Half-sandwich molybdenum compounds with phosphine-alkylthiolate and phosphine-thioether ligands.: Crystal structure of [CpMo(SCH2CH2PPh2)2][BPh4]

The reaction of CpMoCl2 with Ph2PCH2CH2SR (R = H, CH3) yields the corresponding addition products CpMoCl2(Ph2PCH2CH2SR), but only the derivative with R = CH3 (compound 5) is sufficiently stable to be isolated as a crystalline solid. The derivative with R = H evolves rapidly to afford a mixture of compounds [CpMo(SCH2CH2PPh2)(2)]Cl-+(-) 1, and [CpMoCl(SCH2CH2PPh2)](2) 2, the former being favored by a larger ligand:Mo ratio. Compound 1 undergoes metathesis with NaBPh4 to afford [CpMo(SCH2CH2PPh2)(2)](+) BPh4- 3, which has been characterized by X-ray crystallography. The reaction of CpMoCl2 with 2 equivalents of Ph2PCH2CH2S-Li+ affords the paramagnetic complex CpMo(SCH2CH2PPh2)(2) 4, which is readily oxidized by Cp2Fe+ or by H+ to the corresponding cation. The salts 1 and 3, in turn, may be reduced by Na amalgam, MeLi, or (BuOK)-O-t to compound 4. The reversible redox process interconverting 4 and its cation occurs at E 1/2 = -1.23 V relative to the ferrocene standard, while compound 5 shows a reversible oxidation process at E 1/2 = 0.12 V by cyclic voltammetry. The comparison between these potentials and that previously reported for CpMoCl2(dppe) indicates relative donor abilities in the order Ph2P > MeS and RS- > Cl-. Compound 5 can also be synthesized by Na amalgam or Zn reduction of CpMoCl4(Ph2PCH2CH2SCH3) 6, which is obtained by addition of the ligand to CpMoCl4.