Cluster Growth and Fragmentation in the Highly Fluxional Platinum Derivatives of Sn_9~(4-): Synthesis, Characterization, and Solution Dynamics of Pt_2@Sn_(17)~(4-) and Pt@Sn_9H~(3-)

摘要

Sn_9~(4-) reacts with Pt(PPh_3)_4 in ethylenediamine/toluene solvent mixtures in the presence of 2,2,2-cryptand to give four different complexes: "Rudolph's complex" of proposed formula [Sn_9Pt(PPh_3)_x]~(4-), the previously reported [Pt@Sn_9Pt(PPh_3)~(2-) ion, and the title complexes Pt_2@Sn_(17)~(4-) and Pt@Sn_9H~(3-). The use of Pt(norbornene)_3 instead of Pt(PPh_3)_4 gives complex 4 exclusively. The structure of 4 contains two Pt atoms centered in a capsule-shaped Sn_(17) cage. The complex is highly dynamic in solution showing single, mutually coupled ~(119)Sn and ~(195)Pt NMR resonances indicative of an intramolecular liquidlike dynamic exchange process. Complex 5 has been characterized by selectively decoupled ~1H, ~(119)Sn, and ~(195)Pt NMR experiments and shows similar liquidlike fluxionality. In addition, the H atom scrambles across the cage showing small couplings to both Sn and Pt atoms. Neither 3 nor 4 obeys Wades rules; they adopt structures more akin to the subunits in alloys such as PtSn_4. The structural and chemical relevance to supported PtSn_4 heterogeneous catalysts is discussed.