Table 1. Thermodynamic Acidity Constants (pKaH) of the New Amines Determined by Capillary Electrophoresis and Proton Affinity Values Based on Quantum-Chemical Computations.
| formula | no. | refs on synthesis | pKa | proton affinity [kJ mol–1], at BP86/AE1 levela |
|---|---|---|---|---|
| [1-NH2–1,2-C2B9H10)(1′,2′-C2B9H11)-3,3′-Co(III)].Me4N.HCl | 4– | - | <2.5 | 1105 |
| [1,1′-μ-HN-(−CH2–1,2-C2B9H10)2-3,3′-Co]Me4N | I | (29) | <1.9 | 1138 |
| [(1-H2NCH2–1,2-C2B9H10)(1′,2′-C2B9H11)-3,3′-Co].Me4N.HCl | II | (29) | 7.7 | 1139 |
| [(1-H2N(CH2)2–1,2-C2B9H10)(1′,2′-C2B9H11)-3,3′-Co].Me4N.HCl | III | (29) | 9.8 | 1089 |
| [(1-H2N(CH2)3–1,2-C2B9H10)(1′,2′-C2B9H11)-3,3′-Co].Me4N.HCl | IV | (29) | 10.4 | 1143 |
| [(8-H3N–1,2-C2B9H10)(1′,2′-C2B9H11)-3,3′-Co]0 | V | (17) | >12 | 1282 |
| [(8-H3NCH2–1,2-C2B9H10)(8′-CH3O–1,2′-C2B9H10)-3,3′-Co] | VI | (16) | >12 | 1314 |
| [(8-H3NC2H4OC2H4O–1,2-C2B9H10)(1′,2′-C2B9H11)-3,3′-Co]0 | VII | (57) | 11.4 | 1208b |
| rac-[(1,1′-(NH2)2–1,2-C2B9H10)2-3,3′-Co(III)].Me4N.HCl | 5– | - | 4.1 | 1193 |
| rac-[(1,1′-(H2NCH2–1,2-C2B9H10)2-3,3′-Co].Me4N.HCl | VIII | (21) | 7.3 | 1139 |
| rac-[(1,1′-(H2N(CH2)2–1,2-C2B9H10)2-3,3′-Co].Me4N.HCl | IX | (20) | 9.3 | 1160 |
a
The proton affinity (PA) of an anion or a neutral molecule is the negative of the enthalpy change in the reaction between the chemical species and a proton in the gas phase. The higher the proton affinity (in kJ mol–1), the stronger the base and the weaker the conjugate acid.
b
Proton affinity is related to the protonation of the oxygen atom adjacent to the B(8) atom of the cage. PA with respect to the nitrogen amounts to 820 kJ mol–1 only.