Carboxylic acid amide complexes

R te Constants for Reduction of IsOnicotinamide (4-Pyridine Carboxylic Acid Amide) Complexes by [Cr(H20)6] ... 

Table 3 Bond Lengths (A) and Angles at Oxygen in Complexed Carboxylic Acid Amides...

It was reported (1+7) that salicylamide and other aromatic hydroxy carboxylic acid amides undergo autooxidation, when chromatographed in alkaline media. This autooxidation products hinder the development of the complex coloration with ferric ion. However, paper chromatographic separation of salicylamide and analogs in alkaline buffer media can be accomplished by ionophoresis (1+8). 

Final purification by use of metal complexes was also applied in the syntheses of the ligands XS4—H4. These ligands exclusively contain thiolate donors and were prepared by Hahn et al. (23) using 2,3-dimercaptobenzoic acid as starting material (Scheme 8). Isopropyl or benzyl protection of the thiol functions, conversion into the acyl chlorides, reaction with a,oo-diamines, and deprotection of the sulfur atoms enabled the connection of two 1,2-benzene-dithiol units via carboxylic acid amide bonds. 

An example of a more standard, carboxyhc acid amide functionalised imidazolium salt and its apphcations come from the Ghosh group [120]. They reacted chloroacetic acid anilide with A-mesityl imidazole and obtained the respective carboxylic acid amide functionalised imidazolium salt which was reacted with sUver(I) oxide to form the corresponding silver(l) carbene complex featuring two trans-coordinated carbene ligands on the silver(I) ion (see Figure 4.39). 

Figure 4.40 Proposed mechanism for the POP of (L)-lactide by a silver(l) complex of a carboxylic acid amide functionalised carbene.

Liao et al. also synthesised an imidazolium salt carrying two carboxylic acid amide functionalities and generated its silver carbene complex. It is distinguished by absolute linearity of the C-Ag-Cl vector and rather short Ag-C and Ag-Cl bond lengths. 

Carboxylic acid amide functionalised imidazolium salts can be reacted with group 10 halides directly in the presence of an inorganic base (e.g. K COj) to form homoleptic complexes (see Figure 4.41) [122]. Interestingly, the carbene units are cis to each other and not trans as would be expected (see Figures 4.30 and 4.38). The cis complexation is not aided by hydrogen bonding as the carboxylic acid amide functionality loses its proton upon complexation to nickel. 

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

The carboxylic acid amides most conunonly studied as ligands are formamide, acetamide, and the W-substituted derivatives, particularly A,A-dimethylformamide (DMF). These compounds are often used as solvents and have high dielectric constants, particularly when they contain an N-H bond, and such uses helped to stimulate interest in the amides as ligands. There are two possible donor atoms, N or O, but all complexes of the simple amide ligands, characterized by X-ray structure determination at least, have M-O bonds. The amides are usually terminal ligands but can bridge between metal atoms in some instances. 

Pisaniello and Lincoln have made detailed H NMR studies of the amide complexes [ScLs][C104]3 in CD3CN and CDjNOj. With NMF, DMF, A,A-diethylformamide and A,iV-dibutylformamide, exchange between free and bound ligand occurred in the fast exchange limit at all accessible Table 4 Effect of Coordination on Stretching Wavenumbers of Carboxylic Acid Amides ... 

It is not necessary to use phosphorus oxychloride complexes of formamides, because Roh and Kochendorfer in 1937 demonstrated that the iminium chlorides themselves react similarly and Bosshard and Zollinger have shown that comparable yields can be obtained using chlorodimethylformiminium chloride as the reagent. However, in the synthesis of diarylketones good yields are only obtained when the phosphorus oxychloride complex of the corresponding arylcarboxylic acid amide has been used The synthesis of ketones from carboxylic acid amides, phosphorus oxychloride and suitable substrates predates the aldehyde synthesis by approximately 40 years but it is of only limited usefulness because side reactions are very often encountered... 

Dilute solutions ( 10" moldm" ) of Wilkinson s complex in organic solvents such as ethanol/benzene actively catalyse the hydrogenation of alkynes and alkenes at ambient temperature and pressure (1 atm, H2). Traces of oxygen must be excluded. Hydrogenation rates are dependent on steric effects. The following general order has been established 1-alkenes > cis-2-alkenes > trans-2-alkenes > trans-3-alkenes. An exception is ethene itself, which forms a rather stable complex (Fig. 5.19) so that higher temperatures are required. Arenes, esters, ketones, carboxylic acids, amides and nitro compounds are unaffected, but aldehydes are slowly decarbonylated. 

Wallach was the first (1874) to report on the transformation of carboxylic acid amides to amide chlorides by treatment with PCls various types of amides were converted by this reagent to chloromethyleneiminium chlorides (30 equation lg). - > Side reactions can include the a-chlorination of the amide chloride. If excess PCIs is used, the formation of iminium salts with complex ions (31) has been reported. The very labile bromomethyleneiminium bromides (32 equation 19) can be obtained by action of PBrs on tertiary amides. The iodomethyleneiminium salt (33) was prepared from DMF and diphosphorus tetraiodide in CS . ... 

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