Synthesis and characterisation of tetra- and penta-palladium clusters with sulfur dioxide as a ligand

Abstract

Several pentanuclear palladium clusters, [Pd5(SO2)4L5][L = PPh31, PMePh22, PMe2Ph 3, P(C6H4OMe-p)34, P(C6H4OMe-m)35 or AsPh36], have been synthesised from the reaction of [Pd2(dba)3]·CHCl3(dba = dibenzylideneacetone, PhCHCHCOCHCHPh) with L under an atmosphere of SO2. Compounds 1–3 have also been synthesised from the reduction of palladium(II) acetate by NaBH4 in the presence of L and SO2. The molecular structure of 6 has been determined by a single-crystal X-ray study. The palladium cluster core has a distorted trigonal-bipyramidal geometry with two of the equatorial–apical edges bridged by µ-SO2 ligands, and two triangular faces capped by µ3-SO2 ligands. Each metal atom is also co-ordinated to a terminal AsPh3 ligand. Compounds 1–5 have also been characterised on the basis of 31P-{1H} NMR spectroscopy and fast atom bombardment (FAB) mass spectrometry. The reaction of [Pd2(dba)3]·CHCl3 with PMe3 under a SO2 atmosphere does not, surprisingly, give [Pd5(SO2)4(PMe3)5]7 but the tetranuclear cluster [Pd4(SO2)3(PMe3)5]8. This compound has been characterised by 31P-{1H} NMR spectroscopy and FAB mass spectrometry. The reaction of [Pd2(dba)3]·CHCl3 with PMePh2 and SO2 gives a related compound, [Pd4(SO2)3(PMePh2)5]9, as a minor product, which has been characterised by 31P-{1H} NMR spectroscopy.