Reactions of di-2-pyridyl sulfide with the palladium(II) and platinum(II) diene or methoxydiene complexes. Dynamic behaviour of the cationic compounds. Crystal structure of Pd(di-2-pyridyl sulfide)Cl2

Abstract

The complexes [M(dps)Cl2] (MPdII (1); PtII (2)) and the labile compounds [M(MeOdiene)(dps)Cl] (MPdII, MeOdieneCH3OC8H12 (3) or CH3OC10H12 (4); MPtII, MeOdieneCH3OC8H12 (5) or CH3OC10H12 (6)) have been synthesized by reaction of dps (dps=di-2-pyridyl sulfide) with [M(diene)Cl2] (diene=cycloocta-1,5-diene or dicyclopentadiene) and the appropriate chloro-bridged methoxydiene complexes, respectively. The last reactions required drastic conditions. Also the reactions of dps with the solvento species [M(diene)(acetone)2]X2 and [M(MeOdiene)(acetone)2]X (X=BF4, PF6, ClO4) have been studied and the compounds [M(MeOdiene)(dps)]X (MPdII, MeOdieneCH3OC8H12 (7) or CH3OC10H12 (8); MPtII, MeOdieneCH3OC8H12 (9) or CH3OC10H12 (10)) were prepared. The structure of 1 has been determined by X-ray diffraction methods. Crystals are monoclinic, space group P21/n, with Z=4 in a unit cell of dimensions a=9.933(4), b=14.802(5), c=8.465(3) Å, β=101.94(2)°. The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by full- matrix least-squares on the basis of 2163 observed reflections to R and R′ values of 0.0277 and 0.0348, respectively. In the square planar coordination around the Pd atom the dps molecule acts as a chelate ligand through the two pyridinic N atoms and adopts a N,N-inside conformation. The six-membered chelate ring shows a boat conformation with the Pd and S atoms out of the plane through the other four atoms on the same side. Although dissociation in the usual solvents prevents full characterization of 3–6 IR spectra suggest that the dps acts as monodentate ligand. The 1H NMR spectra, at variable temperature, and 13C NMR spectra of 7–10 show that the cationic complexes in solution undergo at least two dynamic processes; a ligand site exchange and a boat to boat inversion of the chelate dps ring. The ligand site exchange is fast, in the NMR time scale, at room temperature for palladium complexes and at higher temperature for the platinum complexes and makes equivalent the pyridine rings of dps. This process is interpreted in terms of formation of stereochemically non-rigid five- coordinate intermediates. The boat to boat inversion is fast at room temperature at least for platinum complexes. At low temperature the latter process is absent or occurs at markedly reduced rate for palladium complexes while the slow ligand site exchange results in equilibria between two conformers.