SYNTHESIS, STRUCTURE AND REACTIVITY OF ANIONIC TRIPALLADIUM CLUSTER COMPOUNDS

The cluster compounds R+[Pd3(mu-SO2)2(mu-X)(PPh3)3]- [R = NEt4, X = Cl 1 or Br 2; R = NEt3(CH2Ph), X = Cl 3; R = PPh3(CH2Ph), X = Cl 4; R = NBu4, X = I 5] have been synthesised from the reaction of [Pd5(mu-SO2)2(mu-3-SO2)2(PPh3)5] and R+X-. The molecular structure of [NEt3(CH2Ph)][Pd3(mu-SO2)2 (mu-Cl) (PPh3)3].0.5Me2CO has been determined by single-crystal X-ray diffractometry. The study, though limited by disorder of the bridging ligands, has demonstrated that the Pd-Pd bond distances are within the expected range for a 44-electron triangulo-palladium cluster. These triangulo-cluster compounds undergo a variety of reactions: one SO2 ligand may be substituted by NO+, giving the neutral triangulo cluster [Pd3(mu-NO) (mu-SO.) (mu-Cl) (PPh3)3] 6 which has been characterised by P-31-{H-1} NMR spectroscopy and fast atom bombardment mass spectrometry. The triangle may be capped by the metal fragments Au(PPh3)+ and Tl+, giving [Pd3Au(SO2)2Cl(PPh3)4] 7 and [Pd3Tl(SO2)2Cl(PPh3)3] 8 respectively and the chloride ligand may be abstracted by AgNO3 leading by cluster aggregation to [Pd5(mu-SO2)2(mu-3-SO2) 2(PPh3)5]. The compound [Pd3(SO2)2X(PPh3)3]- reacts in a reversible manner with SO2 to give [Pd3(SO2)3X(PPh3)3] (X = Cl 9 or I 10). The reversibility of this reaction and the greater stability of the adduct formed from the iodo-triangulo-palladium cluster suggested that the additional SO2 ligand is coordinated to the halide ligand.