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)(eta(2)-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)(eta(2)-SC4H4), (ii) formation of the tungsten butadiene-thiolate intermediate, (eta(5)-C4H5S)W(PMe3)(2)(eta(2)-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 degrees C), whereas the desulfur product was obtained upon thermolysis at elevated temperature (100 degrees 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. (C) 2014 Elsevier B.V. All rights reserved.