand (90 in Scheme 50). Kocovsky et al. [130] prepared a series of chiral bipyridines, also derived from monoterpene (namely pinocarvone or myrtenal). They synthesized and characterized corresponding Mo complexes, which were found to be moderately enantioselective in allylic substitution (up to 22%). 

The reaction of alcohols with CO can also be catalysed by palladium iodides, and various ligands or solvents. Acetic acid is prepared by the reaction of MeOH with CO in the presence of a catalyst system comprising a palladium compound, an ionic iodide compound, a sulfone solvent at conditions similar to those of the rhodium system (180 °C, 60 bar), and, in some cases, traces of a nickel-bipyridine compound were added. Sulfones or phosphine oxides play a stabilising role in preventing metal precipitation [26], Palladium(II) salts catalyse 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 [27],... 

Among the important reagents for which preparative procedures are given are 2,2 -bipyridine (by nickel directed and catalyzed dehydrogenation of pyridine p. 5), formamidine acetate (p. 39), phenyltrichloromethylmercury (p. 98), and trimethyl- and triethyloxonium fluoroborate (pp. 120, 113). The preparation of palladium catalyst ( Lindlar ) for the selective reduction of acetylenes is described (p. 89), as is the use of di-phenyliodonium-2-carboxylate, as a precursor of benzyne in the synthesis of 1,2,3,4-tetraphenylnaphthalene (p. 107). 

The synthesis of five-membered carbo- and hetero-cyclic compounds, including fused rings, has been reported using acetate as a nucleophile in the cyclization of 1,6-enynes under palladium(II) catalysis (Scheme 91). The reaction is initiated by trans-acetoxypalladation of the alkynes and quenched by either trans- or ra-deaceloxypal-ladation in the presence of 2,2/-bipyridine as the ligand.134... 

A recent patent has described the carbonylation of methanol to give acetic acid using a palladium-based system (119). The system requires alkyl halide promoters and electron-rich nitrogen ligands (e.g., 2,2 -bipyridine) and operates in the ranges 125-250°C and 20-210 atm. There is insufficient information available to allow discussion of pathways involved. 

Pd(OAc)2 coordinated with 1,10-phenanthroline or 2,2 -bipyridine is a highly reactive catalyst for the exchange reaction of vinyl ethers. As shown in Scheme 56, only vinyl ethers are formed, the formation of acetals being completely suppressed77. Smooth exchange reaction under mild conditions has been applied to the total synthesis of rhizobitoxine (185). The key step is the palladium-catalyzed exchange reaction of the vinyl ether moiety78. ... 

Synthesis of neutral Ji-allylpalladium complexes having bisnitrogen ligands (mainly, those related to 2-(pyrazol-3-yl)pyridine, 2-(imidazol-2-yl)pyridine, and 2,2-bipyridine) and palladium-catalyzed cyclopropanation of ketene silyl acetals with allylic acetates 00YGK736. 

Moiseev and coworkers showed [10,13] that giant palladium clusters with an idealized formula Pd56iL5o(OAc)igo (L = phenanthroline or bipyridine) are highly active catalysts for allylic oxidation of olefins. The catalytically active solution was prepared by reduction of Pd(OAc)2, e. g. with H2, in the presence of the ligand, L, followed by oxidation with O2. The giant palladium cluster catalyzed the oxidation of propylene to allyl acetate under mild conditions. Even in 10% aqueous acetic acid, allyl acetate selectivity was 95-98 % [10]. Oxidation catalyzed by Pd-561 in water afforded a mixture of allylic alcohol (14%), acrolein (2%), and acrylic acid (60%), and only 5% acetone [10]. 

In his pioneering contributions Moiseev has shown that giant cationic palladium clusters , e.g. Pd56iL6o(OAc)i8o (L = phenanthroline, bipyridine), characterized by use of high-resolution TEM, SAXS, EXAFS, IR and magnetic susceptibility data, catalyze, under mild conditions (293 363 K, 1 bar), the oxidative acetoxylation of ethylene into vinyl acetate, propylene into allyl acetate, and toluene into benzyl acetate. The oxidation of primary aliphatic alcohols to esters, and the conversion of aldehydes into acetals were also studied. ... 

Acetoxylation of arenes. Arenes are acetoxylated by acetic acid (sodium acetate can be added) with potassium persulfate as oxidant and palladium(II) acetate as catalyst. The reaction is unusual in that wie/a-acetoxylation predominates this selectivity can be enhanced by addition of a complexing amine such as 2,2 -bipyridine. Side-chain acetoxylation can be effected with some arenes. Thus mesitylene and durene arc acetoxylated mainly in the a-position of the substituents. ... 

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