Amines 1.4.8.11- tetraazacyclotetradecane

The monovalent Co chemistry of amines is sparse. No structurally characterized example of low-valent Co complexed exclusively to amines is known. At low potentials and in non-aqueous solutions, Co1 amines have been identified electrochemically, but usually in the presence of co-ligands that stabilize the reduced complex. At low potential, the putative monovalent [Co(cyclam)]+ (cyclam = 1,4,8,11-tetraazacyclotetradecane) in NaOH solution catalyzes the reduction of both nitrate and nitrite to give mixtures of hydroxylamine and ammonia.100 Mixed N-donor systems bearing 7r-acceptor imine ligands in addition to amines are well known, but these examples are discussed separately in Section 6.1.2.1.3. 

The first structurally characterized example of a platinum(II) derivative containing a saturated tetraamine macrocycle, 6,13-dimethyl-l,4,8,ll-tetraazacyclotetradecane-6,13-diamine has been reported (80).251 The species crystallizes as the colorless tetra-cationic complex from dilute HC104 solution by slow evaporation, where the two pendant primary amines are protonated. Other macrocyclic tetraamine complexes including [Pt([14]aneN4)]Cl2 have also been described.252... 

In most cases, metal ion coordination by a dendrimer takes place by units that are present along the dendrimer branches (e.g., amine, imine, or amide groups) or appended at the dendrimer periphery (e.g., terpyridine, cathecolamide ligands). When multiple identical coordinating units are present, dendrimers give rise to metal complexes of variable stoichiometry and unknown structures. Luminescent dendrimers with a well defined metal-coordinating site have been reported so far [16, 17], and the most used coordination site is 1,4,8,11-tetraazacyclotetradecane (cyclam). 

System 11 consists of two tetramine ligating compartments, tren (tris(2-ami-noethyl)amine)) and cyclam (1,4,8,11-tetraazacyclotetradecane), that display different coordinating tendencies toward metals and are separated by a 1,4-xylyl spacer.14... 

Ni(04C2)(tet-a)-3H20 (tet = 5,7,7,12,14,14-hexamethyl-l,4,8,ll-tetraazacyclotetradecane a = meso isomer b = racemic isomer) were prepared by the reaction of a concentrated solution of sodium oxalate with an aqueous solution of the appropriate nickel(II) amine complex.1780,1781 In the dinuclear complex [Ni2(04C2)(en)4](N03)2 (234)1740-1741 the bridging oxalato group is planar and symmetrically bonded to the two nickel atoms. The same structure occurs in the complex Ni2(04C2)(0N0)2(py)6 which was obtained as a by-product in a very low yield when a pyridine solution of methanenitrosolic acid and nickel(II) were allowed to stand for several months.1741... 

The energetics of isomer prediction using molecular mechanics is discussed in detail in Chapter 7. One of the results of such a study is the structure of each of the isomers.The archetypal studies in this field relate to the complexes [Co(dien)2]3+ (dien = 3-azapentane-l,5-diamine see Chapter 7). Other important studies include those on macrocyclic ligands (see also Chapter 8). Tetraaza macrocyclic ligands, for example, can adopt a series of configurational isomers, and these have been the subject of numerous molecular mechanics calculations. Consider an equatorially coordinated tetraaza macrocylce. Each of the amine groups can coordinate with the amine proton or substituent disposed above or below the coordination plane. How many isomers result depends on the symmetry of the macrocycle. For example, in the classic case of cyclam (cyclam - 14-ane-N4 = 1,4,8,11-tetraazacyclotetradecane) there are five isomers[12] and these are shown schematically in Fig. 6.3. It is not always possible to prepare or separate all of these isomers and, therefore, in many cases only a minority have been structurally characterized. Thus, the energy-minimized structures represent the best available three-dimensional representations of the other isomers. 

Cyclam, or 1,4,8,11-tetraazacyclotetradecane is a popular macrocyclic ligand for d-tran-sition metal coordination chemistry. It also coordinates to lanthanide ions, although much less strongly than the better size-adapted cyclen. As for the latter, however, derivatization of the amine functions by amide, carboxylate, or phosphinate groups considerably improves the coordination ability of the macrocycle. 

Cyclam, 1,4,8,11-tetraazacyclotetradecane, is a cyclic amine readily synthesized from a linear tetraamine precursor, 1,5,8,12-tetraazaduodecane, which is preorganized by a metal template that promotes square planar complex formation, such as nickel, followed by the addition of ethanedione. Reduction of the Schiff base by a... 

Tritopic cyclen- and isocyclam- (isocyclam = 1,4,7,11-tetraazacyclotetradecane) based ligands 121 and 122 were prepared according to Scheme 17. Tosylated tren derivative (tren = tris(2-aminoethyl)amine) was cyclized under Richman-Atkins conditions to give the fully tosylated amines in relatively high yield considering the [1+3] reaction <2002JOC9107>. 

The coordination of Me2Zn with macrocychc amines (see Macrocyclic Ligands) such as 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (N4-aza crown) and 1,4,7, 10,13,16-hexamethyl-1,4,7,10,13,16-hexaazacyclooctade-cane (Ne-aza crown) has been studied. As shown by X-ray diffraction analysis, the structure of the complexes consists of molecular units with distorted tetrahedral coordination at zinc (Figure 21, Table 5). In (Me2Zn)2[N4-aza crown], the... 

Hambley et al. have also predicted isomer distributions of chlorocobalt(IIl) complexes of pendant-arm macrocycles.The force field used had been detailed earlier. Of the ligands studied (12-methyl-l,4,7,10-tetraazacyclotridecan-12-amine, 6-methyl-l,4,8,1 l-tetraazacyclotetradecan-6-amine, lO-methyl-1,4,8,12-tetraazacyclopentadecan-10-amine, and 3-methyl-l,5,9,13-tetraazacyclohexa-decan-3-amine), the cis isomer (the pendant primary amine is coordinated cis to the chlorine) was found to be the lowest energy form in each case. For 6-methyl-1,4,8,ll-tetraazacyclotetradecan-6-amine, the cis isomer was 4.4 kj/mol more stable than trans (cis/trans = 86 14). The calculated ratio was in reasonable agreement with experiment (cis/trans = 98 2). 

The tetradentate ligand, 1,4,8,11-tetraazacyclotetradecane (cyclam), forms solid diamagnetic orange to brown Ni(II) complexes with iodide and perchlorate anions (9). When the anions are changed to chloride and bromide, the solid complexes are paramagnetic (9). However, all the complexes are soluble in water, methanol, and benzene, giving yellow solutions. The yellow color remains on treatment with 12N HCl and excess chloride ion (9). It is interesting to note that this amine is a derivative of a reduction product of the template syntheses between bis(ethylenediamine)-nickel(II) and acetone reported earlier. 

Despite the large numbers of water-soluble monomers that can be polymerized by ATRP, several problems remain to be solved. For example, Brittain et al. [217] have shown that the aqueous polymerization of 45 (DMA), catalyzed by CuBr/L (L= HMTETA, tris[2-(dimethylamino)ethyl]amine (Meg-TREN) and 1,4,8,11-tetra-methyl-1,4,8,11-tetraazacyclotetradecane (Me4Cyclam)) is not controlled because of the slow but irreversible decomposition of the bromo-terminated end-group of the dormant chains. Aqueous polymerization of acryhc [199] and styrenic monomers [203] also appears to be difficult to control, as imphed by the rarity of known examples. 

Fig. 46. Structure of the binuclear cation [Ni(Me6-[14]ane-N4)(fi-L)Cu(C104)] with H2L = (u,co -bis((l,3-dimethyl-5-nitro8ouracil-6-yl)amine)propane and Me6-(141ane-N4 = ( )-5,7,7,12,14,14-hexamethyl-l,4,8,ll-tetraazacyclotetradecane. Reprinted from Cola-cio et al. (1011 Copyright 1994 American Chemical Society.

Brensted Base Quenching. The trans-Rh(cyclam)(CN)2+ ion (cyclam = 1,4,8,11-tetraazacyclotetradecane) displays luminescence from a ligand field excited state (3LF ) at room temperature, in an aqueous solution with a lifetime (8.1 /is) [53] several orders of magnitude longer than generally observed for rhodium(III) amine complexes [54]. As was observed for some other Rh(III) amines, the 3LF emission from trans-Rh(cyclam)(CN)2 is quenched by OH- in solution (Eq. (13)), a process attributed to amine deprotonation [55],... 

Typical examples of the rich coordination chemistry of saturated tetraaza macrocycles are the complexes given by 1,4,8,11-tetraazacyclotetradecane, also known as cyclam, with nickel(II) (Table 103). Isomerism is expected to occur in the Ni-cyclam system due principally to the different configurations about the asymmetric coordinated secondary amines which, in turn, influence the possible conformations which can be adopted by the chelate rings. In the tram octahedral complexes [NiX2(cyclam)] (373 X = Cl, and [NiI(cyclam)]I-H20 ... 

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