Enantioselective Dearomatization Agents Based on Chiral C2Symmetric Ligands

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)cyclohexa
ne-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)