Exploring the Activation of Atomically Precise [Pt₁₇(CO)₁₂(PPh₃)₈]²⁺ Clusters: Mechanism and Energetics in Gas Phase and on an Inert Surface.

Abstract

Atomically precise clusters such as [Pt₁₇(CO)₁₂(PPh₃)₈]^<i>x</i>+ (<i>x</i> = 1,2) (PPh₃ is triphenylphosphine) are known as precursors for making oxidation catalysts. However, the changes occurring to the cluster upon thermal activation during the formation of the active catalyst are poorly understood. We have used a combination of hybrid mass spectrometry and surface science to map the thermal decomposition of [Pt₁₇(CO)₁₂(PPh₃)₈](NO₃)₂. High-resolution mass and ion mobility spectrometry together with DFT-based modeling were used to probe the sequence of fragmentation reactions and fragment structures generated upon collisional excitation of [Pt₁₇(CO)₁₂(PPh₃)₈]²⁺. This was compared with thermal desorption spectroscopy of [Pt₁₇(CO)₁₂(PPh₃)₈](NO₃)₂ dropcast onto an inert graphite surface. In both cases, a characteristic sequence of CO and benzene desorption steps is observed followed at higher excitation energy by H₂ loss. This behavior is indicative of Pt-catalyzed C-H activation of phenyl groups during partial stripping of the ligand shell while the Pt₁₇P₈ cluster core is retained.