Reactions of Coordinated Heterocyclic Ligands

Related to the above reports is the observation that the reaction of [Zr(OAr)2Bz2] (Ar = 2,6-di-tert-butylphenyl) with 2,2 -bipyridine, 4,4 -dimethyl- 

2 -bipyridine or 1,10-phenanthroline leads to the formation of complexes derived from the nucleophilic attack of the benzyl group on the 6-position of the 2,2 -bipyridine (45). 

The pH-dependent NMR spectrum of [Ru(bipy)2(py)2] salts has been shown not to involve the formation of covalent hydrates. The reaction of 2,4,6-tris(2-pyridyl)-l,3,5-triazine (46) with aqueous copper(I) salts results in a metal-promoted hydrolysis to yield complexes of 2-pyridinecarboxamide and (47). A number of metal complexes have been characterized structurally from these reactions. 

A detailed study of the effect of coordination to a [Rh(NH3)5] center of a range of imidazoles and pyrazoles has been reported. The relative o and tt components controlling the pK of the coordinated heterocycle are discussed and compared with related cobalt(III) and ruthenium(III) complexes. The addition of hydroxide to the ligand in a range of 5-nitro-1,10-phenanthroline complexes has been described. It is proposed that attack upon [Ru(bipy) (5-nitrophen)3 ] can occur at the 4- or 7-positions in addition to the expected 6-position of the Meisenheimer adduct. The spectroscopic data supporting this proposal do not appear to be unambiguous. Finally, the displacement of halide from coordinated 4-halo substituted pyridines has been developed into a new synthetic method. 

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