Ligands heteroaromatic

Heterocyclic ligands such as imidazole, pyridine, 2,2 -bipyridine and 1,10-phenanthroli-ne (Fig. 8-9) have played a formative role in the development of co-ordination chemistry. Many hundreds of thousands of complexes and complex ions containing these ligands, such as [Co(NH3)5(Himid)]3+, [Ag(py)J2+ and [Ni(bpy)3]2+, have been prepared and characterised. The variety of spectroscopic properties and stoichiometries observed led to an improved understanding of the geometry and bonding in complexes and provided a touchstone for bonding theories. 

It is convenient to consider heteroaromatic ligands in two classes - 7t-excessive, five membered rings typified by pyrrole, furan and thiophen, and TC-deficient six-membered rings typified by pyridine. The 7i-excessive heterocycles are usually extremely reactive towards electrophilic attack and, with the exception of thiophen, do not exhibit the chemical inertness often associated with aromatic benzene derivatives. Conversely, the TT-deficient heterocycles are extremely inert with respect to electrophilic attack. Paradoxically, it is the high reactivity of the five-membered rings and the inertness of the six-membered rings that give rise to common synthetic problems. The usual methods for the 

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Volume 78 of Advances in Heterocyclic Chemistry contains four contributions. A. P. Sadimenko of Fort Hare University of South Africa has covered organometal-lic compounds of furan, thiophene, and their benzannulated derivatives. This constitutes the first installment of a projected series on the organometallic chemistry of heteroaromatic ligands, a subject of great fundamental and technical importance that has exploded in the 1990s. 

Complex [RhCl2(Ti -Ph)(py)3] with lV-(2-cyanoethyl)pyrrole) (L) and EtOH yields [RhCl2(Ti -Ph)(L)(py)2] with the ti (N) coordination mode of the heteroaromatic ligand (97P4045). 

The resolution of problems of standard and nonstandard coordinations of typical chelating and heteroaromatic ligands is related in many aspects to the regioselective synthesis [6,10,11,14-16,21]. In particular, it was shown that, on the basis of (5-diketones together with chelates [Sec. 3.1, Schemes (3.6), (3.36), (3.37)], the molecu-... 

The possibility of carrying out the type-programmed synthesis (preparation of different types of coordination compounds from the same ligands) is directly related to the problem discussed [10-12,14], On the basis of the data given above, it follows that both ICC and molecular adducts [Schemes (4.19), (4.24), and (4.34)] can be obtained from chelating ligands. Heteroaromatic ligands form [(4.13) and (4.15)] molecular and -complexes. 

Besides metallocycles, metallodendrimers, and metallo-supramolecular polymers [58], few examples of hollow supramolecular architectures have been obtained from polytopic ligands containing terpyridine units. Lehn et al. used heteroaromatic ligands with terpyridine type coordination sites to obtain cylindrical self-assembled architectures (Fig. 11) [60]. For synthesis of the cage 37, tris-2,4,6-(2-pyrimidyl)-l,3,5-triazine (35) was mixed with lead triflate in... 

Alexander P. Sadimenko was born at Rostov-on-Don in 1951. He studied at Rostov State University, where he obtained his M.Sc. in 1973 and Ph.D. in 1976 under the guidance of Professor O. A. Osipov. During 1976-87 he worked as lecturer, senior lecturer, and associate professor at Rostov State University, 1987-91 as associate professor at Addis Ababa University, 1991-94 as associate professor and professor at National University of Lesotho, and 1994 until the present as professor, Head of the Department, and head of Directorate of physical and earth sciences at the University of Fort Hare. His specific interests include all aspects of organometallic chemistry of the heteroaromatic ligands, in particular, materials chemistry aspects. 

Chan et al. reported this class of highly effective atropisomeric, heteroaromatic ligands consisting of two interconnected 2,6-dimethoxy-pyridyl units. The MeO substituents in an ortho position to the nitrogen in the pyridyl rings are introduced very logically to block the access of the pyridyl ring to the metal center which may exert adverse effects, as it... 

In this study, we investigated the differences in the electronic structures among the dinuclear copper(I) complexes ([Cu2(p,-X)2L] (X = Br and I) (L = N-heteroaromatic ligands)) in order to determine the luminescence mechanism and... 

This involves two aryl groups on each molecule, and usually it is centrosyminetric. As shown in Fig. 14a,b, there is an OFF motif between two groups, each of which is also donor in an EF motif. The (OFF)(EF)2 embrace is also named the parallel fourfold phenyl(aryl) einbrace, to differentiate it from the orthogonal fourfold phenyl embrace. (EF)4. " As the size of a heteroaromatic ligand increases, as in eilatin. the OFF motif in the embrace becomes dominant (Fig. 14c), and the association of the complexes [Ru(phen)2(eilatin)] in acetonitrile is measurable. 

The potential synthetic possibilities for the creation of coordination polymers are enormous. A variety of other types of coordination bonds have been used to create polymeric materials. In most cases, the bonds formed are sufficiently labile for depolymerization to occur in solution. For example, by layering a solution of one equivalent of bipyridine with a diborylferrocene, the coordination polymer 7.52 is formed as an insoluble black crystalline solid. Addition of picoline leads to chain cleavage and the formation of the monomeric adduct 7.53 (Eq. 7.13) [97]. Materials analogous to 7.52 have been prepared with pyrazine as the linker, and these dark-green materials show charge-transfer transitions from the iron to the electron-poor heteroaromatic ligand [98, 99]. 

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