Lutz Volker, Glatthaar Jörg, Würtele Christian, Serafin Michael, Hausmann Heike, Schreiner Peter R
Institut für Organische Chemie, Justus-Liebig-Universität Giessen, Heinrich-Buff-Ring 58, 35392 Giessen (Germany), Fax: (+49) 641-99-34309.
Institut für Anorganische Chemie, Justus-Liebig-Universität Giessen, Heinrich-Buff-Ring 58, 35392 Giessen (Germany).
Chemistry. 2009 Aug 24;15(34):8548-8557. doi: 10.1002/chem.200901379.
We have studied the formation of several N-acetyl-4-(dimethylamino)pyridine (DMAP) salts (with Cl(-), CH(3)COO(-), and CF(3)COO(-) counterions), which are considered to be the catalytically active species in DMAP-catalyzed acetylation reactions of alcohols. Combined crystal structure analyses, variable temperature matrix IR and NMR spectroscopy as well as computational techniques at the UAHF-PCM-B3LYP/6-311+G(d,p)//B3LYP/6-31G(d) level were utilized to examine the structures and dynamics of salt formation. We found clear evidence for the formation of tight ion pairs that are stabilized by dynamic hydrogen-bonding interactions. In nonpolar solvents, the nucleophilicity of acetate in its N-acetyl-DMAP salt only allows a steady-state concentration smaller 1% at room temperature. Thus, we propose additional hydrogen-bonding interactions with alcohols to be the key stabilization factor in subsequent acetylations.
我们研究了几种N-乙酰基-4-(二甲基氨基)吡啶(DMAP)盐(抗衡离子为Cl⁻、CH₃COO⁻和CF₃COO⁻)的形成，这些盐被认为是DMAP催化醇类乙酰化反应中的催化活性物种。结合晶体结构分析、变温基质红外光谱和核磁共振光谱以及在UAHF-PCM-B3LYP/6-311+G(d,p)//B3LYP/6-31G(d)水平的计算技术，来研究盐形成的结构和动力学。我们发现了通过动态氢键相互作用稳定的紧密离子对形成的确切证据。在非极性溶剂中，其N-乙酰基-DMAP盐中乙酸根的亲核性在室温下仅允许稳态浓度小于1%。因此，我们提出与醇类的额外氢键相互作用是后续乙酰化反应中的关键稳定因素。
