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.