The chemisorption of the hydridosilsesquioxane clusters H8Si8O12 and H10Si10O15 onto a freshly evaporated gold surface has been observed by X-ray photoemission and reflection-absorption infrared spectroscopies. On the basis of these analytical techniques and supporting nonlocal density functional calculations, a single Si-Au bond at a cluster vertex is created through a surprising gold-mediated Si-H bond activation. The chemisorbed clusters are stable in a vacuum and when exposed to oxygen or water. Coverage-dependent peak frequency and infrared intensity shifts, characteristic of a chemically dynamic interface, are detected as a function of cluster overpressure. An equilibrium between the clusters and the gold surface is proposed, evidenced by a fairly constant rate of adsorption to gold for several coverage regimes.