Out-Basicity of 1,8-bis(dimethylamino)naphthalene: the experimental and theoretical challenge

被引:16
作者
Ozeryanskii, Valery A. [1 ]
Pozharskii, Alexander F. [1 ]
Antonov, Alexander S. [1 ]
Filarowski, Alexander [2 ]
机构
[1] Southern Fed Univ, Dept Organ Chem, Rostov Na Donu 344090, Russia
[2] Univ Wroclaw, PL-50383 Wroclaw, Poland
基金
俄罗斯基础研究基金会;
关键词
PROTON SPONGE; CRYSTAL-STRUCTURE; MOLECULAR-STRUCTURE; CONFORMERS; STABILIZATION; AMINE; SCALE; STATE; FORM;
D O I
10.1039/c3ob41986j
中图分类号
O62 [有机化学];
学科分类号
070303 ; 081704 ;
摘要
A possibility of non-conventional two-step protonation of 1,8-bis(dimethylamino)naphthalene (proton sponge) is discussed. Unlike the generally accepted mechanism, involving relatively slow direct penetration of a proton into the cleft between the peri-NMe2 groups, it consists of the rapid addition of a proton to the out-inverted NMe2 group with the subsequent slower rotational transfer of the proton into the inter-nitrogen space to produce a stable chelated cation. The following approaches were employed during the work: (1) competitive hydrogen bond formation in a specially designed alcohol in which the OH group might chelate either the proton sponge 1-NMe2 group or another basic center (N,N-dimethylaniline) of known basicity; (2) measuring the basicity of naphtho[1,8-b,c] diazabicyclo[3.3.3] undecane considered to be a close analogue of the proton sponge capable exclusively of out-protonation; (3) X-ray, spectral and DFT studies of structure, energy and stereodynamics of compounds obtained, including their conformers. For the first time, the pK(a) value of an organic base with a perfectly flat nitrogen atom is reported. The final conclusion is made that both pathways of proton sponge protonation, traditional and non-conventional, contribute in parallel with a still undefined ratio. The estimated out-basicity of the proton sponge is at least 5.5 orders of magnitude lower than the directly measured in-basicity.
引用
收藏
页码:2360 / 2369
页数:10
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