SYNTHESIS AND CHARACTERIZATION OF TETRA-PALLADIUM AND PENTA-PALLADIUM CLUSTERS WITH SULFUR-DIOXIDE AS A LIGAND

Several pentanuclear palladium clusters, [Pd5(SO2)4L5] [L = PPh3 1, PMePh2 2, PMe2Ph 3, P(CGH4-OMe-p)3 4, P(CGH4OMe-m)3 5 or AsPh36], have been synthesised from the reaction of [Pd2(dba)3]+CHCl3 (dba - dibenzylideneacetone, PhCH = CHCOCH = CHPh) 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 mu-SO2 ligands, and two triangular faces capped by mu(3)-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 P-31-{H-1} 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 P-31-{H-1} 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)G] 9, as a minor product, which has been characterised by P-31-{H-1} NMR spectroscopy.