Mechanistic insight into the hydrodesulfurization of thiophene by a molecular tungsten complex W(PMe3)4(η2-CH2PMe2)H

• The hydrodesulfurization of thiophene by a W-based complex is theoretically studied.
• The catalyzed hydrodesulfurization process involves five sub-processes.
• The theoretical results rationalize the earlier experimental observations.
• W-based complex may be a potential hydrodesulfurization catalyst.

While the hydrodesulfurization (HDS) of thiophenes has been achieved successfully by tungsten-based complexes, the relevant molecular mechanism is still not well understood. By performing density functional theory calculations, the present work for the first time provides a detailed mechanism study of the entire HDS process of thiophene by a representative tungsten complex W(PMe3)4(η2-CH2PMe2)H. In detail, the HDS process consists of four sub-processes: (i) binding of thiophene to the metal center to give the metallathiacycle species W(PMe3)4(η2-SC4H4), (ii) formation of the tungsten butadiene–thiolate intermediate, (η5-C4H5S)W(PMe3)2(η2-CH2PMe2), (iii) hydrogenation of the butadiene–thiolate intermediate, and (iv) liberation of the desulfur product but-1-ene. The overall barriers of the four sub-processes were calculated to be 25.5, 26.7, 31.5, and 43.3 kcal/mol, respectively, which qualitatively rationalizes the experimental observations that the tungsten butadiene–thiolate intermediate was observed under the mild temperature (60 °C), whereas the desulfur product was obtained upon thermolysis at elevated temperature (100 °C). The regeneration of the tungsten complex is also discussed to evaluate its potential possibility serving as a HDS catalyst. The present theoretical results are expected to shed light on practical heterogeneous HDS mechanism of tungsten-based complexes.

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