Reactivity of the palladium dimer [Pd-2(mu-SO2)(mu-dba)(PBz(3))(2)]. Syntheses and structural characterisation of [Pd-3(mu-SO2)(3)(PBz(3))(3)], [Pd-2(mu-SO2)(mu-dppm)(PBz(3))(2)], [Pd(SO2)(PBz(3))(2)], [Pd-3(mu-CO)(2)(mu-SO2)(PBz(3))(3)] and [Pd-3(mu-SO2)(2)(CNBut)(2)(PBz(3))(3)] (Bz = benzyl)

The reaction between [Pd-2(dba)(3)]. solvent (dba=dibenzylideneacetone, sol vent=CHCl3 or C6H6) and PBz(3) (Bz=benzyl) in the presence of SO2 led to ei ther [Pd-2(mu-SO2)(mu-dba)(PBz(3))(2)] 1 or [Pd-3(mu-SO2)(3)(PBz(3))(3)] 2 depending on the absence or presence of an excess of SO2 in solution or in the recrystallisation. The crystal structure of 2 shows it to be a regular triangulo -cluster with Pd-Pd bond distances 2.7225(9) Angstrom. Complex 1 reacted with dppm with displacement of dba to give [Pd-2(mu-SO2)(mu-dppm)(P Bz(3))(2)] 3. The crystal structure of 3 shows it to have a much shorter Pd -Pd bond length than 1 [2.670(2) Angstrom for 3 cf. 2.885(2) Angstrom for 1 ], which can be rationalised on the basis of the palladium atoms having bee n formally oxidised to Pd-I and the SO2 reduced to SO22-. Complex 1 reacted with PBz(3) to give two mononuclear complexes, the previously characterise d [Pd(dba)(PBz(3))(2)] and the new complex [Pd(SO2)(PBz(3))(2)] 4 which was characterised by a single crystal X-ray analysis. Complex 4 forms a distor ted T-shaped structure with the P-Pd-P angle 163.67(14)degrees. It contains a eta(1)-pyramidal SO2 ligand, and is the first mononuclear palladium SO2 complex to be crystallographically characterised. Complex 1 reacts with CO to give a mixture of the triangulo -clusters [Pd-3(mu-CO)(2)(mu-SO2)(PBz(3) )(3)] 5 and [Pd-3(mu-CO)(mu-SO2)(2)(PBz(3))(3)] 6. Reaction with an excess of CO converted 6 into 5, and the crystal structure of 5 reveals relatively short Pd-Pd bond lengths consistent with a 42-electron cluster. Complex 1 reacted with CNBut to give [Pd-3(mu-SO2)(2)(CNBut)(2)(PBz(3))(3)] which has also been crystallographically characterised.