SYNTHESIS AND CHARACTERIZATION OF DINUCLEAR PALLADIUM COMPLEXES WITH BRIDGING SELENIDE OR SELENOXIDE LIGANDS, INCLUDING X-RAY CHARACTERIZATION OF ANTI-PD2CL2(MU-SE)(MU-DPMME)(2) [DPMME=1,1-BIS(DIPHENYLPHOSPHINO)ETHANE]

The complexes Pd2Cl2(P-P)(2), where (P-P) = mu-bis(diphenylphosphino)methane, dpm, or mu-1,1-bis(diphenylphosphino)ethane, dpmMe, react with elemental selenium to give the A-frame adducts Pd2Cl2(mu-Se)(P-P)(2), which can be oxidized by t-BuOOH to the mu-SeO derivatives. Reaction of H2Se with Pd2Cl2(dpm)(2) generates Pd(2)Ch(2-n)-(SeH)(n)(mu-Se)(dpm)(2) species (n = 0-2). anti-Pd2Cl2(mu-Se)(dpmMe)(2) (2d) crystallizes in the monoclinic space group P2(1)/c with a = 11.986(2) Angstrom, b = 24.141(2) Angstrom, c = 18.921(2 Angstrom), beta = 106.64(1)degrees, V = 5243.2(11)' Angstrom(3), and Z = 4; the structure was refined against F-2 to wR2 = 0.1338 (R1 = 0.0476) for 9838 reflections with I > 2 sigma(1). 2d is the first structurally characterized A-frame complex with anti disposition of substituents at the methylene C atoms of the diphosphine Ligands. A correlation between the Se-77 NMR shift measured for Pd2Cl2(mu-Se)(P-P)(2) and the equilibrium constant for the reversible binding of CO by the Pd2Cl2(P-P)(2) species reflects factors affecting binding at the apical site.