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A crystalline aluminium–carbon-based ambiphile capable of activation and catalytic transfer of ammonia in non-aqueous media

Abstract

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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Fig. 1: Synthesis of the aluminiumcarbon-based ambiphile 2.
Fig. 2: Reversible N–H activation of ammonia.
Fig. 3: Catalytic ammonia transfer reactions in benzene at RT (pressure = 1.1 bar; 20 mol% compound 2).
Fig. 4: Kinetic studies of the catalytic alkylation of benzylbromide.
Fig. 5: Computed reaction profile of the ammonia transfer to Ia.

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Data availability

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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Acknowledgements

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.

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F.B. supervised the project. I.F. performed the quantum chemical calculations. J.P. supported the catalytic studies and the van’t Hoff analysis. F.K. conducted all experiments and wrote the manuscript with input from all authors.

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Correspondence to Frank Breher.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–33, discussion and coordinates of the calculated structures.

Supplementary Data 1

Source data for Supplementary Fig. 23a.

Supplementary Data 2

Source data for Supplementary Fig. 23c.

Supplementary Data 3

Crystallographic structure factor data for compound 2; CCDC reference 2180947.

Supplementary Data 4

Crystallographic structure factor data for compound 3; CCDC reference 2180948.

Source data

Source Data Fig. 2

Raw NMR data.

Source Data Fig. 4

Source data for the kinetic studies of the catalytic alkylation of benzylbromide.

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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. 16, 63–69 (2024). https://doi.org/10.1038/s41557-023-01340-9

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