Stable GaX2, InX2 and TlX2 radicals

Journal name:
Nature Chemistry
Volume:
6,
Pages:
315–319
Year published:
DOI:
doi:10.1038/nchem.1870
Received
Accepted
Published online

Abstract

The chemistry of the Group 13 metals is dominated by the +1 and +3 oxidation states, and simple monomeric M(II) species are typically short-lived, highly reactive species. Here we report the first thermally robust monomeric MX2 radicals of gallium, indium and thallium. By making use of sterically demanding boryl substituents, compounds of the type M(II)(boryl)2 (M = Ga, In, Tl) can be synthesized. These decompose above 130 °C and are amenable to structural characterization in the solid state by X-ray crystallography. Electron paramagnetic resonance and computational studies reveal a dominant metal-centred character for all three radicals (>70% spin density at the metal). M(II) species have been invoked as key short-lived intermediates in well-known electron-transfer processes; consistently, the chemical behaviour of these novel isolated species reveals facile one-electron shuttling processes at the metal centre.

At a glance

Figures

  1. Syntheses of M(II) complexes that feature a supporting bis(boryl) ligand set from either M(I) or M(III) precursors.
    Figure 1: Syntheses of M(II) complexes that feature a supporting bis(boryl) ligand set from either M(I) or M(III) precursors.

    i, For 2-Ga from Ga[N(SiMe3)Dipp*], (thf)2Li[B(NDippCH)2] (1, 2.0 equiv.), toluene, −78 °C to 0 °C over five hours, then 12-crown-4 (2.0 equiv.), room temperature, one hour, 64%; for 2-In from In[N(SiMe3)Dipp*], 1 (2.0 equiv.), toluene, −78 °C to 0 °C over five hours, then 12-crown-4 (2.0 equiv.), room temperature, one hour, 38%; for 2-Tl from Tl[N(SiMe3)2], 1 (1.0 equiv.), hexane, −45 °C, five minutes, 52%; for 2-Tl from TlCl, 1 (1.0 equiv.), hexane, −78 °C to room temperature, 12 hours, 75%. ii, For 2-In from 3-In, K metal (0.94 equiv.), benzene-d6/thf (12:1), room temperature, sonication for two hours, 75% (by NMR spectroscopy), or Sm(η5-C5Me5)2(thf) (1.0 equiv.), benzene, room temperature, 10 minutes, 67% (isolated). The syntheses of 2-Ga and 2-In can also be accomplished from M(I) precursors and 1 (1 equiv.) without the use of 12-crown-4, although slightly lower yields and greater contamination with HB(NDippCH)2 are observed. R and R′ are aryl or silyl groups.

  2. Molecular structures.
    Figure 2: Molecular structures.

    a, 2-Ga. b, 2-In. c, 2-Tl. Ellipsoids are at the 50% probability level, carbon-bound hydrogen atoms are omitted and iPr groups are shown in a wireframe format for clarity. Selected bond lengths: 2-Ga, Ga(1)–B(1) 2.045(2) Å, Ga(1)–B(2) 2.051(2) Å; 2-In, In(1)–B(1) 2.246(3) Å, In(1)–B(2) 2.242(3) Å; 2-Tl, Tl(1)–B(1) 2.173(6) Å, Tl(1)–B(2) 2.167(5) Å.

  3. Field-sweep EPR spectra for 2-Ga, 2-In and 2-Tl measured in frozen pentane/hexane solution (1:1), along with the corresponding simulations.
    Figure 3: Field-sweep EPR spectra for 2-Ga, 2-In and 2-Tl measured in frozen pentane/hexane solution (1:1), along with the corresponding simulations.

    a, X-band continuous-wave EPR spectra. b, W-band echo-detected EPR spectra, first-derivative representation. For 2-Tl the signal starts at ∼4.5 T (g1 = 1.23) and could only be recorded to 6 T (the upper limit of our magnet). The principal g values gi and metal hyperfine couplings Ai derived from the simulation are as follows (the corresponding values calculated using DFT are italicized and in parentheses). 2-Ga, g1, g2, g3 = 1.881, 1.998, 2.014 (1.8760, 1.9960, 2.0113); A(69Ga) = 444, 1,032, 533 = 670 + (226, 362,  −137) MHz (214 + (−185, 312,  −127) MHz). 2-In, g1, g2, g3 = 1.719, 1.954, 1.999 (1.7338, 1.9689, 2.0125); A(115In) = 913, 1,936, 793 = 1,214 + (301, 722,  −421) MHz (645 + (−408, 621,  −214) MHz). 2-Tl, g1 g2, g3 = 0.6, 0.7, 1.23 (1.0047, 1.4381, 1.697); A(205Tl) =  −8,000, 10,300,  −8,100 =  −1,933 + (6,067, 12,233,  −6,167) MHz (−2866 + (−6,105, 7,592,  −1,478) MHz).

  4. Redox chemistry of 2-Tl.
    Figure 4: Redox chemistry of 2-Tl.

    a, One-electron chemical oxidation and reduction processes. b, Molecular structure of [K(18-crown-6)]+[2-Tl]- · OEt2 (ellipsoids are shown at the 50% probability level, diethyl ether solvated molecule, C-bound hydrogen atoms are omitted and iPr groups are shown in a wireframe format for clarity). Selected bond lengths and angles: Tl(1)–B(1) 2.454(4) Å, Tl(1)–B(2) 2.456(4) Å, B(1)–Tl(1)–B(2) 109.8(1)°. i, [Fe(η5-C5H5)2][B(C6H3(CF3)2-3,5)4] (1.0 equiv.), diethyl ether, room temperature, ten minutes, 98%, or [CPh3][B(C6F5)4] (1.0 equiv.), benzene-d6, room temperature, NMR scale. ii, [K(18-crown-6)][C10H8], (1.33 equiv.), THF, −196 °C to room temperature, two minutes, 26%. iii, [2-Tl]+[B(C6H3(CF3)2-3,5)4]- plus [K(18-crown-6)]+[2-Tl]- (1:1), THF/benzene-d6, room temperature, two minutes, quantitative.

Compounds

10 compounds View all compounds
  1. Bis[1,3-bis[2,6-bis(1-methylethyl)phenyl]-1,3-dihydro-2H-1,3,2-diazaborol-2-yl]-indium
    Compound 2-In Bis[1,3-bis[2,6-bis(1-methylethyl)phenyl]-1,3-dihydro-2H-1,3,2-diazaborol-2-yl]-indium
  2. Bis[1,3-bis[2,6-bis(1-methylethyl)phenyl]-1,3-dihydro-2H-1,3,2-diazaborol-2-yl]-thallium
    Compound 2-Tl Bis[1,3-bis[2,6-bis(1-methylethyl)phenyl]-1,3-dihydro-2H-1,3,2-diazaborol-2-yl]-thallium
  3. Tris[1,3-bis[2,6-bis(1-methylethyl)phenyl]-1,3-dihydro-2H-1,3,2-diazaborol-2-yl]-diindium
    Compound 4-In Tris[1,3-bis[2,6-bis(1-methylethyl)phenyl]-1,3-dihydro-2H-1,3,2-diazaborol-2-yl]-diindium
  4. Tetrakis[1,3-bis[2,6-bis(1-methylethyl)phenyl]-1,3-dihydro-2H-1,3,2-diazaborol-2-yl]-octathallium
    Compound Tl8B4 Tetrakis[1,3-bis[2,6-bis(1-methylethyl)phenyl]-1,3-dihydro-2H-1,3,2-diazaborol-2-yl]-octathallium
  5. Bis[1,3-bis[2,6-bis(1-methylethyl)phenyl]-1,3-dihydro-2H-1,3,2-diazaborol-2-yl]-gallium
    Compound 2-Ga Bis[1,3-bis[2,6-bis(1-methylethyl)phenyl]-1,3-dihydro-2H-1,3,2-diazaborol-2-yl]-gallium
  6. Bis[1,3-bis[2,6-bis(1-methylethyl)phenyl]-1,3-dihydro-2H-1,3,2-diazaborol-2-yl]-chloro-indium
    Compound 3-In Bis[1,3-bis[2,6-bis(1-methylethyl)phenyl]-1,3-dihydro-2H-1,3,2-diazaborol-2-yl]-chloro-indium
  7. Bis[1,3-bis[2,6-bis(1-methylethyl)phenyl]-1,3-dihydro-2H-1,3,2-diazaborol-2-yl]-chloro-gallium
    Compound 3-Ga Bis[1,3-bis[2,6-bis(1-methylethyl)phenyl]-1,3-dihydro-2H-1,3,2-diazaborol-2-yl]-chloro-gallium
  8. Tris[1,3-bis[2,6-bis(1-methylethyl)phenyl]-1,3-dihydro-2H-1,3,2-diazaborol-2-yl]-digallium
    Compound 4-Ga Tris[1,3-bis[2,6-bis(1-methylethyl)phenyl]-1,3-dihydro-2H-1,3,2-diazaborol-2-yl]-digallium
  9. Bis[1,3-bis[2,6-bis(1-methylethyl)phenyl]-1,3-dihydro-2H-1,3,2-diazaborol-2-yl]-thallium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate
    Compound [2-Tl]+[B(C6H3(CF3)2-3,5)4]- Bis[1,3-bis[2,6-bis(1-methylethyl)phenyl]-1,3-dihydro-2H-1,3,2-diazaborol-2-yl]-thallium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate
  10. [(18-Crown-6-ether) potassium] bis[1,3-bis[2,6-bis(1-methylethyl)phenyl]-1,3-dihydro-2H-1,3,2-diazaborol-2-yl]-thallate
    Compound [K(18-crown-6)]+[2-Tl]- [(18-Crown-6-ether) potassium] bis[1,3-bis[2,6-bis(1-methylethyl)phenyl]-1,3-dihydro-2H-1,3,2-diazaborol-2-yl]-thallate

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Author information

Affiliations

  1. Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, UK

    • Andrey V. Protchenko,
    • Christina Y. Tang,
    • Andrew D. Schwarz,
    • Michael J. Kelly,
    • Nicholas Phillips,
    • Remi Tirfoin,
    • Philip Mountford &
    • Simon Aldridge
  2. School of Chemistry, PO Box 23, Monash University, Melbourne, Victoria 3800, Australia

    • Deepak Dange &
    • Cameron Jones
  3. Centre for Advanced Electron Spin Resonance, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR

    • Jeffrey R. Harmer
  4. Center for Advanced Imaging, University of Queensland, St Lucia, Queensland 4072, Australia

    • Jeffrey R. Harmer
  5. Department of Chemistry, University College London, Christopher Ingold Laboratories, 20 Gordon Street, London WC1H 0AJ, UK

    • Krishna Hassomal Birjkumar &
    • Nikolas Kaltsoyannis

Contributions

A.V.P. and D.D. synthesized and characterized the compounds. J.R.H. carried out the EPR studies. C.Y.T., A.D.S., M.J.K., N.P. and C.J. mounted the crystals, collected the single-crystal X-ray crystallographic data and solved the crystal structures. K.H.B. and N.K. carried out the DFT calculations. R.T. carried out the electrochemical measurements. N.K., P.M., C.J. and S.A. generated and managed the project and wrote the manuscript. All authors discussed the results and commented on the manuscript.

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The authors declare no competing financial interests.

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Supplementary information

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  1. Supplementary information (6,897 KB)

    Supplementary information

Crystallographic information files

  1. Supplementary information (25 KB)

    Crystallographic data for compound 2-Ga.

  2. Supplementary information (23 KB)

    Crystallographic data for compound 2-In.

  3. Supplementary information (23 KB)

    Crystallographic data for compound 2-Tl.

  4. Supplementary information (39 KB)

    Crystallographic data for compound 3-Ga.

  5. Supplementary information (38 KB)

    Crystallographic data for compound 3-In.

  6. Supplementary information (34 KB)

    Crystallographic data for compound 4-Ga.

  7. Supplementary information (51 KB)

    Crystallographic data for compound 4-In.

  8. Supplementary information (51 KB)

    Crystallographic data for compound Tl8{B(NDippCH)2}4.

  9. Supplementary information (46 KB)

    Crystallographic data for compound [K(18-crown-6)][2-Tl].

  10. Supplementary information (117 KB)

    Crystallographic data for compound [2-Tl][B{C6H3(CF3)2-3,5}].

Additional data