title: Computational (DFT) and Experimental (EXAFS) Study of the Interaction of [Ir(IMes)(H)2 (L)3 ] with Substrates and Co-substrates Relevant for SABRE in Dilute Systems.
abstract: Signal amplification by reversible exchange (SABRE) is an emerging hyperpolarization method in NMR spectroscopy, in which hyperpolarization is transferred through the scalar coupling network of para-hydrogen derived hydrides in a metal complex to a reversibly bound substrate. Substrates can even be hyperpolarized at concentrations below that of the metal complex by addition of a suitable co-substrate. Here we investigate the catalytic system used for trace detection in NMR spectroscopy with [Ir(IMes)(H)2 (L)3 ](+) (IMes=1,3-dimesitylimidazol-2-ylidene) as catalyst, pyridine as a substrate and 1-methyl-1,2,3-triazole as co-substrate in great detail. With density functional theory (DFT), validated by extended X-ray absorption fine structure (EXAFS) experiments, we provide explanations for the relative abundance of the observed metal complexes, as well as their contribution to SABRE. We have established that the interaction between iridium and ligands cis to IMes is weaker than that with the trans ligand, and that in mixed complexes with pyridine and triazole, the latter preferentially takes up the trans position.
authors.affiliation: Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen (The Netherlands).
authors.forename: Bram J A
authors.initials: BJ
authors.lastname: van Weerdenburg
authors.affiliation: Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen (The Netherlands).
authors.forename: Anthonius H J
authors.initials: AH
authors.lastname: Engwerda
authors.affiliation: Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen (The Netherlands).
authors.forename: Nan
authors.initials: N
authors.lastname: Eshuis
authors.affiliation: Dutch-Belgian Beamline (DUBBLE), ESRF - The European Synchrotron, CS40220, 38043 Grenoble Cedex 9 (France).|Istituto per lo Studio dei Materiali Nanostrutturati, CNR-ISMN, Consiglio Nazionale delle Ricerche, Via Ugo La Malfa 153, 90146 Palermo (Italy).
authors.forename: Alessandro
authors.initials: A
authors.lastname: Longo
authors.affiliation: Dutch-Belgian Beamline (DUBBLE), ESRF - The European Synchrotron, CS40220, 38043 Grenoble Cedex 9 (France).
authors.forename: Dipanjan
authors.initials: D
authors.lastname: Banerjee
authors.affiliation: Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen (The Netherlands).
authors.forename: Marco
authors.initials: M
authors.lastname: Tessari
authors.affiliation: Department of Theoretical Chemistry and Amsterdam Center for Multiscale Modeling (ACMM), VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam (The Netherlands).
authors.forename: Célia Fonseca
authors.initials: CF
authors.lastname: Guerra
authors.affiliation: Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen (The Netherlands).
authors.forename: Floris P J T
authors.initials: FP
authors.lastname: Rutjes
authors.affiliation: Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen (The Netherlands). f.m.bickelhaupt@vu.nl.|Department of Theoretical Chemistry and Amsterdam Center for Multiscale Modeling (ACMM), VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam (The Netherlands). f.m.bickelhaupt@vu.nl.
authors.forename: F Matthias
authors.initials: FM
authors.lastname: Bickelhaupt
authors.affiliation: Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen (The Netherlands). m.feiters@science.ru.nl.
authors.forename: Martin C
authors.initials: MC
authors.lastname: Feiters
keywords: NMR spectroscopy; X-ray absorption spectroscopy; density functuional calculations; iridium; ligands