Despite recent achievements in the field of frustrated Lewis pairs (FLPs) for small molecule activations, the reversible activation and catalytic transformations of N–H-activated ammonia remain a challenge. Here we report on a rare combination of an aluminium Lewis acid and a carbon Lewis base. A so-called hidden FLP consisting of a phosphorus ylide featuring an aluminium fragment in the ortho position of a phenyl ring scaffold is introduced. Although the formation of the Lewis acid/base adduct is observed in the solid state, which at first glance leads to formally quenched FLP reactivity, we show that the title compound readily reacts with non-aqueous ammonia thermoneutrally and splits the N–H bond reversibly at ambient temperature. In addition, NH3 transfer reactions mediated by a main-group catalyst are presented. This proof-of-principle study is expected to initiate further activities in utilizing N–H-activated ammonia as a readily available, atom-economical nitrogen source.
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The data that support the findings of this study are available within the paper and its Supplementary Information. Raw and unprocessed NMR, HRMS and gel permeation chromatography data are available from figshare (https://doi.org/10.6084/m9.figshare.24042771)54. Materials and methods, computational studies including cartesian coordinates and energies for the computed structures, experimental procedures, characterization data, NMR spectra and mass spectrometry data are available in the paper with further details in the Supplementary Information. Crystallographic data for the structures reported in this article have been deposited at the Cambridge Crystallographic Data Centre, under deposition numbers 2180947 (2) and 2180948 (3). For further crystallographic details see Supplementary Section 2. Copies of the data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures/. Source data are provided with this paper.
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This work was partly carried out with the support of the Karlsruhe Nano Micro Facility, a Helmholtz research platform at KIT, and we thank D. Fenske, A. Hinz and B. Birenheide for help with X-ray diffraction. We also thank K. Kohnle, A. Mösle, L. Hirsch and A. Hochgesand from the Institute of Organic Chemistry at KIT for performing mass spectral and elemental analysis. R. Nickisch and L. Santos Correa from the Institute of Organic Chemistry at KIT are acknowledged for their help with gel permeation chromatography measurements. The authors acknowledge support by the state of Baden-Württemberg through bwHPC and the German Research Foundation through grant no INST 40/575-1 FUGG (JUSTUS 2 cluster). I.F. is grateful to the Spanish MCIN/AEI/10.13039/501100011033 (grants PID2019-106184GB-I00 and PID2022-139318NB-I00). The authors received no specific funding for this work.
The authors declare no competing interest.
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Supplementary Figs. 1–33, discussion and coordinates of the calculated structures.
Source data for Supplementary Fig. 23a.
Source data for Supplementary Fig. 23c.
Crystallographic structure factor data for compound 2; CCDC reference 2180947.
Crystallographic structure factor data for compound 3; CCDC reference 2180948.
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Krämer, F., Paradies, J., Fernández, I. et al. A crystalline aluminium–carbon-based ambiphile capable of activation and catalytic transfer of ammonia in non-aqueous media. Nat. Chem. (2023). https://doi.org/10.1038/s41557-023-01340-9