Coordinating ability

A large variety of salts of triflic acid formed both from metals and nonmetals are known Many of these salts are versatile reagents for organic synthesis because of such properties of the tnflate anion as very low nucleophilicity and low coordinating ability However, despite low nucleophilicity, the triflate anion can combine with carbocationic intermediates under appropriate conditions to form triflate esters [116, 117, II8. ... 

Exciting developments have occurred in the coordination chemistry of the alkali metals during the last few years that have completely rejuvenated what appeared to be a largely predictable and worked-out area of chemistry. Conventional beliefs had reinforced the predominant impression of very weak coordinating ability, and had rationalized this in terms of the relatively large size and low charge of the cations M+. On this view, stability of coordination complexes should diminish in the sequence Li>Na>K>Rb> Cs, and this is frequently observed, though the reverse sequence is also known for the formation constants of, for example, the weak complexes with sulfate, peroxosulfate, thiosulfate and the hexacyanoferrates in aqueous solutions. 

Because of its generally rather weak coordinating ability quite small changes can determine whether... 

Those in which solvent molecules are directly involved in formation of the ion association complex. Most of the solvents (ethers, esters, ketones and alcohols) which participate in this way contain donor oxygen atoms and the coordinating ability of the solvent is of vital significance. The coordinated solvent molecules facilitate the solvent extraction of salts such as chlorides and nitrates by contributing both to the size of the cation and the resemblance of the complex to the solvent. 

A very few coordination complexes of tetramethylene sulphone [(CH2)4S02] with transition metal ions have been prepared, and the coordinative ability of sulpholane is generally regarded as quite weak224,225. Sulpholane metal complexes should therefore serve as excellent precursors of the coordination compounds containing other weakly nucleophilic ligands. 

In addition to influencing the reactivity, the coordinating ability of the solvent affects the mechanism of CO insertion. Thus, when a poorly coordinating solvent is employed together with a good nucleophile L, the... 

This is intimately related to the nature of the solvent. If the solvent is nonpolar and lacks coordinating ability, then generally [known exceptions are the Pt(II) and Ir(III) complexes mentioned in Section B] the insertion will proceed via attack of L upon the alkyl compound ( 2 path), e.g.. Table I, reaction 6. 

Kinetic studies have been made of the reaction of CpMo(CO)j R (R = Me, Et, CH2Ph, and CH2CH=CH2) (48, 80, 81) and 7r-X2C9H5Mo(CO)jMe (X = H or OMe) (108) with a variety of P donor ligands L. Solvents employed ranged from nonpolar hexane to polar THF and MeCN. Generally, the mechanism is very sensitive to the coordinating ability of the solvent and the nucleophilicity of L. 

It seems reasonable to believe that this problem could be overcome by studying more coordinating ligands with the same structural features. Very recently, it has been demonstrated [56] that the use of iminobis(oxazolines) (Fig. 18) leads to better enantioselectivities and recoverable catalysts, both with laponite and nalion-silica supports (Table 8). Theoretical calculations are consistent with the stronger coordinating ability of iminobis(oxazolines) being the origin of these results [57]. 

In summary the simultaneous reduction method usually provides alloyed bimetallic nanoparticles or mixtures of two kinds of monometallic nanoparticles. The bimetallic nanoparticles with core/shell structure also form in the simultaneous reduction when the reduction is carried out under mild conditions. In these cases, however, there is difference in redox potentials between the two kinds of metals. Usually the metal with higher redox potential is first reduced to form core part of the bimetallic nanoparticles, and then the metal with lower redox potential is reduced to form shell part on the core, as shown in Figure 2. The coordination ability may play a role in some extent to form a core/shell structure. Therefore, the simultaneous reduction method cannot provide bimetallic nanoparticles with so-called inverted core/ shell structure in which the metal of the core has lower redox potential. 

The phosphine-based platinum(O) catalysts do not catalyze the diboration of alkenes because of the high coordination ability of phosphine over the alkene double bond, but platinum(O) complexes without a phosphine ligand such as Pt(dba)2 [128] and Pt(cod)2 [129] are an excellent catalyst allowing the alkene insertion into the B-Pt bond under mild conditions (Scheme 1-30). The diboration of aliphatic and aromatic terminal alkenes takes place smoothly at 50°C or even at room temperature. The reaction is significantly slow for disubstituted alkenes and cyclic alkenes, but cyclic alkenes having an internal strain afford ds-diboration products in high... 

These rod-shaped ligands share a sterically efficient terminal N-donor and their divalent Co chemistry is well established. They will be discussed here only with selected examples. [Co (NCMe)6](TFPB)2 (TFPB- = tetrakis(3,5-bis(trifhioromethyl)phenyl)borate)) has been synthesized and characterized in the solid state along with a number of other divalent transition metal analogs.357 As a result of the extremely poor coordinating ability of the anion and facile loss of MeCN ligands from the cation, the salt is an excellent source of naked Co2+ ions. Thermolysis up to 100 °C leads to the loss of one MeCN and formation of a r -bound nitrile, whereas above 130 °C decomposition occurs with loss of MeCN and abstraction of fluoride from the anion to form CoF2. 

Mixed N,S,0 donor sets are useful to compare the coordination ability and the structural consequences of various donor sets and to induce a variety of structural properties. The solid-state structures of [Ni(pyzs)]BF4, [Ni(pyrs)]BF4 and [Ni(pyzo)]BF4 containing dissymetric tetradentate ligands with N2S2 (543) and N2SO (544) donor sets are square planar.1397 The phenolate-based complexes are essentially planar in nitromethane, but distorted octahedral in methanol, while thiophenolate-containing complexes remain square planar in both solvents. 

Insertion of a thioamide (0[CSNH]) bond into a peptide backbone with noncoordinating side chains increases distinctly the coordination ability of the peptide toward Ni11. The thioamide sulfur is a much more potent donor than the carbonyl-O and it is a basic donor for Ni11 ion coordination around physiological pH.1764... 

To explore the coordination abilities of mixed phenol-bpy/phen/terpy polydentate chelating ligands, Ward et al. investigated complexes (319) (Cu-Cu 3.050 A moderate AF coupling),281,282 (320) (moderate AF coupling),283 and (321) (Cu-Cu 3.324 A weak AF coupling).28... 

The preparation of ZnSe materials is an area of interest and study. The coordinating ability of the solvent used in the solvothermal synthesis of zinc selenide was demonstrated to play an important role in the nucleation and growth of nanocrystalline ZnSe.604 Thermolysis of bis [methyl( -hexyl)di-seleno]carbamato]zinc gave highly monodispersed particles characterized by electronic spectroscopy, photoluminescence, X-ray diffraction, and electron microscopy.605... 

The true role of incorporation of anions in the formation of anodic alumina is being intensively discussed. Baker and Pearson183 have considered the anion effect in modifying the structure of anodic oxides to be due to the coordinative ability of anions to replace alumina tetrahedra in the body of the oxides. Dorsey184,185 has postulated that in porous oxides, anions stabilize the network of alumina tetrahedra and octahedra. 

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