Synthesis, structure and reactivity of anionic tripalladium cluster compounds

Abstract

The cluster compounds R⁺[Pd₃(µ-SO₂)₂(µ-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(µ-SO₂)₂(µ₃-SO₂)₂(PPh₃)₅] and R⁺X^–. The molecular structure of [NEt₃(CH₂Ph)][Pd₃(µ-SO₂)₂(µ-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(µ-NO)(µ-SO₂)(µ-Cl)(PPh₃)₃]6 which has been characterised by ³¹P-{¹H} 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(µ-SO₂)₂(µ₃-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 co-ordinated to the halide ligand.