Lewis Acidic Boranes, Lewis Bases, and Equilibrium Constants: A Reliable Scaffold for a Quantitative Lewis Acidity/Basicity Scale

Abstract

Aq uantitative Lewis acidity/basicitys cale toward boron-centeredL ewis acids has been developed based on a set of 90 experimental equilibrium constantsf or the reactions of triarylboranes with various ON N-, Sand nd P-centered Lewis bases in dichloromethane at 20 8C. Analysis with the linear free energy relationship log K B = LA B + LB B allowse quilibrium constants, K B ,t ob ec alculated fora ny type of borane/Lewisb ase combination through the sum of two descriptors, one for Lewisa cidity (LA B)a nd one for Lewis basici-ty (LB B). The resultingL ewis acidity/basicity scale is independento ff ixed reference acids/bases and valid for various types of trivalent boron-centered Lewisa cids. It is demonstratedt hat the newly developed Lewisa cidity/basicity scale is easily extendable through linear relationshipsw ith quantum-chemically calculated or common physical-organic descriptorsa nd known thermodynamic data (DH BF 3). Furthermore,t his experimental platform can be utilized fort he rationald evelopment of borane-catalyzed reactions.

What Distinguishes the Strength and the Effect of a Lewis Acid: Analysis of the Gutmann–Beckett Method

“…Final single point energies were calculated at the RI‐DSD‐PBEP86‐D3(BJ)/(ma‐)def2‐QZVPP, COSMO‐RS(CH 2 Cl 2 ) level and were combined with the thermal corrections from PBEh‐3c. The reliability of our computed Δ G solv values for TEPO binding were supported by good accordance with experimental values (e.g., for B(C 6 F 5 ) 3 , Δ G solv exp −55 kJ mol −1 vs. Δ G solv comp −67 kJ mol −1 ) [10] . Further, the 31 P NMR chemical shifts of the adducts were computed by hybrid density functional theory, where relativistic effects were approximated by the 2‐component spin–orbit ZORA approach (Δ δ comp , PBE0/SO‐ZORA‐TZ2P) [34]…”

“…On the other hand, the hydride ion affinity (HIA) [9] has been suggested as the defining value for soft Lewis superacids [5] . gLA can also be determined by experimental techniques, such as solution phase studies of association equilibria, [10] or tensimetric methods [11] Effective Lewis acidity (eLA) corresponds to induced changes of physicochemical properties of a probe Lewis base upon binding of the Lewis acid (Figure 1 b).…”

Enthalpies of Adduct Formation between Boron Trifluoride and Selected Organic Bases in Solution: Toward an Accurate Theoretical Entry to Lewis Basicity

“…Owing to the need of data for the Lewis basicity of molecules not experimentally characterized, 27 several attempts were recently made for the estimation of either SbCl5 or BF3 enthalpies of adduct formation by quantum chemistry methods, see for example 22,28,29,30 We also contributed to the evaluation of high-level theoretical methods for calculating the enthalpies for reactions (1) and (2). 31 There are also data corresponding to BF3 enthalpies experimentally determined in the gas phase:…”

Enthalpies of Adduct Formation between Boron Trifluoride and Selected Organic Bases in Solution: Toward an Accurate Theoretical Entry to Lewis Basicity

“…Owing to the need for data on the Lewis basicity of molecules not experimentally characterized [27], several attempts were recently made to estimate either SbCl 5 or BF 3 enthalpies of adduct formation by quantum chemistry methods; see, for example, [22,[28][29][30].…”