As possible models for the coordination of molybdenum by an unsaturated thiolate-thioether ligand in the molybdenum-pterin cofactor of molybdenum enzymes, MoO2(dttd), MoOCl(dttd), and MoO(PPh2Et)(dttd) (dttdH2 = 2,3:8,9-dibenzo-1,4,7,10-tetrathiadecane) have been synthesized. The structure of MoO2(dttd) has been determined by X-ray crystallography. The compound crystallizes in space group P21/c, with a = 14.34 (2) Å, b = 8.168 (6) Å, c= 14.507 (8) Å, β = 103.42 (8)°, and Z = 4. MoO2(dttd) is six-coordinate with substantial distortion from octahedral geometry. The two thiolate S atoms are trans to one another (Mo-Sav = 2.402 (7) Å) and cis to the terminal oxo groups. The thioether S atoms are approximately trans to the terminal oxo groups and exhibit much longer Mo-S distances (2.687 (6) Å). MoO2(dttd) undergoes a one-electron reversible reduction on the cyclic voltammogram time scale, but is reduced irreversibly in the presence of Et4NCl in a two-electron step to [MoOCl(dttd)]- on the coulometric time scale; [MoOCl(dttd)]- in turn is reversibly oxidized to the EPR active monomer MoOCl(dttd). MoOCl(dttd) undergoes a reversible one-electron reduction to [MoOCl(dttd)]-, but cannot be oxidized to MoO2(dttd) in the voltage range used. MoO(PPh2Et)(dttd) appears to lose the PPh2Et group in DMF/Et4NCl solution, exhibiting electrochemical behavior identical with that of [MoOCl(dttd)]-. Reaction of MoO2(dttd) with 1 equiv of PPh2Et in DMF in the presence of Et4NCl gives [MoOCl(dttd)]-, while subsequent addition of Me2SO to the solution regenerates MoO2(dttd). The dimer, Mo2O3(dttd)2, has also been obtained. It is reversibly reduced in a 1.00 electron/Mo process to [MoOCl(dttd)]- and reversibly oxidized in a 0.50 electron/Mo process to a mixture of equal amounts of MoO2(dttd) and MoOCl(dttd) in DMF in the presence of Et4NCl. The EPR parameters of MoOCl(dttd) and the electrochemical parameters of the various complexes are reported.
|Original language||English (US)|
|Number of pages||7|
|Journal||Journal of the American Chemical Society|
|Publication status||Published - 1985|
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