Metal ligand reactions

Chen, X.M. and Tong, M.L. (2007) Solvothermal in situ metal/ligand reactions a new bridge between coordination chemistry and organic synthetic chemistry. Accounts of Chemical Research, 40 (2), 162—170. 

If solution pH pKa(,v) of the ligand, significant complexation of the metal ion will tend to not occur if pH pK (.v). then extensive complexation will occur, and pM will not be strongly dependent on pH in this pH region. The behavior of pM at pH values close to the pK (.v) of the metal-ligand reaction system needs to be understood for each proposed metal ion-ligand system. 

The value of aM can be expressed readily in terms of the ammonia concentration and the formation constants for the various ammine complexes, as described for a general metal-ligand reaction in Feature 17-1. The result is an equation analogous to Equation 17-9 ... 

DYE LASER PHOTOCHEMICAL RELAXATION OF METAL-LIGAND REACTIONS... 

Similarly, a burgeoning literature on DOM fluorescence in aerosols is describing the abundance of atmospheric DOM with chemical properties similar to humic substances. The atmosphere also contains substantial amounts of metals in dust and photochemistry is important. Understanding the sources and reactivities of atmospheric DOM via fluorescence is important because of the many metal-ligand reactions that likely occur, some of which is clearly related to DOM photochemistry in the atmosphere. 

The equilibrium constant for a reaction in which a metal and a ligand bind to form a metal—ligand complex K ). 

The product of this reaction is called a metal-ligand complex. In writing the equation for this reaction, we have shown ammonia as NH3 to emphasize the pair of electrons it donates to Cd +. In subsequent reactions we will omit this notation. 

The formation of a metal-ligand complex is described by a formation constant, K. The complexation reaction between Cd + and NH3, for example, has the following equilibrium constant... 

The most important types of reactions are precipitation reactions, acid-base reactions, metal-ligand complexation reactions, and redox reactions. In a precipitation reaction two or more soluble species combine to produce an insoluble product called a precipitate. The equilibrium properties of a precipitation reaction are described by a solubility product. 

Mole-ratio plots used to determine the stoichiometry of a metal-ligand complexation reaction. 

The concentration of aluminum in serum can be determined by adding 2-hydroxy-1-naphthaldehyde p-methoxybenzoyl-hydrazone and measuring the initial rate of the resulting complexation reaction under pseudo-first-order conditions.The rate of reaction is monitored by the fluorescence of the metal-ligand complex. Initial rates, with units of emission intensity per second, were measured for a set of standard solutions, yielding the following results... 

Polyquiaolines have been used as polymer supports for transition-metal cataly2ed reactions. The coordinatkig abiUty of polyqukioline ligands for specific transition metals has allowed thek use as catalysts ki hydroformylation reactions (99) and for the electrochemical oxidation of primary alcohols (100). 

The side chains of the 20 different amino acids listed in Panel 1.1 (pp. 6-7) have very different chemical properties and are utilized for a wide variety of biological functions. However, their chemical versatility is not unlimited, and for some functions metal atoms are more suitable and more efficient. Electron-transfer reactions are an important example. Fortunately the side chains of histidine, cysteine, aspartic acid, and glutamic acid are excellent metal ligands, and a fairly large number of proteins have recruited metal atoms as intrinsic parts of their structures among the frequently used metals are iron, zinc, magnesium, and calcium. Several metallo proteins are discussed in detail in later chapters and it suffices here to mention briefly a few examples of iron and zinc proteins. 

From a historical perspective it is interesting to note that the Nozaki experiment was, in fact, a mechanistic probe to establish the intermediacy of a copper carbe-noid complex rather than an attempt to make enantiopure compounds for synthetic purposes. To achieve synthetically useful selectivities would require an extensive exploration of metals, ligands and reaction conditions along with a deeper understanding of the reaction mechanism. Modern methods for asymmetric cyclopropanation now encompass the use of countless metal complexes [2], but for the most part, the importance of diazoacetates as the carbenoid precursors still dominates the design of new catalytic systems. Highly effective catalysts developed in... 

Chiral ferrocenes have received niucli attenlion as ligands in metal-calalyzed reactions [39], bul tiieir use in copper cliemislry has been very limited [40, 41]. Hie ferrocene moiety offers die possibility of utilizing botli central and planar cliirality in die ligand. By analogy witli tlie copper arenetiiiolales described above, ferrocenyl copper complex 33 iSclieme 8.20) is extremely inleresling. 

In the light of these results, it becomes important to question whether a particular catalytic result obtained in a transition metal-catalyzed reaction in an imidazolium ionic liquid is caused by a metal carbene complex formed in situ. The following simple experiments can help to verify this in more detail a) variation of ligands in the catalytic system, b) application of independently prepared, defined metal carbene complexes, and c) investigation of the reaction in pyridinium-based ionic liquids. If the reaction shows significant sensitivity to the use of different ligands, if the application of the independently prepared, defined metal-carbene complex... 

Scheme 10.31 Reaction cycle of KG-dependent (KG = a-keto-glutarate) enzymes. Metal ligands from protein side chains and water are omitted for clarity. One of the oxygens of O2 is incorporated into succinate. The other oxygen is either incorporated into the product or reduced to water depending on the nature of the reaction.

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