Andrew E. Ashley - Cochemist

Designing effective ‘frustrated Lewis pair’ hydrogenation catalysts

Co-reporter:Daniel J. Scott;Matthew J. Fuchter

Chemical Society Reviews 2017 vol. 46(Issue 19) pp:5689-5700

Publication Date(Web):2017/10/02

DOI:10.1039/C7CS00154A

The past decade has seen the subject of transition metal-free catalytic hydrogenation develop incredibly rapidly, transforming from a largely hypothetical possibility to a well-established field that can be applied to the reduction of a diverse variety of functional groups under mild conditions. This remarkable change is principally attributable to the development of so-called ‘frustrated Lewis pairs’: unquenched combinations of bulky Lewis acids and bases whose dual reactivity can be exploited for the facile activation of otherwise inert chemical bonds. While a number of comprehensive reviews into frustrated Lewis pair chemistry have been published in recent years, this tutorial review aims to provide a focused guide to the development of efficient FLP hydrogenation catalysts, through identification and consideration of the key factors that govern their effectiveness. Following discussion of these factors, their importance will be illustrated using a case study from our own research, namely the development of FLP protocols for successful hydrogenation of aldehydes and ketones, and for related moisture-tolerant hydrogenation.

Designing effective ‘frustrated Lewis pair’ hydrogenation catalysts

Co-reporter:Daniel J. Scott;Matthew J. Fuchter

Chemical Society Reviews 2017 vol. 46(Issue 19) pp:5689-5700

Publication Date(Web):2017/10/02

DOI:10.1039/C7CS00154A

The past decade has seen the subject of transition metal-free catalytic hydrogenation develop incredibly rapidly, transforming from a largely hypothetical possibility to a well-established field that can be applied to the reduction of a diverse variety of functional groups under mild conditions. This remarkable change is principally attributable to the development of so-called ‘frustrated Lewis pairs’: unquenched combinations of bulky Lewis acids and bases whose dual reactivity can be exploited for the facile activation of otherwise inert chemical bonds. While a number of comprehensive reviews into frustrated Lewis pair chemistry have been published in recent years, this tutorial review aims to provide a focused guide to the development of efficient FLP hydrogenation catalysts, through identification and consideration of the key factors that govern their effectiveness. Following discussion of these factors, their importance will be illustrated using a case study from our own research, namely the development of FLP protocols for successful hydrogenation of aldehydes and ketones, and for related moisture-tolerant hydrogenation.

Cationic silyldiazenido complexes of the Fe(diphosphine)2(N2) platform: structural and electronic models for an elusive first intermediate in N2 fixation

Co-reporter:Adam D. Piascik;Peter J. Hill;Andrew D. Crawford;Laurence R. Doyle;Jennifer C. Green

Chemical Communications 2017 vol. 53(Issue 54) pp:7657-7660

Publication Date(Web):2017/07/04

DOI:10.1039/C7CC04188H

The first cationic Fe silyldiazenido complexes, [Fe(PP)2(NN–SiMe3)]+[BArF4]− (PP = dmpe/depe), have been synthesised and thoroughly characterised. Computational studies show the compounds to be useful structural and electronic surrogates for the more elusive [Fe(PP)2(NN–H)]+, which are postulated intermediates in the H+/e− mediated fixation of N2 by Fe(PP)2(N2) species.

Selective Catalytic Reduction of N2 to N2H4 by a Simple Fe Complex

Co-reporter:Peter J. Hill, Laurence R. Doyle, Andrew D. Crawford, William K. Myers, and Andrew E. Ashley

Journal of the American Chemical Society 2016 Volume 138(Issue 41) pp:13521-13524

Publication Date(Web):October 4, 2016

DOI:10.1021/jacs.6b08802

The catalytic fixation of N2 by molecular Fe compounds is a rapidly developing field, yet thus far few complexes can effect this transformation, and none are selective for N2H4 production. Herein we report that the simple Fe(0) complex Fe(Et2PCH2CH2PEt2)2(N2) (1) is an efficient catalyst for the selective conversion of N2 (>25 molecules N2 fixed) into N2H4, attendant with the production of ca. one molecule of NH3. Notably, the reductant (CoCp*2) and acid (Ph2NH2OTf) used are considerably weaker than conventional chemical H+ and e– sources used in previous demonstrations of N2 turnover by synthetic Fe compounds. These results show that the direct catalytic conversion of N2 to the hydrazine oxidation state on molecular Fe complexes is viable and that the mechanism of NH3 formation by such systems may proceed via Fe–N2H4 intermediates.

Teaching old compounds new tricks: efficient N2 fixation by simple Fe(N2)(diphosphine)2 complexes

Co-reporter:Laurence R. Doyle, Peter J. Hill, Gregory G. Wildgoose and Andrew E. Ashley

Dalton Transactions 2016 vol. 45(Issue 18) pp:7550-7554

Publication Date(Web):05 Apr 2016

DOI:10.1039/C6DT00884D

The Fe(0) species Fe(N2)(dmpe)2 exists in equilibrium with the previously unreported dimer, [Fe(dmpe2)2(μ-N2)]. For the first time these complexes, alongside Fe(N2)(depe)2, are shown unambiguously to produce N2H4 and/or NH3 upon addition of triflic acid; for Fe(N2)(depe)2 this represents one of the highest electron conversion efficiencies for Fe complexes to date.

Facile Protocol for Water-Tolerant “Frustrated Lewis Pair”-Catalyzed Hydrogenation

Co-reporter:Daniel J. Scott, Trevor R. Simmons, Elliot J. Lawrence, Gregory G. Wildgoose, Matthew J. Fuchter, and Andrew E. Ashley

ACS Catalysis 2015 Volume 5(Issue 9) pp:5540

Publication Date(Web):August 17, 2015

DOI:10.1021/acscatal.5b01417

Despite rapid advances in the field of metal-free, “frustrated Lewis pair” (FLP)-catalyzed hydrogenation, the need for strictly anhydrous reaction conditions has hampered wide-scale uptake of this methodology. Herein, we report that, despite the generally perceived moisture sensitivity of FLPs, 1,4-dioxane solutions of B(C6F5)3 actually show appreciable moisture tolerance and can catalyze hydrogenation of a range of weakly basic substrates without the need for rigorously inert conditions. In particular, reactions can be performed directly in commercially available nonanhydrous solvents without subsequent drying or use of internal desiccants.Keywords: catalytic hydrogenation; metal-free; solvent effects; water tolerance; “frustrated Lewis pairs”

H2 activation by a highly electron-deficient aralkylated organoborane

Co-reporter:Peter J. Hill, Thomas J. Herrington, Nicholas H. Rees, Andrew J. P. White and Andrew E. Ashley

Dalton Transactions 2015 vol. 44(Issue 19) pp:8984-8992

Publication Date(Web):31 Mar 2015

DOI:10.1039/C5DT00821B

The electron-deficient and sterically bulky trialkylborane derivative tris[bis(pentafluorophenyl)methyl]borane [1, B(CH(C6F5)2)3], has been synthesised and comprehensively characterised; detailed 1H and 19F NMR studies reveal two dynamic bond rotational processes in the solution phase. Despite conventional probes (Gutmann–Beckett and Childs methods) implying that the compound has a very limited Lewis acidity, it was used to generate frustrated Lewis pairs capable of heterolytically activating H2 in ethereal solutions, which suggests that the hydridophilicity of 1 is comparable to the potent Lewis acid B(C6F5)3.

An Electrochemical Study of Frustrated Lewis Pairs: A Metal-Free Route to Hydrogen Oxidation

Co-reporter:Elliot J. Lawrence ; Vasily S. Oganesyan ; David L. Hughes ; Andrew E. Ashley ;Gregory G. Wildgoose

Journal of the American Chemical Society 2014 Volume 136(Issue 16) pp:6031-6036

Publication Date(Web):April 2, 2014

DOI:10.1021/ja500477g

Frustrated Lewis pairs have found many applications in the heterolytic activation of H2 and subsequent hydrogenation of small molecules through delivery of the resulting proton and hydride equivalents. Herein, we describe how H2 can be preactivated using classical frustrated Lewis pair chemistry and combined with in situ nonaqueous electrochemical oxidation of the resulting borohydride. Our approach allows hydrogen to be cleanly converted into two protons and two electrons in situ, and reduces the potential (the required energetic driving force) for nonaqueous H2 oxidation by 610 mV (117.7 kJ mol–1). This significant energy reduction opens routes to the development of nonaqueous hydrogen energy technology.

Nonmetal Catalyzed Hydrogenation of Carbonyl Compounds

Co-reporter:Daniel J. Scott ; Matthew J. Fuchter

Journal of the American Chemical Society 2014 Volume 136(Issue 45) pp:15813-15816

Publication Date(Web):October 21, 2014

DOI:10.1021/ja5088979

Solutions of the Lewis acid B(C6F5)3 in 1,4-dioxane are found to effectively catalyze the hydrogenation of a variety of ketones and aldehydes. These reactions, the first to allow entirely metal-free catalytic hydrogenation of carbonyl groups under relatively mild reaction conditions, are found to proceed via a “frustrated Lewis pair” mechanism in which the solvent, a weak Brønsted base yet moderately strong donor, plays a pivotal role.

Bypassing a highly unstable frustrated Lewis pair: dihydrogen cleavage by a thermally robust silylium–phosphine adduct

Co-reporter:Thomas J. Herrington, Bryan J. Ward, Laurence R. Doyle, Joe McDermott, Andrew J. P. White, Patricia A. Hunt and Andrew E. Ashley

Chemical Communications 2014 vol. 50(Issue 84) pp:12753-12756

Publication Date(Web):26 Aug 2014

DOI:10.1039/C4CC05905K

The thermally robust silylium complex [iPr3Si–PtBu3]+[B(C6F5)4]− (1) activates H2/D2 at 90 °C (PhCl); no evidence for dissociation into the separated Lewis pair is found. DFT calculations show H2 cleavage proceeds via Si–P bond elongation to form an encounter complex directly from the adduct, thus avoiding the non-isolable iPr3Si+–PtBu3 FLP.

A Convenient Synthetic Protocol to 1,2-Bis(dialkylphosphino)ethanes

Co-reporter:Laurence R. Doyle;Alex Heath;Choon Heng Low

Advanced Synthesis & Catalysis 2014 Volume 356( Issue 2-3) pp:603-608

Publication Date(Web):

DOI:10.1002/adsc.201300787

Metal-Free Dihydrogen Oxidation by a Borenium Cation: A Combined Electrochemical/Frustrated Lewis Pair Approach

Co-reporter:Elliot J. Lawrence;Thomas J. Herrington;Dr. Andrew E. Ashley;Dr. Gregory G. Wildgoose

Angewandte Chemie International Edition 2014 Volume 53( Issue 37) pp:9922-9925

Publication Date(Web):

DOI:10.1002/anie.201405721

Abstract

In order to use H₂ as a clean source of electricity, prohibitively rare and expensive precious metal electrocatalysts, such as Pt, are often used to overcome the large oxidative voltage required to convert H₂ into 2 H⁺ and 2 e⁻. Herein, we report a metal-free approach to catalyze the oxidation of H₂ by combining the ability of frustrated Lewis pairs (FLPs) to heterolytically cleave H₂ with the in situ electrochemical oxidation of the resulting borohydride. The use of the NHC-stabilized borenium cation [(IiPr₂)(BC₈H₁₄)]⁺ (IiPr₂=C₃H₂(NiPr)₂, NHC=N-heterocyclic carbene) as the Lewis acidic component of the FLP is shown to decrease the voltage required for H₂ oxidation by 910 mV at inexpensive carbon electrodes, a significant energy saving equivalent to 175.6 kJ mol⁻¹. The NHC–borenium Lewis acid also offers improved catalyst recyclability and chemical stability compared to B(C₆F₅)₃, the paradigm Lewis acid originally used to pioneer our combined electrochemical/frustrated Lewis pair approach.

Metal-Free Hydrogenation Catalyzed by an Air-Stable Borane: Use of Solvent as a Frustrated Lewis Base

Co-reporter:Daniel J. Scott;Dr. Matthew J. Fuchter ;Dr. Andrew E. Ashley

Angewandte Chemie International Edition 2014 Volume 53( Issue 38) pp:10218-10222

Publication Date(Web):

DOI:10.1002/anie.201405531

Abstract

In recent years ‘frustrated Lewis pairs’ (FLPs) have been shown to be effective metal-free catalysts for the hydrogenation of many unsaturated substrates. Even so, limited functional-group tolerance restricts the range of solvents in which FLP-mediated reactions can be performed, with all FLP-mediated hydrogenations reported to date carried out in non-donor hydrocarbon or chlorinated solvents. Herein we report that the bulky Lewis acids B(C₆Cl₅)_x(C₆F₅)_3−x (x=0–3) are capable of heterolytic H₂ activation in the strong-donor solvent THF, in the absence of any additional Lewis base. This allows metal-free catalytic hydrogenations to be performed in donor solvent media under mild conditions; these systems are particularly effective for the hydrogenation of weakly basic substrates, including the first examples of metal-free catalytic hydrogenation of furan heterocycles. The air-stability of the most effective borane, B(C₆Cl₅)(C₆F₅)₂, makes this a practically simple reaction method.

Metal-Free Dihydrogen Oxidation by a Borenium Cation: A Combined Electrochemical/Frustrated Lewis Pair Approach

Co-reporter:Elliot J. Lawrence;Thomas J. Herrington;Dr. Andrew E. Ashley;Dr. Gregory G. Wildgoose

Angewandte Chemie 2014 Volume 126( Issue 37) pp:10080-10083

Publication Date(Web):

DOI:10.1002/ange.201405721

Abstract

In order to use H₂ as a clean source of electricity, prohibitively rare and expensive precious metal electrocatalysts, such as Pt, are often used to overcome the large oxidative voltage required to convert H₂ into 2 H⁺ and 2 e⁻. Herein, we report a metal-free approach to catalyze the oxidation of H₂ by combining the ability of frustrated Lewis pairs (FLPs) to heterolytically cleave H₂ with the in situ electrochemical oxidation of the resulting borohydride. The use of the NHC-stabilized borenium cation [(IiPr₂)(BC₈H₁₄)]⁺ (IiPr₂=C₃H₂(NiPr)₂, NHC=N-heterocyclic carbene) as the Lewis acidic component of the FLP is shown to decrease the voltage required for H₂ oxidation by 910 mV at inexpensive carbon electrodes, a significant energy saving equivalent to 175.6 kJ mol⁻¹. The NHC–borenium Lewis acid also offers improved catalyst recyclability and chemical stability compared to B(C₆F₅)₃, the paradigm Lewis acid originally used to pioneer our combined electrochemical/frustrated Lewis pair approach.

Metal-Free Hydrogenation Catalyzed by an Air-Stable Borane: Use of Solvent as a Frustrated Lewis Base

Co-reporter:Daniel J. Scott;Dr. Matthew J. Fuchter ;Dr. Andrew E. Ashley

Angewandte Chemie 2014 Volume 126( Issue 38) pp:10382-10386

Publication Date(Web):

DOI:10.1002/ange.201405531

Abstract

In recent years ‘frustrated Lewis pairs’ (FLPs) have been shown to be effective metal-free catalysts for the hydrogenation of many unsaturated substrates. Even so, limited functional-group tolerance restricts the range of solvents in which FLP-mediated reactions can be performed, with all FLP-mediated hydrogenations reported to date carried out in non-donor hydrocarbon or chlorinated solvents. Herein we report that the bulky Lewis acids B(C₆Cl₅)_x(C₆F₅)_3−x (x=0–3) are capable of heterolytic H₂ activation in the strong-donor solvent THF, in the absence of any additional Lewis base. This allows metal-free catalytic hydrogenations to be performed in donor solvent media under mild conditions; these systems are particularly effective for the hydrogenation of weakly basic substrates, including the first examples of metal-free catalytic hydrogenation of furan heterocycles. The air-stability of the most effective borane, B(C₆Cl₅)(C₆F₅)₂, makes this a practically simple reaction method.

Structural and theoretical studies of intermolecular dihydrogen bonding in [(C6F5)2(C6Cl5)B]–H⋯H–[TMP]

Co-reporter:Hasna Zaher, Andrew E. Ashley, Mark Irwin, Amber L. Thompson, Matthias J. Gutmann, Tobias Krämer and Dermot O'Hare

Chemical Communications 2013 vol. 49(Issue 84) pp:9755-9757

Publication Date(Web):16 Sep 2013

DOI:10.1039/C3CC45889J

The product of the intermolecular ‘frustrated Lewis pair’ (FLP) B(C6F5)2(C6Cl5)/2,2,6,6-tetramethylpiperidine and H2 has been studied by single-crystal neutron diffraction. This is the first structurally characterised example of a geometrically unconstrained dihydrogen (H⋯H) bond within a hydrogenated FLP system.

Novel H2 activation by a tris[3,5-bis(trifluoromethyl)phenyl]borane frustrated Lewis pair

Co-reporter:Thomas J. Herrington, Alex J. W. Thom, Andrew J. P. White and Andrew E. Ashley

Dalton Transactions 2012 vol. 41(Issue 30) pp:9019-9022

Publication Date(Web):17 Apr 2012

DOI:10.1039/C2DT30384A

Tris[3,5-bis(trifluoromethyl)phenyl]borane (1, BArF18), has been synthesised on a practical scale for the first time. According to the Gutmann–Beckett method it is a more powerful Lewis acid than B(C6F5)3. It forms a ‘frustrated Lewis pair’ with 2,2,6,6-tetramethylpiperidine which cleaves H2 to form a salt containing the novel anion [μ-H(BArF18)2]−.

Separating Electrophilicity and Lewis Acidity: The Synthesis, Characterization, and Electrochemistry of the Electron Deficient Tris(aryl)boranes B(C6F5)3–n(C6Cl5)n (n = 1–3)

Co-reporter:Andrew E. Ashley ; Thomas J. Herrington ; Gregory G. Wildgoose ; Hasna Zaher ; Amber L. Thompson ; Nicholas H. Rees ; Tobias Krämer ;Dermot O’Hare

Journal of the American Chemical Society 2011 Volume 133(Issue 37) pp:14727-14740

Publication Date(Web):July 25, 2011

DOI:10.1021/ja205037t

A new family of electron-deficient tris(aryl)boranes, B(C6F5)3–n(C6Cl5)n (n = 1–3), has been synthesized, permitting an investigation into the steric and electronic effects resulting from the gradual replacement of C6F5 with C6Cl5 ligands. B(C6F5)2(C6Cl5) (3) is accessed via C6Cl5BBr2, itself prepared from donor-free Zn(C6Cl5)2 and BBr3. Reaction of C6Cl5Li with BCl3 in a Et2O/hexane slurry selectively produced B(C6Cl5)2Cl, which undergoes B–Cl exchange with CuC6F5 to afford B(C6F5)(C6Cl5)2 (5). While 3 forms a complex with H2O, which can be rapidly removed under vacuum or in the presence of molecular sieves, B(C6Cl5)3 (6) is completely stable to refluxing toluene/H2O for several days. Compounds 3, 5, and 6 have been structurally characterized using single crystal X-ray diffraction and represent the first structure determinations for compounds featuring B–C6Cl5 bonds; each exhibits a trigonal planar geometry about B, despite having different ligand sets. The spectroscopic characterization using 11B, 19F, and 13C NMR indicates that the boron center becomes more electron-deficient as n increases. Optimized structures of B(C6F5)3–n(C6Cl5)n (n = 0–3) using density functional theory (B3LYP/TZVP) are all fully consistent with the experimental structural data. Computed 11B shielding constants also replicate the experimental trend almost quantitatively, and the computed natural charges on the boron center increase in the order n = 0 (0.81) < n = 1 (0.89) < n = 2 (1.02) < n = 3 (1.16), supporting the hypothesis that electrophilicity increases concomitantly with substitution of C6F5 for C6Cl5. The direct solution cyclic voltammetry of B(C6F5)3 has been obtained for the first time and electrochemical measurements upon the entire series B(C6F5)3–n(C6Cl5)n (n = 0–3) corroborate the spectroscopic data, revealing C6Cl5 to be a more electron-withdrawing group than C6F5, with a ca. +200 mV shift observed in the reduction potential per C6F5 group replaced. Conversely, use of the Guttmann-Beckett and Childs’ methods to determine Lewis acidity on B(C6F5)3, 3, and 5 showed this property to diminish with increasing C6Cl5 content, which is attributed to the steric effects of the bulky C6Cl5 substituents. This conflict is ascribed to the minimal structural reorganization in the radical anions upon reduction during cyclic voltammetric experiments. Reduction of 6 using Na(s) in THF results in a vivid blue paramagnetic solution of Na+ [6]•–; the EPR signal of Na+[6]•– is centered at g = 2.002 with a(11B) 10G. Measurements of the exponential decay of the EPR signal (298 K) reveal [6]•– to be considerably more stable than its perfluoro analogue.

Bypassing a highly unstable frustrated Lewis pair: dihydrogen cleavage by a thermally robust silylium–phosphine adduct

Co-reporter:Thomas J. Herrington, Bryan J. Ward, Laurence R. Doyle, Joe McDermott, Andrew J. P. White, Patricia A. Hunt and Andrew E. Ashley

Chemical Communications 2014 - vol. 50(Issue 84) pp:NaN12756-12756

Publication Date(Web):2014/08/26

DOI:10.1039/C4CC05905K

The thermally robust silylium complex [iPr3Si–PtBu3]+[B(C6F5)4]− (1) activates H2/D2 at 90 °C (PhCl); no evidence for dissociation into the separated Lewis pair is found. DFT calculations show H2 cleavage proceeds via Si–P bond elongation to form an encounter complex directly from the adduct, thus avoiding the non-isolable iPr3Si+–PtBu3 FLP.

Teaching old compounds new tricks: efficient N2 fixation by simple Fe(N2)(diphosphine)2 complexes

Co-reporter:Laurence R. Doyle, Peter J. Hill, Gregory G. Wildgoose and Andrew E. Ashley

Dalton Transactions 2016 - vol. 45(Issue 18) pp:NaN7554-7554

Publication Date(Web):2016/04/05

DOI:10.1039/C6DT00884D

The Fe(0) species Fe(N2)(dmpe)2 exists in equilibrium with the previously unreported dimer, [Fe(dmpe2)2(μ-N2)]. For the first time these complexes, alongside Fe(N2)(depe)2, are shown unambiguously to produce N2H4 and/or NH3 upon addition of triflic acid; for Fe(N2)(depe)2 this represents one of the highest electron conversion efficiencies for Fe complexes to date.

Cationic silyldiazenido complexes of the Fe(diphosphine)2(N2) platform: structural and electronic models for an elusive first intermediate in N2 fixation

Co-reporter:Adam D. Piascik, Peter J. Hill, Andrew D. Crawford, Laurence R. Doyle, Jennifer C. Green and Andrew E. Ashley

Chemical Communications 2017 - vol. 53(Issue 54) pp:NaN7660-7660

Publication Date(Web):2017/06/19

DOI:10.1039/C7CC04188H

The first cationic Fe silyldiazenido complexes, [Fe(PP)2(NN–SiMe3)]+[BArF4]− (PP = dmpe/depe), have been synthesised and thoroughly characterised. Computational studies show the compounds to be useful structural and electronic surrogates for the more elusive [Fe(PP)2(NN–H)]+, which are postulated intermediates in the H+/e− mediated fixation of N2 by Fe(PP)2(N2) species.

Structural and theoretical studies of intermolecular dihydrogen bonding in [(C6F5)2(C6Cl5)B]–H⋯H–[TMP]

Co-reporter:Hasna Zaher, Andrew E. Ashley, Mark Irwin, Amber L. Thompson, Matthias J. Gutmann, Tobias Krämer and Dermot O'Hare

Chemical Communications 2013 - vol. 49(Issue 84) pp:NaN9757-9757

Publication Date(Web):2013/09/16

DOI:10.1039/C3CC45889J

The product of the intermolecular ‘frustrated Lewis pair’ (FLP) B(C6F5)2(C6Cl5)/2,2,6,6-tetramethylpiperidine and H2 has been studied by single-crystal neutron diffraction. This is the first structurally characterised example of a geometrically unconstrained dihydrogen (H⋯H) bond within a hydrogenated FLP system.

H2 activation by a highly electron-deficient aralkylated organoborane

Co-reporter:Peter J. Hill, Thomas J. Herrington, Nicholas H. Rees, Andrew J. P. White and Andrew E. Ashley

Dalton Transactions 2015 - vol. 44(Issue 19) pp:NaN8992-8992

Publication Date(Web):2015/03/31

DOI:10.1039/C5DT00821B

The electron-deficient and sterically bulky trialkylborane derivative tris[bis(pentafluorophenyl)methyl]borane [1, B(CH(C6F5)2)3], has been synthesised and comprehensively characterised; detailed 1H and 19F NMR studies reveal two dynamic bond rotational processes in the solution phase. Despite conventional probes (Gutmann–Beckett and Childs methods) implying that the compound has a very limited Lewis acidity, it was used to generate frustrated Lewis pairs capable of heterolytically activating H2 in ethereal solutions, which suggests that the hydridophilicity of 1 is comparable to the potent Lewis acid B(C6F5)3.

Novel H2 activation by a tris[3,5-bis(trifluoromethyl)phenyl]borane frustrated Lewis pair

Co-reporter:Thomas J. Herrington, Alex J. W. Thom, Andrew J. P. White and Andrew E. Ashley

Dalton Transactions 2012 - vol. 41(Issue 30) pp:NaN9022-9022

Publication Date(Web):2012/04/17

DOI:10.1039/C2DT30384A

Tris[3,5-bis(trifluoromethyl)phenyl]borane (1, BArF18), has been synthesised on a practical scale for the first time. According to the Gutmann–Beckett method it is a more powerful Lewis acid than B(C6F5)3. It forms a ‘frustrated Lewis pair’ with 2,2,6,6-tetramethylpiperidine which cleaves H2 to form a salt containing the novel anion [μ-H(BArF18)2]−.