The conformations of 13-vertex ML2C2B10 metallacarboranes: experimental and computational studies

Kelly J. Dalby, David Ellis, Stefan Erhardt, Ruaraidh D McIntosh, Stuart A. Macgregor, Karen Rae, Georgina M. Rosair, Volker Settels, Alan J. Welch, Bruce E. Hodson, Thomas D. McGrath, F. Gordon A. Stone

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The docosahedral metallacarboranes 4,4-(PMe2Ph) 2-4,1,6-closo-PtC2B10H12, 4,4-(PMe2Ph)2-4,1,10-closo-PtC2B 10H12, and [N(PPh3)2][4,4-cod-4,1, 10-closo-RhC2B10H12] were prepared by reduction/ metalation of either 1,2-closo-C2B10H 12 or 1,12-closo-C2B10H12. All three species were fully characterized, with a particular point of interest of the latter being the conformation of the {ML2} fragment relative to the carborane ligand face. Comparison with conformations previously established for six other ML2C2B10 species of varying heteroatom patterns (4,1,2-MC2B10, 4,1,6-/WC2Bi0, 4,1,10-MC2B10, and 4,1,12-MC2B10) reveals clear preferences. In all cases a qualitative understanding of these was afforded by simple MO arguments applied to the model heteroarene complexes [(PH3)2PtC2B4H6] 2- and [(PH3)2PtCB5H 6]3-. Moreover, DFT calculations on [(PH3) 2PtC2B4H6]2 in its various isomeric forms approximately reproduced the observed conformations in the 4,1,2-, 4,1,6-, and 4,1,10-MC2B10 species, although analogous calculations on [(PH3)2PtCB5H 6]3- did not reproduce the conformation observed in the 4,1,12-MC2B10 metallacarborane. DFT calculations on (PH3)2PtC2B10H12 yielded good agreement with experimental conformations in all four isomeric cases. Apparent discrepancies between observed and computed Pt-C distances were probed by further refinement of the 4,1,2- model to 1,2-(CH2) 3-4,4-(PMe3)2-4,1,2-closo-PtC2B 10H10. This still has a more distorted structure than measured experimentally for 1,2-(CH2)3-4,4-(PMe 2Ph)2-4,1,2-closo-PtC2B10H 10, but the structural differences lie on a very shallow potential energy surface. For the model compound a henicosahedral transition state was located 8.3 kcal mol-1 above the ground-state structure, consistent with the fluxionality of 1,2-(CH2)3-4,4-(PMe 2Ph)2-4,1,2-closo-PtC2B10H 10 in solution. © 2007 American Chemical Society.

Original languageEnglish
Pages (from-to)3302-3314
Number of pages13
JournalJournal of the American Chemical Society
Issue number11
Publication statusPublished - 21 Mar 2007

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    Dalby, K. J., Ellis, D., Erhardt, S., McIntosh, R. D., Macgregor, S. A., Rae, K., Rosair, G. M., Settels, V., Welch, A. J., Hodson, B. E., McGrath, T. D., & Stone, F. G. A. (2007). The conformations of 13-vertex ML2C2B10 metallacarboranes: experimental and computational studies. Journal of the American Chemical Society, 129(11), 3302-3314.