Versatility in the mode of coordination [(C)(-), (N,S), (C,N)(-) or (C,N,S)(-)] of the Schiff base: C6H5CH=N-CH2-CH2-SEt to palladium(II). X-ray crystal structures of cis-[Pd{C6H5-CH=N-CH2-CH2-SEt}Cl-2] and [Pd{C6H4-CH=N-CH2-CH2-SEt}Cl]

The reaction of ligand C6H5-CH=N-CH2-CH2-SEt (1) with Na-2[PdCl4] is studie d. It yields, depending on the experimental conditions, two different sorts of palladium(II) complexes: cis-[Pd{C6H5-CH=N-CH2-CH2-SEt}Cl-2] (2b) and [ Pd{C6H4-CH=N-CH2-CH2-SEt}Cl] (3b). Compounds 2b and 3b differ in the mode o f binding of the ligand to the palladium: as a neutral (N,s) group in 2b or as a monoanionic (C,N,S)(-) terdentate ligand in 3b. The results presented here show that the formation of 3b is promoted thermally and requires the presence of sodium acetate. The cyclopalladated complex 3b reacts with PPh3 , in a 1:1 or 1:2 molar ratio, to produce [Pd{C6H4-CH=N-CH2-CH2-SEt}Cl(Phh( 3))] (4b) or [Pd{C6H4-CH=N-CH2-CH2-SEt}Cl(PPh3)(2)] (5b), respectively. All the complexes have been characterised by elemental analysis, infrared and NMR spectroscopy. Compounds 2b and 3b have also been characterised structur ally: 2b is triclinic, space group P (1) over bar, with a = 8.081(2), b = 8 .230(2), c = 10.836(2) Angstrom, alpha = 109.16(3), beta = 96.65(3) and gam ma = 92.29(3)degrees and 3b is triclinic, space group P (1) over bar, with a = 10.201(2), b = 11.927(2), c = 17.568(4) Angstrom, alpha = 104.35(3), be ta = 94.21(3) and gamma = 111.56(3)degrees. The structural studies confirme d the mode of binding of the ligand to the palladium and revealed that the ligand has the Z-form in 2b and the E-form in 3b. Semiempirical calculation s based on the pm3(tm) method have also been used to explain the isomerisat ion of 2b. (C) 2001 Elsevier Science B.V. All rights reserved.