Toward extension of the gas-phase basicity scale by novel pyridine containing guanidines

Towards the Strongest Neutral Organic Superbases Based on Intramolecular H-bonds

“…The conjugate acid of IHB superbases possesses three intramolecular hydrogen bonds that stabilize protonated central guanidine core. [8][9][10][11][12] It should be noted that according to the classification, this type of hydrogen bonds belongs to the charge assisted hydrogen bonds. 16 To estimate the stabilization energy of three Hbonds on protonated TMG cation, we calculated the stabilization enthalpies of tri-complexes (ΔH 298 (tri-)) according to the Equation (4).…”

“…9 Subsequently, some modifications of the original idea have been utilized to obtain more or less basic compounds. Glasovac synthesized compounds with methoxy 10 and pyridino 11 group at the end of alkyl chain. Recently, utilizing the same motif combined with use of a very strong H-bond acceptors at the end alkyl chain, we designed a series of very strong neutral organic superbases ("IHB-superbases") with a gas phase proton affinity (PA) up to 293.3 kcal mol -1 and pK a in acetonitrile up to 33.2 (IV, V, Scheme 1).…”

The Utility of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as a Hydrogen Bond Acceptor in the Design of Novel Superbasic Guanidines – A Computational Study

“…This motif was found in the crystal structure of N,N',N''-tris-(3-dimethylaminopropyl)guanidinium hexafluorophosphate 18 and was also predicted to be the most stable in the 2-(2-pyridyl)ethyl substituted guanidine derivatives. 19 Next, the 1,1-hydrogen bonding motif, present in c2 conformation, results from IMHB between the TBD-imino nitrogen atom and the proton located at the same nitrogen atom where the alkyl-TBD substituent is attached. Finally, the unfolded conformation c3, without any IMHB, was considered as well.…”

“…In the case of 1Et-c3, the increase in basicity of 27 and 30 kJ mol ) and MTBD (1038 kJ mol −1 ). 19 These values could also be considered as a result of the replacement of one methyl group located on trimethylguanidine or MTBD with either TBDethyl or dimethylguanidine-ethyl subunit, respectively. The replacement of the second and third methyl groups located at the guanidine moiety with TBD-ethyl groups enhances the basicity of the guanidine part by 26 and 24 kJ mol −1 , respectively, while the basicity of the TBD subunit rises by ca 10 kJ mol −1 per additional TBD-ethyl substituent added.…”

Proton Affinities of Organocatalysts Derived from Pyridine N-oxide

“…[1][2][3][4][5] Development of new superbases is usually based on two approaches. One can either conceive molecules with a potential of very efficient delocalization of the positive charge over a large molecular scaffold or alternatively, molecules with more than one highly basic functions cooperating in binding of the proton can be considered.…”