The catalytic cyclotrimerization of alkynes on reduced TiO2(0 0 1) surfaces has been explored to probe the active sites for carbon-carbon bond formation. The influence of surface-adsorbate interactions on the reaction mechanism was further probed by studies designed to characterize the steric effects of differently functionalized alkynes. The chemistry of trimethylsilyl acetylene on surfaces containing Ti2+ Sites Clearly demonstrates that cyclotrimerization of heteroatom-containing alkynes is feasible. Trimethylsilyl acetylene can be cyclized to form tris-(trimethylsilyl)-benzene on the reduced titania surface. However, the principal product on both reduced and stoichiometric surfaces of TiO2(0 0 1) is the hydrogenation product, trimethylvinylsilane (TMVS). The low yield of oligomeric products is attributed to the steric effect of the bulky trimethylsilyl group. (C) 2002 Elsevier Science B.V. All rights reserved.