SUBSTITUTION AND FRAGMENTATION REACTIONS OF PENTAPALLADIUM CLUSTER COMPOUNDS

The reactions of the pentapalladium cluster compounds [Pd5(mu-SO2)2(mu-3-SO2)2L5] [L = PPh3, P(C6H4OMe-p)3 or PMe2Ph] with carbon monoxide and xylyl isocyanide are discussed. In the reaction with CO the structure of the reaction product is dependent on the nature of the phosphine. The compound [Pd5(mu-SO2)2(mu-3-SO2)2(PR3)5] reacts to give [Pd5(SO2)2(CO)2(PR3)5] (R = Ph 1a or C6H4OMe-p 1b) whereas [Pd5(mu-SO2)2(mu-3-SO2)2(PMe2Ph)5] reacts to give [Pd5(mu-SO2)3(mu-CO)(mu-3-CO)(PMe2Ph)5] 2. The molecular structure of 2 has been determined by a single-crystal X-ray diffraction study. It consists of an edge-bridged tetrahedron of palladium atoms with three edges bridged by sulfur dioxide ligands and two faces capped by carbon monoxide ligands. Both capping CO ligands are asymmetric, one so much so that it is best regarded as an edge-bridging carbonyl. Each palladium atom also carries a terminal phosphine ligand. The identities of 1a and 1b were confirmed by P-31-{H-1 }-NMR spectroscopy and fast atom bombardment mass spectrometry. The compound [Pd5(mu-SO2)2(mu-3-SO2)2(PPh3)5] reacts with xylyl isocyanide to give the triangulo-palladium compound [Pd3(mu-SO2)2(CNC8H9)2(PPh3)3] 3. The molecular structure of 3 has been determined by a single-crystal X-ray diffraction study. It is based on a triangle of palladium atoms with Pd-Pd distances between 2.7369(4) and 2.7947(40 angstrom, within the previously observed range for 44-electron tripalladium cluster compounds.