Structural analyses of N-acetylated 4-(dimethylamino)pyridine (DMAP) salts.
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.
Lutz
Volker
V
Institut für Organische Chemie, Justus-Liebig-Universität Giessen, Heinrich-Buff-Ring 58, 35392 Giessen (Germany), Fax: (+49) 641-99-34309.
Glatthaar
Jörg
J
Institut für Organische Chemie, Justus-Liebig-Universität Giessen, Heinrich-Buff-Ring 58, 35392 Giessen (Germany), Fax: (+49) 641-99-34309.
Würtele
Christian
C
Institut für Anorganische Chemie, Justus-Liebig-Universität Giessen, Heinrich-Buff-Ring 58, 35392 Giessen (Germany).
Serafin
Michael
M
Institut für Anorganische Chemie, Justus-Liebig-Universität Giessen, Heinrich-Buff-Ring 58, 35392 Giessen (Germany).
Hausmann
Heike
H
Institut für Organische Chemie, Justus-Liebig-Universität Giessen, Heinrich-Buff-Ring 58, 35392 Giessen (Germany), Fax: (+49) 641-99-34309.
Schreiner
Peter R
PR
Institut für Organische Chemie, Justus-Liebig-Universität Giessen, Heinrich-Buff-Ring 58, 35392 Giessen (Germany), Fax: (+49) 641-99-34309.