Metal Complexes of Biologically Important Ligands, CX. Orthopalladation of N-(Diphenylmethylene) Schiff Bases from Peptide Esters - C,N versus C,N,O Coordination - Crystal Structure of ClPd[C6H4(C6H5)C=N(Gly-L-Pro -L-Ala-OMe)-C,N,O] with cis/trans Peptide Bonds

Abstract

The reaction of the N-(diphenylmethylene) Schiff base from glycyl-L-prolyl-L-alanine methyl ester 1 with tetrachloropalladate in the presence of sodium acetate affords the orthopalladated bicyclic C ,N ,O chelate 2. Complex 2 was characterized by X-ray diffraction. Remarkably, the unit cell contains two independent molecules, the cis isomer 2a and the trans isomer 2b (referring to the peptide bond). 2 reacts with PPh3 by substitution of the carbonyl oxygen atom to give the C,N chelate 3.