Complexes with Macrocyclic Quadridentate Ligand

Dockal etal. [57] used slow-scan CV to determine the 21 values for 17 Cu(II/I) complexes in 80% methanol —20% water (w/w) - including nine complexes with macrocyclic terdentate, quadridentate, quinquedentate, and sexaden-tate thioethers and eight complexes with acyclic quadridentate ligands containing thioether sulfur and/or amine nitrogen donor atoms. (In naming the denticity of multidentate ligands, Dwyer, Lions, and coworkers have pointed out that dentate is a Latin root and proper nomenclature requires that Latin prefixes be used. 

Bernardo etal. [51] subsequently determined the potentials of a series of copper(II/I) complexes formed with 14-membered macrocyclic quadridentate ligands involving amine nitrogen and thioether sulfur donor atoms and found that the substitution of each sulfur donor atom by an amine nitrogen resulted in an average decrease of 0.3 V in the Cu(II/I) potential. Since the Afcu L values had been determined previously for these systems [99], Bernardo et al. were able to calculate the A (jji values using Eq. (9). The latter values proved to be nearly constant, indicating that Cu(I) does not discriminate... 

The absorption and c.d. spectra of 4,4 -(i -propylene-di-iminato)di(3-penten-2-one)-copper(ii) (133) has been interpreted to show that the complex is tetrahedrally distorted with the absolute configuration A 2f-ray diffraction has confirmed this. The synthesis of new binucleating agents (134) and their dimeric cupric complexes has been reported. The new macrocyclic quadridentate ligands of type (135) form... 

The formation and dissociation kinetics for the complexation of Cu, Zn, Co and Ni with the quadridentate l,4,8,ll-tetramethyl-l,4,8,ll-tetraazacyclotetradecane to give five-coordinate species have been reported.1203 The rate order (Cu > Zn > Co > Ni) is the same as that for H2O exchange, but the rates are much slower, probably owing to conformational changes occurring in the ligand. The dissociation is acid-catalyzed the five-coordinate species are found to be much less kinetically inert than four- or six-coordinate complexes. No macrocyclic effect was observed. 

As far as quadridentate ligands are concerned, the easiest attainment of the Ni state, denoted by the less positive redox potential, is observed with the 14-membered macrocycle, 5, known as cyclam. Both contraction and expansion of tetramine ring atomicity, to 12 and to 16, respectively, makes the potential more positive, thus destabilizing Ni with respect to Ni Moreover, the isomeric 14-membered macrocycle, 6 (isocyclam) stabilizes the Ni state to a much lesser extent than cyclam. Notice that the two macrocyclic complexes simply differ in the sequence of the five-... 

The Schiff base condensation of 2,6-diacetylpyridine with 4,7-dithiadecane-1,10-diamine yields the similar NjSj macrocycle (129). This ligand is able to form complexes with iron(II) but its mode of coordination adapts to the monodentate coligand. Thus X-ray crystal structures show that in [Fe(L)(NCS)] and [Fe(L)(MeOH)Cl]+ (L = 129) the iron atom has a distorted octahedral geometry. In the first complex the macrocycle is quinquedentate and wraps around the iron atom. In the second complex the macrocycle is quadridentate with one sulfur atom weakly coordinated and one free. A compound with the formulation [Fe(L)(NCS)2] (L = 129) has been observed and evidently exists in three different forms (from IR, Mossbauer and magnetic data). Although X-ray structural data are not available on these isomers it is likely that they also reflect different ligand conformations of the NjS, macrocycle. 

The complexes with hexadentate cage-like ligands result from tautomeric conversion of conjugated n systems of quadridentate macrocycles catalysed by bases due to the migration of protons of two secondary amino groups to y-carbon atoms, followed by coordination of the two C=N groups produced (Scheme 4-14). Poten-... 

Poon and Mak have classified the reactivities of a range of macrocyclic ligand complexes of the type /ra 5-[Co(L)(X)(Y)]+ (L=quadridentate N-donor macrocycle X and Y unidentate anionic ligands with X the leaving group) into three categories as shown in Table 30. Those ions in classification I react with a rate-determining proton transfer and kon=ki reactions (30)—(32), and at... 

The complex rm f-[Fe(LLH)2(py)a], with LL = diphenylgjyoximate, reacts with carbon monoxide in chlorobenzene solution. The determined rate law, the positive activation entropy, and the variation of the rate constant where the py ligands are replaced by their p-methyl or m-chloro-derivatives, are all consistent with a limiting 5n1 D) mechanism for these reactions as for those of the [Fe(CN)6L] complexes discussed in the previous paragraph. Preparative and equilibrium studies have been made of the complex [Fe(tim)(NCMe)2] +, where tim is the quadridentate macrocyclic ligand (36) derived from 1,3-diaminopropane and 2,3-butanedione. These studies suggest that kinetic studies of reactions of this complex could provide information on novel substitution reactions of iron(n), for example the (reversible) replacement of the acetonitrile ligand by carbon monoxide. ... 

The reaction sequence for a quadridentate macrocyclic ligand reacting with an octahedral metal to form a planar complex is given in Scheme 3. ... 

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