1
|
Jay RM, Coates MR, Zhao H, Winghart MO, Han P, Wang RP, Harich J, Banerjee A, Wikmark H, Fondell M, Nibbering ETJ, Odelius M, Huse N, Wernet P. Photochemical Formation and Electronic Structure of an Alkane σ-Complex from Time-Resolved Optical and X-ray Absorption Spectroscopy. J Am Chem Soc 2024; 146:14000-14011. [PMID: 38713061 PMCID: PMC11117182 DOI: 10.1021/jacs.4c02077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2024] [Revised: 04/29/2024] [Accepted: 04/30/2024] [Indexed: 05/08/2024]
Abstract
C-H bond activation reactions with transition metals typically proceed via the formation of alkane σ-complexes, where an alkane C-H σ-bond binds to the metal. Due to the weak nature of metal-alkane bonds, σ-complexes are challenging to characterize experimentally. Here, we establish the complete pathways of photochemical formation of the model σ-complex Cr(CO)5-alkane from Cr(CO)6 in octane solution and characterize the nature of its metal-ligand bonding interactions. Using femtosecond optical absorption spectroscopy, we find photoinduced CO dissociation from Cr(CO)6 to occur within the 100 fs time resolution of the experiment. Rapid geminate recombination by a fraction of molecules is found to occur with a time constant of 150 fs. The formation of bare Cr(CO)5 in its singlet ground state is followed by complexation of an octane molecule from solution with a time constant of 8.2 ps. Picosecond X-ray absorption spectroscopy at the Cr L-edge and O K-edge provides unique information on the electronic structure of the Cr(CO)5-alkane σ-complex from both the metal and ligand perspectives. Based on clear experimental observables, we find substantial destabilization of the lowest unoccupied molecular orbital upon coordination of the C-H bond to the undercoordinated Cr center in the Cr(CO)5-alkane σ-complex, and we define this as a general, orbital-based descriptor of the metal-alkane bond. Our study demonstrates the value of combining optical and X-ray spectroscopic methods as complementary tools to study the stability and reactivity of alkane σ-complexes in their role as the decisive intermediates in C-H bond activation reactions.
Collapse
Affiliation(s)
- Raphael M. Jay
- Department
of Physics and Astronomy, Uppsala University, 75120 Uppsala, Sweden
| | - Michael R. Coates
- Department
of Physics, AlbaNova University Center, Stockholm University, 10691 Stockholm, Sweden
| | - Huan Zhao
- Center
for Free-Electron Laser Science, Department of Physics, University of Hamburg, 22761 Hamburg, Germany
| | - Marc-Oliver Winghart
- Max
Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, 12489 Berlin, Germany
| | - Peng Han
- Max
Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, 12489 Berlin, Germany
| | - Ru-Pan Wang
- Center
for Free-Electron Laser Science, Department of Physics, University of Hamburg, 22761 Hamburg, Germany
| | - Jessica Harich
- Center
for Free-Electron Laser Science, Department of Physics, University of Hamburg, 22761 Hamburg, Germany
| | - Ambar Banerjee
- Department
of Physics and Astronomy, Uppsala University, 75120 Uppsala, Sweden
| | - Hampus Wikmark
- Department
of Physics and Astronomy, Uppsala University, 75120 Uppsala, Sweden
| | - Mattis Fondell
- Institute
for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und
Energie GmbH, 12489 Berlin, Germany
| | - Erik T. J. Nibbering
- Max
Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, 12489 Berlin, Germany
| | - Michael Odelius
- Department
of Physics, AlbaNova University Center, Stockholm University, 10691 Stockholm, Sweden
| | - Nils Huse
- Center
for Free-Electron Laser Science, Department of Physics, University of Hamburg, 22761 Hamburg, Germany
| | - Philippe Wernet
- Department
of Physics and Astronomy, Uppsala University, 75120 Uppsala, Sweden
| |
Collapse
|
2
|
Mascarenhas EJ, Fondell M, Büchner R, Eckert S, Vaz da Cruz V, Föhlisch A. The Role of the Lowest Excited Triplet State in Defining the Rate of Photoaquation of Hexacyanometalates. J Phys Chem Lett 2024; 15:241-247. [PMID: 38164541 PMCID: PMC10788954 DOI: 10.1021/acs.jpclett.3c02775] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2023] [Revised: 12/01/2023] [Accepted: 12/21/2023] [Indexed: 01/03/2024]
Abstract
Photosolvation is a type of ligand substitution reaction started by irradiation of a solution with light, triggering the replacement of a ligand with a molecule from the solvent. The excited state is created through many possible pathways. For the class of hexacyanides of groups 8 and 9 of the periodic table, irradiation in the ligand field band is followed by intersystem crossing to the lowest excited triplet state, which we propose to mediate the photoaquation reaction in this class of complexes. In this study, we present time-resolved X-ray absorption data showing indications of the triplet intermediate state in the cobalt(III) hexacyanide complex and we discuss general aspects of the photoaquation reaction in comparison with reported data on the isoelectronic iron(II) hexacyanide. Quantum chemical calculations are analyzed and suggest that the nature of the lowest excited triplet state in each complex can explain the drastically different rate of reactions observed.
Collapse
Affiliation(s)
- Eric J. Mascarenhas
- Institute
for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und
Energie GmbH, 12489 Berlin, Germany
| | - Mattis Fondell
- Institute
for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und
Energie GmbH, 12489 Berlin, Germany
| | - Robby Büchner
- Institute
for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und
Energie GmbH, 12489 Berlin, Germany
| | - Sebastian Eckert
- Institute
for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und
Energie GmbH, 12489 Berlin, Germany
| | - Vinicius Vaz da Cruz
- Institute
for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und
Energie GmbH, 12489 Berlin, Germany
| | - Alexander Föhlisch
- Institute
for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und
Energie GmbH, 12489 Berlin, Germany
- Institute
of Physics and Astronomy, Universität
Potsdam, 14476 Potsdam, Germany
| |
Collapse
|