Jiayao Zhang, Saurav Bhattacharya, Mahmoud Elcheikh Mahmoud, Talha Nisar, Khaoula Merimi, Xavier López, Josep M. Poblet, V. Wagner, Ulrich Kortz
The platinum-containing isopolytungstates [Pt3W11O41]6.4− (Pt3W11), [PtII2W5O18((CH3)2AsO2)2]4− (PtII2W5), and [PtIII2W5O18((CH3)2AsO2)4]4− (PtIII2W5) have been synthesized in aqueous media and characterized by single-crystal XRD and multinuclear (195Pt, 13C, 1H) NMR spectroscopy. The polyanion [Pt3W11O41]6.4− comprises three {W3O13} and one {W2O10} fragments connected by three platinum atoms forming a linear {Pt3O12} triad exhibiting direct Pt–Pt bonding (2.64 to 2.68 Å). The distances between the two outer Pt ions and oxygens from neighboring Pt3W11 clusters (2.34 and 2.65 Å, respectively) are consistent with [4+1] coordination. Quantum mechanical calculations allowed assigning the Pt oxidation states for the mixed-valence polyanion Pt3W11. The polyanion PtII2W5 comprises a monolacunary {W5O18}6− Lindqvist fragment coordinated by two PtII ions with square-planar coordination and two terminal dimethylarsinate groups, exhibiting a 195Pt NMR signal at 610 ppm in water. On the other hand, PtIII2W5 comprises two PtIII ions with square-pyramidal coordination and direct Pt–Pt bonding (2.64 Å). The polyanions Pt3W11 and PtII2W5 were immobilized on SBA-15-apts and then tested as precatalysts for the hydrogenation of o-xylene under continuous-flow, high pressure hydrogenation conditions.