Electrochemical potential ligands

Transition metal centered bond activation reactions for obvious reasons require metal complexes ML, with an electron count below 18 ("electronic unsaturation") and with at least one open coordination site. Reactive 16-electron intermediates are often formed in situ by some form of (thermal, photochemical, electrochemical, etc.) ligand dissociation process, allowing a potential substrate to enter the coordination sphere and to become subject to a metal mediated transformation. The term "bond activation" as often here simply refers to an oxidative addition of a C-X bond to the metal atom as displayed for I and 2 in Scheme 1. 

Scheme 4.10. Calalyttc cycle for the reduction of alkyl halides by cobalamins. The outer circle represents the combined photo and electrochemical process, "fhe inner shunt is the wholly electrochemical process at more negative potentials. Ligands are omitted for clarity.

In summary, the direct redox reactions can be largely used in the preparation of bimetallic catalysts with a close interaction between the metallic constituents. In that case a metal with a high electrochemical potential is deposited on a metal with a lower potential. The applicability of the technique can be extended significantly by using different ligands which, by chelating metallic ions, modify the standard electrochemical potentials. 

Redox potential-electronic sttucture relationships in 18-and 17-electron mononitrile complexes of Re have been established. It was possible to estimate, for the nitrile and related ligands, for example, in complexes (3-6), the values of the electrochemical Pl ligand parameter, a measure of the net electron donor minus tt-acceptor character of a ligand. The... 

Ligand. The redox potential of the single silver atom solvated in water was calculated with the aid of a thermodynamic cycle including the electrochemical potential of the bulk metal in aqueous solution and the subhmation energy of the metal (3). The hydration energy of the neutral species is considered neghgible relative to that of the cation. 

The cyclic voltammograms (CV) of the bipyridine nitrosyl ruthenium complexes may reveal multiple couples resulting from redox processes centered at the metal, the nitrosyl ligand, and the bpy ligands. Two couples are evident in the CV electrochemical potential range of +1.0 to —1.0 V vs. Ag/AgCl of a 5/ira s-[Ru(bpy)2L(NO)] complexes in organic solvent or aqueous solution. The reduction peak at the more positive value is chemically reversible, whereas the second reduction peak is practically irreversible in the CV time scale such peaks correspond to the NO "° and pro-... 

Since an MLCT excitation effectively involves oxidation of the metal and reduction of the ligand (or vice versa for LMCT), i.e., for example, a formal ground state M L generates an MLCT excited state M L , it has long been known that these charge transfer energies should correlate with electrochemical potentials. ... 

A second major application is in design - the ability to synthesize a molecule with predetermined redox potentials or spectroscopic absorption. For example, by using a selection of different ligands attached to the central ion, fine tuning of the electrochemical potentials and optical spectrum can be achieved. " ... 

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