The σ-alkane complexes of transition metals, which contain an essentially intact alkane molecule weakly bound to the metal, have been well established as crucial intermediates in the activation of the strong C–H σ-bonds found in alkanes. Methane, the simplest alkane, binds even more weakly than larger alkanes. Here we report an example of a long-lived methane complex formed by directly binding methane as an incoming ligand to a reactive organometallic complex. Photo-ejection of carbon monoxide from a cationic osmium–carbonyl complex dissolved in an inert hydrofluorocarbon solvent saturated with methane at −90 °C affords an osmium(II) complex, [η5-CpOs(CO)2(CH4)]+, containing methane bound to the metal centre. Nuclear magnetic resonance (NMR) spectroscopy confirms the identity of the σ-methane complex and shows that the four protons of the metal-bound methane are in rapid exchange with each other. The methane ligand has a characteristically shielded 1H NMR resonance (δ –2.16), and the highly shielded carbon resonance (δ –56.3) shows coupling to the four attached protons (1JC–H = 127 Hz). The methane complex has an effective half-life of about 13 hours at –90 °C.
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The authors declare that the data supporting the findings of this study are available within the paper and its Supplementary Information files.
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This research was supported (partially or fully) by the Australian Government (1) through the Australian Research Council’s Discovery Projects funding scheme (project DP170104301) and (2) with the assistance of resources and services from the National Computational Infrastructure. This research includes computations using the computational cluster Katana supported by Research Technology Services at University of New South Wales Sydney. We acknowledge the technical expertise and assistance of J. Richards in the Science/Engineering workshop at University of New South Wales for modifying and constructing a bespoke NMR tube cap to enable sample preparation and irradiation at low temperature under rigorous inert atmosphere conditions.
The authors declare no competing interests.
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Supplementary Figs. 1–16, Tables 1–6, Discussion and references.
Data for graphs in Supplementary Figs. 12 and 13.
Text file containing coordinates of all calculated structures in xyz format (viewable with common software such as Mercury).
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Watson, J.D., Field, L.D. & Ball, G.E. Binding methane to a metal centre. Nat. Chem. 14, 801–804 (2022). https://doi.org/10.1038/s41557-022-00929-w