Molybdenum(VI)-dioxo, molybdenum(V)-oxo, and molybdenum(IV)-oxo complexes with 2,3: 8,9-dibenzo-1,4,7,10-tetrathiadecane. Models for the molybdenum binding site of the molybdenum cofactor

Bharat B. Kaul, John H. Enemark, Shannath L. Merbs, Shannath L Merbs

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Abstract

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 languageEnglish (US)
Pages (from-to)2885-2891
Number of pages7
JournalJournal of the American Chemical Society
Volume107
Issue number10
Publication statusPublished - 1985
Externally publishedYes

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ASJC Scopus subject areas

  • Chemistry(all)

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