Preparation and characterization of rhenium(I) compounds with amino ester derivatized diimine ligands. Investigations of luminescence. Crystal structures of Re(CO)3Cl(pyca-β-Ala-OEt) and Re(CO)3Cl(pyca-l-Asp(OMe)-OMe)

The title compounds were prepared in good yield by heating ester protected amino acids (H-l-Ala-OEt, H-β-Ala-OEt, H-L-Val-OMe, H-GABA-OMe, H-L-Asp(OMe)-OMe, H-L-Met-OMe) with Re(CO)5Cl in the presence of pyridine-2-carboxaldehyde. The resulting novel complexes contain a bound, conjugated diimine ligand with a pendant ester group. All compounds were characterized by 1H and 13C NMR, IR and UV–Vis spectroscopy. Compounds prepared from chiral amino esters give diastereomers because of the presence of a stereogenic metal center. Syntheses using Re(CO)5Br as starting material were discontinued because of metathesis involving the chloride in the amino ester · HCl salts and the metal bromide. Photophysical studies on Re(CO)3Cl(pyca-β-Ala-OEt), 2, show that it is luminescent in organic solvents in air at room temperature. The crystal structures of 2 and Re(CO)3Cl(pyca-l-Asp(OMe)-OMe), 5, were determined.