Ferrosalen and ferrosalen-type ligands: Structural modulation and applications in asymmetric catalysis

Article abstract of DOI:10.1021/om2002206

Several ferrosalen and ferrosalen-type ligands, 1-10, were prepared and fully characterized. The structure of one of these ligands ligated to Cu(II) was determined by single-crystal X-ray diffraction analysis. In comparison with the parent ligand 1, the two six-membered rings of ligand 2 are not aromatized and the synthesis was more facile. Diastereoisomers 3 and 4, containing substituents on the ethylene chain, were synthesized. The aromatized versions of 3 and 4, namely 5 and 6, were also prepared. Further modulation of the ethylene backbone produced ligands 7 and 8. Replacing the Cp ligands with Cp* and Cp ^Ph5 gave ligands 9 and 10, respectively. All these ligands were tested for catalytic asymmetric reactions, including the Co(III)-catalyzed carbonyl-ene reaction, Al(III)-catalyzed Strecker reaction, and Al(III)-catalyzed silylcyanation of aldehyde.