Cobalt complexes ureas

Apart from the commonly used NaOCl, urea—H2O2 has been used/ With this reaction, simple alkenes can be epoxi-dized with high enantioselectivity. The mechanism of this reaction has been examined.Radical intermediates have been suggested for this reaction, polymer-bound Mn -salen complex, in conjunction with NaOCl, has been used for asymmetric epoxidation. Chromium-salen complexes and ruthenium-salen complexes have been used for epoxidation. Manganese porphyrin complexes have also been used. Cobalt complexes give similar results. A related epoxidation reaction used an iron complex with molecular oxygen and isopropanal. Nonracemic epoxides can be prepared from racemic epoxides with salen-cobalt(II) catalysts following a modified procedure for kinetic resolution. 

NjPtSioHg, Platinate(II), bis(pentasuIfido)-, bis(tetrapropylammonium), 21 13 NzPtSijHg, Platinate(IV), tris(penta-sulfido)-, diammonium, 21 12, 13 N2SCH4, Urea, thio-chromium(O) complexes, 23 2 N2SC2, Sulfur dicyanide, 24 125 N2SC4H6, 2H-Imidazole-2-thione, 1,3-di-hydro-1-methyl-cobalt complexes, 23 171 N2SCSH12, Thiourea, N,N,N methyl-... 

Oxidative carbonylation of amines to carbamates and ureas in the presence of cobalt complexes was recently reported (24-25), We have found that Co(II) complexes bearing nitrogen and oxygen-donor ligands such as carboxylates, acetylacetonates and Schiff bases produce DMC with high selectivity in methanol under CO and Oj. (Table VII) (26-27),... 

Such criteria cannot be simultaneously satisfied in the case of the NHa group. Studies have thus been undertaken to examine the mode of interaction of complexes where such a group is the potential bridging site. The reductions of penta-ammine cobalt complexes of urea, carbamate, N-cyanoguanidine [N=C—N=C(NH2)2l, and cyanamide (N=C—NHa), by chromium(n) involve an outer-sphere path with the exception of the carbamato-species, where, however, there is no evidence of a nitrogen-bonded chromium(in) species as product. The cyanamide-complex reaction follows the rate law... 

When 65d-i were heated in quinoline with various organic (acetate of zinc) or inorganic (chlorides of other metals) salts in the presence of urea and tributylamine the zinc, vanadium, copper, aluminum, cobalt complexes 129d-p,s have been obtained (1996CJC508). 

Iron(II) complex of tris(N -tert-butylurea-ylato)-N-ethylene]aminato activates dioxygen at room temperature to afford an iron(III) complex containing a single terminal oxo ligand. X-ray structures show that the three urea molecules act as a tridentate N,N,N-hgand [52]. The tripodal ligand was also used to synthesise complexes of cobalt, iron or zinc with terminal hydroxo ligands (Scheme 8) [53]. 

The reactions of the pentaamminecobalt(III) complex of urea (O-coordinated) have also been studied.506 Under basic conditions [Co(NH3)5OH]2+ is the only cobalt(III) product. The main reaction pathway (ca. 97%) is SN1CB displacement of coordinated urea (Scheme 40) with kOH = 15.3 M s-1 at 25 °C. A limiting rate was approached at high pH as the complex dissociated to its inactive conjugate base. Hydrolysis of coordinated urea was not observed. 

Catalysis by cobalt(III) has been the subject of several papers.185-187 The N.N-bis(sahcyldene)ethylnediaminocobalt(III)-catalysed oxidative carbonylation of o-, m-and -substituted primary aromatic amines in MeOH gives ureas, isocyanates, carbamates, and azo derivatives. A Hammett p value of —0.5 for the reaction indicates that electrophilic attack of CO at a nitrogen anion complexed to Co in the TS is... 

The tetrasulfo-Pc complexes of a number of metals are made by the urea melt process by heating the powdered metal, or its acetate, with triammonium-4-sulfophthalate, urea, boric acid, and ammonium molybdate. The metals or metal compounds used are those of chromium (III), manganese(II), iron(II), iron(III), cobalt(II), and zinc(II). Selected synthetic examples of sulfo- and other derivatives of metal phthalocyanines are presented below. 

A number of model studies have been carried out using cobalt(III) and rhodium(III) complexes of O- and N-bonded ureas (Dixon et al., 1982, 1983 Curtis... 

The X-ray crystal structures of pyrazine V.JV -dioxide (134) <02AX(E)1253>, the P-polymorph of phenazine (135) <02AX(C)181>, cobalt(III) complexes of pyrazine-2,6- and pyridine-2,6-dicarboxylic acids <02JIC458>, and bis-urea-substituted phenazines <02ZN(B)937> were reported. Fluorescent pyrido[l,2-a]quinoxalines 136 prepared as pH indicators were examined by X-ray crystallography <02JCS(P2)181>, as were macrocyclic quinoxaline-bridged porphyrinoids obtained from the condensation of dipyrrolylquinoxalines 137 and 1,8-diaminoanthracene... 

Selenourea is less stable than urea or thiourea, as it is sensitive to air and light, particularly in solution, and tends to dimerize in certain systems. In general, the donor properties of selenourea are similar to those of thiourea,2.3 and complexes with cobalt(II),4,5 palladium(II), platinum(n), zinc, cadmium, and mercury acceptors can be obtained by appropriate modification of the methods used for the preparation of the analogous thiourea derivatives. 

We have already dealt with the case of the sulfamido (NH2SO2NH") ligand, for which aquation is enhanced much more than 10 -fold by protonation (168). When complete or significant protonation of the donor atom can occur in aqueous acid, it is clear that a substantial effect is possible. The cobalt(III) complex of the AT-bonded urea... 

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