Protonation of a ligand

This notation has been proposed and used by Sillen and Martell [1964SIL/1V1AR], bnt it has been simplified later by the same authors [1971SIL/MAR] from to K.  

This notation has been proposed and used by Sillen and Martell [64SIL/MAR], but it has been simplified later by the same authors [7ISIL/MAR] from Ai,. to K. This review retains, for the sake of consistency, cf. Eqs.(ll.7) and (11.8), the older formulation of K,. 

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Protonation of a ligand normally leads to a significant increase in its net electron-withdrawing ability (or decrease of its net electron-donor character), as observed for the following pairs (Pi increase of 0.3-0.5 V) (Table 2) carbynes CCH2R versus vinylidenes C=CHR [14], aminocarbyne CNH2 versus isocyanide CNR [17],... 

The addition of a proton to a metal carbonyl compound may occur in either of two modes the formation of metal-hydrogen bond, or protonation of a ligand attached to the central metal atom. If the ligand protonated is an organic radical, a carbonium ion is produced, which may be stabilized by suitable delocalization of charge over the complex, including the central metal atom. Consequently, such protonated species may be legitimately considered as examples of cationic metal carbonyl compounds. 

The molecular structure of SG(l)-TEPA-propyl is shown in Figure 7.21. There are five functional nitrogen atoms on a branch available for the anionic species after protonation. The mechanism of protonation of a ligand can be described if we assume each numbered site in Figure 7.21 has a distinctive pKa value ... 

In recent years, enantioselective variants of the above transannular C-H insertions have been extensively stiidied. The enantiodetermining step involves discrimination between the enantiotopic protons of a meso-epoxide by a homochiral base, typically an organolithium in combination with a chiral diamine ligand, to generate a chiral nonracemic lithiated epoxide (e.g., 26 Scheme 5.8). Hodgson... 

A series of complexes in which the cyanide ligands are modified or replaced arises from the decomposition of methyl and pyridiomethylcobalt(111) pentacyanide derivatives in acid solution. The reactions include protonation of a cyanide ligand, insertion of a cyanide ligand between the organic group and the cobalt atom to produce an imine (see Section VI,D), decomposition of this imine to an acyl product, and replacement of a cyanide ligand by water 100, 101). The products are listed in Table III, 29. 

In the spectra of alkyl cobinamides two peaks have been observed at 3.89 and 4.42 which were assigned to the protons of a water molecule coordinated at the lower axial site (130). To confirm this assignment, it was found that addition of cyanide to methyl cobinamide, which displaces coordinated water, caused the peaks to disappear. Likewise, addition of excess D2O caused disappearance of the peaks through either ligand exchange or proton-deuteron exchange. 

Addition of a ligand, at constant pH, increases surface protonation while the addition of a metal ion (that is specifically adsorbed) lowers surface protonation. 

Effect of ligands and metal ions on surface protonation of a hydrous oxide. Specific Adsorption of cations and anions is accompanied by a displacement of alkalimetric and acidimetric titration curve (see Figs. 2.10 and 3.5). This reflects a change in surface protonation as a consequence of adsorption. This is illustrated by two examples ... 

The properties of sulfur-rich, mononuclear Fe(CO) compounds as described by the group of Sellmann (Sellmann et al. 1996) alerted the hydrogenase workers that the protonation of a thiol ligand to Fe shifts the v(CO) in such compounds by about 40cm to higher frequency, whereas the redox potential of the Fe ion increases by 500-600 mV. 

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