Binucleating

Do binucleating ligands have a biological relevance D. E. Fenton, Adv. Inorg. Bioinorg. Mech., 1983,2,188 (264). 

The binucleating bis (amidinate) ligands based on the 9,9-dimethylxanthene backbone have also been used to prepare new dititanium(lV) complexes of the general formula [bis(amidinate)]Ti2Cp2R4 (R = CH3, CD3). Reaction of... 

Based on these observations a selective receptor for lithium 117 has been synthesized from a smaller diazadioxa macrocycle [160]. Ligands 110 and 117 may be regarded also as binucleating ligands capable of binding two cations at a time. 

The final category of binucleating ligands are those which incorporate more than one linkage between the cyclic subunits [see (118)]. The additional linkages between rings will tend to reduce the flexibility of the system and, for example, usually enable the relative positions of the metal centres to be controlled more precisely. The most common examples in this category have been termed co-facial dimers. 

Besides (166), other binucleating cryptands have been synthesized (Lehn, 1980). The availability of systems such as these once again provides a means for fixing a pair of metal ions in close proximity in a well-defined environment. Such species are ideal for the types of studies involving binuclear systems outlined in Section 3.4. 

A few mixed-donor binucleating macrocycles incorporating some ether oxygen functions have already been mentioned in Chapter 3. This earlier discussion is now expanded to include cyclic systems in which the donor sets consist (totally or predominantly) of ether oxygens. 

Related structures to the binucleating crown (206), in which three or four individual macrocycles are linked by spiro-groups, have been synthesized (Weber, 1979 Weber, 1982). Other ligands of this general type, showing a variety of topological arrangements, are also known (Weber ... 

Love and coworkers have reported a series of dinuclear cobalt complexes derived from a rigid binucleating macrocycle H4L 18 as shown in Fig. 26 (150). The synthesis of the dicobalt complex [Co2(L18)] (36) was achieved by an anaerobic transamination reaction between H4L18 and [Co(thf) N(SiMe3)2 2] in THF. The unsaturated species 36 forms a bis(pyridine) adduct, 36 py2 (py — pyridine), which has a cleft-like structure reminiscent of pacman diporphyrin complexes (151,152). Both cobalt ions are square pyramidal, with Col and Co2 displaced out of the N4-basal planes by 0.17 and 0.18 A, respectively. The apical sites are occupied by pyridine nitrogen atoms that are exo and endo to the cleft. Interestingly the endo pyridine is canted and reflects the... 

III. Metalated Container Molecules of Binucleating Polyaza-Dithiophenolate Macrocycles... 

Fig. 30. Binucleating aza-thioethers 40c-40p and amine-thiophe-nolate macrocycles H2L24-H2L31 (see Table I for ligand designations).

The S-oxygenation of the hexaamine-dithiophenolate macrocycles should provide a potential entry into the novel class of binucleating polyamine-disulfonate and -disulfinate macrocycles. Indeed, such ligands can be prepared by the oxidation of dinuclear nickel complexes of the parent hexaaza-dithiopheno-late macrocycles followed by the decomposition of the oxidation products in acidic solution. The dinuclear nickel complexes [Nin2(L36)(L )]+ (L = Cr (70) and OAc (71)) of the hexaaza-diphenylsulfonate ligand (L36)2- (Fig. 38) are obtained by... 

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