Pyridine, methyl-2- metal complexes

First, 1 2 metal complexes of (mainly mono-) azo dyes, without sulfonic or carboxylic acid groups, and trivalent metals (see Section 3.11). The metals are preferably chromium and cobalt nickel, manganese, iron, or aluminum are of lesser importance. Diazo components are mainly chloro- and nitroaminophenols or amino-phenol sulfonamides coupling components are (3-naphthol, resorcinol, and 1-phe-nyl-3-methyl-5-pyrazolone. Formation of a complex from an azo dye and a metal salt generally takes place in the presence of organic solvents, such as alcohols, pyridine, or formamide. An example is C.I. Solvent Red 8, 12715 [33270-70-1] (1). 

Another key feature of the metal complex cycle in which the iodide acts most effectively is the nature of the active catalyst itself. The oxidative addition step is considered to be nucleophilic in nature, based on activation parameters and relative rate data (23, 24a) (Section II,C), and the presence of a negative charge on the metal center appears to significantly enhance the nucleophilicity (and hence reactivity toward methyl iodide) of the metal relative to neutral rhodium(I) species (20). Extrapolations of available data (24-26) indicate that, at 25°C, the diiododicarbonylrhodium(I) species has a Pearson nucleophilicity parameter (25) toward methyl iodide of 5.5. In relation to other common nucleophiles, this value corresponds to nucleophilic reactivity toward methyl iodide comparable to that of pyridine (n = 5.2), an order of magnitude greater than chloride (n = 4.4), and two orders of magnitude slower than iodide (n = 7.4). 

In 1998, Kempe and coworkers [34] reported the first aminopyridinato rare-earth metal complexes. 4-Methyl-2-[(trimethylsilyl)amino]pyridine(HLl) was utilized in this complex. The reaction of lithiated LI and YCI3 in ether and pyridine led to the ate complex [Y(Ll)4(LiPy)] (Py = pyridine) (1). The complex 1 catalytically mediated a ligand transfer reaction to form [Pd(Ll)2] and [Y(Ll)3(py)] (2) from [Pd(cod)Cl2] (cod = cyclooctadiene). The LI ligand transfer from yttrium to palladium and the regeneration of 1 are significant in the efficient synthesis of the very strained amido palladium complexes (Scheme 2). Lithiated LI underwent a salt metathesis reaction with ScCb, at low temperature in THF, to yield the homoleptic complex [Sc(L1)3] (3) (Scheme 2). 3 is the first reported scandium aminopyridinato complex [35]. 

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