Crystal structure of [Pd(μ 3-2-propenyl)(dps)][Pd(μ 3-2-propenyl)Cl 2]. NMR evidence of binuclear μ 3-allyl palladium(II) species with bridging dps

Abstract

The reactions of di-2-pyridyl sulfide (dps) with (μ 3-allyl)palladium chloride dimers gave the ionic compounds [Pd(μ 3-allyl)(dps)][Pd(μ 3-allyl)Cl 2] (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 P 1 , with Z=2 in a unit cell of dimensions a=8.840(1), b=8.928(1), c=12.317(2) Å, α= 98.82(1), β=90.46(1), γ=95.46(1)°. 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 relections 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) Å) which determines pseudo-five-coordination for the cation. At low temperature the 1H NMR spectra in CD 3OD of 1 and 2 confirm the presence of the cation and the anion while in CDCl 3 they also indicate the presence of a binuclear species with bridging dps. The 1H NMR spectra, at variable temperature, show that 1, 2 and 3 in solution undergo dynamic processes. In CDCl 3, a lower energy process makes the π-allyl groups equivalent at room temperature, a higher energy process determines the magnetic equivalence of syn and anti π-allyl protons at high temperature.