Mechanistic Insight Gained into the Ligand Substitution Reactions of Bis(<i>o</i>‐benzosemiquinonediiminato)(triphenylphosphane)cobalt(<scp>III</scp>) − Kinetic, Solvent, and Volume Profile Studies

Alzoubi, Basam M.; Hamza, Mohamed S. A.; Dücker-Benfer, Carlos; Eldik, Rudi van

doi:10.1002/ejic.200300107

Cited by 5 publications

(6 citation statements)

References 19 publications

(26 reference statements)

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“…32 Distortion arising from the interaction of the axial alkyl group with the equatorial ligand can be ascribed to (a) changes in the C-Co-N(eq) bond angles; (b) widening of the Co-CH 2 -R′ angles and shortening of the Co-R bond lengths; (c) lengthening of the Co-C bond; (d) deformation of the equatorial ligand unit. 32 It can be concluded that the variety of chelates, R groups, entering ligands, and solvents selected in this and our earlier studies [1][2][3][4][5][6] enables a systematic tuning of the lability of alkyl cobalt(III) complexes, which results in a systematic tuning of the ligand displacement process in terms of a dissociative interchange (I d ) and a limiting dissociative (D) mechanism.…”

Section: Resultsmentioning

confidence: 88%

“…The Co-C bond lengthens from 1.990 to 2.044 Å as the bulk of the alkyl group increases from CH 3 to CH 2 CMe 3 in the case of the dimethylglyoximate complex, and clearly depends on the steric interaction between the axial alkyl and the equatorial ligands. 31 In addition, the hybridization of the carbon atom affects the Co-C bond length, which was found to be 2.00, 1.96, and 1.90 Å for sp 3 , sp 2 , and sp hybridization, respectively. 32 Distortion arising from the interaction of the axial alkyl group with the equatorial ligand can be ascribed to (a) changes in the C-Co-N(eq) bond angles; (b) widening of the Co-CH 2 -R′ angles and shortening of the Co-R bond lengths; (c) lengthening of the Co-C bond; (d) deformation of the equatorial ligand unit.…”

Section: Resultsmentioning

confidence: 99%

“…∆S q , J mol -1 K -1 ∆V q , cm3 mol -1 imidazole b,c 70.3 ( 0.5 74 ( 2 +40 ( 8 +3.7 ( 0.2 pyrazole b,c 91 ( 2 7 9 ( 2 +56 ( 7 +4.5 ( 0.4 1,2,4-triazole b,c 70.6 ( 0.7 72 ( 3 +31 ( 9 +4.0 ( 0.1 N-acetylimidazole b,c 48 ( 1 7 0 ( 1 +22 ( 3 +3.1 ( 0.2 5-chloro-1-methylimidazole b,c 105.1 ( 0.5 89 ( 2 +92 ( 6 +2.5 ( 0.1 NO2 -b,c113.9 ( 0.8 84 ( 3 +78 ( 10 +2.3 ( 0.1 Ph3P d,e 19.6 ( 0.1 94 ( 2 +97 ( 8 +12.3 ( 0.4 imidazole d,e 23.6 ( 0.2 74 ( 2 +29 ( 5 +7.3 ( 0.1 Ph3As(forward reaction) d,e 20.1 ( 1.1 103 ( 4 +126 ( 14 +10.6 ( 0.5 Ph3As(reverse reaction) d,e 1.66 ( 0.03 s -1 114 ( 5 +143 ( 18 +15.9 ( 0.2 Ph3Sb(forward reaction) d,e 20.3 ( 1.7 89 ( 3 +77 ( 10 Ph3Sb(reverse reaction) d,e 10.24 ( 0.04 s -1 95 ( 3 +95 ( 9 +11.3 ( 0.4 Ph3P f,g 252.0 ( 0.8…”

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Mechanistic Elucidation of the Substitution Behavior of Alkyl Cobaloximes in Water and Methanol as Solvents

2004

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The ligand substitution behavior of trans-[Co(Hdmg)2(R)S] (R = CH3, PhCH2; Hdmg = dimethylglyoximate; S = H2O and/or MeOH) was studied for imidazole, pyrazole, 1,2,4-triazole, N-acetylimidazole, 5-chloro-1-methylimidazole, NO2-, Ph3P, Ph3As, and Ph3Sb as entering ligands. In all cases, except for Ph3As and Ph3Sb, the observed kinetics shows a linear dependence on the entering nucleophile concentration with no evidence for a back reaction. In the case of Ph3As and Ph3Sb as entering nucleophiles, kinetic evidence for a reverse solvolysis reaction is at hand. Activation parameters (DeltaH++, DeltaS++, and DeltaV++) were determined from the temperature and pressure dependence of all studied reactions and support the operation of a dissociatively activated substitution mechanism. The rate and activation parameters show that there is an increase in the dissociative character from a dissociative interchange to a limiting dissociative mechanism that depends on the nature of R and the entering nucleophile. The crystal structure of trans-[Co(en)2(Me)H2O]2+ was determined by X-ray analysis. The Co-O and Co-C bond lengths were found to be 2.153(6) and 1.995(10) angstroms, respectively. The kinetic and structural data are discussed in reference to a series of earlier studied systems for which data are reported in the literature.

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Section: Resultsmentioning

confidence: 88%

Section: Resultsmentioning

confidence: 99%

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Mechanistic Elucidation of the Substitution Behavior of Alkyl Cobaloximes in Water and Methanol as Solvents

2004

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“…The slope is the second-order rate constant, k II , which is related to K os and k 4 by eqn. (9); 2.59 (7) a…”

Section: Rate Constantsmentioning

confidence: 99%

Probing the nature of the Co(iii) ion in cobalamins: a comparison of the reaction of aquacobalamin (vitamin B12a) and aqua-10-chlorocobalamin with some anionic and N-donor ligands

Knapton

Marques

2005

Dalton Trans.

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To probe the cis effect of the corrin macrocycle in vitamin B12 derivatives, equilibrium constants for the substitution of coordinated H2O in aquacobalamin (vitamin B12a, H2OCbl+) and in aqua-10-chlorocobalamin, H2O-10-ClCbl+, (in which Cl has replaced the C10 H) by an exogenous ligand, L (L = an anion, NO2-, SCN-, N3-, OCN-, S2O3(2-), NCSe- or a neutral N-donor, CH3NH2, pyridine, imidazole) have been determined. The cis influence reported in the electronic spectra of the cobalamins is observed in the spectra of L-10-ClCbls as well. Anionic ligands bind more strongly to H2O-10-ClCbl+ than to H2OCbl+ with log K values between 0.10 and 0.63 (average 0.26) larger; the converse is true for the neutral N-donor ligands, where log K is between 0.17 and 0.3 (average 0.25) smaller. Semi-empirical molecular orbital (SEMO) calculations using the ZINDO/1 model on the hydroxo complexes show that charge density is delocalised from the axial donor atom to the metal and Cl. This explains why coordinated OH- is a poorer base in HO-10-ClCbl than in HOCbl and the pK(a) of H2O-10-ClCbl+ is lower than that of H2OCbl+. It further explains why, because of the ability of the metal in concert with the C10 Cl to accept charge density from the ligand, an anionic ligand will bind more strongly to Co(III) in H2O-10-ClCbl+ than in H2OCbl+. The kinetics of the replacement of coordinated H2O by two probe ligand, pyridine and azide, were determined. The rate constants for substitution of H2O in H2O-10-ClCbl+ by pyridine show saturation, whilst those for substitution by N3- do not; this is inconsistent with a purely dissociative mechanism and the reactions proceed through an interchange mechanism. The values of the activation parameters are more positive for the reaction between these ligands and H2OCbl+, than for their reaction with H2O-10-ClCbl+. This is interpreted to mean that the transition state in the reaction of H2O-10-ClCbl+ occurs earlier along the reaction coordinate. In the temperature range studied, H2O-10-ClCbl+ reacts more slowly with py and N3- than does H2OCbl+. SEMO calculations indicate that as the Co-O bond to the departing H(2)O molecule is stretched, the charge density on Co in H2OCbl+ is always lower than on Co in H2O-10-ClCbl+. This suggests that the former is a better electrophile towards the incoming ligand, and offers an explanation for the kinetics observations.

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“…2 O in trans-[Co(en) 2 Me(H 2 O)] 21 by pyrazole, 1,2,4-triazole and N-acetylimidazole indicate an I d mechanism 138. Bis(o-benzosemiquinonediiminato)(triphenylphosphane)cobalt(III), [Co III (s-BQDI) 2 (PPh 3 )(S)], where S is a molecule of solvent, undergoes substitution with imidazole and 4-dimethylaminopyridine in methanol or acetonitrile 139. The reactions feature an early step involving dissociation of a solvent molecule yielding a five-coordinate intermediate, followed by rate-determining combination with the nucleophile and loss of triphenylphosphane.…”

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confidence: 99%

27 Mechanisms of reactions in solution

Davies

2004

Annu. Rep. Prog. Chem., Sect. A: Inorg. Chem.

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Mechanistic Insight Gained into the Ligand Substitution Reactions of Bis(o‐benzosemiquinonediiminato)(triphenylphosphane)cobalt(III) − Kinetic, Solvent, and Volume Profile Studies

Abstract: The ligand substitution reactions of bis (o-benzosemiquinonediiminato)

Cited by 5 publications

References 19 publications

Mechanistic Elucidation of the Substitution Behavior of Alkyl Cobaloximes in Water and Methanol as Solvents

Mechanistic Elucidation of the Substitution Behavior of Alkyl Cobaloximes in Water and Methanol as Solvents

Probing the nature of the Co(iii) ion in cobalamins: a comparison of the reaction of aquacobalamin (vitamin B12a) and aqua-10-chlorocobalamin with some anionic and N-donor ligands

27 Mechanisms of reactions in solution

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