Reactions of the ?-Thiophene Ligand in (η-C4H4S)Mn(CO)3+. Mechanistic Possibilities for Catalytic Hydrodesulfurization

Article abstract of DOI:10.1021/ja00322a027

Reaction of Mn(CO)5OSO2CF3 with refluxing thiophene gives a high yield of SO3CF3 (1).This complex reacts with CN^- to give Mn(CO)3(thiophene*CN) (2a) and BH4^-, HFe(CO)4^-, and HW(CO)5^- to give Mn(CO)3(thiophene*H) (2c).A single-crystal X-ray diffraction study of 2a shows that it crystallizes in the monoclinic cell P2₁/c with a = 12.008(2) Angstroem, b = 6.6935(8) Angstroem, c = 12.172(2) Angstroem, β = 95.63(2) deg, and four molecules per unit cell.The structure demonstrates that cyanide addition occurs at a carbon atom adjacent to sulfur causing this now-saturated carbon to be 0.59 Angstroem out of the plane of the thiophene ring.Compound 1 reversibly adds P(n-Bu)3 to form Mn(CO)3(thiophene*PBu3)⁺.Protonation of 2c by HCl, HSO3CF3, HI, and CF3CO2H yields an unstable complex of 2,3-dihydrothiophene.The dihydrothiophene is readily displaced by MeCN or CO.Hydride addition to the ?-bonded thiophene in 2c, followed by protonation, is suggested as a possible model for the first steps in hydrodesulfurization of thiophene.