The Conformations of 13-Vertex ML2C2B10 Metallacarboranes: Experimental and Computational Studies
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- 作者：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. St
- 刊名：Journal of the American Chemical Society
- 出版年：2007
- 出版时间：March 21, 2007
- 年：2007
- 卷：129
- 期：11
- 页码：3302 - 3314
- 全文大小：708K
- 年卷期：v.129,no.11(March 21, 2007)
- ISSN：1520-5126
文摘
The docosahedral metallacarboranes 4,4-(PMe2Ph)2-4,1,6-closo-PtC2B10H12, 4,4-(PMe2Ph)2-4,1,10-closo-PtC2B10H12, and [N(PPh3)2][4,4-cod-4,1,10-closo-RhC2B10H12] were prepared by reduction/metalation of either 1,2-closo-C2B10H12 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 thecarborane ligand face. Comparison with conformations previously established for six other ML2C2B10 speciesof varying heteroatom patterns (4,1,2-MC2B10, 4,1,6-MC2B10, 4,1,10-MC2B10, and 4,1,12-MC2B10) revealsclear preferences. In all cases a qualitative understanding of these was afforded by simple MO argumentsapplied to the model heteroarene complexes [(PH3)2PtC2B4H6]2- and [(PH3)2PtCB5H6]3-. Moreover, DFTcalculations on [(PH3)2PtC2B4H6]2- in its various isomeric forms approximately reproduced the observedconformations in the 4,1,2-, 4,1,6-, and 4,1,10-MC2B10 species, although analogous calculations on[(PH3)2PtCB5H6]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 fourisomeric cases. Apparent discrepancies between observed and computed Pt-C distances were probedby further refinement of the 4,1,2- model to 1,2-(CH2)3-4,4-(PMe3)2-4,1,2-closo-PtC2B10H10. This still has amore distorted structure than measured experimentally for 1,2-(CH2)3-4,4-(PMe2Ph)2-4,1,2-closo-PtC2B10H10,but the structural differences lie on a very shallow potential energy surface. For the model compound ahenicosahedral transition state was located 8.3 kcal mol-1 above the ground-state structure, consistentwith the fluxionality of 1,2-(CH2)3-4,4-(PMe2Ph)2-4,1,2-closo-PtC2B10H10 in solution.