Synthesis of bis-µ-diorganosilanediyl-af-dihydridobis(triorganophosphine)diplatinum complexes: crystal and molecular structure of [{PtH(µ-SiMe2)[P(C6H11)3]}2]

Abstract

The compound [{Pt(µ-H)(SiMe₂Ph)[P(C₆H₁₁)₃]}₂] decomposes in hexane at reflux to give in low yield (10%) the diplatinum complex [{PtH(µ-SiMe₂)[P(C₆H₁₁)₃]}₂]. A single-crystal X-ray diffraction study shows that the crystals are monoclinic, space group P2₁/c, with Z= 2 in a unit cell of dimensions a= 9.158(2), b= 11.725(3), c= 20.252(9). Å, and β= 92.37(3)°. The structure has been solved by heavy-atom methods from automated diffractometer data, and refined to R 0.065 (R′ 0.080) for 5 998 reflections. The molecule is constrained crystalographically to C_i, symmetry, and the two platinum atoms are asymetrically bridged by two dimethylsilyl groups, giving two distinct Pt–Si bond lengths [2.420(2) and 2.324(2)Å]. The Pt, Si, and P atoms are essentially coplanar, with a P–Pt–Pt angle of 159.5(1)° and a Pt–Pt distance of 2.708(1)Å. Hydrido-ligands have been located trans to the shorter Pt–Si bonds at a distance of 1.78 Å from the Pt atoms, sites which are also only 1.72 Å from the other Si atoms. These hydrido-ligands might therefore be considered to bridge the longer Pt–Si bonds, and in any case complete very distorted ‘square’ planar configurations around the Pt atoms. The tricyclohexylphosphine ligands show no unusual features, and possess the usual chair conformation for the C₆ rings. The complex [{PtH(µ-SiMe₂)[P(C₆H₁₁)₃]}₂] may be synthesised in high yield by treating [Pt(C₂H₄)₂{P(C₆H₁₁)₃}] with SiMe₂H₂, and similar reactions afford the compounds [{PtH(µ-SiR₂)(PR′₃)}₂][R = Me, PR′₃= PMeBu^t₂, PPrⁱ₂Ph, or PPh₃; R = Ph, PR′₃= P(C₆H₁₁)₃, PPh₃, PPrⁱ₂Ph, or PMeBu^t₂] from, SiR₂H₂(R = Me or Ph). These hydridoplatinum complexes do not show ¹H n.m.r. resonances above τ 10, but the ²H spectrum of [{Pt²H(µ-SiMe₂)(PMeBu^t₂)}₂] has a signal due to ²HPt at τ 8.13. This property, and the occurrence in the i.r. spectra of all the complexes [{PtH(µ-SiR₂)(PR₃)}₂] of ν(PtH) bands at ca. 1 650 cm^–1, are interpreted as indicating the presence of delocalised three-centre two-electron Pt–H–Si bonding in the title compounds.