title: Orbital-specific mapping of the ligand exchange dynamics of Fe(CO)5 in solution.
abstract: Transition-metal complexes have long attracted interest for fundamental chemical reactivity studies and possible use in solar energy conversion. Electronic excitation, ligand loss from the metal centre, or a combination of both, creates changes in charge and spin density at the metal site that need to be controlled to optimize complexes for photocatalytic hydrogen production and selective carbon-hydrogen bond activation. An understanding at the molecular level of how transition-metal complexes catalyse reactions, and in particular of the role of the short-lived and reactive intermediate states involved, will be critical for such optimization. However, suitable methods for detailed characterization of electronic excited states have been lacking. Here we show, with the use of X-ray laser-based femtosecond-resolution spectroscopy and advanced quantum chemical theory to probe the reaction dynamics of the benchmark transition-metal complex Fe(CO)5 in solution, that the photo-induced removal of CO generates the 16-electron Fe(CO)4 species, a homogeneous catalyst with an electron deficiency at the Fe centre, in a hitherto unreported excited singlet state that either converts to the triplet ground state or combines with a CO or solvent molecule to regenerate a penta-coordinated Fe species on a sub-picosecond timescale. This finding, which resolves the debate about the relative importance of different spin channels in the photochemistry of Fe(CO)5 (refs 4, 16 - 20), was made possible by the ability of femtosecond X-ray spectroscopy to probe frontier-orbital interactions with atom specificity. We expect the method to be broadly applicable in the chemical sciences, and to complement approaches that probe structural dynamics in ultrafast processes.
authors.affiliation: Institute for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Strasse 15, 12489 Berlin, Germany.
authors.forename: Ph
authors.initials: P
authors.lastname: Wernet
authors.affiliation: 1] Institute for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Strasse 15, 12489 Berlin, Germany. [2] Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Strasse 24/25, 14476 Potsdam, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Kunnus
authors.affiliation: Department of Physics, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden.
authors.forename: I
authors.initials: I
authors.lastname: Josefsson
authors.affiliation: IFG Structural Dynamics of (bio)chemical Systems, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
authors.forename: I
authors.initials: I
authors.lastname: Rajkovic
authors.affiliation: IFG Structural Dynamics of (bio)chemical Systems, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
authors.forename: W
authors.initials: W
authors.lastname: Quevedo
authors.affiliation: Institute for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Strasse 15, 12489 Berlin, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Beye
authors.affiliation: 1] Institute for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Strasse 15, 12489 Berlin, Germany. [2] Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Strasse 24/25, 14476 Potsdam, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Schreck
authors.affiliation: IFG Structural Dynamics of (bio)chemical Systems, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Grübel
authors.affiliation: IFG Structural Dynamics of (bio)chemical Systems, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Scholz
authors.affiliation: Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
authors.forename: D
authors.initials: D
authors.lastname: Nordlund
authors.affiliation: PULSE Institute, SLAC National Accelerator Laboratory, Stanford University, Stanford, California 94305, USA.
authors.forename: W
authors.initials: W
authors.lastname: Zhang
authors.affiliation: PULSE Institute, SLAC National Accelerator Laboratory, Stanford University, Stanford, California 94305, USA.
authors.forename: R W
authors.initials: RW
authors.lastname: Hartsock
authors.affiliation: Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
authors.forename: W F
authors.initials: WF
authors.lastname: Schlotter
authors.affiliation: Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: Turner
authors.affiliation: MAX-lab, PO Box 118, 221 00 Lund, Sweden.
authors.forename: B
authors.initials: B
authors.lastname: Kennedy
authors.affiliation: MAX-lab, PO Box 118, 221 00 Lund, Sweden.
authors.forename: F
authors.initials: F
authors.lastname: Hennies
authors.affiliation: Department of Chemistry, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, Netherlands.
authors.forename: F M F
authors.initials: FM
authors.lastname: de Groot
authors.affiliation: PULSE Institute, SLAC National Accelerator Laboratory, Stanford University, Stanford, California 94305, USA.
authors.forename: K J
authors.initials: KJ
authors.lastname: Gaffney
authors.affiliation: 1] IFG Structural Dynamics of (bio)chemical Systems, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany. [2] Institute for X-ray Physics, Göttingen University, Friedrich Hund Platz 1, 37077 Göttingen, Germany. [3] Structural Dynamics of (Bio)chemical Systems, DESY, Notkestrasse 85, 22607 Hamburg, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Techert
authors.affiliation: Department of Physics, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Odelius
authors.affiliation: 1] Institute for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Strasse 15, 12489 Berlin, Germany. [2] Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Strasse 24/25, 14476 Potsdam, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Föhlisch
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