Crystallographic characterization of the palladium(I) dimers, syn-Pd2Cl2(dppmMe)2 and Pd2Cl2(dppm)2; solution conformational behavior of syn- and anti-Pd2Cl2(dppmMe)2 and their (μ-Se) adducts [dppmMe=μ-1,1-bis(diphenylphosphino)ethane, and dppm=μ-bis(diph

An X-ray diffraction study on syn-Pd2Cl2(dppmMe)2, syn-1, shows an unusual boat-like conformation of the eight-membered Pd2P4C2 ring. This conformation, containing equatorial Me groups, facilitates access of the PdPd bond to small molecules such as CO, SO2, and elemental sulfur or selenium, and makes the syn isomer more reactive than anti-1. A comparison of bond angles around the Pd and P atoms in the syn- and anti-isomers reveals a more strained geometry of the former, which may also contribute to the stronger propensity of syn-1 to form A-frame adducts. Solution NMR/NOE studies on syn- and anti-1 and their (μ-Se) adducts reveal the structural rigidity of these complexes; the Me groups inhibit the interchange of axial and equatorial positions on the bridging methine C-atom, and solution structures correspond to those in the solid state. The X-ray structure of Pd2Cl2(dppm)2 is, as expected, like that of the corresponding bromo complex; both are analogous to that of anti-1 which adopts a chair conformation within both the fused, five-membered rings.