Remote Back Strain: A Strategy for Modulating the Reactivity of Triarylboranes

Abstract

A strategy for modulating the Lewis acidity of triarylboranes is proposed based on the concept of remote back strain. Steric repulsion and noncovalent interactions, both generated between the aryl meta-substituents of triarylboranes, are found to be critical for determining the strength of the remote back strain. Applying this concept, we synthesized B[2,6-F₂-3,5-(TMS)₂-C₆H]₃ and the liquid B[2,6-F₂-3,5-(allyl)₂-C₆H]₃ and we demonstrated their superior catalytic activity for the hydrogenation of quinoline relative to B(C₆F₅)₃ or B(2,6-F₂C₆H₃)₃. Moreover, we established the first example of the catalytic hydrogenation of quinoline by using B[2,6-F₂-3,5-(allyl)₂-C₆H]₃ in the presence of a gaseous 1:1:1 molar mixture of H₂, CO, and CO₂.

Key words

triarylboranes - Lewis acids - frustrated Lewis pairs - hydrogenation - boron catalysis - hydrogen separation

Publication History

Received: 30 May 2023

Accepted after revision: 14 June 2023

Accepted Manuscript online:
14 June 2023

Article published online:
14 September 2023

• References and Notes

• 1a Carden JL, Dasgupta A, Melen RL. Chem. Soc. Rev. 2020; 49: 1706
• 1b Berger SM, Ferger M, Marder TB. Chem. Eur. J. 2021; 27: 7043
• 1c Berionni G. Chem. Synth. 2021; 1: 10
• 1d He J, Rauch F, Finze M, Marder TB. Chem. Sci. 2021; 12: 128
• 1e Lawson JR, Melen RL. Inorg. Chem. 2017; 56: 8627
• 1f Nori V, Pesciaioli F, Sinibaldi A, Giorgianni G, Carlone A. Catalysts 2022; 12: 5
• 2a Jupp AR, Stephan DW. Trends Chem. 2019; 1: 35
• 2b Hoshimoto Y, Ogoshi S. ACS Catal. 2019; 9: 5439
• 2c Scott DJ, Fuchter MJ, Ashley AE. Chem Soc. Rev. 2017; 46: 5689
• 2d Fasano V, Ingleson MJ. Synthesis 2018; 50: 1783
• 2e Paradies J. Acc. Chem. Res. 2023; 56: 821
• 2f Stephan DW, Erker G. Angew. Chem. Int. Ed. 2015; 54: 6400

Recently, Greb et al. have proposed that Lewis acidity could be classified as global, effective, or intrinsic. These labels refer to the thermodynamic energy change during adduct formation (∆E/ΔG), the spectroscopic changes observed on the Lewis base (e.g., the Gutmann–Beckett method) upon forming an adduct, and the intrinsic properties of the free boranes (e.g., the energy level of the empty p orbitals and its electron affinity), respectively, for details, see:
• 3a Erdmann P, Greb L. Angew. Chem. Int. Ed. 2022; 61: e202114550
• 3b Greb L. Chem. Eur. J. 2018; 24: 17881
• 3c Rodrigues Silva D, de Azevedo Santos L, Freitas MP, Fonseca Guerra C, Hamlin TA. Chem. Asian J. 2020; 15: 4043
• 3d Muller P. Pure Appl. Chem. 1994; 66: 1077
• 4 Sivaev IB, Bregadze VI. Coord. Chem. Rev. 2014; 270–271: 75
• 5a Zhang Y. Inorg. Chem. 1982; 21: 3889
• 5b Brown ID, Skowron A. J. Am. Chem. Soc. 1990; 112: 3401
• 5c Chattaraj PK, Sarkar U, Roy DR. Chem. Rev. 2006; 106: 2065
• 5d Jupp AR, Johnstone TC, Stephan DW. Dalton Trans. 2018; 47: 7029
• 6 Chase PA, Henderson LD, Piers WE, Parvez M, Clegg W, Elsegood MR. J. Organometallics 2006; 25: 349

For selected examples, see:
• 7a Morgan MM, Marwitz AJ. V, Piers WE, Parvez M. Organometallics 2013; 32: 317
• 7b Ashley AE, Herrington TJ, Wildgoose GG, Zaher H, Thompson AL, Rees NH, Krämer T, O’Hare D. J. Am. Chem. Soc. 2011; 133: 14727
• 7c Erős G, Mehdi H, Pápai I, Rokob TA, Király P, Tárkányi G, Soós T. Angew. Chem. Int. Ed. 2010; 49: 6559
• 7d Erős G, Nagy K, Mehdi H, Pápai I, Nagy P, Király P, Tárkányi G, Soós T. Chem. Eur. J. 2012; 18: 574
• 7e Gyömöre Á, Bakos M, Földes T, Pápai I, Domján A, Soós T. ACS Catal. 2015; 5: 5366
• 7f Dorkó É, Kótai B, Földes T, Gyömöre Á, Pápai I, Soós T. J. Organomet. Chem. 2017; 847: 258
• 7g Hoshimoto Y, Kinoshita T, Hazra S, Ohashi M, Ogoshi S. J. Am. Chem. Soc. 2018; 140: 7292
• 8 Hashimoto T, Asada T, Ogoshi S, Hoshimoto Y. Sci. Adv. 2022; 8: eade0189
• 9 Timoshkin AY, Davydova EI, Sevastianova TN. Suvorov A. V, Schaefer HF. Int. J. Quantum Chem. 2002; 88: 436
• 10a Poater A, Cosenza B, Correa A, Giudice S, Ragone F, Scarano V, Cavallo L. Eur. J. Inorg. Chem. 2009; 1759
• 10b Falivene L, Cao Z, Petta A, Serra L, Poater A, Oliva R, Scarano V, Cavallo L. Nat. Chem. 2019; 11: 872
• 10c Zapf L, Riethmann M, Föhrenbacher SA, Finze M, Radius U. Chem. Sci. 2023; 14: 2275
• 11a Adams R, Yuan HC. Chem. Rev. 1933; 12: 261
• 11b Patton A, Dirks JW, Gust D. J. Org. Chem. 1979; 44: 4749

For examples that include trialkylsilyl groups, see:
• 11c Gorecka J, Heiss C, Scopelliti R, Schlosser M. Org. Lett. 2004; 6: 4591
• 12 Tris[2,6-difluoro-3,5-bis(trimethylsilyl)phenyl]borane (B¹) Colorless crystals; yield: 717.8 mg (35%; 4% after recrystallization). ¹H NMR (400 MHz, C₆D₆): δ = 7.78 [t, ⁴ J _H,_F = 7.0 Hz, 3 H, Ar-H), 0.26 (s, 54 H, Si(CH ₃)₃]. ¹¹B NMR (128 MHz, C₆D₆): not observed. ¹³C{¹H} NMR (101 MHz, C₆D₆): δ = 172.2 (dd, ¹ J _C,_F = 248.5 Hz, ³ J _C,_F = 12.1 Hz), 146.6 (dt, J = 15.2 Hz, J = 3.0 Hz), 121.3 (m), 118.7 (t, J = 28.3 Hz), –1.0. ¹⁹F NMR (376 MHz, C₆D₆): δ = –86.7 (d, ⁴ J _H,_F = 7.5 Hz, 6 F).
• 13 Murakami K, Hirano K, Yorimitsu H, Oshima K. Angew. Chem. Int. Ed. 2008; 47: 5833
• 14 CCDC 2265357, 2265358, and 2265359 contains the supplementary crystallographic data for compounds B¹ , CH₃CN–B² , and (Et₃P=O–B¹ ). The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/structures
• 15 Tris(3,5-diallyl-2,6-difluorophenyl)borane (B²) Liquid; yield: 265.1 mg (23%). ¹H NMR (400 MHz, C₆D₆): δ = 6.93 (t, ⁴ J _H,_F = 8.2 Hz, 3 H, Ar-H), 5.75 (m, 6 H, CH₂CH=CH₂), 4.94 (m, 12 H, CH₂CH=CH ₂), 3.13 (d, J = 6.4 Hz, 12 H, CH ₂CH=CH₂). ¹¹B NMR (128 MHz, C₆D₆): not observed. ¹³C{¹H} NMR (101 MHz, C₆D₆): δ = 161.6 (dd, ¹ J _{C, F} = 249.5 Hz, ³ J _{C, F} = 11.1 Hz), 136.3, 135.9, 122.7 (m), 116.3, 32.9. Resonances of the C_ipso with respect to the boron atom were not observed.¹⁹F NMR (376 MHz, C₆D₆): δ = –110.0 (d, ⁴ J _{H, F} = 7.5 Hz, 6 F).
• 16 Reineke MH, Sampson MD, Rheingold AL, Kubiak CP. Inorg. Chem. 2015; 54: 3211
• 17 We also calculated the tetrahedral character for each boron center and obtained results identical to the τ_δ(B) values; for details, see SI: Figures S9–S13.
• 18 Holtrop F, Helling C, Lutz M, van Leest NP, de Bruin B, Slootweg JC. Synlett 2023; 34: 1122

For selected examples, see:
• 19a Geier SJ, Chase PA, Stephan DW. Chem. Commun. 2010; 46: 4884
• 19b Scott DJ, Fuchter MJ, Ashley AE. Angew. Chem. Int. Ed. 2014; 53: 10218
• 19c Zhang Z, Du H. Org. Lett. 2015; 17: 6266
• 19d Han C, Zhang E, Feng X, Wang S, Du H. Tetrahedron Lett. 2018; 59: 1400
• 20 Mahdi T, del Castillo JN, Stephan DW. Organometallics 2013; 32: 1971
• 21 1,2,3,4-Tetrahydroquinoline; Typical Procedure A 30 mL autoclave was charged with Qin (263.2 mg, 2.0 mmol), B² (59.8 mg, 0.1 mmol; 5 mol%), tetradecane (142.5 mg; internal standard), and toluene (1.3 mL). Once sealed, the autoclave was pressurized with H₂, CO, CO₂ (20 atm each) and heated 100 °C for 8 h; yield: >99% (GC).
• 22a Jorschick H, Vogl M, Preuster P, Bösmann A, Wasserscheid P. Int. J. Hydrogen Energy 2019; 44: 31172
• 22b Li S, Lin L, Wang Z, Ma D. Innovation 2023; 4: 100353