Cyclam complexes

Kimura, E., Kurogi, Y, Koike, T., Shionoya, M. and litaka, Y. (1993) Gold (Ill)-cyclam complexes. X-ray crystal structure and a useful macrocydic effect on the reduction of gold(III). Journal of Coordination Chemistry, 28, 33. 

The redox properties of complexes with hexaaza monocyclic ligands (e.g., (568)-(570)) are similar to those of the cyclam complex, indicating that the electrochemical properties of the complexes are only slightly affected by the presence of uncoordinated tertiary nitrogen atoms,... 

Run/Nin heteronuclear complexes such as (653), in which a photosensitizer [Ru(bpy)3]2+ or [Ru(phen)3]2+ is covalently attached to the Ni1 cyclam complex, have been synthesized in order to improve the efficiency of electron transfer from the photoexcited photosensitizer to the catalytic site.1 44-1646 However, these complexes did not perform particularly well, either due to unfavorable configuration of the Nin-cyclam subunit and the resulting steric hindrance or due to short lifetime of the excited states of the Ru photosensitizer moieties. A stable catalytic system has been prepared by immobilizing macrocyclic Ni11 complexes and [Ru(bipy)3]2+ in a nafion membrane.164... 

Cobalt(III) sepulchrate (l)8 and tetrazamacrocyclic complexes of cobalt(II) (2)9 and nickel(II) (3) (6)9-11 catalyze the electroreduction of water to dihydrogen, at potentials ranging from - 0.7 V (complex (1)) to — 1.5 V (complexes (4)-(6)) vs. SCE in aqueous electrolytes, with current efficiencies as high as 95% for complex (4).9 It is noteworthy that the binuclear nickel biscyclam complex (6) is 10 times more active (at pH 7) than the mononuclear nickel cyclam complex (5). This behavior tends to indicate that some cooperativity between the two metal centers occurs in complex (6), as depicted in the possible reaction (Scheme 3) involving a dihydride intermediate.11... 

Liang X, Sadler PJ (2004) Cyclam complexes and their applications in medicine. Chem Soc Rev 33 246-266... 

In contrast to the above heterogeneous catalyst based on a Co(III)cyclam complex, in the catalyst reported earlier by Das Clark [26], pyridine which was used as an ancillary ligand to stabilize the cobalt(III) complex in the immobilized state was foimd to escape from reaction mixtures heated between 110-130°C. However, no metal leaching was observed. Catalysis reuse was possible for this catalyst after catalyst regeneration achieved by addition of pyridine to the substrate-used catalyst reaction systems. 

The Ni(II) complexes l-3g with hexaaza and pentaaza macrocyclic ligands as well as the Ni(II) cyclam complex display a low-spin square-planar and high-spin octahedral complex interconversion in aqueous solution (7, 12-14). However, complexes l-3a favor formation of the high-spin form upon addition of acid, which is in contrast to the cyclam complex. The protonation of tertiary nitrogen atoms at the bridgehead position facilitates the axial coordination of anion or water because of hydrogen-bonding between them 12, 14a). 

Ni(II) complexes of cyclam and oxocyclam derivatives catalyze the epoxidation of cyclohexene and various aryl-substituted alkenes with PhIO and NaOCl as oxidants, respectively. In the epoxidation catalyzed by the Ni(II) cyclam complex using PhIO as a terminal oxidant, the high-valent nickel- complexes (e.g., LNiin-0, LNi=0, LNiin-0-... 

Coordinated secondary amines can also be alkylated, but only after deprotonation by a strong base generates a suitable nucleophile. Work on rhodium(III) complexes of ethylenediamine12 has been extended to nickel(II) complexes of various fully saturated macrocycles such as cyclam (Scheme l).13,14 The methylated cyclam complex is kinetically inert, unlike the isomer with all four methyl groups on the same side of the ring, which is obtained on reaction of the preformed tetramethyl cyclam with nickel ions. 

Fig. 6.3. The five isomers of square planar [M(cyclam)]"+complexes.

Figure 5-32. The methylation of a nickel(n) cyclam complex to give one specific conformer of the N, N, N", yV"-tetramethylcyclam complex.

Figure 5-33. The co-ordination of nickel(n) to /V A A -tetramethylcyclam gives a different con-former to that obtained from the methylation of nickel(n) cyclam complexes.

In addition to their thermodynamic stability, complexes of macrocyclic ligands are also kinetically stable with respect to the loss of metal ion. It is often very difficult (if not impossible) to remove a metal from a macrocyclic complex. Conversely, the principle of microscopic reversibility means that it is equally difficult to form the macrocyclic complexes from a metal ion and the free macrocycle. We saw earlier that it was possible to reduce co-ordinated imine macrocycles to amine macrocyclic complexes in order to remove the nickel from the cyclam complex that is formed, prolonged reaction with hot potassium cyanide solution is needed (Fig. 6-24). 

We are grateful to Professor Karl Wieghardt for providing samples of the substituted [9]aneN3 ligands. Professor N. A. P. Kane-Maguire kindly provided us with a number of useful details about the cyclam complexes prior to publication. The research described in this paper has been generously supported by the National Science Foundation. 

Katsumata and colleagues reported the first electrochemically mediated Ni(I)-catalyzed tandem radical cyclization reactions [139]. A bromoacetaldehyde dienyl acetal or the corresponding enynyl acetal underwent tandem 5-exo/5-exo cyclization reactions in the presence of Ni(cyclam) complex 98a under electrochemical reductive conditions (see Part 2, Sect. 5.3.3, Fig. 68). Bicyclic esters were isolated in 35% and 72% yields as a mixture of two and four diastereomers, respectively. 

Marcondes FG, Ferro AA, Sousa-Torsoni A, et al. In vivo effects of the controlled NO donor/scavenger ruthenium cyclam complexes on blood pressure. Life Sci 2002 70 2735-52. 

KEYWORDS Copper(II)-cyclam complex, XANES, DV-Xa method, electronic transition probability... 

In the present study, we synthesized dibromo(l,4,8,ll-tetraazacyclotetradecane)copper(II) ([CuBr2(cyclam)]) and diaqua(l,4,8,ll-tetraazacyclotetradecane)copper(II) difluoride four hydrate ([Cu(cyclam)-(H20)2]F2 4H20) complexes and performed single crystal structure analysis and X-ray absorption near-edge structure (XANES) measurements in crystals and in aqueous solution. Furthermore, DV-Xa molecular orbital calculations have been made for models based on these results, and the structures and electronic states of the [Cu(cyclam)] complexes in crystals and in aqueous solution are discussed, in particular, on the axial coordination to Cu(II). 

Synthesis and Single Crystal Structure Analysis of [CuBr2(cyclam)] complex... 

It has been found that the structure of [Cu(cyclam)] complex with Br in aqueous solution is different from that with Cf in aqueous solution obtained by Ohtaki et al. (5). The different axial coordination within both structures correspond to the larger ligation constants of CuL and CuL with Bf than those with Cl in water (4). Therefore, it is concluded that the predominant complex in the aqueous solution of [CuBr2(cyclam)] is model B, [CuBr(cyclam)(H20)] ... 

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