The molecular complex [W(&3bond; CtBu)(CH(2)tBu)(3)], 1, reacts with SiO2-(700) to give as major species 2a, [(&3bond; SiO)W(CtBu)(CH(2)tBu)(2)], while a bisgrafted surface species 3a, [(&3bond; SiO)(2)W-(&3bond; CtBu)(CH(2)tBu)], is obtained on SiO2-(200). As in molecular organometallic chemistry, the alkylalkylidyne tautomeric form is favored. Despite these structural features, these surface organometallic complexes are very active olefin metathesis catalysts, as reported earlier, and it is very likely that the necessary metallocarbene intermediates are generated under the reaction conditions.