Macrocycles dinuclear complexes

The effective utilization of the it-it stacking phenomenon for drug designs is described in Section 6.3. Assembly of the macrocyclic dinuclear complex bearing 2,3,5,6-tetrafluoro-1,4-phenylene moiety 21 includes electron-rich aromatics as a guest into its cavity. The complex (21) associates with the electron-rich aromatics more efficiently than with the electron-deficient aromatics as shown in Scheme 1.30. A noteworthy fact is that 21 does not complex with nonaromatics, 1,4-dimethoxycyclohexane (Scheme 1.30, Table 1.24) [22]. 

From 2,6-diacetylpyridine dioxime, ferric chloride hydrate, and phenylboronic acid as starting materials the macrocyclic dinuclear iron(ll) complexes 133 can be prepared (Fig. 36). 

Complex (51b) was prepared according to Equation (11). The dangling formyl groups can be used for further derivatization (e.g., (517) shown in Figure 16), and (516) serves as a valuable starting material for the synthesis of macrocyclic dinuclear species (compare Section 6.3.4.12).1367... 

Macrocyclic Schiff base compartmental ligands (750) (Robson-type ligands) derived from the [2 + 2] condensation of a 2,6-diformyl- or 2,6-diketo-substituted phenol and a diamine are very prominent in dinuclear Ni coordination chemistry.1901-1903 Particular interest lies in magnetic exchange interactions between the adjacent metal ions as well as in bioinorganic chemistry, where such dinuclear complexes have been proposed as synthetic analogues for bimetallosites. 

Similarly, by Schiff-base condensation reactions have been used to generate free cryptands from triamines and dicarbonyls in [2+3] condensation mode. These ligands react with silver(I) compounds to give dinuclear or trinuclear macrocyclic compounds where Ag Ag interactions may be present. Thus, with a small azacryptand a dinuclear complex with a short Ag- Ag distance (55) is found.498 With bigger azacryptand ligands also dinuclear complexes as (56) are achieved but without silver-silver interaction. 65,499-501 A heterobinuclear Ag1—Cu1 cryptate has also been... 

The zinc complex of a 14-membered CA-N2S2 dibenzo macrocycle with two pendent pyridyl-methyl groups was studied (L = 8,ll-bis(2-pyridylmethyl)5,6,7,8,9,10,16,17-octahydro-diben-zo[e,m][l,4]dithia[8,ll]diazacyclotetradecine). In solution, [ZnL]2+ takes up atmospheric carbon dioxide and transforms to the dinuclear complex [(//-C03)(ZnL)2](C104)2. The structures of both complexes have been elucidated. The zinc atoms, which are situated outside the macrocyclic ring, are unsymmetrically bridged by the //-carbonato group.739... 

Macrocyclic ligands 1,4,7-triazacyclonona-iV-acetate 221 and iV-(2-hydroxybenzyl)-l,4,7-cyclononane 225 have been prepared from l,4,7-triazacyclio[5.2.1.04 10]decane 40 and were subsequently used for the synthesis of a series of mono- and dinuclear complexes of vanadium(rv) and (v) (Scheme 35) <1995ICA(240)217>. 

The azamacrocycle 1,4,7-triazacyclononane (tacn) and its tris(A -methyl) analog (Me3tacn) are popular ligands in macrocyclic chemistry. Complexes of both and M (M = Ru, Os) containing the tacn ligand are dealt with together in this section along with several dinuclear, M—M bonded species. 

Before we obtained the X-ray structure determinations of both the knotted and unknotted dicopper(I) complexes, we could identify them after careful comparative H NMR and mass spectroscopy studies performed not only on the dinuclear complexes but also on their respective free ligands afforded by demetalation. Treatment of Cii2(m-43) + by a large excess of potassium cyanide led indeed quantitatively to a plain 43-membered macrocycle whereas an analogous treatment of Cii2(K-86r+ led to the free knot K-86 whose topological chirality could be demonstrated by NMR and mass spectroscopy (Figure 20). 

The tetrathia macrocycles containing up to 13-membered chelate rings are too small to encircle the nickel(II) atom in a square-planar chelation like tetraaza macrocycles do, and give rise to dinuclear complexes. In contrast, a planar chelation was found with the 14-membered macrocycle l,4,8,ll-[S4]-14-ane.1967... 

In the case of the purely aliphatic ligand 2,2,6,6-tetrakis(amino-methyl)-4-azaheptane (12), complex formation with copper appears to proceed in two steps, as elucidated by titration experiments with the fully protonated ligand (12 5 HC1). Three and two protons from (Hr,12) + are sequentially abstracted, and the predominant species after full deprotonation appears to be a dinuclear complex in which two copper(II) ions are coordinated, each in square planar fashion, by the l,3-diaminoprop-2-yl units of two molecules of pentaamine ligand, thus forming a macrocyclic complex of composition [Cu2(12)2]4+ (23). The UV/vis spectral data show an interesting solvent dependence, suggesting an equilibrium between [Cu2(12)2]4 + and two equivalents of mononuclear complex [Cu(12)]2+ under suitable conditions. ESR spectroscopic data are also compatible with the formulation of a dinuclear species. Further addition of base to an aqueous solution of [Cu2(12)2]4+ gives the mononuclear hydroxo complex [(12)Cu(OH)]+, as inferred from the UV/vis spectroscopic data. 

However, several intriguing macrocyclic ligands which form dinuclear complexes have been synthesized by Lehn and coworkers. Ligands 146 and 147 are synthesized by a route which results in the formation of uncomplexed ligands (Scheme IX). Both ligands form dinuclear copper(II) complexes, in which the copper-copper distance in 146 is 4.79 A 120>. 

The hexaaza [ISJaneNe forms complexes with transition metal ions and with certain alkali and alkaline earth and lanthanide ions. For the higher aza macrocycles with seven or more donor atoms, dinuclear complexes become possible. A systematic investigation of both the structural and thermodynamic aspects of copper complexes formed with the larger polyaza macrocycles from heptaaza to dodecaaza has been published. All of the macrocycles were found to form hydroxo species as well as polynuclear complexes. A number of structures have been determined for the higher polyaza macrocycles, both in complexed and noncomplexed forms, and structures range from highly boat shaped to nearly planar. ... 

Other studies have been concerned with trapping the C0-O2 monomeric complex in an environment where dimerisation is impossible. Nakamoto and co-workers have published a series of papers on Co(II) complexes trapped in 02-doped argon matrices " and a report has appeared of Co " complexed by a nitrogen macrocycle in a micellar phase . Co complexed by ethylenediamine in zeolite cages forms an 1 mononuclear complex at low concentration but j/ dinuclear complexes are observed at higher concentrations. There is some evidence for formation of free Of ion Similar results were found for Go(II) ethylenediamine complexes absorbed on a cation exchange resin ... 

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