A molecular mechanics force field for rhodium(I) carbonyl phosphine complexes and its application on the oxidative addition reactions of these complexes
“…From experiments performed in the temperature range 22.5−50.9 °C, the values of enthalpy of activation Δ H ⧧ = 11 (±1) kcal mol -1 and entropy of activation Δ S ⧧ = −41 (±2) cal mol -1 K -1 have been calculated for the oxidative addition reaction. The large negative value of Δ S ⧧ is in agreement with a rate-determining associative step, in line with the S N 2 pathway proposed for the reaction of neutral and anionic rhodium(I) complexes. , The large solvent effect here observed for 1 (MeCN vs MeI) also supports this mechanistic pattern. The reactivity of complex 1 toward MeI is compared with that of other rhodium(I) complexes in Table , along with the corresponding values of ν CO .…”
The cationic rhodium(I) carbonyl complex mer-[Rh(L)(CO)]PF6 coordinated by a tridentate
S,N,S donor ligand (L = 2,6-bis(benzylthiomethyl)pyridine) reacts with MeI to give the
corresponding acetyl derivative [Rh(L)(COMe)I]PF6, by consecutive oxidative addition−migratory insertion reactions via observable methyl−rhodium(III) intermediate complexes.
Rate constants and activation parameters have been obtained for both reaction steps in
MeCN, and compared with those of complexes coordinated by mono- and bidentate ligands.
This is the first report on the organometallic reactivity of a rhodium(I) and carbonyl complex
of S,N,S ligands.
“…From experiments performed in the temperature range 22.5−50.9 °C, the values of enthalpy of activation Δ H ⧧ = 11 (±1) kcal mol -1 and entropy of activation Δ S ⧧ = −41 (±2) cal mol -1 K -1 have been calculated for the oxidative addition reaction. The large negative value of Δ S ⧧ is in agreement with a rate-determining associative step, in line with the S N 2 pathway proposed for the reaction of neutral and anionic rhodium(I) complexes. , The large solvent effect here observed for 1 (MeCN vs MeI) also supports this mechanistic pattern. The reactivity of complex 1 toward MeI is compared with that of other rhodium(I) complexes in Table , along with the corresponding values of ν CO .…”
The cationic rhodium(I) carbonyl complex mer-[Rh(L)(CO)]PF6 coordinated by a tridentate
S,N,S donor ligand (L = 2,6-bis(benzylthiomethyl)pyridine) reacts with MeI to give the
corresponding acetyl derivative [Rh(L)(COMe)I]PF6, by consecutive oxidative addition−migratory insertion reactions via observable methyl−rhodium(III) intermediate complexes.
Rate constants and activation parameters have been obtained for both reaction steps in
MeCN, and compared with those of complexes coordinated by mono- and bidentate ligands.
This is the first report on the organometallic reactivity of a rhodium(I) and carbonyl complex
of S,N,S ligands.
“…The change of k 2 with solvent (acetonitrile > acetone > neat methyl iodide ≅ dichloromethane) indicates that increased solvent polarity assists the oxidative addition reaction, presumably characterized by the development of charge in the rate-determining step. The overall mechanistic information, composed of dependence on [MeI], solvent effect, and activation parameters in acetonitrile, conform with the classical bimolecular S N 2 mechanism exhibited by neutral and anionic rhodium(I) carbonyl complexes, involving Rh−Me bond formation and C−I bond breaking in the rate-determining step 1 Plot of k obs values vs concentration of methyl iodide for the reaction of complex 1 in acetonitrile and in acetone, at 31 °C. 2 Plot of k obs values vs concentration of methyl iodide for the reaction of complex 1 in dichloromethane, at 31 °C.
1 Values of k o bs (s -1 ) for the Reaction of the Complex [Rh(L)(CO)]PF 6 (1; L = 2,6-Bis((benzylthio)methyl)pyridine) with Methyl Iodide in Methanol, Acetone, and Dichloromethane at 31 °C a [MeI], M k obs , s -1 in CH 2 Cl 2 [MeI], M k obs , s -1 in CH 2 Cl 2 0.76 1.6 × 10 -5 2.09 2.3 × 10 -5 1.46 2.1 × 10 -5 3.20 3.2 × 10 -5 [MeI], M k obs , s -1 in Me 2 CO[MeI], M k obs , s -1 in Me 2 CO 0.392 2.99 × 10 -5 0.944 6.15 × 10 -5 0.618 4.35 × 10 -5 1.120 7.35 × 10 -5 [MeI], M k obs , s -1 in MeOH[MeI], M k obs , s -1 in MeOH 0.16 6.5 × 10 -6 1.53 7.8 × 10 -5 0.50 3.6 × 10 -5 2.09 8.7 × 10 -5 1.05 6.3 × 10 -5 a [ 1 ] = 0.005−0.010 M.
2 Values of Kinetic Constants for the Reaction of [Rh(L)(CO)]PF 6 (1; L = 2,6-Bis((benzylthio)methyl)pyridine) with MeI in Various Solvents, at 31 °C solventε a k 1 (s -1 ) k 2 (M -1 s -1 ) k - 1 / k 3 CH 2 Cl 2 9.1 [1.1(±0.1)] × 10 -5 [6.4(±0.6)] × 10 -6 MeCOMe 20.7 [6.7(±1)] × 10 -6 [5.9(±0.1)] × 10 -5 MeCN 37.5 [1.7(±0.6)] × 10 -5 [1.4(±0.1)] × 10 -4 MeOH 32.6 [1.7(±0.1)] × 10 -4 1.8 (±0.05) a Dielectric constant.
…”
Section: Resultsmentioning
confidence: 59%
“…The kinetic behavior of the reaction of complex 1 with MeI appears peculiar. In fact, while the linear dependence on concentration of MeI is characteristic of oxidative addition to d 8 transition-metal complexes, 7a, we have found only one case in which a plot of k obs vs [MeI] reveals a non-zero intercept on the y axis, among the reactions of rhodium(I) complexes . The reaction of the complex [Rh(cupferrate)(CO)(PPh 3 )], coordinated by the bidentate anionic ligand PhNONO, with methyl iodide proceeds through two competing rate-determining steps, one of which is zero order in methyl iodide.…”
Section: Resultsmentioning
confidence: 84%
“…The occurrence of a four-coordinate 16-electron and of a transient three-coordinate 14-electron species reacting in parallel toward methyl iodide represents an interesting case among oxidative addition reactions , the oxidative addition reaction of MeI generally proceeds via the four-coordinate complex. 7c, In the context of hemilability, it should be noted that oxidative addition of methyl iodide to iridium(I) complexes of the type [IrCl(CO)(phosphine)] was found to be 100 times faster when the phosphine ligand is PMe 2 ( o -MeOC 6 H 4 ) than when it is PMe 2 ( p -MeOC 6 H 4 ) or PMe 2 Ph. This effect has been attributed to temporary coordination of the o -methoxy group on iridium, with enhanced electron density, and hence reactivity, on the metal …”
Kinetic experiments of the oxidative addition of methyl iodide to the cationic rhodium(I) carbonyl complex [Rh(L)(CO)]PF 6 (1; L ) 2,6-bis(benzylthiomethyl)pyridine) forming the observable rhodium(III) methyl species [RhI(L)(CO)Me)]PF 6 have been performed by FT-IR. The reaction yields the isolable rhodium acyl complex [RhI(L)(COMe)]PF 6 . Plots of k obs versus concentration of methyl iodide indicate that the reaction proceeds by two parallel pathways, one which is first order in complex 1 and zero order in MeI (k 1 ) and one which is first order in complex 1 and first order in MeI (k 2 ). The first-order pathway displays scarce dependence on the nature of the solvent (k 1 (31°C): 6.7 × 10 -6 s -1 , acetone; 1.1 × 10 -5 s -1 , dichloromethane; 1.7 × 10 -5 s -1 , acetonitrile), while a larger solvent effect is observed for the second-order pathway (k 2 (31°C): 6.4 × 10 -6 M -1 s -1 , dichloromethane; 5.9 × 10 -5 M -1 s -1 , acetone; 1.4 × 10 -4 M -1 s -1 , acetonitrile), in agreement with the dissociative and associative character of the two routes, respectively. The k obs values for the reaction in methanol exhibit a saturation behavior when plotted against the concentration of methyl iodide. 1 H NMR spectra of complex 1 at different temperatures in the range 208-302 K display a fluxional behavior typical of tridentate complexes of S,N,S ligands, due to pyramidal inversion at the sulfur centers. The methyl iodide independent pathway and the saturation behavior in methanol are due to reversible decoordination of one thiobenzyl arm from rhodium, yielding a transient three-coordinate bidentate N,S species which reacts rapidly with MeI. The data are discussed in terms of the concept of kinetic detection of hemilability.
Ein HRTEM‐Bild genügt, um eine Potentialabbildung als Startpunkt für eine Computersimulation zur Lösung komplexer Zeolithstrukturen aufzustellen. Die Atome werden zunächst randomisiert platziert und dann in Bereiche mit hohem Potential „gestoßen“ (siehe Schema). Modelle, die eine sinnvolle Bindungsgeometrie und gute Übereinstimmung mit dem HRTEM‐Bild aufweisen, werden als Kandidaten für die abschließende Strukturlösung ausgewählt.
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