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Activation and Deactivation of a Robust Immobilized Cp*Ir-Transfer Hydrogenation Catalyst: A Multielement

DOI: 10.1021/ja512868a DOI Help

Authors: Grant J. Sherborne (University of Leeds) , Michael Chapman (University of Leeds) , A. John Blacker (University of Leeds) , Richard Bourne (University of Leeds) , Thomas Chamberlain (University of Nottingham) , Benjamin D. Crossley (Yorkshire Process Technology Ltd.) , Stephanie J. Lucas (University of Leeds) , Patrick C. Mcgowan (University of Leeds) , Mark Newton (European Synchrotron Radiation Facility) , Thomas E. O Screen (Yorkshire Process Technology Ltd) , Paul Thompson (University of Liverpool) , Charlotte E. Willans (University of Leeds) , Bao Nguyen (University of Leeds)
Co-authored by industrial partner: Yes

Type: Journal Paper
Journal: Journal Of The American Chemical Society , VOL 137 (12)

State: Published (Approved)
Published: March 2015
Diamond Proposal Number(s): 8071

Open Access Open Access

Abstract: A highly robust immobilized [Cp*IrCl2]2 precatalyst on Wang resin for transfer hydrogenation, which can be recycled up to 30 times, was studied using a novel combination of X-ray absorption spectroscopy (XAS) at Ir L3-edge, Cl K-edge, and K K-edge. These culminate in in situ XAS experiments that link structural changes of the Ir complex with its catalytic activity and its deactivation. Mercury poisoning and “hot filtration” experiments ruled out leached Ir as the active catalyst. Spectroscopic evidence indicates the exchange of one chloride ligand with an alkoxide to generate the active precatalyst. The exchange of the second chloride ligand, however, leads to a potassium alkoxide–iridate species as the deactivated form of this immobilized catalyst. These findings could be widely applicable to the many homogeneous transfer hydrogenation catalysts with Cp*IrCl substructure.

Subject Areas: Chemistry, Technique Development

Instruments: B18-Core EXAFS

Other Facilities: BM28, ESRF