Gas phase acidities of N-substituted amine-boranes

Abstract

Complexation energies and acidities of 19 primary, secondary and tertiary amine-boranes were investigated using MP2/6-311+G(d,p) and B3LYP/6-311+G(d,p) methods. Gas phase acidities for free amines were also calculated. Acidity values for studied complexes range from 327.3 to 349.1 kcal mol(-1) and the most acidic are the ones with direct connection between deprotonation center and a π-system. Results obtained by both computational methods are in good agreement with each other and with known experimental data. Addition of BH3 increases the acidity of amines by 30 to 50 kcal mol(-1). This enhancement effect was compared to the respective effect witnessed in phosphine-boranes and traced back to changes of charge delocalization on nitrogen. A question about the structural stability of several deprotonated amine-borane anions in the gas phase was also raised.

Relative stability and proton transfer reactions of unsaturated isocyanides and cyanides

“…The calculations were carried out using the GAUSSIAN 09 program package under the programs default conditions (298.15 K and 1 atm) if not stated otherwise. In our work we used MP2 method with 6‐311 + G(d,p) basis set which has been shown to be adequate and relatively cheap method for calculating proton transfer reactions . In some cases, G2 method was also used to calculate energies for different deprotonation centers with close energies.…”

“…In our work we used MP2 [18][19][20][21][22] method with 6-311 + G(d,p) basis set [23][24][25][26] which has been shown to be adequate and relatively cheap method for calculating proton transfer reactions. [27][28][29] In some cases, G2 method [30] was also used to calculate energies for different deprotonation centers with close energies. A full conformational search was done for each species and vibrational analyses for zero-point energies, and thermal corrections were performed.…”

Proton transfer reactions of hydrazine-boranes

“…Both values are also comparable to complexation values of amine‐boranes. For example ΔG for unsubstituted amine‐borane is −14.1 kcal/mol and values for substituted complexes vary from −15 to −22 kcal/mol, if we leave aside phenyl substituted amine‐borane with an exceptionally low stability …”

“…The hydrogen release reaction as well as intrinsic properties related to hydrogen storage, like gas‐phase basicity and acidity, has been studied . It has been found that complexation greatly alters the properties of amines, for example the acidity is enhanced by 30–50 kcal/mol . The protonation centre of such complexes is located on the boron moiety, and the resulting structure can be described as R 1 R 2 R 3 N‐BH 2 + ••H 2 .…”