Azamacrocyclic ligands

Another important class of iron compounds is that of the tetra-azamacrocycle ligands. As a typical example we can cite the Fe(II) complexes of the 14-membered macrocycles illustrated in Scheme 10, which have different degrees of unsaturation. 

Spectrophotometric data on some Ni(II) macrocyclic complexes are summarized in Table I. The maximum absorption of the square-planar Ni(II) complex with neutral azamacrocyclic ligand shifts to a longer... 

The discussed examples clearly demonstrate the importance of azamacrocycles as structural element to create supramolecular function. Their rigid structure, the basicity and transition metal-ion coordinating ability make them suitable as scaffolds and binding sites. Lanthanide chemosensors containing azamacrocyclic ligands have already reached applications in medical diagnostics. Other applications of azamacrocyclic systems with supramolecular functions, particularly in biochemistry, will follow. 

The main emphasis of our EC project is in electrocatalytic C02 reduction, where we explore synthetic pathways for novel binuclear Co complexes with tetra-azamacrocyclic ligands and their use in electrochemical measurements and synthesis. Although several routes for ligand synthesis have been briefly described in the literature, we find upon repeated attempts that well-characterised samples are hard to obtain. In one case (bis-dioxocyclam XI) We have obtained a pure product. In addtion, the rotating-ring disk electrode has been introduced in this study for obtaining kinetic information on mono-and binuclear complexes. For their use in anhydrous media, water-free compelxes have been prepared. 

Lattermann and co-worker have reported a series of mesomorphic metal tricarbonyl complexes, 77, formed by complexation of the metal fragments M(C0)3 (77 M = Cr(0), Mo(0) and W(0)) by the non-mesomorphic tridentate azamacrocyclic ligand, i.e. l,4,7-tri-(3, 4 -didecyloxy)benzyl-l,4,7-triazacyclononane [139]. 

Costamagna, J., J. Canales, J. Vargas, A. Alvarado, and G. Ferraudi (1993). Spectroscopic and electrochemical characterization of some complexes with azamacrocyclic ligands. J. Indian Chem. Soc. 70(11-12), 877-883. 

Other important tetra-azamacrocycle ligands displaying interesting electrochemistry particularly with metals of the iron group are phthalocyanines, porphyrins, and related species. We now discuss two examples of catalytic small molecule reduction by iron-porphyrin catalyst. 

Azamacrocyclic ligands with pendant arms have recently attracted considerable attention mainly due to their analytical, biological and catalytic applications [l]. Compounds of this class combine the properties of a rigid macrocyclic structural unit with those of a flexible side-chain to which the functional group can be bound. Such systems are especially interesting for studying the influence of axial coordination on the properties of the coordinated metal ion. 

Kimura and co-workers have made a major contribution to this area with dizinc azamacrocycle complexes characterized including phosphate ester X-ray structures.445,446 They have also studied ligands with pendent alcohol groups.44... 

It is well-established that the molecular and electronic structures of metal complexes of azamacrocycles are greatly affected upon N-alkylation (197). This is mainly due to two factors (a) the decrease of the ligand field strength and (b) the increase in the steric requirements upon going from a secondary to a tertiary amine donor function (251). To examine whether the properties of the dinuclear amine-thiophenolate complexes are affected by the N-alkyl substituents, analogous complexes of the... 

This kind of argument may also be invoked for some Cr(III)-azamacrocyclic complexes. In this regard, it is noted that the macrocycle effect (which is essentially an enhanced chelate effect) stabilizes metal ions entrapped in the cavity formed by macrocyclic organic ligands... 

The study of the complexing of macrocycle ligands should be considered for its intrinsic importance rather than for its value in illuminating the mechanism of substitution. Kinetic (but much more thermodynamic °) data are available for the reactions of the different macrocycle ligand types, shown in Fig. 4.5, including azamacrocycles,crown ethers and cryp-tands, and porphyrins. ... 

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. 

A bicyclic azamacrocycle (127) has been prepared from [bisiV-(2-aminoethyl)-tacn)Cun] by reduction of the aminal formed with glyoxal (Scheme 30). The tricyclic ligands (128) and (129) formed by Richman-Atkins synthesis from tetrakis(3-aminopropyl)- and tetrakis(2-aminoethyl)-cyclam, respectively, form binuclear compounds.174... 

VII Mixtures of hydrogen bond donor ligands and inuoi ooycles VIII Macrocycles or chelates with pendant hydrogen bond donor functions IX Azamacrocycles... 

A P-CD 6-0- substituted with the macropolycyclic ligand 1,4,10,13-tet-raoxa-7,16-diazacyclooctadecane(82) affords a nice example of sensitization by an included molecule [241]. The Eu " is efficiently encapsulated by the free azamacrocycle and emits a red luminescence in DjO when excited at 254 nm. Addition of benzene slightly increases the emission as a result of bimolecular energy transfer. This emission is rather inefficient at the benzene concentrations used. However, the same amount of benzene added to the solution of Eu, encapsulated by the macrocycle bound to P-CD, caused an appreciable enhancement of luminescence emission. The enhancement is attributed to a more efficient energy transfer between the benzene included in the cavity of P-CD and Eu bonded to the azamacrocycle. Benzoic and... 

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