Tetraaza macrocycles

Tetraaza macrocycles nickel complexes, 5, 5 synthesis, 2, 903 Tetraazaporphyrin, octaphenyl-metallation, 2, 858 Tetraazaporphyrins synthesis, 2, 857... 

A facile procedure for the synthesis of fcispolyazamacrocycles by the condensation of iV,A -di-BOC protected triazamacrocycles or iV,iV ,lV -tri-BOC protected tetraaza-macrocycles with aromatic feiselectrophiles was reported the BOC protection is readily removed by the treatment with acid <96BSC(Fr)65>. Treatment of 1,5,9-... 

Woo et al. [54] prepared new chiral tetraaza macrocyclic hgands (48 in Scheme 23) and their corresponding iron(II) complexes and tested them, as well as chiral iron(II) porphyrin complexes such as Fe (D4 -TpAP) 49, in asymmetric cyclopropanation of styrene. 

In addition, iron(II) complexes of tetraaza macrocyclic ligands 17-20 were encapsulated within the nanopores of zeolite-Y and were used as catalysts for the oxidation of styrene with molecular oxygen under mild conditions (Scheme 9) [57]. 

Scheme 9 Tetraaza macrocyclic ligands for supported iron catalysts...

Halides are ubiquitous co-ligands for cobalt(III), and are met throughout this review. Anation of (solvent)cobalt(III) complexes by halide has been examined from time to time. An example is substitution of coordinated acetonitrile in [Co(L)(MeCN)2]3+ (L = tetraaza-macrocycle) by Cl-and Br-.1096 A mechanism involving interchange from within tight ion pairs was proposed. Halo-bridged polymeric complexes are well known with both classical and organometallic complexes. 

In a comparative study, the semiempirical PM3(tm) method was shown to be less effective than molecular mechanics for modeling the structures of Ni11 complexes with tetraaza macrocycles.398 In contrast, local DFT calculations (VWN5 method), coupled with appropriately large basis sets, accurately describes the geometries of the isomers of [Ni(cyclam]2+. 

The effect of steric crowding on the rates of reaction of the Ni1 tetraaza macrocycle complex [Ni(dmc)]+ with organic halides and hydroperoxides has also been examined. Reaction with this complex was found to be about 104 times slower than with the corresponding [Ni(tmc)]+ complex.2329... 

Other complexes with tetraaza macrocycles have been prepared by reaction of [Au(en)2]Cl3, ethylenediamine, or nitroethane and formaldehyde, although with nitroethane an acyclic ligand was also obtained (293).1715,1716 A gold(III) complex with a hexaaza macrocycle (1,8-dimethyl-1,3,6,8,10,13-hexaazacyclotetradecane) has been obtained by a transmetallation reaction from the nickel compound [NiL]2+ by reaction with [AuC14], 1717 The chemistry of tetraazamacrocycles in aqueous solution has been reported.1718... 

Ito and co-workers observed the formation of zinc bound alkyl carbonates on reaction of carbon dioxide with tetraaza macrocycle zinc complexes in alcohol solvents.456 This reversible reaction was studied by NMR and IR, and proceeds by initial attack of a metal-bound alkoxide species. The metal-bound alkyl carbonate species can be converted into dialkyl carbonate. Spectroscopic studies suggested that some complexes showed monodentate alkyl carbonates, and varying the macrocycle gave a bidentate or bridging carbonate. Darensbourg isolated arylcarbonate compounds from zinc alkoxides as a by-product from work on polycarbonate formation catalysis.343... 

Tri- and tetraaza macrocycles A-functionalized with imidazole and pyrazole groups have been coordinated to zinc. The zinc complexes of functionalized 1,5,9-trizacyclododecane and 1,4,8, 11-tetraazacyclododecane have been synthesized, (76) and (77).680-685 The formation constants with the mono-armed 1,5,9-triazacyclododecane were calculated and found to be higher than for the non-functionalized macrocycle and coordination was demonstrated to be through four nitrogen... 

Moore and co-workers have also studied the complexation of zinc with other tetraaza macrocycles and pendent arm derivatives. Zinc complexes of 11-(2 -dimethylaminoethyl)-1,4,7-trimethyl-1,4,7,11-tetra-azacyclotetradecane have been characterized.695 A pyridine analog of this... 

Zinc complexes have been characterized with hexadentate macrocycles formed from a tetraaza macrocycle functionalized with pyridylmethyl or pyrazolylemthyl groups.700... 

The catecholate and semiquinonate complexes of zinc with tetraaza macrocycles have been synthesized and CD spectra recorded.710... 

Table 6.1 summarizes the thermodynamic parameters relating to the macrocyclic effect for the high-spin Ni(n) complexes of four tetraaza-macrocyclic ligands and their open-chain analogues (the open-chain derivative which yields the most stable nickel complex was used in each case) (Micheloni, Paoletti Sabatini, 1983). Clearly, the enthalpy and entropy terms make substantially different contributions to complex stability along the series. Thus, the small macrocyclic effect which occurs for the first complex results from a favourable entropy term which overrides an unfavourable enthalpy term. Similar trends are apparent for the next two systems but, for these, entropy terms are larger and a more pronounced macrocyclic effect is evident. For the fourth (cyclam) system, the considerable macrocyclic effect is a reflection of both a favourable entropy term and a favourable enthalpy term. 

Table 6.1. Parameters illustrating the macrocyclic effect for the high-spin Ni(n) complex of the tetraaza macrocycles L, L4, L6 and L8 (Micheloni, Paoletti Sabatini, 1983). 

M(iii) and Cn(m) complexes. In early classic studies the redox chemistry of tetraaza macrocyclic complexes of Ni(n) and Cu(n) (of the Curtis and reduced Curtis type) was investigated in acetonitrile (Olson Vasilevskis, 1969 1971). These authors were the first to report the electrochemical generation of Ni(m) and Cu(m) complexes of such N4-cyclic ligands. Since this time, a considerable number of related studies, involving both nickel and copper macrocyclic species, have been reported. 

The Em values corresponding to the Ni(ii)/Ni(m) couple for a selection of tetraaza macrocyclic complexes in acetonitrile are given in Figure 8.1. Overall, for such square-planar Ni(n) complexes, a potential range spanning almost two volts has been observed. 

In the presence of a saturated tetraaza macrocycle such as cyclam, disproportionation of Ag(i) occurs to produce a silver mirror and a stable Ag(n) complex of the macrocycle (Kestner Allred, 1972 Barefield Mocella, 1973). In some cases the Ag(n) complexes so formed may then be oxidized further to Ag(m) species either electrochemically or chemically [using nitrosyl (NO+) salts]. 

Stable Cu(i) complexes of tetraaza macrocycles are able to be generated in oxygen-free aprotic solvents (Palmer, Papaconstantinou Endicott, 1969 Olson Vasilevskis, 1971). In aqueous solvents there is a tendency for such species to decompose via loss of ligand (Freiberg, Meyerstein Yamamoto, 1982). Indeed, aqueous Cu(i) is unstable with respect to disproportionation to Cu(n) and elemental copper. However, extensive N- and C-alkylation of the macrocycle, as occurs in (291), slows... 

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