Carbamic acid metal complexes

The most versatile reagent of this group is diethyldithiocarbamic acid (40), which forms coloured and extractable complexes with very many metals, selectivity being assured by control of the pH and the presence of masking agents.52 Here again the practical disadvantages stem from the ease of oxidation and many alternate carbamic acids derived from pyrrolidine and other dialkylamines have been studied. 

Guanidine, H2N(G=NH)NH2, is the amidine of carbamic acid, H2N(CO)OH. Guanidine forms three types of complexes with metals cationic (in which the guanidinium cation is formed by taking up a proton), adducts with neutral molecules or coordination products with ionic salts, and substitution products. A brief account of each type is presented below. 

The fixation of C02 by amines, which has been recognized for a long time, can either take place directly or it can be mediated by metal or nonmetal species to provide a carbamate group, RR NC02 , which is bound either ionic or covalently to an electrophilic center [1-5]. The direct interaction of C02 with primary or secondary amines can afford carbamic acids or alkylammonium carbamates (Equations 6.1 and 6.2) [1, 2], In the presence of metals, metal salts (Equation 6.3) [3j, k] or metal-complexes, metal carbamates can be obtained [3, 4] ... 

Hill and co-workers studied the thermal decomposition of a large number of metal complexes of various alkyl derivatives of xanthic and dithiocarbamic acids. The complexes were studied by using TG. DSC. and other TA techniques. Compounds investigated included Nil IB alkyl xanthates (79), Cu(II) dithiocarbamate complexes (80), dihalotin (IV) bisdiethyldithio-carbamates (81), bisldiethyldithiocarbamatoi diphenyl tin (IV) (82), tetrakis-(diethyldithiocarbamatoi tin(lV) (83, 84), and bisidieihyldithiocarbamato) tin(IV) (85). 

Cadmium pseudohalides, 981 solid state, 985 Carbamic acid, thio-metal complexes, 978 Carbaplatinaboranes conformation, 374 Carbazide, thio-metal complexes, 978 Carbonic anhydrases zinc, 1001,1004 zinc-carbonyl mechanism, 1003 Carbon monoxide estimation... 

More remarkably, structurally well-characterized Phen-containing transition metal complexes have been prepared and further applied in challenging organic transformations. Thus, cationic palladium complexes of t)fpe Pd(phen)2X2 (where X = CF3SO3, PFs, BF4) are very stable and found fairly active in combination with either benzoic acids or phosphorus acids as cocatalysts in the conversion of nitroarenes to the corresponding carbamate derivatives. Extensive studies have evidenced the key role of the nature of counteranion X of such Phen-based catalysts in the reaction outcome and even metaUacycles of type A have been isolated and identified as active intermediates in the reductive carbonyla-tion of nitrobenzene (eq l). ... 

Acid dissociation of metal protein complexes is a property common to all nonporphyrin proteins in fact the copper of hemocyanin becomes dialyzable at pH 4. This, however, does not mean that the metal is easily accessible, because most of complexing agents such as versene or ionic exchange resins seem not to be able to bind the copper of native hemocyanin in neutral or slightly alkaline solutions. The copper of hemocyanin reacts with diethyldithio-carbamate only after denaturation of the protein with alcohol (Zuckerkandl, 1951). These results agree with the failure of hemocyanin to exhange radioactive Cu(II), as observed by Joselow and Dawson (1955), and the inability of amino acids to complex the copper from the protein (Lontie, 1958). 

The reaction of metal N-alkylcarbamates M(C)2CN 11 R) (M = Na, Mn(II), Co(II) R = Ph, Pr, Cy) with R C(0)C1 (R = Me, Ph) takes place, at ambient temperature, in a more complex way with the formation of isocyanates (RNCO), carboxylic anhydrides (R C(0)0C(0)CR ), amides (RNHC(O)R ) and C02. Amide formation and the evolution of C02 can be due to (i) the decomposition of mixed anhydride RNHC(0)0C(0)R obtained by addition of the acyl chloride to the oxygen atom of the carbamate group or (ii) the direct reaction of acyl chloride at the carbamic nitrogen atom of M(02CNHR) . The mixed anhydride RNHC(O) 0C(0)R might also decompose via another route so as to afford isocyanate and carboxylic acid. However, a different pathway (Scheme 6.6) has been also envisaged for the formation of RNCO and R C(0)0C(0)CR, which excludes any intermediacy of the mixed anhydride [61a], Two acetic acid molecules, bound to the same metal or to different metal centers, would then be dehydrated and acetic... 

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