Complex Formation and Ligand Substitution Reactions of (2-Picolylamine)palladium(II) with Various Biologically Relevant Ligands. Characterization of (2-Picolylamine)(1,1-cyclobutanedicarboxylato)palladium(II)

1997 ◽  
Vol 36 (7) ◽  
pp. 1454-1463 ◽  
Author(s):  
Tobias Rau ◽  
Mohamed Shoukry ◽  
Rudi van Eldik
Keyword(s):  
Complex Formation ◽  
Ligand Substitution ◽  
Substitution Reactions ◽  
Biologically Relevant ◽  
Ligand Substitution Reactions

scholarly journals Impact of Chloride Concentration on Ligand Substitution Reactions of Zinc(II) Complexes with Biologically Relevant Nitrogen Nucleophiles

2018 ◽  
Vol 43 (3-4) ◽  
pp. 244-253 ◽  
Author(s):  
Enisa Selimović ◽  
Tanja Soldatović
Keyword(s):  
Complex Anion ◽  
Ligand Substitution ◽  
Octahedral Complex ◽  
Coordination Geometry ◽  
Substitution Reactions ◽  
Biologically Relevant ◽  
Additional Coordination ◽  
Nitrogen Nucleophiles ◽  
Metal Ligand ◽  
Ligand Substitution Reactions

The mole-ratio method was used to determine the metal–ligand stoichiometry between [ZnCl2(en)] and [ZnCl2(terpy)] (where en = 1,2-diaminoethane or ethylenediamine and terpy = 2,2′:6′,2″-terpyridine) and imidazole at pH 7.2 in the presence of different chloride concentrations. The results indicated step-wise formation of 1:1 and 1:2 complexes in the presence of 0.010 M NaCl and 1:1 complexes in the presence of 0.001 M NaCl for the [ZnCl2(en)] complex. These results are correlated with additional coordination of chlorides in the first coordination sphere and with changes in coordination geometry. In the presence of 0.001 M NaCl the five-coordinate complex anion [ZnCl3(en)]- is formed initially and then a substitution reaction with imidazole occurs. In the presence of 0.010 M NaCl the octahedral complex anion [ZnCl4(en)]2- is formed. Additional coordination of chloride in the [ZnCl2(terpy)] complex is not found and the metal–ligand stoichiometry is 1:2. The kinetics of ligand substitution reactions of zinc(II) complexes and biologically relevant nitrogen nucleophiles such as imidazole, 1,2,3-triazole and L-histidine were investigated at pH 7.2 as a function of nucleophile concentration in the presence of 0.001 M and 0.010 M NaCl. The reactions were followed under pseudo first-order conditions by UV-Vis spectrophotometry. The substitution reactions included two steps of consecutive displacement of chlorido ligands with changes only in the coordination geometry of the [ZnCl2(en)] complex. The order of reactivity of the investigated nucleophiles for the first reaction step towards both complexes was L-histidine > 1,2,3-triazole > imidazole, while in the presence of 0.010 M NaCl the most reactive ligand was 1,2,3-triazole towards the [ZnCl2(en)] complex.

scholarly journals Synthesis, Characterization and Reactivity of Chromium(VI) Alkylidenes

2019 ◽  
Author(s):  
Pengcheng Wu ◽  
Glenn P. A. Yap ◽  
Klaus Theopold
Keyword(s):  
Ligand Substitution ◽  
X Ray Diffraction ◽  
Substitution Reactions ◽  
X Ray ◽  
Chromium Vi ◽  
Organic Products ◽  
Ligand Substitution Reactions

Chromium(VI) dialkyls are remarkably acidic, yielding a new set of anionic chromium alkylidenes upon deprotonation with KN(TMS)<sub>2</sub>. We describe the characterization of three anionic chromium alkylidenes of the type [(ArN)<sub>2</sub>Cr(=CHR)(CH<sub>2</sub>R]<sup>-</sup> (R = <i><sup>t</sup></i>Bu, SiMe<sub>3</sub>, Ph; Ar = 2,6-diisopropylphenyl). NEt<sub>4</sub>[(ArN)<sub>2</sub>Cr(=CHSiMe<sub>3</sub>)(CH<sub>2</sub>SiMe<sub>3</sub>)] has been structurally characterized by X-ray diffraction. We have also studied the C-H activation of cyclohexane effected by the transient neopentylidene (ArN)<sub>2</sub>Cr(=CHCMe<sub>3</sub>). This reaction generated a tri-nuclear chromium(IV) complex, namely ‘[Cr(NAr)<sub>2</sub>]<sub>3</sub>’, as well as the two organic products cyclohexene and neopentane. A probable intermediate in this reaction could be trapped by PPh<sub>3</sub> to form (ArN)<sub>2</sub>Cr(PPh<sub>3</sub>)<sub>2</sub>. The latter undergoes ligand substitution reactions with ethylene and CO to produce p-acid complexes of tetravalent chromium.

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