Synthesis and crystal structure of the trimetal compound [Pt3(C2H4)(C8H8)2(1,5-C8H12)2]: a complex of platinum(0) and platinum(II)

Abstract

Bis(cyclo-octa-1,5-diene)platinum, dissolved in ethylene-saturated diethyl ether, reacts with cyclo-octatetraene to give the triplatinum complex [Pt₃(C₂H₄)(C₈H₈)₂(1,5-C₈H₁₂)₂], which has been characterised by a single-crystal X-ray diffraction study. Crystals of the triplatinum compound are monoclinic, space group C2/c, with Z= 4 in a unit cell of dimensions a= 16.370(17), b= 7.465(5), c= 24.603(37)Å, β= 102.55(10)°. The structure has been solved by heavy-atom methods and refined by least squares to R 0.062 (R′ 0.062) for 3 341 independent diffracted intensities measured at 200 K. The molecule lies astride a crystallographic two-fold axis, with the trimetal system being significantly non-linear [Pt(2)–Pt(1)–Pt(2′) 158°]. The Pt–Pt separations of 3.166(1)Å indicate little or no direct metal–metal bonding. Two cyclo-octa-1,5-diene ligands, in their usual tub-like configuration, are η⁴-co-ordinated to Pt(2) and Pt(2′). The Pt(1)–Pt(2) and Pt(1)–Pt(2′) vectors are bridged by two C₈H₈ ligands which employ four adjacent carbon atoms for bonding to the metal atoms. Of these carbon atoms, the central pair form a CC bond η²-co-ordinated to Pt(1) while the outer two are attached to Pt(2)[or Pt(2′)] by σ bonds. The central metal atom Pt(1) is also bonded to an ethylene molecule so that it is in a distorted trigonal configuration, in contrast to Pt(2) and Pt(2′) which have an essentially square-planar environment comprising the two σ bonds from one C₈H₈ ligand and the CC bonds of a C₈H₁₂ ring. Hence Pt(1) can be regarded as platinum (0), and the Pt(2) and Pt(2′) atoms as being in a Pt^II oxidation state. From variable-temperature ¹H n.m.r. studies it was shown that the compound undergoes dynamic behaviour in solution. The mechanism is discussed, and the spectrum analysed by spin-decoupling experiments. The ¹³C n.m.r. spectrum is also reported.