CRYSTAL-STRUCTURE OF [PD(ETA-3-2-PROPENYL)(DPS)][PD(ETA-3-2-PROPENYL)CL2] - NMR EVIDENCE OF BINUCLEAR ETA-3-ALLYL PALLADIUM(II) SPECIES WITH BRIDGING DPS

The reactions of di-2-pyridyl sulfide (dps) with (eta3-allyl)palladium chloride dimers gave the ionic compounds [Pd(eta3-allyl)(dps)][Pd(eta3-allyl)Cl2] (allyl=2-propenyl (1), 2-methyl-2-propenyl (2), 2-butenyl (3)). The structure of 1 has been determined by X-ray diffraction methods. Crystals are triclinic, space group P1BAR, with Z=2 in a unit cell of dimensions a=8.840(1), b=8.928(1), c=12.317(2) angstrom, alpha=98.82(1), beta=90.46(1), gamma=95.46(1)degrees. The structure has been solved from diffractometer data by direct and Fourier methods and refined by full-matrix least-squares on the basis of 3855 observed reflections to R and R(w) values of 0.0269 and 0.0339, respectively. Compound 1 consists of discrete complex ion pairs, containing allyl groups coordinated to both the cationic and anionic palladium centres. In the cationic portion the dps acts as a chelate ligand and adopts an N,N inside conformation. The six-membered chelate ring shows a boat conformation. The cation and anion are connected by a short Pd2...Cl2 interaction (3.073(1) angstrom) which determines pseudo-five-coordination for the cation. At low temperature the H-1 NMR spectra in CD3OD of 1 and 2 confirm the presence of the cation and the anion while in CDCl3 they also indicate the presence of a binuclear species with bridging dps. The H-1 NMR spectra, at variable temperature, show that 1, 2 and 3 in solution undergo dynamic processes. In CDCl3. a lower energy process makes the pi-allyl groups equivalent at room temperature, a higher energy process determines the magnetic equivalence of syn and anti pi-allyl protons at high temperature.