Coordination of ligands

The coordination of ligands at the surface of metal nanoparticles has to influence the reactivity of these particles. However, only a few examples of asymmetric heterogeneous catalysis have been reported, the most popular ones using a platinum cinchonidine system [65,66]. In order to demonstrate the directing effect of asymmetric ligands, we have studied their coordination on ruthenium, palladium, and platinum nanoparticles and the influence of their presence on selected catalytic transformations. 

The chemistry of the multistep reactions of Ti+ with propylene was also examined. Bare Ti+ exhibits an active reactivity toward breaking C-H bonds of the alkene molecules. But, the coordination of ligands on Ti+ was found to dramatically alter its dehydrogenation reactivity. For propylene, the multistep reactions were terminated at the fourth step, whereas the reactions with ethylene molecules were found to proceed far beyond the fourth step. Over 20 ethylene molecules have been... 

Several directed syntheses of catenanes have also been reported. One of these relies upon coordination of ligands to a metallic ion to achieve the proper geometry. An example is shown in Figure 19.1,729 2,9-Bis(/7-hydroxyphenyl)-l, 10-phenanthroline 40 is converted to the macrocycle 42 by treatment with the polyether 41, in a Williamson reaction, under... 

The sole coordination of the phosphine sites has also been observed with PBs featuring the flexible (CH2)2 linker. The coordination of ligands 40e and 40f to the [Ru(p-cymene)Cl2] fragment affords complexes 74a and 74b (Scheme 44). Despite the modest steric hindrance around boron, neither Cl-B (coordination mode F) nor Ru-B (coordination mode FI) interaction was found. Coordination mode E was established spectroscopically (8nB = 82 and 87 ppm for 74a and 74b, respectively) and confirmed crystallographically.55... 

In addition to the mimicking of natural enzymes, a fascinating goal in supramolecular chemistry is the development of entirely artificial catalysts. While both heterogeneous and homogeneous catalysts based in particular on coordination of ligands to transition metals are common, supramolecular catalysts use either exclusively, or in addition, some aspect of molecular recognition and non-covalent... 

Scheme 1.3.3. Stabilization of a loop-type structure at a tripeptide by coordination of ligand 3 to the MoC>22+ fragment.

The addendum to the Tresent Status summary discussed the matter of locant designators (Rule 11), the coordination of ligands in less than their maximum functionality (Rule 13), abbreviations (Rule 16), and the coordination of tautomeric forms of a ligand. 

Kawaguchi, S. In Variety in Coordination of Ligands in Metal Complexes Inorganic Concepts Kawaguchi, S., Ed. Springer Verlag, Berlin, 1988, Vol. 11, pp 75-119. 

Bulky ligands are especially useful for synthesizing highly reactive, coordinatively unsaturated complexes such as PtL2 and Ru(CO)2L2 [9], since they prevent further coordination of ligands and/or oligomerization which would normally occur to satisfy the 18 electron rule. However, one should not ignore the electronic factors for the structural consideration, since they essentially determine the structure of transition metal complexes. 

In this section we introduce some general principles concerning the coordination of ligands to ions in aqueous solution. These definitions and principles will be used again when we discuss complex formation in detail later in the book. The... 

If a concerted three-center oxidative addition mechanism is realized (path b), first a lone electron pair of an atom X (X = O, N) is used to form the M-X bond resulting in a complex 5 (step bi). Formation of the M-C bond and cleavage of the C-X bond constitute a concerted process resulting in a five coordinate intermediate, which can be stabilized by coordination of a solvent molecule (Sol) as in structure 6 (step b-2) similar to 4. Finally, by coordination of ligand L, the intermediate 6 can produce an octahedral reaction product (step b ) shown in Fig. 3, b. The configuration of the carbon atom present in R-Z is retained during oxidative addition to the metal. 

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