A new platinum complex bearing bulky N-heterocyclic carbene ligand of the general formula [Pt(IPr*Ph)(dvtms)] (where IPr*Ph = 1,3-bis{2,4,6-tris(diphenylmethyl)phenyl}imidazol-2-ylidene, dvtms = divinyltetramethyldisiloxane) exhibits a high catalytic activity towards E-selective dimerization of ethynyl substituted siloxysilsesquioxanes. This process leads to a novel class of functionalized silsesquioxane derivatives, resembling their dumbbell-shaped silsesquioxane analogues.