Oxamides metal complexes

The direct conversion of alcohols and amines into carbamate esters by oxidative carbonylation is also an attractive process from an industrial point of view, since carbamates are useful intermediates for the production of polyurethanes. Many efforts have, therefore, been devoted to the development of efficient catalysts able to operate under relatively mild conditions. The reaction, when applied to amino alcohols, allows a convenient synthesis of cyclic urethanes. Several transition metal complexes, based on Pd [218— 239], Cu [240-242], Au [243,244], Os [245], Rh [237,238,246,247], Co [248], Mn [249], Ru [224,250-252], Pt [238] are able to promote the process. The formation of ureas, oxamates, or oxamides as byproducts can in some cases lower the selectivity towards carbamates. 

Four main types of antioxidants are commonly used in polypropylene stabilizer systems although many other types of chemical compounds have been suggested. These types include hindered phenolics, thiodi-propionate esters, aryl phosphites, and ultraviolet absorbers such as the hydroxybenzophenones and benzotriazoles. Other chemicals which have been reported include aromatic amines such as p-phenylenediamine, hydrocarbon borates, aminophenols, Zn and other metal dithiocarbamates, thiophosphates, and thiophosphites, mercaptals, chromium salt complexes, tin-sulfur compounds, triazoles, silicone polymers, carbon black, nickel phenolates, thiurams, oxamides, metal stearates, Cu, Zn, Cd, and Pb salts of benzimidazoles, succinic acid anhydride, and others. The polymeric phenolic phosphites described here are another type. 

Metal Complexes.—In order to determine the effect of the presence of a nitrogen donor on the ortho-metallation of the thiobenzoyl function, Alper and Chan treated NN-dimethylthiobenzamide with di-iron enneacar-bonyl. However, no sulphur-donor ligand ortho-metallated complex was obtained, as happens in the case of thiobenzophenone, but instead the complexes (245) and (246) were formed. - NN-Dimethylthioacetamide similarly yielded the complexes (247) and (248), whereas the unsubstituted thiobenzamide on treatment with di-iron enneacarbonyl gave the complexes (249) and (250). The synthesis and properties of metal complexes of dithio-oxamides, dithiomalonamides, 2-thiocarbamoyl-l,10-phenan-throlines, thiomorpholine-3-thione, and 2,4-dithiouracil have also been described recently. 

The construction of suitable dialdehydes for macrocycle formation by metal template methods has more recently been extended to include a range of oxamides. In the first case, the simple 2,2 -(oxalyldiimino)bisbenzaldehyde underwent rather sluggish template reactions but yielded extremely stable macrocyclic complexes (Scheme 31).167 168 These products could be sulfonated in oleum, without destruction of the macrocyclic structure. This general synthetic route has been extended to include reactions of diketones and the formation of complexes of macrocyclic ligands such as (70) and (71). Attempts to incorporate a malonamide fragment in place of the oxamide... 

Deactivators. Metal deactivators combine with metal ions to limit the potential for chain propagation. Metal deactivators are commonly used in polyolefin inner coverings in wire and cable applications where the plastic comes in contact with the metal. In effect, the deactivator acts as a chelating agent to form a stable complex at the metal interface, thereby preventing catalytic activity. The most common deactivators contain an oxamide moiety that complexes with and deactivates the metal ions. Atypical product is Ciba s IRGANOX MD-1024. 

H2L435 and diamines. Attempts to carry out non-template macrocyclisation under conditions of high dilution were also unsuccessful only starting materials and small amounts of insoluble polymeric materials were isolated from the reaction mixture. It proved to be impossible to demetallate the oxamide macrocyclic nickel(II) complexes using cyanide because of the high stability of the metal-amide bonds 382]. 

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