High Hydride Count Rhodium Octahedra, [Rh6(PR3)6H12][BArF4]2: Synthesis, Structures, and Reversible Hydrogen Uptake under M
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- 作者：Simon K. Brayshaw ; Michael J. Ingleson ; Jennifer C. Green ; J. Scott McIndoe ; Paul R. Raithby ; Gabriele Kociok-Kö ; hn ; and Andrew S. Weller
- 刊名：Journal of the American Chemical Society
- 出版年：2006
- 出版时间：May 10, 2006
- 年：2006
- 卷：128
- 期：18
- 页码：6247 - 6263
- 全文大小：896K
- 年卷期：v.128,no.18(May 10, 2006)
- ISSN：1520-5126
文摘
A new class of transition metal cluster is described, [Rh6(PR3)6H12][BArF4]2 (R = iPr (1a), Cy(2a); BArF4 = [B{C6H3(CF3)2}4]-). These clusters are unique in that they have structures exactly like thoseof early transition metal clusters with edge-bridging 
rs/pi.gif" BORDER=0 >-donor ligands rather than the structures expected forlate transition metal clusters with rs/pi.gif" BORDER=0 >-acceptor ligands. The solid-state structures of 1a and 2a have beendetermined, and the 12 hydride ligands bridge each Rh-Rh edge of a regular octahedron. Pulsed gradientspin-echo NMR experiments show that the clusters remain intact in solution, having calculatedhydrodynamic radii of 9.5(3) Å for 1a and 10.7(2) Å for 2a, and the formulation of 1a and 2a wasunambiguously confirmed by ESI mass spectrometry. Both 1a and 2a take up two molecules of H2 toafford the cluster species [Rh6(PiPr3)6H16][BArF4]2 (1b) and [Rh6(PCy3)6H16][BArF4]2 (2b), respectively, ascharacterized by NMR spectroscopy, ESI-MS, and, for 2b, X-ray crystallography using the [1-H-CB11Me11]-salt. The hydride ligands were not located by X-ray crystallography, but 1H NMR spectroscopy showed a15:1 ratio of hydride ligands, suggesting an interstitial hydride ligand. Addition of H2 is reversible: placing1b and 2b under vacuum regenerates 1a and 2a. DFT calculations on [Rh6(PH3)6Hx]2+ (x = 12, 16) supportthe structural assignments and also show a molecular orbital structure that has 20 orbitals involved withcluster bonding. Cluster formation has been monitored by 31P{1H} and 1H NMR spectroscopy, andmechanisms involving heterolytic H2 cleavage and elimination of [HPiPr3]+ or the formation of trimetallicintermediates are discussed.
rs/pi.gif" BORDER=0 >-donor ligands rather than the structures expected forlate transition metal clusters with rs/pi.gif" BORDER=0 >-acceptor ligands. The solid-state structures of 1a and 2a have beendetermined, and the 12 hydride ligands bridge each Rh-Rh edge of a regular octahedron. Pulsed gradientspin-echo NMR experiments show that the clusters remain intact in solution, having calculatedhydrodynamic radii of 9.5(3) Å for 1a and 10.7(2) Å for 2a, and the formulation of 1a and 2a wasunambiguously confirmed by ESI mass spectrometry. Both 1a and 2a take up two molecules of H2 toafford the cluster species [Rh6(PiPr3)6H16][BArF4]2 (1b) and [Rh6(PCy3)6H16][BArF4]2 (2b), respectively, ascharacterized by NMR spectroscopy, ESI-MS, and, for 2b, X-ray crystallography using the [1-H-CB11Me11]-salt. The hydride ligands were not located by X-ray crystallography, but 1H NMR spectroscopy showed a15:1 ratio of hydride ligands, suggesting an interstitial hydride ligand. Addition of H2 is reversible: placing1b and 2b under vacuum regenerates 1a and 2a. DFT calculations on [Rh6(PH3)6Hx]2+ (x = 12, 16) supportthe structural assignments and also show a molecular orbital structure that has 20 orbitals involved withcluster bonding. Cluster formation has been monitored by 31P{1H} and 1H NMR spectroscopy, andmechanisms involving heterolytic H2 cleavage and elimination of [HPiPr3]+ or the formation of trimetallicintermediates are discussed.