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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

DOI: 10.1021/jacs.8b13848 DOI Help

Authors: Stuart A. Bartlett (DySS, Research Complex at Harwell; The University of Sydney; University of Bath) , Nicholas A. Besley (University of Nottingham) , Andrew J. Dent (Diamond Light Source Ltd) , Sofia Diaz-moreno (Diamond Light Source) , John Evans (DySS, Research Complex at Harwell; Diamond Light Source; University of Southampton) , Michelle L. Hamilton (DySS, Research Complex at Harwell; University of Nottingham) , Magnus W. D. Hanson-heine (University of Nottingham) , Raphael Horvath (University of Nottingham) , Valentina Manici (DySS, Research Complex at Harwell; University of Nottingham) , Xue-zhong Sun (University of Nottingham) , Michael Towrie (DySS, Research Complex at Harwell; Central Laser Facility) , Lingjun Wu (University of Nottingham) , Xiaoyi Zhang (Argonne National Laboratory) , Michael W. George (DySS, Research Complex at Harwell; University of Nottingham; University of Nottingham Ningbo China)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of The American Chemical Society

State: Published (Approved)
Published: July 2019

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.

Subject Areas: Chemistry

Facility: Advanced Photon Source