Dimeric macrocyclic complex

It is essential to characterize the reactant species in solution. One of the problems, for example, in interpreting the rate law for oxidation by Ce(IV) or Co(III) arises from the difficulties in characterizing these species in aqueous solution, particularly the extent of formation of hydroxy or polymeric species. We used the catalyzed decomposition of HjOj by an Fe(III) macrocycle as an example of the initial rate approach (Sec. 1.2.1). With certain conditions, the iron complex dimerizes and this would have to be allowed for, since it transpires that the dimer is catalytically inactive. In a different approach, the problems of limited solubility, dimerization and aging of iron(III) and (Il)-hemin in aqueous solution can be avoided by intercalating the porphyrin in a micelle. Kinetic study is then eased. 

Complexes of 107 have been isolated for copper(II), cobalt(II), and nickel(II) cations103). Condensation of 2,6-diaminopyridine with 108 affords the dimeric macrocycle 111 (70%). No complexes have been reported for ligands 111l08) or 113104 106>. in addition, the reaction of l,3-6is[(l-imino-4,5,6,7-tetrahydro-3-iso-indoline)amino]benzene with 2,6-diaminopyridine gives 113 (70%) 104>107>. 

These authors have also reported the preparation of a series of chlorotriazines 115-118 with 2,6-diaminopyridine to generate the corresponding dimeric macrocycles 119-122. The copper(II) complexes of these macrocycles (119-122) have also been synthesized and characterized108). 

The related phenylthiyl radical complexes are also known.31 The Ru complex of L3 (Scheme 4) is oxidized by four electrons in an unusual reaction to give the dimeric macrocyclic complex.32... 

It is well established that 1,2- and 1,3 diols form cyclic boronate esters," whereas 1,4- and 1,5-alkane diols principally give rise to dimeric macrocycles." While the crude product is a mixture of various size cycles and oligomeric materials, distillation, which likely shifts this dynamic equilibrium toward the compounds with higher volatility, can be used to isolate the 2 2 complex (Fig. 15a). Analogously if dithioboronate esters are heated with bisphenols, cyclic dimeric diboronates are isolated (Fig. 15b)." ... 

With sp bond angles calculated to be around 162°, macrocycle 131 would be highly strained and was therefore expected to be quite reactive [79]. The octa-cobalt complex 132, on the other hand, should be readily isolable. Indeed, 132 was prepared easily from 133 in five steps, and was isolated as stable, deep maroon crystals (Scheme 30). All spectroscopic data supported formation of the strain-free dimeric structure. Unfortunately, all attempts to liberate 132 from the cobalt units led only to insoluble materials. Diederich et al. observed similar problems when trying to prepare the cyclocarbons [5c]. Whether the failure to prepare these two classes of macrocycles is due to the extreme reactivity of the distorted polyyne moiety or to the lack of a viable synthetic route is not certain. Thus, isolation and characterization of smaller bent hexatriyne- and octatetrayne-containing systems is an important goal that should help answer these questions. 

Goff (54) synthesized an Fe(III) porphyrin with a 2-hydroxyphenyl group at one meso position (35, Fig. 12a). Under basic conditions, the system spontaneously dimerizes due to phenolate-Fe(III) coordination. The complex is very stable and was isolated and fully characterized. In the solid state, the X-ray crystal structure confirmed the structure of the assembly as a macrocyclic head-to-tail dimer with two intermolecu-... 

Bis(triazacyclononane) ligands (73) where the two macrocycles are linked with chains two to eight carbons in length have been complexed with zinc to form monomeric and dimeric... 

A strong decrease in relaxivity (from 12.8mM-1s-1 to 2mM-1s-1) between pH 6 and 11 has been reported for a positively charged macrocyclic Gdm complex (Scheme 10), which was explained by the successive deprotonation of the coordinated water molecules.167 Luminescence lifetime measurements of a Yb111 analogue proved that the complex possesses three bound waters at pH 5.5. Above pH 11, a di-oxo-bridged dimer is formed that has no more bound water or OH groups. 

Pentacoordinated Pc complexes with planar macrocycle are very scarce. Very recently, Galezowski and Kubicki [25] reported a o-bonded ComPc(CH3CH2) (2) with an alkyl group as axial ligand. Investigation of its crystal structure revealed that the solid consists of centrosymmetric face-to-face dimers. The cobalt atom in 2 is pentacoordinated and has a distorted square pyramidal geometry. The cobalt atom... 

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