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In situ formation of reactive (di)gallenes for bond activation

Nature Synthesis volume 3, pages 732–743 (2024)Cite this article

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Abstract

Access to reactive low-valent main-group complexes capable of bond activation commonly requires multistep syntheses, limiting options for electronic or steric fine-tuning. Here we present a one-pot synthesis of highly reactive Ga(I) complex cations for the activation of strong bonds that works analogously to the in situ generation of active transition-metal catalysts. Commercially available phosphines, selected by computational screening, react with the easily accessible salt [Ga(PhF)2-3]+[Al(ORF)4]− (PhF = C6H5F; RF = C(CF3)3) to form ambiphilic gallene cations in situ. Their dimerization tendency is reduced or even inhibited by variation of the electronic and steric properties of the chiral or achiral ligands. As an example, the reactivity of the in situ formed gallene [Ga(dipf)]+ (dipf = 1,1-bis(diisopropylphosphino)ferrocene) was studied. The cation reversibly dimerizes to the respective digallene in solution. Carbon–carbon multiple bonds in acyclic alkynes and alkenes undergo [2π + 2π] cycloadditions with the digallene [{Ga(dipf)}2]2+. The resulting digallacyclobutanes form reversibly at room temperature, yielding an equilibrium between the Ga(I) and Ga(II) species. Importantly, gallene [Ga(dipf)]+ inserts into H–Ga, H–Si and H–B bonds. Finally, reactivities of the dicationic digallene and cationic gallene are analysed by density functional theory and compared to neutral Al(I) and Ga(I) ambiphiles.

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Fig. 1: Examples of ambiphilic main-group metal complexes.
Fig. 2: Screening of bisphosphines.
Fig. 3: Structures of the gallium complexes in solid state and in solution.
Fig. 4: Analysis of digallene bonding.
Fig. 5: Overview on reactivity of [{Ga(dipf)}x]x+ (x = 1–2).
Fig. 6: DFT analysis of H–B bond insertion.

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Data availability

All data needed to evaluate the presented work are included in the article and/or the Supplementary Information. The X-ray crystallographic coordinates for the structures reported in this study have been deposited at the Cambridge Crystallographic Data Centre (CCDC), under deposition numbers CCDC 2306731 (1), 2306758 (2), 2306761 (3), 2306764 (4), 2306760 (5), 2306762 (6), 2306759 (7), 2306767 (9anti), 2306773 (9sym), 2306768 (12), 2306772 (13), 2306770 (14), 2307660 (17), 2306771 (18), 2308493 (19), 2306769 (20). These data can be obtained free of charge from the CCDX via www.ccdc.cam.ac.uk/data_request/cif. DFT structures, energies and orbitals are available free of charge via https://doi.org/10.6084/m9.figshare.25067939.

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Acknowledgements

We thank the German Research Foundation (DFG) for the funding of project KR2046/35-1 and 35-2 (I.K.) as well as the Albert-Ludwigs-University Freiburg for supporting the work. Furthermore, we thank B. Butschke for help with the scXRD structure solution. Furthermore, the authors acknowledge support by the state of Baden-Württemberg through bwHPC and the DFG through grant number INST 40/575-1 FUGG (I.K., JUSTUS 2 cluster).

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  1. Albert-Ludwigs-Universität Freiburg, Institute for Inorganic and Analytical Chemistry, Freiburg Materials Research Center FMF, Freiburg im Breisgau, Germany

    Philipp Dabringhaus, Harald Scherer & Ingo Krossing

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P.D. planned and conducted the experiments upon discussion with I.K. H.S. ran the NMR experiments. P.D. and H.S. analysed the NMR data. P.D. conducted the ultraviolet–visible, scXRD and infrared analyses and the DFT analysis, and analysed and discussed the data with I.K. P.D. and I.K. wrote the paper.

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Correspondence to Philipp Dabringhaus or Ingo Krossing.

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Supplementary experimental data, NMR spectra, infrared spectra, ultraviolet–visible spectra and DFT data.

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Cif files of the molecular structures

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Raw data for ultraviolet–visible spectra.

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Raw data for Van’t Hoff NMR analysis of the cycloaddition of styrene to 2.

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Dabringhaus, P., Scherer, H. & Krossing, I. In situ formation of reactive (di)gallenes for bond activation. Nat. Synth 3, 732–743 (2024). https://doi.org/10.1038/s44160-024-00521-9

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