One-step synthesis and reduction of triphenylphosphine carbonyl palladium clusters of variable nuclearities

Heteroleptic triphenylphosphine carbonyl palladium clusters of different nuclearities were prepared under mild conditions by only varying the amount of ligand (PPh3) used in the synthesis: three different clusters were successfully isolated after CO bubbling in a solution of [Pd2(dba)3] (dba = dibenzylideneacetone) with 3, 1 or 0.5 equiv of PPh3, which led, respectively, to [Pd4(CO)5(PPh3)4] (1), [Pd10(CO)12(PPh3)6] (2) and [Pdn(CO)x(PPh3)y] (3) (n ≈ 24). The molecular structures of compounds 1 and 2 were determined by X-ray crystallography. The metal cores in these compounds were shown to consist in a butterfly for 1 and a bridged octahedron for 2. Compound 3 was shown to be at the boundary between molecular clusters and colloidal particles with tentative formulation arising from characterization data. These three clusters and the known [Pd10(CO)12(PBu3)6] and [Pd12(CO)15(PBu3)7] were submitted to NaBH4 reduction. The Pd4 cluster 1 did not react. The colloidal Pdn species led to no isolable product. By contrast, the two Pd10 and the Pd12 clusters led to reduction products, isolated as NEt 4 + salts. In the case of the reduced Pd12 cluster, its structure was resolved by X-ray crystallography: the metal core consists of a face-capped octahedron. The reduced species reacted readily with Au(PPh3)+, confirming their anionic nature.