Complex monodentate

The CK" ion can act either as a monodentate or bidentate ligand. Because of the similarity of electron density at C and N it is not usually possible to decide from X-ray data whether C or N is the donor atom in monodentate complexes, but in those cases where the matter has been established by neutron diffraction C is always found to be the donor atom (as with CO). Very frequently CK acts as a bridging ligand - CN- as in AgCN, and AuCN (both of which are infinite linear chain polymers), and in Prussian-blue type compounds (p. 1094). The same tendency for a coordinated M CN group to form a further donor-aceeptor bond using the lone-pair of electrons on the N atom is illustrated by the mononuclear BF3 complexes... 

Another way to describe this non-cyclic phosphino methanide derivatives consists of theuse of monodentate complexes with themono-oxide [203] or monosulfide [204] dppm giving the methanide or methanediide derivatives (14) after addition of the appropriate amounts of [Au(acac)PPh3[. A mixed-valence Au(I)-Au(III) can be isolated by coordination of the fragment AuPPh3 to the free sulfur atom in the mono-oxide starting material [204]. 

Stability of the bidentate and multidentate complexes in aqueous solution [16] compared with monodentate complexes. Kinetic studies of gold(III) reactions with ethylenediamine and related ligands show that the initial displacement of one end of the chelate is most often followed by rapid reclosure of the ring, rather than displacement of the second bond to the metal ion [15]. 

Starting with (5) and (2), it was possible to isolate and characterize two stable unusnal complexes. This supports the premise of a bidentating structure. In comparison to monodentating complexes, (4a and 4b) those new complexes are expected to behave differently than that of catalysts mentioned in literature (1). 

Complexation is a phenomenon that involves a coordinate bond between a central atom (the metal) and a ligand (the anions). In a coordinate bond, the electron pair is shared between the metal and the ligand. A complex containing one coordinate bond is referred to as a monodentate complex. Multiple coordinate bonds are characteristic of polydentate complexes. Polydentate complexes are also referred to as chelates. An example of a monodentate-forming ligand is ammonia. Examples of chelates are oxylates (bidentates) and EDTA (hexadentates). 

Mixed O, N donor molecules are truly extensive and structurally diverse, and only a few selected examples will be presented. In line with other 2-substituted pyridine analogs reported in this chapter, it is worthwhile noting the chemistry of 2-pyridone (or 2-hydroxypyridine, Hopy), which can form O-bonded monodentate complexes such as Co(Hopy)4(N03)2, but as the monoanion is an effective chelate ligand, forming Co(opy)2 and Co(bpy)(opy)2 compounds.454 An unusual solid state melt reaction with Co(OAc)2 yields the dodecanuclear cluster Co12 (OH)6(OAc)6(opy )12.455... 

The effect of pKa on the stability constant of the 1 1 monodentate complexes of Me3 SnX with amino acids in aqueous solutions was studied by potentiometric methods281. 

Such bidentate chelation is found to be favored over monodentate complexation in many cases, this being the so-called chelate effect. ... 

Fig. 29. Geometry-optimized structure of the three stable Ti-peroxo intermediates (a) rj1-monodentate complex, (b) i72-bidentate complex, and (c) i71-02H2 complex [from Cora et al. (59)].

Carbohydrates have found widespread use as chiral auxiliaries in asymmetric Diels-Al-der reactions156. A recent example is a study conducted by Ferreira and colleagues157 who used carbohydrate based chiral auxiliaries in the Lewis acid catalyzed Diels-Alder reactions of their acrylate esters 235 with cyclopentadiene (equation 66). Some representative results of their findings, including the ratios of products 236 and 237, have been summarized in Table 9. The formation of 236 as the main product when diethylaluminum chloride was used in dichloromethane (entry 3) was considered to be the result of an equilibrium between a bidentate and monodentate catalyst-dienophile complex. The bidentate complex would, upon attack by the diene, lead to 236, whereas the monodentate complex would afford 236 and 237 in approximately equal amounts. The reversal of selectivity on changing the solvent from dichloromethane to toluene (entry 2 vs 3) remained unexplained by the authors. 

Iridium 2-pyridinylmethyl imidazolylidene C,N-chelates were obtained by transmetallation of the silver carbene complexes and tested for catalytic activity in the TH of benzophenone and nitroarenes by isopropanol [55]. The neutral monodentate complexes [(L-KC)Ir(COD)Clj [61a,b L = l-methyl-3-(6-mesityl-2-pyridinylmethyl)-2-imidazolylidene, l-mesityl-3-(6-mesityl-2-pyridinylmethyl)-2-... 

ATR-FTIR data indicated that on goethite, glycophosphate adsorbs mainly as an inner-sphere, monodentate complex via the phosphonate group the carboxylate group does not appear to be involved in surface coordination in this case (Sheals et al 2002). 

The major structural types found for lithium amide complexes in the solid state are illustrated in Fig. 34. These comprise ladders of limited extent when the L Li ratio is less than 1 1 (Fig. 34a), dimeric (NLi)2 rings, when this ratio is 1 1 and, usually, when the complexants are monodentate (Fig. 34b), and monomers, both contact-ion pairs (CIPs) and solvent-separated ion pairs (SSIPs) (Fig. 34c). Monomers occur always when there are two or more monodentate complexants per Li. This also is usual with bidentate ligands, and is always found when the ligands have higher denticity. 

The substrate for many phosphotransferases is MgATP. Which of the possible isomers of this chelate complex is utilized by these enzymes Since Mg2+ associates and dissociates rapidly from the complexes there are several possibilities a tridentate complex with oxygens from a, (3, and y phospho groups coordinated with the metal ion, an a,(3-bidentate, a (3,y-bidentate, or a monodentate complex. Most evidence suggests that P,y-bidentate complexes of the following types are the true substrates. 

Numerous other aromatic nitrogen compounds are known, and a significant number have been used to prepare complexes of platinum(II). Phthalazine (101) is one such compound, and the complex ds-PtCl(phthalazine)(PEt3)2 has been prepared in order to compare its fluxional properties with the phenanthroline and naphthyridine analogues. The monodentate complex is fluxional, but in this phthalazine case the orientation of the lone pairs is unsuitable for the five-coordinate intermediate required by an intramolecular process and the mechanism of exchange becomes dissociative.11 6... 

Mikami has also reported a related ene-like process involving glyoxylates and ketone-derived enolsilanes 42 (Eq. 8B2.11) [17]. The enol ether adducts 43 yield the corresponding P-hydroxy ketone upon treatment with mild acid. On the basis of an analysis of the stereo- and regiochemical outcome of the addition reaction Mikami has invoked a monodentate complex between aldehyde and metal, in contrast to the typical transition-state structures involving glyoxylates that are suggested to involve metal/aldehyde chelates. 

Previous workers concluded that cadmium ions adsorb onto the goethite surface by the formation of bidentate surface complexes.11,12 However, the cadmium adsorption data and our calculations (see Figure 3) shows that cadmium adsorbs on goethite mainly on one surface hydroxyl group, forming monodentate complexes, according the following reaction ... 

The y-monodentate and bidentate Cr-ATP complexes can be prepared by heating Cr(H20) + salts with ATP, brief heating producing mainly y-monodentate and longer heating the /S,y-bidentate complexes [62], The y-monodentate Cr-ATP can be essentially quantitatively converted to the diastereomeric mixture of /J,y-bidentate complexes by heating briefly at pH 3. The diastereomeric mixture of a,/ ,y-tridentate Cr-ATP can be prepared by acid treatment of the / ,y-bidentate complexes. The diastereomeric mixture of Cr-ADP complexes have also been prepared by heating ADP with Cr(H20)j+ however, the / - and a-monodentate complexes have not been described. 

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