Cyclic metal containing

ROP reactions of cyclic metal-containing monomers have been utilized to prepare polymeric materials. This method has led to seminal advances in preparing high MW polymers with ferrocene in the mainchain. Ring-opening methods have led to enhanced control of polymer architecture. As with the other methods of polymerization, the metal can either be part of the cyclic structure or attached to an organic ligand bonded to the cychc system. 

The strength of this bonding depends on the kind of ether Simple ethers form relatively weak complexes with metal ions but Charles J Pedersen of Du Pont discovered that cer tain polyethers form much more stable complexes with metal ions than do simple ethers Pedersen prepared a series of macrocyclic polyethers cyclic compounds contain mg four or more oxygens m a ring of 12 or more atoms He called these compounds crown ethers, because their molecular models resemble crowns Systematic nomencla ture of crown ethers is somewhat cumbersome and so Pedersen devised a shorthand description whereby the word crown is preceded by the total number of atoms m the ring and is followed by the number of oxygen atoms... 

The presence of the cyclic backbone in ligands of this type makes a substantial contribution to their metal-ion complexing ability even though coordination involves donors which are not directly incorporated in the ring fragment. The origins of the enhanced stability of the metal-containing species may be considered to reflect the operation of an indirect macrocyclic effect (see Chapter 6) in these systems. 

There are two general classes of naturally-occurring antibiotics which influence the transport of alkali metal cations through natural and artificial membranes. The first category contains neutral macrocyclic species which usually bind potassium selectively over sodium. The second (non-cyclic) group contains monobasic acid functions which help render the alkaline metal complexes insoluble in water but soluble in non-polar solvents (Lauger, 1972 Painter Pressman, 1982). The present discussion will be restricted to (cyclic) examples from the first class. 

Cyclic compounds containing a heavier group 14 element, chalcogens, and a boron are prepared by the reaction of boron dichalcogenolates bearing a bulky substituent with group 14 metal dichlorides (Scheme 2).25... 

The six or seven-membered cyclic ethers that comprise the Brevetoxin subunits could be prepared by Mo-catalyzed RCM (Eq. 42) [13]. It is noteworthy that the most successful substrates were those in which R, =H and R2=Me. The first metal-containing intermediate in that circumstance therefore is likely to be that in which there is an oxygen bound to the alkylidene carbon atom yet that alkyli-dene behaves in a ring-closing reaction in the expected manner. 

This class of compounds, which includes 1,4,8,11-tetraazacyclotetradecane (otherwise known as cyclam), consists of a cyclic macrostructure containing four central nitrogen atoms. These nitrogens form a complex with a transition metal, holding it in the center of a square-planar configuration. Often, the cavity size formed by the macrocycle will stabilize one oxidation state of the transition metal over others due to the size of the metal center... 

Molecular metals are molecular solids with metallic electrical conductivity. Most molecular metals contain one-dimensional chains composed of stacks of two unsaturated cyclic molecules arranged alternately. The first one of this class discovered was TTF-TCNQ. The two molecules involved are tetrathiafulvalene (TTF) and tetracyanoquinonedimethane (TCNQ). These are depicted in Figure 6.7, which also shows how they are stacked in the crystal. 

In addition to the hydrolysis of monoesters of phosphoric acid, the hydrolysis of diesters of phosphoric acid is also susceptible to metal ion catalysis, in particular by multivalent cations such as barium, stannous, and cupric ions. The diesters which undergo metal ion-catalyzed hydrolyses include open-chain diesters and cyclic diesters containing both five- and six-membered rings (54). 

The D, A or PS units may be metal coordination centres. Metal to ligand charge transfer (MLCT) in metal complexes (such as Ru(n) or Re(l)-diimine centres) has been extensively used for generating PeT processes [8.64-8.68, A. 10, A.20]. Our own work has been concerned with photoinduced charge separation in macropoly-cyclic coreceptors containing both a photosensitive porphyrin group and binding sites for silver(i) ions as acceptor centres. Thus, complexation of silver ions by the... 

The THECOMAC database contains the stability constant, enthalpy, and entropy values for the complexations of the alkaline and alkaline earth metal cations with cyclic polyethers in water and organic solvents, and includes more than 3,500 records. Each record contains 22 textual and digital fields and 2D chemical structures of ligands. The database includes thermodynamic values for 330 cyclic polyethers containing oxygen coordination centers only.41... 

There is a long standing interest in the chemistry and the properties of cyclic compounds containing sulfur atom in modern material chemistry due to their redox chemistry. In particular, the focus has been on dithiole derivatives, e.g., dithiafulvenes and tetrathiafulvalenes, since the finding of metallic conductivity and low temperature superconductivity in radical cation salts. The quite low oxidation potentials of 1,4-dithiin compounds have been reported, recently [109]. On the other hand, thioketene dimers (2,4-bis(alkyli-dene)-l,3-dithietane) have been known for more than 100 years and synthesized by various methods [110-115]. The structure of these dimer compounds is similar to that of the redox-active sulfur compounds therefore, the potential electronic property of the thioketene dimer moiety is considerably attractive with the aim of application to a new and better -donor. 

Isslieb and Boettcher described a general procedure for the preparation of cyclic molecules containing the P—E—P functionality. The preparation involves reaction of metal phosphides with appropriate electrophiles, such as N,N-dichloroethylamine, to give 79 (76MI2). 

Conformational properties of a series of cyclic hexapeptides containing sarcosine have been described in Section 3.8.2. The interactions of these cyclic hexapeptides with metal salts will now be discussed in connection with their conformational properties (ii 9). 

Cyclic organoboranes containing mnltiple boron atoms within the ring stracture have been extensively stndied as precursors to (multidecker) transition-metal complexes and to nonclassical organoboranes (see Boron Metallacarbabo-ranes and Boron Polyhedral Carboranes). Earlier efforts have been thoroughly reviewed. Recently, a series of triboracyclopentane derivatives were reported by Bemdt and Schleyer (Scheme 6). " Reduction of these boracy-cles gave the nonclassical bishomoaromatic anions (28) and homoaromatic dianions (29). Related trishomoaromatic dianions obtained via reduction of 1,3,5-triboracyclohexane derivatives with lithium were studied by Siebert and Schleyer. i 5> ... 

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