Chemical and Thermal Behavior of the Molecular Models [Os 3 (CO) 10 (μ-H)(μ-OSiR 2 R‘)] (R = Et, Ph; R‘ = Et, Ph, OH, OSiPh 2 OH):  Molecular Approach to the Clarification of the Surface Chemistry of the Silica-Anchored Cluster [Os 3 (CO) 10 (μ-H)(μ-OSi⋮)]