Tungsten(VI) carbene complexes are important because they have a high catalytic activity in olefin metathesis reactions. However, little is known about their conformational preferences. In this work a theoretical conformational study on the Cl4W=CH2 complex, in its 1A1electronic state, has been performed. Extended Hückel and ab initio methods have been used. Four conformations corresponding to a trigo-nalbipyramidal structure have been considered. We have found that the equatorial parallel conformation is the most stable one. Finally, it has been shown that there exists a low-lying triplet 3B2 state very close in energy to the one. 1A1 one. © 1989, American Chemical Society. All rights reserved.