Ligands ionic

Since no special ligand design is usually required to dissolve transition metal complexes in ionic liquids, the application of ionic ligands can be an extremely useful tool with which to immobilize the catalyst in the ionic medium. In applications in which the ionic catalyst layer is intensively extracted with a non-miscible solvent (i.e., under the conditions of biphasic catalysis or during product recovery by extraction) it is important to ensure that the amount of catalyst washed from the ionic liquid is extremely low. Full immobilization of the (often quite expensive) transition metal catalyst, combined with the possibility of recycling it, is usually a crucial criterion for the large-scale use of homogeneous catalysis (for more details see Section 5.3.5). 

The Lewis bases attached to the central metal atom or ion in a d-metal complex are known as ligands they can be either ions or molecules. An example of an ionic ligand is the cyanide ion. In the hexacyanoferrate(II) ion, [Fe(CN)6]4, the CN- ions provide the electron pairs that form bonds to the Lewis acid Fe2+. In the neutral complex Ni(CO)4, the Ni atom acts as the Lewis acid and the ligands are the CO molecules. 

Monoketones are poor ligands. Di-2-pyridylketone ((py)2C O) accommodates this deficiency in an unusual way when it reacts with Co(OAc)2 to form clusters, including [Co4(HQ)4(0 Ac)4] II20, where the monodeprotonated hydrated gem-diol form of the ketone (HQ-) (Equation (5)) binds as an ionic ligand.423 This cluster adopts a tetranuclear cubane shape with four deprotonated O atoms of the diol occupying the alternating vertices to the Co ions. 

Ionic ligand-functionalized resins suitable for use in recovering rhodium from polar and non-polar liquid solution starting materials in accordance with the present invention can be prepared simply by contacting under ambient conditions an anion-exchange resin with an acidic or acidic salt derivative of an organo-... 

The possibility of adjusting solubility properties is of particular importance for liquid-liquid biphasic catalysis. Liquid-liquid catalysis can be realised when the ionic liquid is able to dissolve the catalyst, especially if it displays partial solubility of the substrates and poor solubility of the reaction products. Under these conditions, the product phase, which also contains the unconverted reactants, is removed by simple phase decantation. The ionic liquid containing the catalyst can then be recycled. In such a scenario the ionic catalyst solution may be seen as part of the capital investment for a potential technical process (in an ideal case) or at least as a working solution (only a small amount has to be replaced after a certain time of application). A crucial aspect of this concept is the immobilisation of the transition metal catalyst in the ionic liquid. While most transition metal catalysts easily dissolve in an ionic liquid without any special ligand design, ionic ligand systems have been applied with great success to... 

A summary of the research activities of the last four years reveals three different important trends (a) The design of new ionic ligands for excellent catalyst immobilisation in ionic liquids and high regioselectivity (b) the successful application of cheap, halogen-free ionic liquids in the biphasic Rh-catalysed hydroformylation (c) the successful development of unusual multiphasic reaction concepts for Rh-catalysed hydroformylation, namely catalysis in ionic liquid/supercritical C02 and SILP-catalysts. 

The above results appear to indicate that the chemistry of zero-valent model carbene systems does not adequately reflect the behavior of conventional active metathesis catalysts having intermediate oxidation states and bearing ionic ligands. 

To illustrate the dependence of hypervalency on steric and electrostatic factors, let us consider cu-additions of neutral or ionic ligands to [PtF4]2+, a duodectet-rule-conforming Pt(VI) species with Lewis-like formula... 

Noteworthy is the activity of the catalyst with the zwitter-ionic ligand 4, in which the P atoms are also separated by 3 atoms [102]. 

In the case of rare earths r changes more sharply than R, and Dq value decreases in the series. This change should be less marked for water because the metal-ligand distance is smaller and appears to a higher power than in the case of an ionic ligand. 

No detailed studies on catalyst degradation pathways in ionic liquids have yet been reported. Due to the reaction of [PF6] with water, transformation of P(OR)3 to P(OR)nF3.n has been observed/471 In the case of aqueous biphasic catalysis with TPPTS as ligand, it is known that migration of a phenyl ring and ultimately elimination of sulfonated phenyl derivatives can take place/59,601 However, when suitable (ionic) ligands are employed, the catalyst can remain active for more than 10 cycles and may be stable for more than 14 days under air/4 1... 

When metal cations are placed in aqueous solutions two kinds of spheres normally appear (a) a sphere of water molecules that binds directly to the metal, called inner coordination sphere (or simply, inner sphere), and (b) a more loosely bound group of water molecules (not directly bound to the metal), called outer coordination sphere (or simply, outer sphere). In this way, a cationic complex can have an outer sphere interaction with an ionic ligand or a solvent molecule without displacing the inner ligands directly bonded to the metal. At higher anion concentrations, the outer sphere complex [M(H20)6]n+An is more prevalent than its corresponding inner sphere complex, [M(H20)5A], Interestingly, the number of inner-... 

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