Synthesis of trans-di-µ-hydridobis(silyl)bis(trialkylphosphine)di-platinum complexes: crystal and molecular structure of di-µ-hydrido-bis(tricyclohexylphosphine)bis(triethylsilyl)diplatinum

Abstract

Bis(ethylene)(tricyclohexylphosphine)platinum reacts with silanes SiR₃H [SiR₃= Sicl₃, SiClMe₂, SiMe₂Ph, SiMe₂(CH₂Ph), SiMe₂Et, SiEt₃, or Si(OEt)₃] to give hydrido-bridged diplatinum complexes [{Pt(µ-H)(SiR₃)-[P(C₆H₁₁)₃]}₂]. The complex [{Pt(µ-H)(GeMe₃)[P(C₆H₁₁)₃]}₂] has been similarly prepared using trimethyl-germane. A single-crystal X-ray diffraction study of [{Pt(µ-H)(SiEt₃)[P(C₆H₁₁)₃]}₂] shows that the crystals are monoclinic, with space group P2₁/c and Z= 4 in a unit cell of dimensions a= 20.72(2), b= 13.88(1), c= 18.97(1)Å, and β= 101.15(7)°. The structure has been determined by heavy-atom methods from automated diffractometer data and refined to R 0.071 (R′ 0.083) for 3 100 independent reflections. The results establish that the six atoms (SiPtP)₂ comprising the main skeleton of the molecule are significantly non-coplanar with a dihedral angle of 21 ° between the two SiPtP planes. There is a platinum-platinum separation of 2.692 Å. The bridging hydrido-ligands have not been located. An interesting property of the diplatinum complexes is the absence in their ¹H n.m.r. spectra of a high-field resonance. However, n.m.r. studies on [{Pt(µ-H)[Si(OEt)₃](PMeBu^t₂)}₂] show that this class of complex is dynamic, and the signal corresponding to the hydrido-bridge occurs at ca.τ 7. This low-field PtH resonance, coupled with deuteriation studies, and bridge-cleavage reactions with C₂H₄, CO, P(OPh)₃, Bu^tNC, PMe₃, and AsMe₂Ph, provides evidence for asymmetric Pt(µ-H)₂Pt bridges.