Publisher: John Wiley & Sons Inc
E-ISSN: 1521-3765|21|42|14823-14833
ISSN: 0947-6539
Source: CHEMISTRY - A EUROPEAN JOURNAL, Vol.21, Iss.42, 2015-10, pp. : 14823-14833
Disclaimer: Any content in publications that violate the sovereignty, the constitution or regulations of the PRC is not accepted or approved by CNPIEC.
Abstract
AbstractWhereas the cluster [Mo3S4(acac)3(py)3]+ ([1]+, acac=acetylacetonate, py=pyridine) reacts with a variety of alkynes, the cluster [W3S4(acac)3(py)3]+ ([2]+) remains unaffected under the same conditions. The reactions of cluster [1]+ show polyphasic kinetics, and in all cases clusters bearing a bridging dithiolene moiety are formed in the first step through the concerted [3+2] cycloaddition between the CC atoms of the alkyne and a Mo(μ‐S)2 moiety of the cluster. A computational study has been conducted to analyze the effect of the metal on these concerted [3+2] cycloaddition reactions. The calculations suggest that the reactions of cluster [2]+ with alkynes feature ΔG≠ values only slightly larger than its molybdenum analogue, however, the differences in the reaction free energies between both metal clusters and the same alkyne reach up to approximately 10 kcal mol−1, therefore indicating that the differences in the reactivity are essentially thermodynamic. The activation strain model (ASM) has been used to get more insights into the critical effect of the metal center in these cycloadditions, and the results reveal that the change in reactivity is entirely explained on the basis of the differences in the interaction energies Eint between the cluster and the alkyne. Further decomposition of the Eint values through the localized molecular orbital‐energy decomposition analysis (LMO‐EDA) indicates that substitution of the Mo atoms in cluster [1]+ by W induces changes in the electronic structure of the cluster that result in weaker intra‐ and inter‐fragment orbital interactions.
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