CHARACTERIZATION AND REACTION STUDIES OF DIMERIC MOLYBDENUM(III) COMPLEXES WITH BRIDGING DITHIOLATE LIGANDS - CATALYTIC REDUCTION OF ACETYLENE TO ETHYLENE

The complexes [C5H5MoSCnH2nS]2(where n = 2 and 3) have been prepared by the reaction of ethylene sulfide and propylene sulfide, respectively, with C5H5MoH(CO)3 or with [C5H5Mo(CO)3]2. Cyclic voltammetry shows that each complex undergoes two reversible oxidations at 0.13 and 0.79 V vs. SCE (in acetonitrile with 0.1 M Bu4NBF4). Both the one-electron and two-electron oxidation products have been synthesized and characterized by spectral and magnetic data. Electrochemical data for the oxidized complexes support the conclusion that the complexes have the same gross structural features in all three oxidation states. A single crystal of the monocation [C5H5MoSC3H6S]2BF4 has been characterized by an X-ray diffraction study. The compound crystallizes in the space group C2/c with a = 18.266 (1) Å, b = 9.206 (4) Å, c = 12.911 (5) Å,β = 100.83 (3)°, and V = 2128 °3. The metal ions of the cation are bridged by two 1, 2-propanedithiolate ligands. The four sulfur atoms of these ligands form a plane which bisects the metal-metal distance. The neutral dimeric complexes undergo a unique reaction with alkenes and alkynes in which the hydrocarbon portion of the bridging dithiolate ligands is exchanged. The reaction has been characterized with olefins with both electron-withdrawing and electron-donating substituents. When [C5H5MoSC2H4S]2(1) is reacted with acetylene at 25 °C, ethene is produced and the complex [C5H5MoSC2H2S]2 is isolated. The latter complex is reduced by hydrogen (2 atm) at 60 °C to re-form 1. The utility of these reactions in the catalytic reduction of acetylene to ethylene has been investigated. The role of the sulfur ligands in this catalytic cycle is discussed. © 1979, American Chemical Society. All rights reserved.