Lewis Superacidic Ionic Liquids with Tricoordinate Borenium Cations

Abstract

The first examples of ionic liquids based on borenium cations, [BCl2L]+, are reported. These compounds form highly Lewis acidic liquids under solvent‐free conditions. Their acidity was quantified by determining the Gutmann acceptor number (AN). Extremely high ANs were recorded (up to AN=182, δ31P=120 ppm), demonstrating that these borenium ionic liquids are the strongest Lewis superacids reported to date, with the acidity enhanced by the ionic liquid environment.

Applying neutron diffraction with isotopic substitution to the structure and proton-transport pathways in protic imidazolium bis{(trifluoromethyl)sulfonyl}imide ionic liquids

“…15 We have an on-going interest in understanding the role of ionassociation and speciation in ionic liquids [16][17][18] and the nature of the 'complex ions' that can be formed when acids and bases, or salts and acids or bases are mixed. [19][20][21] Here, we compare the liquid structures of 1:1 and 2:1 base:acid mixtures of imidazole with H[NTf 2 ], determined using neutron diffraction with isotopic substitution, in order to identify whether persistent homo-conjugated complex cations can be observed in the basic-rich region of phase space and, if present, to try to understand how these contribute to the liquid structure and proton conductivity. 2 ] was also run to provide isotopic contrast between the C-H and N-H sites in the 2:1 system.…”

Synthesis of hydroxymethylfurfural from sucrose using brönsted-lewis acidic ionic liquid

“…When x value was 0.55, the reaction of sucrose was effectively catalyzed. This can be explained by that, when the molar fraction of metal chloride (x) was more than 0.5, IL was Brönsted and Lewis acidic, and by increasing the x value, the Lewis acidity was increased [18], which can increase the catalytic activity of IL. But further increased x value, the result was not good.…”

Borenium ionic liquids as catalysts for Diels–Alder reaction: tuneable Lewis superacids for catalytic applications

“…For a range of ligands, homogenous ionic liquids were obtained as products. 5 The ionic liquid environment enabled the measurement of Lewis acidity of borenium cations under solventless conditions. Gutmann Acceptor Numbers were extremely high, up to AN = 182: this was attributed to the positive charge on the boron centre, combined with lack of solvation from a molecular solvent in neat ionic liquid.…”

“…Monomeric cations are stronger coordinating, which resulted in stronger cation-anion interactions, and consequently weaker Lewis acidity -this is also in agreement with prior observations. 5 The reaction of cyclopentadiene with ethyl acrylate (Scheme 2) was used as a model Diels-Alder transformation. The reaction was carried out solventless, with very small amount of ionic liquid catalyst dissolved in neat reactants (with diene in excess).…”

“…3 The same scrambling was indeed reported for borenium ionic liquids. 5 2 -. This demonstrates that the dienophile binds to the borenium cation and, despite its excess, to a very small extent it exchanges with chlorides in [AlCl 4 ] -.…”