Tetradentate macrocycles

The spectra and structure of transition metal complexes with tetradentate macrocyclic ligands. K. B. Yatsimirskii and Y. D. Lampeka, Russ. Chem. Rev. (Engl. Transl), 1980, 49,1003-1020 (191). 

A dinuclear iron(ll/Ill) complex bearing a hexadentate phenol ligand displayed moderate activity toward aziridination of alkenes with PhlNTs a large excess of alkene (2,000 equiv. vs PhlNTs) was required for good product yields (Scheme 22) [76]. It is noteworthy that complex 4 is active in the aziridination of aliphatic alkenes, affording higher product yields than copper (11) catalysts with tetradentate macrocyclic ligands [77]. 

The electrochemical processes involving cobalt complexes have already been thoroughly investigated [62, 66], Additional results have been reported with cobalt complexes different from vitamin Bxj and also with nickel ligated to tetradentated macrocyclic ligands. Both series of complexes lead to radicals. 

Fig. 4j6 Stepwise eomplexing of Cu(OH)4 by a tetradentate macrocyclic ligand. The first Cu(II)-N bond is formed by replacement of an axial solvent molecule (k ) followed by a Jahn-Teller inversion (Ar, ) which brings the coordinated nitrogen into an axial position. Second-bond formation follows a similar pattern (k2 and 2b)- Reproduced with permisson from J. A. Drumhiller, F. Montavon, J. M. Lehn and R. W. Taylor, Inorg. Chem. 25, 3751 (1986). (1986) American Chemical Society.

The role of the metal ion may be purely conformational, acting to place the reactants in the correct spatial arrangement for cyclisation to occur, or it may play a more active role in stabilising the enol, enolate, imine or enamine intermediates. The prototypical example of such a reaction is shown in Fig. 6-18. The nickel(n) complex of a tetradentate macrocyclic ligand is the unexpected product of the reaction of [Ni(en)3]2+ with acetone. There are numerous possible mechanisms for the formation of the tetradentate macro-cyclic ligand and the exact mechanism is not known with any certainty. 

Consider a planar tetradentate macrocycle, and draw a best-fit circle through the centres of the four donor atoms (Fig. 6-25). The radius of this circle (from the centre of the circle to the centre of the donor atoms) may be considered to be dictated by two... 

In many cases it is possible to utilise the hole size effects for the synthesis of specific types of macrocycle. Thus, a tetradentate macrocycle (6.33) is expected to be obtained from a template condensation of 2,6-diacetylpyridine with 1,5,9-triazanonane in the presence of small, first-row transition metal dications. The hole size of 6.33 closely matches the size of these metal ions. This is indeed what happens when Ni2+ (r = 0.8 A) is used as a template for the condensation and the nickel(n) complex of 6.33 is obtained in good yield (Fig. 6-32). However, when Ag+ (r = 1.0 A) is used as a template, the metal ion... 

However, the changes in environment which occurred with the change from a reductive to an oxidative atmosphere rendered iron sulfide-based redox systems inconvenient, as they were very sensitive to (irreversible) oxidation. We saw in earlier chapters the facile formation of porphyrin and phthalocyanines from relatively simple precursors, and these systems were adopted for the final steps of electron transfer in oxidative conditions. The occurrence of iron centres in planar tetradentate macrocycles is ubiquitous, and metalloproteins containing such features are involved in almost every aspect of electron transfer and dioxygen metabolism. A typical example is seen in the electron transfer protein cytochrome c (Fig. 10-10). 

The meso form of the saturated tetradentate macrocycle (194) has been used to synthesize the... 

Table 6 Magnetic and Mossbauer Data2 for Fem Complexes [FeN4SR] of Tetradentate Macrocyclic...

Five-coordination is often observed when CrCl3 forms numerous adducts with ethers, nitriles, amines, and phosphines, which have formulas CrCl3 2L or CrCl3 3L. An example is CrCl3 2NMe3 where X-ray studies confirm the trigonal bipyramidal structure with axial amine groups. The only known square pyramidal complex (17-C-Villa) is formed with the tetradentate macrocycle, tmtaa, (17-C-VIIIb).17... 

When 2-aminobenzaldehyde was heated in absolute ethanol in the presence of nickel nitrate, the tridentate and tetradentate macrocyclic complexes (7 and 8, respectively) were isolated.17 The presence of copper(II) nitrate produced only the latter (8).17 Although the monomer has two functional groups and the oligomers have reactive azomethine groups, the formation of macrocyclic ligands stabilized by a metal halts further polymerization. 

A more preorganized ligand system is derived from the self-condensation of o-aminobenzaldehyde. The tridentate form of the hgand (25) (TRT) imparts considerable inertness toward substitution. For example, the salts of the [Ni(TRl)(H20)3] + ion can be resolved into optical isomers. A copper(ll) complex of the methyl-substituted tetradentate macrocycle Me4TAAB, in which bis-coordination occurs, displays a dynamic Jahn Teller distortion based on crystallographic evidence. ... 

M. A. Watzky, D. Waknine, M. J. Heeg, J. F. Endicott, and L. A. Ochrymowyzc, Inorg. Chem., 32, 4882 (1993). Tetradentate Macrocyclic Complexes of Platinum. Evaluation of the Stereochemical Alterations of Redox Behavior and the X-Ray Crystal Structure of (l,4,7,10-Tetrathiacyclodecane)platinum(II) Chloride. 

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