Enhancement of London Dispersion in Frustrated Lewis Pairs: Towards a Crystalline Encounter Complex

Flip Holtrop; Christoph Helling; Martin Lutz; Nicolaas P. van Leest; Bas de Bruin; J. Chris Slootweg

doi:10.1055/a-1928-4902

Synlett, Table of Contents

CC BY 4.0 · Synlett 2023; 34(10): 1122-1128
DOI: 10.1055/a-1928-4902

cluster

Dispersion Effects

Enhancement of London Dispersion in Frustrated Lewis Pairs: Towards a Crystalline Encounter Complex

Flip Holtrop‡

^aVan ’t Hoff Institute for Molecular Sciences, University of Amsterdam, PO Box 94157, 1090 GD Amsterdam, The Netherlands

,

Christoph Helling‡

^aVan ’t Hoff Institute for Molecular Sciences, University of Amsterdam, PO Box 94157, 1090 GD Amsterdam, The Netherlands

,

Martin Lutz

^bStructural Biochemistry, Bijvoet Centre for Biomolecular Research, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, The Netherlands

,

Nicolaas P. van Leest

^aVan ’t Hoff Institute for Molecular Sciences, University of Amsterdam, PO Box 94157, 1090 GD Amsterdam, The Netherlands

,

Bas de Bruin

^aVan ’t Hoff Institute for Molecular Sciences, University of Amsterdam, PO Box 94157, 1090 GD Amsterdam, The Netherlands

,

J. Chris Slootweg ∗

^aVan ’t Hoff Institute for Molecular Sciences, University of Amsterdam, PO Box 94157, 1090 GD Amsterdam, The Netherlands

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Abstract

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Abstract

The encounter complex, i.e., the pre-organized assembly consisting of a Lewis acid and a Lewis base, is a fundamental concept in frustrated Lewis pair (FLP) chemistry. However, this donor–acceptor complex is challenging to study due to its transient nature. Here, we present a combined theoretical and experimental investigation on the potential isolation of an encounter complex enabled by enhancement of London dispersion forces between a sterically encumbered Lewis acid and base pair. Guided by computational analyses, the FLP originating from the bulky triarylamine N(3,5-tBu₂C₆H₃)₃ and the novel triarylborane B(3,5-tBu₂C₆H₃)₃ was investigated, leading to the isolation of a 1:1 co-crystal of both FLP components.

Key words

frustrated Lewis pairs - encounter complex - London dispersion forces - Lewis acid - Lewis base

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References

References and Notes
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23 Synthesis of N(3,5-tBu₂C₆H₃)₃/B(3,5-tBu₂C₆H₃)₃ N(3,5-tBu₂C₆H₃)₃ (10 mg, 0.017 mmol) and B(3,5-tBu₂C₆H₃)₃ (10 mg, 0.017 mmol) were dissolved in toluene-d ₈ (0.5 mL). Storage of the solution at –30 °C overnight afforded colorless crystals of N(3,5-tBu₂C₆H₃)₃/B(3,5-tBu₂C₆H₃)₃. Yield: 16 mg (0.014 mmol, 80%); mp 224 °C. IR (neat): ν = 2951, 2902, 2866, 1582, 1495, 1476, 1461, 1447, 1426, 1413, 1391, 1361, 1307, 1246, 1221, 1204, 1130, 1038, 1008, 993, 924, 896, 886, 865, 822, 727, 720, 711, 694, 671, 539, 463 cm^–1. ¹H NMR (500 MHz, C₆D₆): δ 8.03 (s, 3 H, p-CH), 7.86 (s, 6 H, o-CH), 7.46 (s, 3 H, p-CH), 7.27 (s, 6 H, o-CH), 1.32 (s, 54 H, tBu), 1.23 (s, 54 H, tBu).

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