Mechanistic Changeover for the Water Substition on fac-[(CO)3Re(H2O)3]+ Revealed by High-Pressure NMR.
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| Title: | Mechanistic Changeover for the Water Substition on fac-[(CO) |
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| Authors: | Grundler, Pascal V.1, Salignac, Bernadette1, Cayemittes, Sonia1, Alberto, Roger2, Merbach, André E.1 Andre.Merbach@epfl.ch |
| Source: | Inorganic Chemistry. 2/9/2004, Vol. 43 Issue 3, p865-873. 9p. |
| Subjects: | Substitution reactions, Ligands (Chemistry), Nuclear magnetic resonance, Water, Scission (Chemistry), Dimethyl sulfide, Carbon compounds, Metal complexes |
| Abstract: | The complex formation in water between the stable tricarbonyltriaqua fac-[(CO) 3Re(H 2O) 3]+ (1) complex and N- and S-donor ligands has been studied by high-pressure 1H NMR. Rate and equilibrium constants for the formation of [(CO)3Re(Pyz)(H2O)2]+, [(CO)3(H2O)2Re(μ-Pyz)Re(H2O)2(CO)3]²+, [(CO)3Re(THT)(H2O)2]+, and [(CO)3Re(DMS)n(H2O)3-n]+ (n = 1−3) (Pyz = pyrazine, THT = tetrahydrothiophene, DMS = dimethyl sulfide) have been determined and are in accord with previous results (Salignac, B.; Grundler, P. V.; Cayemittes, S.; Frey, U.; Scopelliti, R.; Merbach, A. E.; Hedinger, R.; Hegetschweiler, K.; Alberto, R.; Prinz, U.; Raabe, G.; Kölle, U.; Hall, S. Inorg. Chem. 2003, 42, 3516). The calculated interchange rate constant k′i (Eigen;Wilkins mechanism) increases from the hard O- and N-donors to the soft S-donors, as exemplified by the following series: TFA (trifluoroacetate) (k′i = 2.9 × 10−³ S−¹) < Br- < CH3CN < Pyz < THT < DMS < TU (thiourea) (k′i= 41.5 × 10−³ s−¹). On the other hand, k′i values remain close to that of water exchange kex on 1 (kex = 6.3 × 10−³ S−¹). Thus, an Id mechanism was assigned, suggesting however the possibility of a slight deviation toward an associatively activated mechanism with the S-donor ligands. Activation volumes determined by high-pressure NMR, for Pyz as ΔV≠f,1 = +5.4 ± 1.5, ΔV≠r,1 = +7.9 ± 1.2 cm3 mol−¹, for THT as ΔV≠f,1 = −6.6 ± 1, ΔV≠r,1 = −6.2 ± 1 cm3 mo1−¹, and for DMS as ΔV≠f,1 = −12 ± 1, ΔV≠r,1 = −10 ± 2 cm3 mol−¹ revealed the ambivalent character of 1 toward water substitution. Hence, these findings are interpreted as a gradual changeover of the reaction mechanism from a dissociatively activated one (Id), with the hard O- and N-donor ligands, to an associatively activated one (la), with the soft S-donor ligands. [ABSTRACT FROM AUTHOR] |
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| Database: | Engineering Source |
| Abstract: | The complex formation in water between the stable tricarbonyltriaqua fac-[(CO) 3Re(H 2O) 3]+ (1) complex and N- and S-donor ligands has been studied by high-pressure 1H NMR. Rate and equilibrium constants for the formation of [(CO)3Re(Pyz)(H2O)2]+, [(CO)3(H2O)2Re(μ-Pyz)Re(H2O)2(CO)3]²+, [(CO)3Re(THT)(H2O)2]+, and [(CO)3Re(DMS)n(H2O)3-n]+ (n = 1−3) (Pyz = pyrazine, THT = tetrahydrothiophene, DMS = dimethyl sulfide) have been determined and are in accord with previous results (Salignac, B.; Grundler, P. V.; Cayemittes, S.; Frey, U.; Scopelliti, R.; Merbach, A. E.; Hedinger, R.; Hegetschweiler, K.; Alberto, R.; Prinz, U.; Raabe, G.; Kölle, U.; Hall, S. Inorg. Chem. 2003, 42, 3516). The calculated interchange rate constant k′i (Eigen;Wilkins mechanism) increases from the hard O- and N-donors to the soft S-donors, as exemplified by the following series: TFA (trifluoroacetate) (k′i = 2.9 × 10−³ S−¹) < Br- < CH3CN < Pyz < THT < DMS < TU (thiourea) (k′i= 41.5 × 10−³ s−¹). On the other hand, k′i values remain close to that of water exchange kex on 1 (kex = 6.3 × 10−³ S−¹). Thus, an Id mechanism was assigned, suggesting however the possibility of a slight deviation toward an associatively activated mechanism with the S-donor ligands. Activation volumes determined by high-pressure NMR, for Pyz as ΔV≠f,1 = +5.4 ± 1.5, ΔV≠r,1 = +7.9 ± 1.2 cm3 mol−¹, for THT as ΔV≠f,1 = −6.6 ± 1, ΔV≠r,1 = −6.2 ± 1 cm3 mo1−¹, and for DMS as ΔV≠f,1 = −12 ± 1, ΔV≠r,1 = −10 ± 2 cm3 mol−¹ revealed the ambivalent character of 1 toward water substitution. Hence, these findings are interpreted as a gradual changeover of the reaction mechanism from a dissociatively activated one (Id), with the hard O- and N-donor ligands, to an associatively activated one (la), with the soft S-donor ligands. [ABSTRACT FROM AUTHOR] |
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| ISSN: | 00201669 |
| DOI: | 10.1021/ic034969a |
