Binuclear methylplatinum(II) complexes. The molecular structure and fluxional behaviour of the face-to-face dimer [Pt2I2Me2(µ-Me2PCH2PMe2)2]

Abstract

The complexes cis,cis-[Pt₂Cl₂Me₂(µ-dmpm)₂](6), trans,trans-[Pt₂I₂Me₂(µ-dmpm)₂](8), and [Pt₂(µ-I)Me₂(µ-dmpm)₂][PF₆](11)(dmpm = Me₂PCH₂PMe₂) have been prepared and characterized spectroscopically. The crystal structure of (8) was determined by X-ray diffraction techniques and refined to R= 0.036 for 2 598 unique reflections with I 3σ(I). The crystals are monoclinic, space group P2₁/n, a= 8.611(2), b= 16.971(3), c= 8.405(1)Å, β= 102.83(2)°, Z= 2. The molecular structure shows a face-to-face geometry with crystallographically imposed C_i symmetry. It contains two square-planar metal centres [Pt ⋯ Pt 3.353 5(4)Å] bridged by mutually trans dmpm ligands to afford an eight-membered Pt₂P₄C₂ dimetallacycle with an anti configuration of the trans-PtIMe groups. Complex (8) has been shown to undergo a novel fluxional process involving overall inversion of the face-to-face structure. Differences in properties between the dmpm complexes (6), (8), and (11) and related known Ph₂PCH₂PPh₂complexes are rationalized in terms of steric effects.