Versatility in the mode of coordination [(C)−, (N,S), (C,N)− or (C,N,S)−] of the Schiff base: C6H5–CH=N–CH2–CH2–SEt to palladium(II). X-ray crystal structures of cis-[Pd{C6H5–CH=N–CH2–CH2–SEt}Cl2] and [Pd{C6H4–CH=N–CH2–CH2–SEt}Cl]

Abstract

he reaction of ligand C6H5–CH=N–CH2–CH2–SEt (1) with Na2[PdCl4] is studied. It yields, depending on the experimental conditions, two different sorts of palladium(II) complexes: cis-[Pd{C6H5–CH=N–CH2–CH2–SEt}Cl2] (2b) and [Pd{C6H4–CH=N–CH2–CH2–SEt}Cl] (3b). Compounds 2b and 3b differ in the mode of 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(PPh3)] (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 structurally: 2b is triclinic, space group P1̄, with a=8.081(2), b=8.230(2), c=10.836(2) Å, α=109.16(3), β=96.65(3) and γ=92.29(3)° and 3b is triclinic, space group P1̄, with a=10.201(2), b=11.927(2), c=17.568(4) Å, α=104.35(3), β=94.21(3) and γ=111.56(3)°. The structural studies confirmed 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 calculations based on the pm3(tm) method have also been used to explain the isomerisation of 2b.