Synthesis, characterization, and metal complexes of a salen ligand containing a quinoline base

Metal salen complexes containing intramolecular bases have been designed for use as bifunctional catalysts. A ligand containing a quinoline base and the salen core has been synthesized for this purpose. Ruthenium, chromium, titanium, and zinc complexes of the salen have been formed and characterized. A crystal structure of a mu-oxo-titanium dimer incorporating the bifunctional ligand shows a typical salen coordination pattern and illustrates that the nitrogens of the quinoline groups participate in neither intra- nor intermolecular coordination. In addition, the quinoline groups orient in an appropriate manner to act as bases toward substrates coordinated at the apical positions of these complexes. As an indication that the quinoline bases can alter the activity of salen metal complexes, the addition of dialkylzincs to aldehydes was shown to be accelerated by the quinoline salen ligand relative to a salen lacking the quinoline groups.