1. Enantioselective Dearomatization Agents Based on Chiral C2-Symmetric Ligands
Joseph M. Keane, Department of Chemistry, Muhlenberg College, Allentown, PA
Aromatic molecules have a rich potential as synthons for pharmaceutical development. Unfortunately, current uses are limited by the paucity of transformations which do not leave the aromatic core intact. Recent work has shown that bonding an aromatic to a pi-basic metal fragment can activate the aromatic toward a wide range of otherwise inaccessible addition reactions. We are intrigued by the possibility that inclusion of a chiral ligand in the metal fragment might allow such transformations to be performed enantioselectively. We have begun our study by looking at the synthesis of d6 molybdenum and tungsten complexes involving chiral C2-symmetric tetraamine ligands. We find that ligands of the type trans-N,N’-bis(heterocycle-2-methyl)cyclohexane-1,2-diamine form robust tridentate tricarbonyl complexes. Exposure to an NO+ sources gives mononitrosylation, the product of which can be thermally decarbonylated to give a tetradentate complex. While the initial product of this reaction involves the tetraamine ligand complexed in a non-C2-symmetric cis-b configuration, for pyridine versions of the ligand the cis-b complex can be thermally driven to give the more desirable cis-a complex, in which the ligand retains its C2 symmetry. The structures of several compounds from this study have been crystallographically solved.
[(cis-b-ImchxnMe2)Mo(NO)(CO)]+
[(cis-b-Picchxn)W(NO)(CO)]+
[(cis-a-PicchxnMe2)W(NO)(CO)]+