Polydentate ligands synthesis

Other Compounds with Polydentate Ligands Synthesis of Ca, Sr, and Ba... 

The synthesis of di- or tri-nudear pentafluorophenyl derivatives by the use of polydentate ligands with [AulCgFsjltht)] is quite a general procedure as shown in Table 3.4. Many of these complexes have been characterized by X-ray diffraction and show short Au Au contacts as in [(CgFsjAulSdppmSjAulCfiFs)] [88] of 3.163(1) Aor in the dinuclear complex [57] shown in Figure 3.8 of 3.4671(9) A. 

Another novel synthesis of phenazines was introduced by Vagg and co-workers <00JHC151>. The key step was the reaction of dicarboxylic acid 230 with various 1,2-diamines to give 231, 232, and 233. Each was a potential polydentate ligand capable of interacting with DNA via their extended phenanthroline or phenazine components. 

Immobilization of phase-transfer catalysts on polymeric matrices avoids the problem of separating and recycling the catalysts. In this case the chemical stability of the immobilized catalyst becomes very important quaternary salts often decompose under drastic reaction conditions whereas polydentate ligands are always stable. However, the difficult synthesis of cryptands, despite their high catalytic efficiency, can hardly justify their use. Synthesis of crown-ethers is much easier, but catalytic efficiences are often too low. 

The possibility of generating a 1 1 complex of aluminium by tethering together three aryloxide moieties has been explored. Synthesis [165] of the tripodal, polydentate ligand N[2-[(CH2)2N(H)CH2]-Ar 3 (Ar = 4-chlor-ophenol) allows subsequent treatment with one equivalent of (H20)9 A1(C104)3 in the presence of excess (H20)3 NaOAc to afford a tris(phen-oxide) complex [166]. More recently, the formation of Al-N(H) interactions has been precluded in the tris(2-hydroxybenzoyl)-2-aminoethylamine and tris(2-hydroxy-3-methoxybenzoyl)-2-aminoethylamine trianion complexes... 

Among the NHC ligands with N-substituents containing centers of chirality, polydentate ligands that combine the NHC unit with an anionic functional group have been developed recently. They thus combine two complementary ligating anchor units, which avoids the rotation of the chiral substituents around the C - N axis. Arnold and coworkers reported the synthesis of the... 

This section describes the synthesis as well as chemical and physical properties of Group 2 metal /3-diketonate compounds that also contain coordinated polydentate ligands to prevent oligomerization. 

The final part of the synthesis and properties section of this review addresses other alkaline-earth complexes containing mono-, bi-, or polydentate ligands and anionic ligands such as carboxylates, halides, thiocyanates, or nitrates, where the low degree of oligomerization may result in sufficient volatility for CVD. We have not attempted to be comprehensive in this section, but rather to present examples of the different types of compounds formed by these anionic ligands. More comprehensive coverage of this area can be found elsewhere.74170 223 224... 

Soluble low-valent metal alkoxides can also be synthesized by replacing small alkoxy group OR by bulky polydentate ligands such as 2-methoxyethanol CH3OC2H4OH. This solvent is currently used to prevent polymerization and get soluble molecular precursors with low-valent metal cations such as Cu + in the sol-gel synthesis of advanced ceramics such as high Tc superconductors YBa2Cu307 j (see Sulfur Organic Polysulfanes) ... 

Neutral polydentate ligands are widely used for the synthesis of coordination compounds of transition metal ions. -i When different synthetic routes are possible for a given ligand, those which give the highest yields with the least number of steps and minimize the number of possible isomeric or by-products will obviously be preferred. The above criteria may be exemplified by a series of neutral tetradentate ligands of the tripod or umbrella type with a nitrogen atom as the top donor these may be described as 2-substituted triethylamine derivatives (I) ... 

The synthesis of cahx[4]arene dimelamines with different functionalities and their self-assembly with barbituric and cyanuric acid to hydrogen-bonded nanostructures have been published <05OBC3727> Unique ionophores of penta-crown ethers have been prepared by the reaction of l,3,5-triacryloylhexahydro-l,3,5-triazine (TAHTA) with diaza 18-crown-6 followed by Michael addition, and their binding capabilities towards alkali metal cations studied <05SL2257>. New silver complexes of polydentate ligands including a derivative of pyrazol-l-yl-l,3,5-triazine have been reported <05EJ14370>. 

Chirality is often met with polydentate ligands at a number of different centres in the complex, and separation of all optical isomers is either impractical or, in effect, impossible. In many cases, working with a racemate has no significant influence on the chemistry, and optical resolution of complexes is attempted on only very limited occasions, such as where researchers wish to record the chiroptical properties, or where a chiral complex is required to assist in achieving a chiral reaction, such as use of a chiral complex as a catalyst in synthesis of organic molecules where a particular optical isomer is sought (exemplified in Chapter 9). 

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