TY - JOUR

T1 - 1,8-Bis(dimethylamino)naphthyl-2-ketimines: Inside vs. Outside Protonation

AU - Tolstoy, Peter M.

AU - Filarowski, Aleksander

AU - Pozharskii, Alexander F.

AU - Хорошилова, Олеся Валерьевна

AU - Антонов, Александр Сергеевич

N1 - Funding Information: This work was supported by the Russian Foundation for Basic Research (project 16-33-60030). Experimental measurements were performed in Centre for Magnetic Resonance, Chemical Analysis and Materials Research Centre, Centre for X-ray Diffraction Studies at St. Petersburg State University Research Park. The authors also thank Mr. Daniel Raith for proofreading the paper in terms of the English language.

PY - 2018/11/28

Y1 - 2018/11/28

N2 - The structure and protonation behaviour of four ortho-arylketimines of 1,8-bis(dimethylamonio)naphthalene with a different number of methoxy groups in an aromatic substituent were investigated in solution by NMR (acetone, DMSO, MeCN), in solid state by X-ray analysis and in the gas phase by DFT calculations. Both mono- and diprotonated species were considered. It has been shown that E-isomers of neutral imines can be stabilised by an intramolecular C=N−H···OMe hydrogen bond with a neighbouring methoxy group. Electron-donating OMe groups dramatically increase the basicity of the imino nitrogen, forcing the latter to abstract a proton from the proton sponge moiety in monoprotonated forms. The participation of the out-inverted and protonated 1-NMe 2 group in the Me 2N−H···NH=C hydrogen bond is experimentally demonstrated. It was shown that the number and position of OMe groups in the aromatic substituents strongly affects the rate of the internal hindered rotation of the NH 2 + fragment in dications.

AB - The structure and protonation behaviour of four ortho-arylketimines of 1,8-bis(dimethylamonio)naphthalene with a different number of methoxy groups in an aromatic substituent were investigated in solution by NMR (acetone, DMSO, MeCN), in solid state by X-ray analysis and in the gas phase by DFT calculations. Both mono- and diprotonated species were considered. It has been shown that E-isomers of neutral imines can be stabilised by an intramolecular C=N−H···OMe hydrogen bond with a neighbouring methoxy group. Electron-donating OMe groups dramatically increase the basicity of the imino nitrogen, forcing the latter to abstract a proton from the proton sponge moiety in monoprotonated forms. The participation of the out-inverted and protonated 1-NMe 2 group in the Me 2N−H···NH=C hydrogen bond is experimentally demonstrated. It was shown that the number and position of OMe groups in the aromatic substituents strongly affects the rate of the internal hindered rotation of the NH 2 + fragment in dications.

KW - Hydrogen bond

KW - Imine

KW - NMR

KW - Proton sponge

KW - Superbase

KW - superbase

KW - STABILIZATION

KW - imine

KW - BASICITY

KW - SCALE

KW - proton sponge

KW - CONFORMERS

KW - SPONGES

KW - WATER

KW - hydrogen bond

UR - http://www.scopus.com/inward/record.url?scp=85057765779&partnerID=8YFLogxK

UR - https://www.beilstein-journals.org/bjoc/articles/14/273

UR - http://www.mendeley.com/research/18bisdimethylaminonaphthyl2ketimines-inside-vs-outside-protonation-1

U2 - 10.3762/bjoc.14.273

DO - 10.3762/bjoc.14.273

M3 - Article

C2 - 30546478

VL - 14

SP - 2940

EP - 2948

JO - Beilstein Journal of Organic Chemistry

JF - Beilstein Journal of Organic Chemistry

SN - 2195-951X

ER -