Cobalt complexes monodentate

Pyridine ligands 186 are monodentate, forming complexes of the kind presented by 189. Pyridine is coordinated in the same way in copper acetate 194 [314] and iron rhodanide complexes [315], adducts of cobalt complex with fe(salicylidene)ethyle-nediamine 195 [316] and nickel chelate, formed by tridentate N,S-donor azomethine ligand 196 [317] ... 

Table 71 Preparations Some S-Bonded Sulfito, Sulfinato Complexes of Cobalt(IlI) (Monodentate)... 

Metal ion complexation rates have been studied by the T-jump method. ° Divalent nickel and cobalt have coordination numbers of 6, so they can form complexes ML with monodentate ligands L with n = 1—6 or with bidentate ligands, n = 1-3. The ligands are Bronsted bases, and only the conjugate base form undergoes coordination with the metal ion. The complex formation reaction is then... 

Diketonate cobalt(III) complexes with alkyl peroxo adducts have been prepared recently and characterized structurally, and their value in hydrocarbon oxidation and olefin epoxidation examined.980 Compounds Co(acac) 2(L) (O O / - B u) with L = py, 4-Mepy and 1-Meim, as well as the analog of the first with dibenzoylmethane as the diketone, were prepared. A distorted octahedral geometry with the monodentates cis is consistently observed, and the Co—O bond distance for the peroxo ligand lies between 1.860(3) A and 1.879(2) A. 

Thiocarbamate (tc, RHNCSO-) is a monodentate ambidentate ligand, and both oxygen- and sulfur-bonded forms are known for the simple pentaamminecobalt(III) complexes. These undergo redox reactions with chromium(II) ion in water via attack at the remote O or S atom of the S- and O-bound isomers respectively, with a structural trans effect suggested to direct the facile electron transfer in the former.1045 A cobalt-promoted synthesis utilizing the residual nucleophilicity of the coordinated hydroxide in [Co(NH3)5(OH)]2+ in reaction with MeNCS in (MeO)3PO solvent leads to the O-bonded monothiocarbamate, which isomerizes by an intramolecular mechanism to the S-bound isomer in water.1046... 

Examples in organometallic systems are known. Reaction of thiuram disulfides, (R2NCS2)2, with Co(Cp)(CO)2 produces dithiocarbamato pseudo-octahedral cobalt(III) complexes Co(Cp)(dtc)2 with one chelated and one monodentate dtc, also accessible via Co(Cp)I(dtc).1050 Fluxional behavior, including monodentate chelate exchange, was observed for some complexes in temperature-dependent NMR studies. The Co(Cp)I(dtc) complex was defined in a crystal structure. 

Several complexes of bivalent cobalt and zinc with imidazoline-(l//,3i/)-2-thione (34 R = H) of the forms ML2X2 (X = halide ion) and ML4X2 (X = N03 or C104) have been isolated and characterized by physicochemical techniques.247 In contrast with the S monodentate behaviour concluded for the earlier-reported Ni11 complexes, the ligands are N—S bidentate in these metal salts to form four-membered chelate rings. Similar coordination behaviour has been observed for the... 

In the case of inert cobalt(m) complexes it is possible to isolate the chelated products of the reaction. Let us return to the hydrolysis of the complex cations [Co(en)2(H2NCH2C02R)Cl]2+ (3.1), which contain a monodentate iV-bonded amino acid ester, that we encountered in Fig. 3-8. The chelate effect would be expected to favour the conversion of this to the chelated didentate AO-bonded ligand. However, the cobalt(iu) centre is kinetically inert and the chloride ligand is non-labile. When silver(i)... 

In conclusion, the hydrolytic and other reactions of co-ordinated amino acid derivatives with nucleophiles may proceed by two major routes. The first involves a moderate acceleration by general acid catalysis of a monodentate TV-bonded ligand, whilst the second may involve very dramatic rate increases (by a factor of a million or so) associated with didentate chelating TV O-bonded ligands. There is little evidence for the widespread involvement of co-ordinated nucleophiles attacking the carbonyl in amino acid derivatives, although some special, and well characterised, examples with cobalt(m) complexes are considered in the next chapter. 

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