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Monitoring the formation and reactivity of organometallic alkane and fluoroalkane complexes with silanes and xe using time-resolved X-ray absorption fine structure spectroscopy

Monitoring the formation and reactivity of organometallic alkane and fluoroalkane complexes with silanes and xe using time-resolved X-ray absorption fine structure spectroscopy
Monitoring the formation and reactivity of organometallic alkane and fluoroalkane complexes with silanes and xe using time-resolved X-ray absorption fine structure spectroscopy

Complexes with weakly coordinating ligands are often formed in chemical reactions and can play key roles in determining the reactivity, particularly in catalytic reactions. Using time-resolved X-ray absorption fine structure (XAFS) spectroscopy in combination with time-resolved IR (TRIR) spectroscopy and tungsten hexacarbonyl, W(CO)6, we are able to structurally characterize the formation of an organometallic alkane complex, determine the W-C distances, and monitor the reactivity with silane to form an organometallic silane complex. Experiments in perfluorosolvents doped with xenon afford initially the corresponding solvated complex, which is sufficiently reactive in the presence of Xe that we can then observe the coordination of Xe to the metal center, providing a unique insight into the metal-xenon bonding. These results offer a step toward elucidating the structure, bonding, and chemical reactivity of transient species by X-ray absorption spectroscopy, which has sensitivity to small structural changes. The XAFS results indicate that the bond lengths of metal-alkane (W-H-C) bond in W(CO)5(heptane) as 3.07 (±0.06) Å, which is longer than the calculated W-C (2.86 Å) for binding of the primary C-H, but shorter than the calculated W-C (3.12 Å) for the secondary C-H. A statistical average of the calculated W-C alkane bond lengths is 3.02 Å, and comparison of this value indicates that the value derived from the XAFS measurements is averaged over coordination of all C-H bonds consistent with alkane chain walking. Photolysis of W(CO)6 in the presence of HSiBu3 allows the conversion of W(CO)5(heptane) to W(CO)5(HSiBu3) with an estimated W-Si distance of 3.20 (±0.03) Å. Time-resolved TRIR and XAFS experiments following photolysis of W(CO)6 in perfluoromethylcyclohexane (PFMCH) allows the characterization of W(CO)5(PFMCH) with a W-F distance of 2.65 (±0.06) Å, and doping PFMCH with Xe allows the characterization of W(CO)5Xe with a W-Xe bond length of 3.10 (±0.02) Å.

0002-7863
11471-11480
Bartlett, Stuart A.
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Besley, Nicholas A.
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Dent, Andrew J.
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Diaz-Moreno, Sofia
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Evans, John
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Hamilton, Michelle L.
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Hanson-Heine, Magnus W.D.
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Horvath, Raphael
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Manici, Valentina
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Sun, Xue Zhong
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Towrie, Michael
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Wu, Lingjun
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Zhang, Xiaoyi
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George, Michael W.
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Bartlett, Stuart A.
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Besley, Nicholas A.
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Dent, Andrew J.
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Diaz-Moreno, Sofia
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Evans, John
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Hamilton, Michelle L.
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Hanson-Heine, Magnus W.D.
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Horvath, Raphael
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Manici, Valentina
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Sun, Xue Zhong
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Towrie, Michael
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Wu, Lingjun
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Zhang, Xiaoyi
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George, Michael W.
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Bartlett, Stuart A., Besley, Nicholas A., Dent, Andrew J., Diaz-Moreno, Sofia, Evans, John, Hamilton, Michelle L., Hanson-Heine, Magnus W.D., Horvath, Raphael, Manici, Valentina, Sun, Xue Zhong, Towrie, Michael, Wu, Lingjun, Zhang, Xiaoyi and George, Michael W. (2019) Monitoring the formation and reactivity of organometallic alkane and fluoroalkane complexes with silanes and xe using time-resolved X-ray absorption fine structure spectroscopy. Journal of the American Chemical Society, 141 (29), 11471-11480. (doi:10.1021/jacs.8b13848).

Record type: Article

Abstract

Complexes with weakly coordinating ligands are often formed in chemical reactions and can play key roles in determining the reactivity, particularly in catalytic reactions. Using time-resolved X-ray absorption fine structure (XAFS) spectroscopy in combination with time-resolved IR (TRIR) spectroscopy and tungsten hexacarbonyl, W(CO)6, we are able to structurally characterize the formation of an organometallic alkane complex, determine the W-C distances, and monitor the reactivity with silane to form an organometallic silane complex. Experiments in perfluorosolvents doped with xenon afford initially the corresponding solvated complex, which is sufficiently reactive in the presence of Xe that we can then observe the coordination of Xe to the metal center, providing a unique insight into the metal-xenon bonding. These results offer a step toward elucidating the structure, bonding, and chemical reactivity of transient species by X-ray absorption spectroscopy, which has sensitivity to small structural changes. The XAFS results indicate that the bond lengths of metal-alkane (W-H-C) bond in W(CO)5(heptane) as 3.07 (±0.06) Å, which is longer than the calculated W-C (2.86 Å) for binding of the primary C-H, but shorter than the calculated W-C (3.12 Å) for the secondary C-H. A statistical average of the calculated W-C alkane bond lengths is 3.02 Å, and comparison of this value indicates that the value derived from the XAFS measurements is averaged over coordination of all C-H bonds consistent with alkane chain walking. Photolysis of W(CO)6 in the presence of HSiBu3 allows the conversion of W(CO)5(heptane) to W(CO)5(HSiBu3) with an estimated W-Si distance of 3.20 (±0.03) Å. Time-resolved TRIR and XAFS experiments following photolysis of W(CO)6 in perfluoromethylcyclohexane (PFMCH) allows the characterization of W(CO)5(PFMCH) with a W-F distance of 2.65 (±0.06) Å, and doping PFMCH with Xe allows the characterization of W(CO)5Xe with a W-Xe bond length of 3.10 (±0.02) Å.

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e-pub ahead of print date: 15 July 2019
Published date: 24 July 2019

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Local EPrints ID: 433840
URI: http://eprints.soton.ac.uk/id/eprint/433840
ISSN: 0002-7863
PURE UUID: 96edc0d7-8601-4f39-a1f9-aab633c67913

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Date deposited: 04 Sep 2019 16:30
Last modified: 07 Oct 2020 06:41

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Contributors

Author: Stuart A. Bartlett
Author: Nicholas A. Besley
Author: Andrew J. Dent
Author: Sofia Diaz-Moreno
Author: John Evans
Author: Michelle L. Hamilton
Author: Magnus W.D. Hanson-Heine
Author: Raphael Horvath
Author: Valentina Manici
Author: Xue Zhong Sun
Author: Michael Towrie
Author: Lingjun Wu
Author: Xiaoyi Zhang
Author: Michael W. George

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