INCLUSION INDUCED RESOLUTION OF A BIS-BIBENZIMIDAZOLE DERIVATIVE BY ACHIRAL ACIDS. By Petra Bombicz and Mátyás Czugler, Central Research Institute for Chemistry, Hungarian Academy of Sciences, H-1525 Budapest 114, POB 17, Hungary.

Crystallization of 2,2'bis-(3,4,5-trimethoxyphenyl) -1,1'-bibenz-imidazole (1) with simple acids such as formic (a), acetic (b), propionic (c), butyric (d) and trimethyl-acetic (e) acid yields to spontaneous resolution in the case of acetic and propionic acids due to inclusion formation (Table) with stoichiometry always 1:2 only. X-ray diffraction structure analyses of these solid associates offer a rationale for this behavior of these five cases.

Analysis of the packing motifs enlightens a possible reason for enantiomer resolution. There are helices of host molecules close packed through inversion centers. The enantiomerically opposite molecules crystallize in different columns placement of which are governed by steric and a multiple of other weak electronic effects. The central methoxy group is the very place which is influenced by the presence and size of an additional acid component. Molecular graphics analyses reveal that the host conformation is hardly changed (1a, 1b, 1c, 1d) thus crystal building is the subject of the interactions of a steady host molecule with the varying guests.

Inclusion        1[1]    1a      1b      1c      1d      1e     
Space group      C 2/c   C 2/c   P3121   P3221   C 2/c   C 2/c  
L.S. fit [Å]*    0       0.096   0.070   0.054   0.046   0.704  

[1] Speier, G.; Párkányi, L.: J.Org.Chem. 51, 218, 1986.