Transition metal complexes macrocyclic ligands

Q. Zeng, J. Sun, S. Gou, K. Zhou, J. Fang, and H. Chen, Synthesis and spectroscopic studies of dinuclear copper(II) complexes with new pendant-armed macrocyclic ligands, Transition Metal Chemistry, vol. 23, no. 4, pp. 371-373, 1998. 

The spectra and structure of transition metal complexes with tetradentate macrocyclic ligands. K. B. Yatsimirskii and Y. D. Lampeka, Russ. Chem. Rev. (Engl. Transl), 1980, 49,1003-1020 (191). 

A. W. Johnson Transition metal complexes of macrocyclic ligands, pp. 101-132 (83). 

Fig. 2 Depiction of common transition-metal chelates (or transition metal complexes of macrocyclic N4 ligands) reproduced from ref. 9.

One of the most fundamental questions when dealing with the activation of dioxygen by transition metal complexes is whether the process is controlled kinetically by ligand substitution or by electron transfer. A model system that involved the binding of dioxygen to a macrocyclic hexamethylcyclam Co(II) complex to form the correspond-... 

Many transition-metal complexes have been widely studied in their application as catalysts in alkene epoxidation. Nickel is unique in the respect that its simple soluble salts such as Ni(N03)2 6H20 are completely ineffective in the catalytic epoxidation of alkenes, whereas soluble manganese, iron, cobalt, or copper salts in acetonitrile catalyze the epoxidation of stilbene or substituted alkenes with iodosylbenzene as oxidant. However, the Ni(II) complexes of tetraaza macrocycles as well as other chelating ligands dramatically enhance the reactivity of epoxidation of olefins (90, 91). 

Virtually all types of metal ions have been complexed with macrocyclic ligands.2-7 Complexes of transition metal ions have been studied extensively with tetraaza macrocycles (Chapter 21.2). Porphyrin and porphyrin-related complexes are of course notoriously present in biological systems and have been receiving considerable investigative attention (Chapter 22).8 Macrocyclic ligands derived from the Schiffbase and template-assisted condensation reactions of Curtis and Busch also figure prominantly with transition metal ions.6,7 The chemistry of these ions has been more recently expanded into the realm of polyaza, polynucleating and polycyclic systems.9 Transition metal complexes with thioether and phosphorus donor macrocycles are also known.2... 

Macrocyclic polyarsanes (43) have been reported by Ennen and Kauffman.62 The complexation tendencies of these ligands are as yet unexplored, although they should, due to the soft arsenic donors, form stable transition metal complexes. 

Phosphorus-containing macrocycles, 990, 996, 998 macrocychc effect, 1002 ring size, 1003 stereochemistry, 1003 Phosphorus heterocycles transition metal complexes, 1041 Phosphorus ligands, 989-1061 ir-acid series, 1033 bonding, 1030-1041 cone angle concept, 1012 trigonal bipyramidal complexes, 1036 Phosphorus oxychloride metal complexes, 500 Phosphorus ylides transition metal complexes, 1056 Phosphorylation biological, 978 Phosvitin, 975 Photochromism... 

Table 9.3. In-plane ligand field splitting (Dq ) or transition energies (cm ) for square planar trans-octahedral transition metal complexes with tetraaza macrocyclic ligands 1 .

Bipyridines have been intensely used as ligands in transition metal complexes[6]. Within a broader investigation of the redox and photophysical behavior of Ru and Os complexed macrocycles[4,8], the Ru(II) and Os(II) complexes shown in Schemes 4 and 5 were prepared. 

Until the late 1960s, whereas there had been considerable interest in the transition metal complexes of natural and synthetic macrocyclic ligands (1—4), relatively few reports described complexes of alkaline earth and more particularly alkali metal cations. Research in this area was stimulated by the recognition of the importance of the biological role of Na+, K, Ca2 , and Mg2 and also the discovery and characterization of the natural antibiotic ionophores (5, 6). These macrocyclic antibiotics, such as valinomycin and nonactin, were shown to complex alkali metal cations with remarkable selectivity (7-9). 

Figure 12. Supramolecular porphyrins obtained by coordination of transition metal complexes to the periphery of the macrocyclic ring (a similar scheme can be extended to the 3-TPyP and analogous porphyrazine species), [dmso = dimethyl sulfoxide (ligand), form = A,A-9-di- -tolyformamidinate, and TFA = trifluoroacetate.l...

In such a large subject, this article can only focus on certain aspects, namely those that involve complexation with inorganic substrates. We only consider the synthetic macrocycles, with emphasis on transition metal complexation. Aza, oxa, and, to a lesser extent, thia and phospha macrocycles are also covered. The naturally occurring porphyrins, corrins, corphins, chlorins, and phthalocyanins, as well as the cyclodextrins, are not included. Because of the general complexity of macrocychc systems and the resulting complicated systematic names, commonly used abbreviations or simplified names will be employed. This review will encompass the synthesis, thermodynamics, stmcture, and applications of macrocychc ligands. 

Attempts to achieve macrocycles that are capable of stabilizing highly oxidized transition metal complexes has led to the design of noninnocent ligands. The structures of high-valent chrominm(V) oxo species with the two tetraamido N ligands (36) and (37) were determined. Both stmctnres were found to contain distinctly nonplanar amide gronps, and in (36) all fonr amides are nonplanar. 

Transition metal complexes of the larger polyaza macrocyclic ligands have been less extensively studied than for the smaller ring systems. For the pentaaza macrocycles, [ISJaneNs with ethylene bridges appears to form the most stable complexes with most metal ions. Structural data for a variety of pentaaza macrocyclic complexes have been reviewed. The N-H bonds as well as the different sized chelate rings must be considered in calculating the... 

In the crown ethers (18) the interactions between the ligand and metal ion are considered to be more electrostatic in nature, rather than the covalent binding observed for the transition metal complexes of the aza, thia, and phospha macrocycles. The thermodynamic properties of these macrocycles have been extensively studied, with numerous reviews covering complexation, selectivity, and structural aspects, some with extensive tables of thermodynamic data. Considerable efforts have been made to correlate the interrelationship between cavity size of the macrocycles and stability of alkali and alkaline earth metal complexes. From X-ray and CPK models, cavity radii are determined as 0.86-0.92A for 15-crown-5 (64), 1.34-1.43 A for 18-crown-6 (65), and about 1.7 A for 21-crown-7 (66). For complex formation between the alkali metal ions and 18-crown-6, the maximum stability... 

Simple chiral phosphines have already been mentioned (Section 3.1.3) and the macrocycle enantiomers are discussed below (Section 4.6). Current research in this area is concentrated on bidentate chiral phosphines, such as the ligands (24)-(27). Although their transition metal complexes are normally used for stereospecific synthesis, Whitmire and coworkers used the molybdenum complexes to resolve their racemic bisphosphines via flash chromatography. The phosphines were decomplexed by reductive cleavage at low temperatures (-78 °C) using sodium naphthalenide (Scheme 1). 

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