Cooperative Intramolecular Hydrogen Bonding Effect and Basicity –An Ab Initio and DFT Study of the Superbasic Properties ofN‐[(Dimethylamino)alkyl]‐2,3‐diaminocycloprop‐2‐ene‐1‐imines

Abstract

The MP2(fc)/6‐311+G**//HF/6‐31G* and B3LYP/6‐311+G**//HF/6‐31G* calculations show that N‐[3‐(dimethylamino)propyl] and N‐[4‐(dimethylamino)butyl] derivatives of 2,3‐diamino‐cycloprop‐2‐ene‐1‐imine (CPI) possess high gas phase proton affinities (PA) and pronounced basicities in acetonitrile (MeCN). Tris[N‐dimethylaminopropyl(‐butyl)]‐CPI derivatives achieve superbasic PA and pKa values. The reason behind these remarkable features is the stability of the resulting conjugate acids. They are stabilized by aromatization of the three‐membered ring accompanied by the cationic resonance between the cyclopropyl ring and amino nitrogen atoms of the side chains, and, last but not least, by the cooperative multiple intramolecular hydrogen bonding effect. The latter is particularly enhanced in tris‐substituted CPIs. It was found that the N‐[4‐(dimethylamino)butyl] side chains contribute more to the stability of the conjugate acids than those of the corresponding compound with a propyl chain, because they undergo a somewhat larger relaxation upon protonation. The studied compounds might be helpful in building up a dense ladder of strong bases and superbases, which could contribute to the development of the chemistry of superacids and superbases. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Engineering Neutral Organic Bases and Superbases by Computational DFT Methods – Carbonyl Polyenes

“…The intramolecular hydrogen bonding (IHB) motif has been employed for this purpose too, being particularly useful if utilized in a cooperative way by including multiple hydrogen bonds. [30][31][32] Special interest has been focused on neutral organic bases known as "proton sponges" possessing chelating proton acceptor functionalities. The archetypal compound is Alder's DMAN [1,8-bis(dimethylamino)naphthalene] synthesized some 35 years ago.…”

Design of Brønsted Neutral Organic Bases and Superbases by Computational DFT Methods: Cyclic and Polycyclic Quinones and [3]Carbonylradialenes

“…[31][32][33][34][35] The intramolecular hydrogen bonding (IMHB) motif proved very useful for this purpose too, [36,37] being particularly effective if utilized in a cooperative way by including multiple hydrogen bonds. [38][39][40] A lot of attention has been focused on neutral organic bases known as "proton sponges" possessing chelating proton-acceptor functionalities. The archetypal proton sponge is Alder's DMAN [1,8-bis(dimethylamino)naphthalene] synthesized some 35 years ago.…”

Gas phase basicities of polyfunctional molecules. Part 5: Non‐aromatic sp2 nitrogen containing compounds

“…Furthermore, owing to their strong basicities, guanidines serve as useful catalysts in a wide range of base‐catalyzed organic reactions (Raab et al, ; Glasovac et al, ; Ishikawa, ) and their gas‐phase basicities were experimentaly determined (Amekraz et al, ; Raczynska et al, ; Glasovac et al, , ). Finally, in line with the preceding properties, the guanidine fragment was employed as an essential building block in computational tailoring of superbases (Maksic & Kovacevic ; Howard et al, ; Kovacevic, Glasovac, & Maksic, ; Kovacevic & Maksic, ; Kovacevic et al, ; Raab et al, ; Gattin et al, ; Maksic, Kovacevic, & Vianello, ; Baric, Dragicevic, & Kovacevic, ]. In the course of these studies, considerable attention has been devoted to molecular modifications of the parent molecule leading to an enhancement of its basicity.…”

“…From examination of Scheme 6, the reverse is clearly evident when comparing endocyclic imines and amines. Maksic & Kovacevic (1999); Gattin, Kovacevic, & Maksic (2005), Baric, Dragicevic, & Kovacevic (2014); S Ciftcio glu & Trindle (2014) used quantum chemical methods to explore the potentialities of iminocyclopropene ring in building strong organic bases (Scheme 8). It is found that the parent iminocyclopropene itself, 1, with a proton affinity of ca 960 kJ/mol is rather a strong base.…”