Palladium complexes carboxylic acid amide

Figure 4.42 Synthesis of homoleptic palladium(ll) carbene complexes using a carboxylic acid amide functionalised NHC ligand.

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. ... 

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... 

Kaneda et al. [33,34] have recently utilized acid-base interactions to non-covalently attach diphenylphosphine-4-benzoic acid palladium complexes to the exterior of poly(propyleneimine) dendrimers and to cavities within these dendrimers (Fig. 9) via the interaction of the benzoic acid with the carboxyl groups of amide moieties positioned within the dendrimer. Interestingly, the supramolecular dendritic catalyst gave rise to much more active catalysts for... 

Combination of silicon hydrides with catalytic amounts of a ruthenium(II) complex in tetrahydrofuran, chloroform or benzene has afforded a new reducing system capable of efficient reduction of a,p-unsatu-rated carboxylic acids, esters, amides, etc. Addition of a weak proton source, such as a sterically hindered phenol significantly increases reaction rates. The ruthenium mixture was found to exhibit the same regioselectivity observed with the above-described palladium systems. 

The reaction of a,P- or P,y-unsaturated carboxylic acids or amides with nickel(O) or palladium(O) complexes also leads to metallacycles. Thus, reactions of acrylic or methacrylic acid with Ni(COD)2 and PCyj lead to the formation of the corresponding five-membered ring derivatives 26 (Eq. 12). Similarly, reaction of a,P-unsaturated carboxylic acids with a nickel(O) complex with bidentate ligand 22 leads to complexes 27 (Eq. 13). ... 

Before discussing the double carbonylation processes it may be helpful to understand the mechanism of the single carbonylation of aryl halides into carboxylic acid derivatives (Heck processes). The first step in the catalytic process is oxidative addition of an aryl halide to Pd(0) species formed from a catalyst precursor to yield an arylpal-ladium halide intermediate (A) in Scheme 1. Insertion of carbon monoxide into the aryl-palladium bond in A gives an acylpalladium halide complex (B). Attack of a nucleophile such as alcohol, amine, and water assisted by a base on the acylpalladium complex yields carboxylic ester, amide, and carboxylic acid, although details of the mechanism have not been unequivocally established. The palladium(O) species regenerated in the process further undergoes oxidative addition to carry out the catalytic cycle (Scheme 1). 

The acyl palladium intermediate may also be trapped by heteroatom nucleophiles (Schemes 4.17 and 4.18), such as alcohols and amines as part of the catalytic process, to give esters (Scheme 4.19) and amides (Scheme 4.20), respectively. Less commonly used nucleophiles include water, to give carboxylic acids, carboxylate salts, to give anhydrides, and ketones, via their enol form, to give enol esters. Metal carbonyl complexes may be used as both the source of CO and as the catalyst for the reaction (Scheme 4.21). ... 

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