“…The present structure was determined for a complex obtained through an unexpected reaction, that of [Co(dmpmetacn)(ONO)](ClO 4 ) 2 isomerized in Me 2 SO, which led to reduction of perchlorate to chloride and its subsequent incorporation into the coordination sphere . Controlled reduction of ClO 4 - is rare, it is normally explosive, but there is a precedent in the similar reaction of cis -[Co(en) 2 (OSMe 2 ) 2 ](ClO 4 ) 2 NO 3 with N 3 - in Me 2 SO, in which cis -[Co(en) 2 (OSMe 2 )Cl]ClO 4 ·NO 3 is a significant product along with cis -[Co(en) 2 (OSMe 2 )N 3 ]ClO 4 ·NO 3 , and we are pursuing this chemistry in another arena. 7 ORTEP diagram for asym -[Co(dmpmetacn)Cl] 2+ with 30% thermal ellipsoids.…”
A novel [Co(pentaamine)Cl](2+) complex having all tertiary amine or pyridine donors has been synthesized (pentaamine = 1,4-bis(2'-pyridyl)-7-methyl-1,4,7-triazacyclononane). This asym-[Co(dmpmetacn)Cl](2+) species has been completely characterized through 1D and 2D NMR studies, and through the X-ray structure for the ZnCl(4)(2)(-) salt. Despite the lack of an activating NH center, remarkably its hydrolysis to [Co(pentaamine)OH](2+) is base catalyzed (k(OH) 0.70 M(-)(1) s(-)(1), 25 degrees C, I = 1.0 M, NaCl). Detailed NMR studies reveal that the base catalyzed substitution leads to the exchange of just one deuterium in one of the two -CH(2)- pyridyl arms, that is approximately trans to the leaving group, and this occurs during and not after base hydrolysis. Quenching experiments for the reaction of asym-[Co(dmpmetacn)Cl](2+) and control experiments on H/D exchange for the product asym-[Co(dmpmetacn)OD](2+) in OD(-) show that each act of deprotonation at the acidic methylene leads to loss of Cl(-). This is the first established case of base catalyzed substitution for a complex where the effective site of deprotonation is at a pyridyl group. A pronounced kinetic isotope effect is observed for the species perdeuterated at the pyridyl methylenes (k(H)/k(D) = 5.0), consistent with rate limiting deprotonation which is a rare event in Co(III) substitution chemistry. The activation afforded by the carbanion is discussed in terms of a new process coined the pseudo-aminate mechanism.
“…The present structure was determined for a complex obtained through an unexpected reaction, that of [Co(dmpmetacn)(ONO)](ClO 4 ) 2 isomerized in Me 2 SO, which led to reduction of perchlorate to chloride and its subsequent incorporation into the coordination sphere . Controlled reduction of ClO 4 - is rare, it is normally explosive, but there is a precedent in the similar reaction of cis -[Co(en) 2 (OSMe 2 ) 2 ](ClO 4 ) 2 NO 3 with N 3 - in Me 2 SO, in which cis -[Co(en) 2 (OSMe 2 )Cl]ClO 4 ·NO 3 is a significant product along with cis -[Co(en) 2 (OSMe 2 )N 3 ]ClO 4 ·NO 3 , and we are pursuing this chemistry in another arena. 7 ORTEP diagram for asym -[Co(dmpmetacn)Cl] 2+ with 30% thermal ellipsoids.…”
A novel [Co(pentaamine)Cl](2+) complex having all tertiary amine or pyridine donors has been synthesized (pentaamine = 1,4-bis(2'-pyridyl)-7-methyl-1,4,7-triazacyclononane). This asym-[Co(dmpmetacn)Cl](2+) species has been completely characterized through 1D and 2D NMR studies, and through the X-ray structure for the ZnCl(4)(2)(-) salt. Despite the lack of an activating NH center, remarkably its hydrolysis to [Co(pentaamine)OH](2+) is base catalyzed (k(OH) 0.70 M(-)(1) s(-)(1), 25 degrees C, I = 1.0 M, NaCl). Detailed NMR studies reveal that the base catalyzed substitution leads to the exchange of just one deuterium in one of the two -CH(2)- pyridyl arms, that is approximately trans to the leaving group, and this occurs during and not after base hydrolysis. Quenching experiments for the reaction of asym-[Co(dmpmetacn)Cl](2+) and control experiments on H/D exchange for the product asym-[Co(dmpmetacn)OD](2+) in OD(-) show that each act of deprotonation at the acidic methylene leads to loss of Cl(-). This is the first established case of base catalyzed substitution for a complex where the effective site of deprotonation is at a pyridyl group. A pronounced kinetic isotope effect is observed for the species perdeuterated at the pyridyl methylenes (k(H)/k(D) = 5.0), consistent with rate limiting deprotonation which is a rare event in Co(III) substitution chemistry. The activation afforded by the carbanion is discussed in terms of a new process coined the pseudo-aminate mechanism.
“…It has been pointed out that, for reactions involving two phases, relationships may exist between rate constants and extinction coefficients such that there can be “accidental” single exponential behavior; one can be measuring either k 1 or k 2 depending upon the particular relationship . Furthermore, where the two rate constants are within a factor of 2, consecutive reactions can be intrinsically difficult to resolve into two exponentials, , and this was anticipated to be true of the present systems. In such circumstances a fit to a single exponential is usually quite good, and the rate constant extracted can be more or less than k 1 or k 2 depending upon the extinction coefficient relationships among reactant, intermediate, and product.…”
The bis(pentadentate) ligand tmpdtne binds two Co(II) centers, and the entity is readily oxidized to the dicobalt(III) derivative [Co(2)(tmpdtne)Cl(2)](4+) which has been separated into two isomeric forms. NMR studies establish these as meso and rac isomers arising from the different or same absolute configurations for the asym configuration about each Co(III) center. Each dinuclear ion base hydrolyses to the dihydroxo derivative [Co(2)(tmpdtne)(OH)(2)](4+) with retained asym configurations about each metal ion and also retained rac or meso configurations. The kinetics for the stepwise loss of the two Cl(-) ligands is uniphasic, and data are presented to show that the loss of the first chloride is rate determining and is followed by very rapid intramolecular and loss of the second Cl(-) via a hydroxo-bridged species to yield the observed dihydroxo derivative. Meso and rac forms of the latter have been crystallized. The X-ray crystal structure of the rac-dihydroxo complex is reported, and it establishes the configurations of all the complexes reported. The (1)H NMR spectra for the hydroxo ions show very high field Co-OH resonances (ca. delta-0.5 ppm) not observed previously for such ions, and this result is discussed in the context of published (1)H NMR data for bridged Co-OH-Co species. The base hydrolysis kinetics for the dichloro ions are first order in [OH(-)], and deprotonation at an alpha-CH(2) center (alpha to a pyridyl) is identified as the source of the catalysis, since there is no NH center available for deprotonation on the ligand. These data further support the new pseudoaminate base hydrolysis mechanism first reported in 2003. The values of k(OH) for the second-order base-catalyzed reaction are ca. 4.0 M(-1) s(-1) for both the rac and meso isomers, and these results are discussed in terms of the increased acidities of these 4+ cations compared to their 2+ ion counterparts.
“…Later, new evidence was found for a short‐lived pentacoordinate intermediate from the study of the rate law and the product distribution [75, 76]. In addition, the stereochemistry of the NO + induced aquation of cis ‐[Co(en) 2 ( X )(N 3 )] + to give [Co(en) 2 ( X )(OH 2 )] 2+ was investigated 76. The nitrosation of [Co(CN) 5 N 3 ] 3– 63 and of [Cr(NH 3 ) 5 N 3 ] 2+ 77 with NO + was used for the preparation of several [Co(CN) 5 L] 2,3– and [Cr(NH 3 ) 5 L] 3+ complexes.…”
Section: Nitrosation Of the Coordinated Azide Ligandmentioning
, Contents, 1. Introduction, 2. Reactions of Carbonyl Metal Complexes with the Azide Ion, 3. Reactions of Azido Metal Complexes with Carbon Monoxide, 4. Reactions of the Azide Ion with the NO+ Cation, 5. Reaction of Nitrosyl Complexes with the Azide Ion, 6. Nitrosation of the Coordinated Azide Ligand
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