Ligand ambidentate

The S-donor ligands SO, S2O2 and SO2 are mentioned in Section 15.2.5 and S-N ligands in Section 15.2.7. Thiocyanate (SCN ) is ambidentate. but towards heavier metaLs it... 

Ambidentate ligands possess more than 1 donor atom and can coordinate through either one or the other. This leads to the possibility of linkage isomerism (p. 920). The commonest examples are the ions NO2 (p. 463) and SCN (p. 325). Such ligands can also coordinate via both donor sites simultaneously, thereby acting as bridging ligands. 

This is in principle possible in any compound containing an ambidentate ligand. However, that... 

It should be noted that, by convention, the ambidentate ligand is always written with its donor atom first, i.e. NO2 for the nitro, ONO for the nitrito, NCS for the A-thiocyanato and SCN for the 5 -thiocyanato complex. Differences in infrared spectra arising from the differences in bonding are often used to distinguish between such isomers. 

Bis(phosphonio)isophosphindolium cations were expected to act as attractive ambidentate ligands toward the transition-metal-containing moieties. These expectations did not materialize with respect to CpM(CO)3 (M = Mo, W), since the anionic metathesis occurred to yield the ionic products 178 (96PSS125). 

DMSO is an ambidentate ligand, capable of coordinating via either S or O. The m-isomers have three S-bound and one O-bound ligand while in the Ira/w-isomers all are S-bonded IR spectra show the presence of both S-and O-bound DMSO in the m-isomers with absorption owing to i (S-O) around 1100 cm-1 (S-bonded) and 930 cm-1 (O-bonded), while the trans-isomers only have i (S-O) around 1100 cm-1 (Figure 1.38). 

An ambidentate ligand has the choice of using two different types of donor atom. Two that have been extensively studied in their bonding to platinum and palladium are sulphoxides and thiocyanate. 

A number of general features in Table 1-3 is apparent. Complexes may be cationic, neutral or anionic. Ligands may be simple monatomic ions, or larger molecules or ions. Many ligands are found as related neutral and anionic species (for example, water, hydroxide and oxide). Complexes may contain all of the same type of ligand, in which case they are termed homoleptic, or they may contain a variety of ligand types, whereby they are described as heteroleptic. Some ligands such as nitrite or thiocyanate can coordinate to a metal ion in more than one way. This is described as ambidentate behaviour. In such cases, we commonly indicate... 

Keywords Group 13 metals (aluminum, gallium, indium, thalhum), Ambidentate ligands. Phosphorus-nitrogen bidentate ligands, Pyridyl phosphanes, Aminoiminophosphoranes, Lewis acid catalysis... 

Thus it appears that the presence of two soft carbons on the palladium stabilizes the trans coordination of hard ligands and drives the selective coordination of ambidente ligands through their hardest atom. These results, as those described in the previous scheme, constitute other examples of the antisymbiotic effect which can be observed in soft palladium(II) complexes. 

Thiocarbamate (tc, RHNCSO-) is a monodentate ambidentate ligand, and both oxygen- and sulfur-bonded forms are known for the simple pentaamminecobalt(III) complexes. These undergo redox reactions with chromium(II) ion in water via attack at the remote O or S atom of the S- and O-bound isomers respectively, with a structural trans effect suggested to direct the facile electron transfer in the former.1045 A cobalt-promoted synthesis utilizing the residual nucleophilicity of the coordinated hydroxide in [Co(NH3)5(OH)]2+ in reaction with MeNCS in (MeO)3PO solvent leads to the O-bonded monothiocarbamate, which isomerizes by an intramolecular mechanism to the S-bound isomer in water.1046... 

The choice of tridentate amine has a critical impact on the coordination mode of the ambidentate nitrite ligand, N02.499,500 Complexes with substituted tri- and tetraamines have shown that bulky substituents may prevent the formation of the -N02 bridged polymeric complexes, and the intramolecular hydrogen network may stabilize N coordination of nitrite. 

A very special class of phosphorus based ligands are ambidentate, anionic phosphinomethanides I, since, due to the same number of valence electrons and bonds, both phosphorus and carbon are comparable in their reactivity and may compete for electrophiles. 

Amino acids are ambidentate ligands with N-donor and O-donor atoms, which exhibit abundant coordination modes. As shown in Scheme 1, there are six main coordination modes (a-f) for the amino acids ... 

An ambidentate ligand has the choice of using two different types of donor... 

Co3+ when bonded to five CN ligands that are soft, has become soft as a result of the symbiotic effect. Ligands with the ability to bond by using different donor atoms are known as ambidentate ligands. 

Many studies have been carried out on this reaction. Some of the unusual features of this reaction will be described in Chapter 20. Note that in writing the formulas for linkage isomers, it is customary to write the ligand with the atom that functions as the electron pair donor closest to the metal ion. Special consideration will be given in Chapter 20 to the behavior of cyanide complexes because CN-is also an ambidentate ligand. 

In the absence of steric effects, the effect of tt bonding that results from back donation is partially responsible for ambidentate ligands such as SCN bonding in different ways. For example, SCN is bonded differendy in the stable complexes cis-[Pt(NH3)2(SCN)2] and ds-[Pt(PR3)2(NCS)2]. In the first of these, the bonding is shown as... 

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