Abstract
The kinetics for the isomerization of the 50e cluster Os3(μ-TeTol-p)2(CO)10 (), where the tellurides bridge two different Os-Os edges, to one in which the tellurides bridge the same open OsOs edge () have been measured experimentally by (1)H NMR spectroscopy. The determined activation parameters are ΔH(‡) = 77 ± 9 kJ mol(-1) and ΔS(‡) = -12 ± 28 J mol(-1) K. The conversion of to has been computationally investigated by electronic structure calculations using the model compound Os3(μ-TeMe)2(CO)10. The computed isomerization pathway is consistent with the kinetic data and the thermodynamic preference for the product stereoisomer that possesses a slipped, eclipsed conformation for the two p-tolyl groups.
Highlights
An interesting aspect of organometallic cluster chemistry is the possibility of fluxionality and isomerization
In order to study the isomerization, we prepared the p-tolyl analogs Os3(μ-Te-p-tolyl)2(CO)10, 3-Tol-p and 4-Tol-p, using the same synthetic route previously reported;[2] the singlet 1H resonances for the methyl groups would enable the straightforward monitoring of the isomerization by NMR spectroscopy
A variable-temperature 1H NMR experiment conducted up to 90 °C showed no evidence of isomerization or the presence of any of the other isomers, suggesting that the stereoisomer A1 is thermodynamically the most stable. This is supported by a computational study, using density functional theory (DFT), on the three possible isomers
Summary
Isomerization of the osmium–tellurium cluster Os3(μ-TeR)2(CO)[10]: a kinetic and computational study†. The kinetics for the isomerization of the 50e cluster Os3(μ-TeTol-p)2(CO)[10] (3), where the tellurides bridge two different Os–Os edges, to one in which the tellurides bridge the same open Os⋯Os edge (4) have been measured experimentally by 1H NMR spectroscopy. The determined activation parameters are ΔH‡ = 77 ± 9 kJ mol−1 and ΔS‡ = −12 ± 28 J mol−1 K. The computed isomerization pathway is consistent with the kinetic data and the thermodynamic preference for the product stereoisomer that possesses a slipped, eclipsed conformation for the two p-tolyl groups
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