4‑(Dimethylamino)pyridine (DMAP) as an Acid-Modulated Donor Ligand for PAH Dearomatization

The dearomatization of naphthalene
and anthracene is explored by
their η2 coordination to {TpMo­(NO)­(MeIm)} and {TpMo­(NO)­(DMAP)}
(where Tp = hydridotris­(pyrazolyl)­borate, MeIm = 1-methylimidazole,
and DMAP = 4-(dimethylamino)­pyridine). The DMAP and MeIm complexes
have nearly identical redox properties and abilities to bind these
polycyclic aromatic hydrocarbons (PAHs), but unlike MeIm, the DMAP
ligand can be protonated at N while remaining bound to the metal.
This action enhances the π-acidic properties of DMAP, resulting
in greater stability of the molybdenum toward oxidation by acid. Utilizing
this feature of the DMAP ligand, several new 1,2-dihydronaphthalenes
and 1,2-dihydroanthracenes were prepared. Furthermore, it was found
that acetals and Michael acceptors could function as electrophiles
for the PAHs using the DMAP system, resulting in several new mono-
and 1,4-dialkylated products.