Pseudohalides metal complexes

One successful strategy for ligand substitution by ion exchange involves the use of halide or pseudohalide metal complexes as starting materials in reactions with silver salts that contain the anion that is to be introduced as a new ligand. Since the solubility of silver halides in nonpolar, aprotic solvents is low (see Table 3.1), ion exchange in solvents of poor donor ability typically occurs according to Eq. 5.1 ... 

Most hydrated metal ions are more soluble in water than in ILs. The distribution ratios of some metal ions between aqueous and IL phases may be enhanced in the presence of coordinating anions, such as halides or pseudohalides, capable of modifying the metal complex hydrophobicity, increasing partitioning from water [41]. 

The effect of halide, cyanate, cyanide, and thiocyanate ions on the partitioning of Hg in [BMIM][PF6]/aqueous systems (Figure 3.3-2) has been studied [8]. The results indicate that the metal ion transfer to the IL phase depends on the relative hydrophobicity of the metal complex. Hg-I complexes have the highest formation constants, decreasing to those of Hg-F [42]. Results from pseudohalides, however, suggest a more complex partitioning mechanism, since Hg-CN complexes have even higher formation constants [42], but display the lowest distribution ratios. 

There is considerable and widespread interest in the metal complexes of these anions and current research topics comprise for example (i) the spectroscopic study of the binding in these anions (linkage isomerism) and their complexes, (ii) the synthesis of regular polymers of their transition metal complexes and study of the semiconducting properties of these polymers, (iii) the use of the pseudohalides in pharmacological (e.g. low toxicity of —SCN) and biochemical studies (easy complexation of SCN- to metals), and (iv) the use of the activation of these triatomic anions by coordination to metals for their selective conversion in organic synthesis. 

Examples of side on bonding, i.e. involvement of the a-electrons, have not been established. This type of metal-ligand bonding is often encountered in metal complexes of the organic pseudohalides such as RNCS. 

Innovations in the chemistry of aromatic compounds have occurred by recent development of many novel reactions of aryl halides or pseudohalides catalysed or promoted by transition metal complexes. Pd-catalysed reactions are the most important [2,29], The first reaction step is generation of the arylpalladium halide by oxidative addition of halide to Pd(0). Formation of phenylpalladium complex 1 as an intermediate from various benzene derivatives is summarized in Scheme 3.1. 

Diorganyl tellurides are starting materials for the preparation of diorganyltellurium dihahdes, pseudohalides, and carboxylates, of telluroxides, and of teUuronium salts, and are used as ligands for the synthesis of transition metal complexes. 

There are essentially two possibilities to accomplish two-electron or multielectron transfer at metal complexes without formation of one-electron transfer intermediates (e.g., radicals). Appropriate metal centers should have available stable oxidation states that differ by at least two emits. T5rpical examples that represent such photoredox reactions are reductive eliminations such as (X = halide, pseudohalide) (5) ... 

Detailed crystal structures of only a few of the other heavy metal pseudohalides are available in the literature. Among them are, cuprous azide which has a relatively simple tetragonal lattice and cupric azide, mercuric fulminate and a-lead azide which have increasingly complex orthorhombic lattices. a-Lead azide has four types of anion sites of varying amounts of as5nnmetry (33) while cupric azide (35) and mercuric fulminate (72) have two such sites. The structure of cupric azide which is built up of distorted octahedra of asymmetric Ns ions about the central cupric ion is analogous to that of a transition metal complex. 

Transition Metal Complexes Containing Bidentate Phosphine Ligands W. Levason and C. A. McAuliffe Beryllium Halides and Pseudohalides... 

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