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

The reaction of the N-(diphenylmethylene) Schiff base frost glycyl-L-prolyl-L-alanine methyl ester I 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.