Ligand preference

The structures of several adducts can be rationalized on the basis [128] that in a 5-coordinate low-spin d8 tbp system, the acceptor ligands prefer to occupy an equatorial site (IrCl(CO)2(PPh3)2) whereas a 7r-donor prefers an axial site. In a square pyramidal situation, it is weakly bonded acceptors that prefer the apical position, e.g. (IrCl(S02)(C0)(PPh3)2. 

TABLE 5 Ligand Preferences for Metals Commonly Found in Metalloproteins... 

Ligands Preferred by Different Metal Ions in Simple Coordination... 

Ligand Preferences. The LVC s are electron rich and in order to exist in stable compounds they require ligands, such as CO, that are weak donors and good tt acceptors. On the other hand the HVC clusters are not attractive to such ligands nor do they require them for stability. In this respect, there is a direct parallel to mononuclear compounds where M° prefers CO, RNC or similarly ir-acidic ligands while the Mn+ (n = 2-4) ions do not generally form CO complexes. 

Ligand preference and possible coordination geometries of the metal center are important bioinorganic principles. Metal ligand preference is closely related to the hard-soft acid-base nature of metals and their preferred ligands. These are listed in Table 1.7.6... 

X — ligand, preferably chelate with O-donor atom, oxalate, NTA, citrate, EDTA, etc. 

Reductive eliminations can be promoted by stabilisation of the low-valent state of the product. This means ligands that are good K-acceptors, bulky ligands, and ligands preferring bite angles more suited for tetrahedral than for square-planar complexes, when we deal with group 10 metals. 

The other elements of group 10 and gold do not form stable binary carbonyls. The stabilization of carbonyl complexes of these elements requires the introduction of other ligands, preferably sigma-bonded, that is the compounds [Pd(CO)Cl2] , [Pt(CO)2Cl2] and [Au(CO)Cl] are relatively stable. 

EF hand domains, 46 442, 443-445 EGF-like domains, 46 471-479 extracellular, 46 442, 470-485 intracellular, 46 442, 443-456 ligand preferences, 46 442 binding sites, 42 113-114 biological coordination chemistry, 46 442 biological roles, 46 441-442 cation, nuclear properties, 27 11 complexes... 

An explanation could be achieved by the consistent application of the mechanistic concepts used to explain data at tetravalent phosphorus compounds (48). Most of the available data on nucleophilic displacements are usually explained by an apical entry of the nucleophile displacement of the leaving group occurs from an apical position (Scheme 3). The first invoked TBP intermediate is the most stable one on the basis of the relative apicophilicity of the groups attached to phosphorus the more electronegative ligands prefer apical positions. Since both inversion and retention can proceed, the retention pathway has been rationalized on the basis of intramolecular ligand exchange by pseudorotation (Scheme 3). 

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