Macrocycle-metal complex properties

The metal complexing properties of macrocyclic compounds, coupled with the solubilities of their metal complexes in a variety of organic solvents, make them especially useful as reagents in organic syntheses. They provide a unique method for solubilizing inorganic salts such as KC1 in organic solvents. Despite their promise and the favorable results obtained thus far, it has been observed that few synthetic applications of these compounds have been reported (53). 

In a manner similar to that used to prepare 112, the reaction of the diformyl-tripyrrane 114 with o-phenylenediamine was found by Sessler and coworkers to result in the synthesis of a pentaazamacrocycle 115 (Scheme 13) [59], An X-ray structure of a derivative of 115 is shown in Fig. 19. Unfortunately, no structurally characterized metal complexes of 115 have been reported to date. However, oxidation of 115 in the presence of cadmium(II) was found to give the aromatic pentaaza-macrocycle metal complex 116, which has been characterized by X-ray diffraction [60]. The properties and chemistry of these tripyrroledimethine-derived texaphyrins is reported in the next section. 

In the following we will discuss some unconventional properties of macrocyclic metal complexes, preferentially semiconductive and liquid crystalline behavior. There are several reviews available on low-dimensional conductive compounds based on these macrocycles [21]. A detailed description of newer developments in the field of bridged macrocyclic metal complexes especially with transition metals was published recently [22]. In order to use the 7t-electrons in these macrocyclic systems for a conduction pathway, polymerization of the metallo-macrocycles is necessary. A polymerization can be carried out in three different ways as explained in Sections 1.2.1-1.2.3. 

Besides the macrocyclic metal complexes, many dyes have been used to fabricate organic photovoltaic cells. Correlations between the cell performance and the molecular structure of the dyes have been studied and the desirable properties of photovoltaic dyes discussed... 

A review article dealing with the synthesis and properties of conducting bridged macrocyclic metal complexes including poly[(phthalocyaninato)siloxanes and germoxanes] has been published. See reference [94],... 

Synthesis and Properties of Conducting Bridged Macrocyclic Metal Complexes... 

J. Mezger, M. Schneider, O. Schulze, H.-J., "Synthesis and Properties of Conducting Bridged Macrocyclic Metal Complexes", Chapter 5 133)... 

SYNTHESIS AND PROPERTIES OF CONDUCTING BRIDGED MACROCYCLIC METAL COMPLEXES... 

Factors influencing the macrocyclic hole size. The hole size of a macrocyclic ligand is a fundamental structural parameter which will usually influence, to a large degree, the properties of resultant metal complexes relative to those of the corresponding non-cyclic ligands. The large number of X-ray diffraction studies now complete for macrocyclic systems makes it possible to define many of the parameters which affect hole size... 

Metalated container molecules can be viewed as a class of compounds that have one or more active metal coordination sites anchored within or next to a molecular cavity (Fig. 2). A range of host systems is capable of forming such structures. The majority of these compounds represent macrocyclic molecules and steri-cally demanding tripod ligands, as for instance calixarenes (42), cyclodextrins (43,44), and trispyrazolylborates (45-48), respectively. In the following, selected types of metalated container molecules and their properties are briefly discussed and where appropriate the foundation papers from relevant earlier work are included. Porphyrin-based hosts and coordination cages with encapsulated metal complexes have been reviewed previously (49-53) and, therefore, only the most recent examples will be described. Thereafter, our work in this field is reported. 

Coordination compounds composed of tetrapyrrole macrocyclic ligands encompassing a large metal ion in a sandwich-like fashion have been known since 1936 when Linstead and co-workers (67) reported the first synthesis of Sn(IV) bis(phthalocyanine). Numerous homoleptic and heteroleptic sandwich-type or double-decker metal complexes with phthalocyanines (68-70) and porphyrins (71-75) have been studied and structurally characterized. The electrochromic properties of the lanthanide pc sandwich complexes (76) have been investigated and the stable radical bis(phthalocyaninato)lutetium has been found to be the first example of an intrinsic molecular semiconductor (77). In contrast to the wealth of literature describing porphyrin and pc sandwich complexes, re-... 

A review of the stabilities and catalytic properties of binuclear metal complexes of large-ring N,0 macrocycles concentrates on the iron(II) and iron(III) complexes of (184) and (185). ... 

For the alkali metal cations, the stability (14) and permeability (43) sequences for dicyclohexyl-18-crown-6 have been found to be the same (K+ > Rb+ > Cs+ > Na+ > Li+). Thus, a direct relationship exists between the ability of a macrocyclic compound to complex a particular cation (as measured by the log K value for complex formation) and its influence on the biological transport of that cation. Furthermore, it would appear that the biological ion-transport mechanism may in part be due to the complexation properties of the macrocyclic carrier molecules. This subject with respect to cyclic antibiotics has been treated extensively by Si wow and co-workers (2). 

Although there has heen a great deal of research concerning how platinum(II) complexes hind to biological molecules and the hkely mechanism of antitumor activity of these platinum-containing species, far less attention has heen paid to the properties of other metal complexes in this arena. Recent attention has fallen on cohalt(II)-Schiff hase complexes, as several have heen discovered to have promise as antiviral agents. A review of recent work has appeared elsewhere [64], so the topic will not he covered here however, in addition to focusing on recent developments, emphasis is placed on the introduction of the new head unit, 3,6-diformylpyridazine (13), into Schiff-hase macrocyclic electrochemistry. 

This group of compounds is widely found in nature as metal complexes in the chlorophylls, the haem groups of many iron proteins and the corrinoids. They have in common a macrocyclic structure which provides four N donor atoms at the comers of a square plane. Metal coordination to the N atoms results in the displacement of two H+ ions. An extremely important feature of these molecules is their extensive -electron delocalization. The complexation of these and synthetic analogues has been the subject of a number of texts.143-145 Some of these aspects are also covered by Dolphin (Chapter 21,1), and biological related properties by Hughes (Chapter 62.1). 

---