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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

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.

Journal Article Type Article
Publication Date Jul 24, 2019
Journal Journal of the American Chemical Society
Print ISSN 0002-7863
Electronic ISSN 1520-5126
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 141
Issue 29
Pages 11471-11480
Institution Citation Bartlett, S. A., Besley, N. A., Dent, A. J., Diaz-Moreno, S., Evans, J., Hamilton, M. L., …George, M. 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. https://doi.org/10.1021/jacs.8b13848
DOI https://doi.org/10.1021/jacs.8b13848
Keywords Colloid and Surface Chemistry; Biochemistry; General Chemistry; Catalysis
Publisher URL https://pubs.acs.org/doi/10.1021/jacs.8b13848
Additional Information This document is the Acccepted Manuscript version of a Published Work that appeared in final form in ACS Journal of American Chemical Society, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/jacs.8b13848