Ligands entering

The lithium salt of 2-(di-wo-propylamino)-l,2-thiaborolide with [( -Cp ) RuC1]4 or [(i -Cp )ZrCl3] yields sandwiches similar to 39 (M = Ru, ZrCl2) (OOOM4935). The same anionic ligand enters a sequence of reactions with dimethylchlorosilane, lithium cyclopentadienyl, lithium di-wo-propylamide, and zirconium(IV) chloride to give sandwich 41. 

As a complex functions as a catalyst, it is often necessary for one ligand to enter the coordination sphere of the metal and another to leave (before or as the other ligand enters). These processes are substitution reactions, which were discussed in some detail in Chapter 20. As the catalytic processes are illustrated, it will be seen that some of the elementary steps are substitution reactions. A substitution reaction can be shown by the general equation... 

We have already mentioned a very strong dyadic association in the formally d5 cobalt complexes such as [Cp Co(dddt)]+ which dimerizes in the solid state to a fully diamagnetic dicationic dyad (Fig. 6a). It represents the extreme situation where the two radicals form a true 2e bond, with the sulfur atom of one dithiolene ligand entering the coordination sphere of the other metal. It should be considered as the consequence of the electron deficiency of these cationic [CpCo(dt)]+ 15-electron complexes. 

Palladium (II) chloride The ion Pd2+ has the configuration d which is also characteristic of many other soft acceptors, e.g. iridium(I), platinum (II) and gold(III). In the chloride system of Pd2+ the ligands entering are evidently aU bonded in the same manner, though the coordination around the d acceptor is square planar instead of tetrahedral as is amply proved by numerous investigations referring to solutions (65—67) as well as solids (68). 

The equilibria considered up to now have all involved inner sphere complexes. There is the possibility that an inner sphere complex may react with free ligands in solution this includes the solvent itself, to give an outer sphere complex where the ligand enters the secondary solvation shell of the inner sphere complex. If the two species involved in this type of interaction are of opposite sign, which is the situation where this type of complex formation is expected to be most effective, the outer sphere complex is called an ion pair. Fuoss65 has derived an expression (equation 38) for the ion pair formation constant, XIP, from electrostatic arguments ... 

Although not a complete explanation of these reactions, all the reported inversion reactions occur under conditions in which a conjugate base mechanism is possible. The orientation of the ligand entering the proposed trigonal-bipyramidal intermediate... 

F. 10.14. Formation of a clathrin-coated vesicle. Ligands entering the cell through receptor-mediated endocytosis bind to receptors that cluster in an area of the membrane. Adaptor proteins bind to the receptor tails and to the clathrin molecules to enclose the budding membrane in a cage-like clathrin coat. 

According to the burst model (37), the cell presumably moves away from equilibrium, and then bursts or pulses of free Zn(II) (or as complexes with water or small compounds like glutathione as ligands) enter the cytoplasm from the extracellular medium, and from the periplasm (prokaryotes) or subcellular compartments (eukaryotes) via the transporters mentioned above. This scenario is reminiscent of Zn(II) release into the synapse from nerve cells (35). The Zn(II) ions would then distribute into the cytoplasm and bind to newly-made, apo-Zn(II)-metalloproteins, to the ribosomes, etc., as well as to non-specific sites on proteins, amino acids, or nucleic acids. The cell apparently returns to equilibrium by the activities of the membrane-spanning Zn(II) transporters listed above. 

Ai l 15 enlarged side chains may bind ligands entering cavity... 

A certain complex of metal M is formulated as MCI3 3 H2O. The coordination number of the complex is not known but is expected to be 4 or 6. (a) Would conductivity measurements provide information about the coordination number (b) In using conductivity measurements to test which ligands are bound to the metal ion, what assumption is made about the rate at which ligands enter or leave the coordination sphere of... 

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