2,2 -Bipyridines chelate formation

Of special interest is the comparison of the inactivity of bipyridine-Cu(II) as a catalyst in salicyl phosphate hydrolysis, with its strong catalytic effect on the hydrolysis of dicarboxyphenyl-2-phosphate. A comparison of formulas XXVII with XXXIV and XXXVI shows that mixed complex formation of Cu+2 with salicyl phosphate and bipyridine would prevent attack of the phosphate group via the proposed mechanism. The formation of the analogous mixed chelate with DCPP (XXXIV and XXXVI) would produce a reaction intermediate for the reaction, since the metal ion would tie up one of the carboxylate ions but leave... 

Polyhalosilanes form neutral intermolecular hexacoordinate complexes with donor molecules such as pyridine, triethylamine, 2,2 -bipyridine and 1,10-phenanthroline. This topic has recently been reviewed6. It was demonstrated that electronegative substituents on the silicon are essential for the formation of intermolecular complexes. Thus, while SiCLt and Cl2CHSiCl3 react with 1,10-phenanthroline and with 2,2 -bipyridine to form hexacoordinate chelates, MeSiCl3 does not react224,225. For completion we discuss here a few examples, and compare some of the properties of intermolecular complexes with those of the intramolecular complexes. 

The widespread occurrence of iron ores, coupled with the relative ease of extraction of the metal, has led to its extensive use as a constructional material with the result that the analysis of steels by both classic wet and instrumental methods has been pursued with vigour over many years.3 Iron complexes are themselves widely used as the basis of convenient analytical methods for the detection and estimation of iron down to parts per million. Familiar tests for iron(III) in aqueous solution include the formation of Prussian blue as a result of reaction with [Fe(CN)6]4, and the formation of the intensely red-coloured [Fe(H20)5SCN]2+ on reaction with thiocyanate ion.4 Iron(II) forms particularly stable red tris chelates with a,a -diimines such as 1,10-phenanthroline or 2,2 -bipyridine that have been used extensively in spectrophotometric determinations of iron and in the estimation of various anions.5 In gravimetric estimations, iron(III) can be precipitated as the insoluble 8-hydroxyquinoline or a-nitroso-jS-naphthol complex which is then ignited to Fe203.6 In many situations the levels of free [Fe(H20)6]3+ may be controlled through complex formation by addition of edta. 

Bipyridine is a strong field ligand that forms relatively stable complexes, with the inherent M—N bond strength enhanced by the chelate effect. These factors favor the formation of 4-coordinate bis and 6-coordinate tris complexes. The tris complexes of the first row transition metals in normal oxidation states (+2 or +3) are best prepared by the reaction of a suitable metal salt with an excess of bpy in water, methanol, or other organic solvent. The solid complexes can be obtained by crystallization or by the precipitation of the perchlorate, hexafluorophosphate, tetrafluoroborate, or other salts. Because bpy is a strong field ligand, the lower oxidation states tend to be favored, and reduction of M(III) complexes can occur in these preparations. The M(III) complexes are usually readily obtained by the chemical, aerobic, or electrochemical oxidation of the M(II) species. 

The ligands discussed above are widely diversified certain of them can only serve as monodentate (imidazole, acetonitrile and isothiocyanate), bidentate (bipyridine, phenanthroline) or terdentate (terpyridine, TPTZ), others being the polyfunctional ligands with different donor sites may coordiate to the metal in various modes. In the latter case, the formation of chelate metallo-rings and/or the linking of the adjacent An coordination polyhedra is observed. 

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