Structure and properties of carbonylbis(η-cyclopentadienyl)(η-diphenyl-acetylene) titanium: the first titanium complex containing a two-carbon η-bonded ligand

Abstract

The reaction of [Ti(cp)₂(CO)₂](cp =η-C₅H₅) with diphenylacetylene gives mononuclear [Ti(cp)₂(C₂Ph₂)(CO)] characterised by ν(CO) at 1 995 and ν(CC) at 1 780 cm^–1 The new complex shows high catalytic activity in the hydrogenation of olefins and acetylenes at room temperature under 1 atm of H₂. At >30 °C and in solutions of aromatic hydrocarbons it decomposes to [Ti(cp)₂(CO)₂] and [[graphic omitted]Ph)]. Its stability in the solid state has allowed an X-ray structural analysis: orthorhombic, space group P2₁2₁2₁, a= 18.464(5), b= 13.301(4), c= 7.822(4)Å. Z= 4, and D_c= 1.49 g cm^–3. Full-matrix least-squares refinement has led to a final R value of 0.067 based on 1 647 independent observed reflections. The titanium atom is η-bonded to two C₅H₅ rings and η-bonded to the diphenylacetylene ligand. The two ‘eclipsed’ C₅H₅ rings are bent back to make room in the horizontal (molecular) plane for a CO ligand and a ‘σ,π’-bonded C₂Ph₂ molecule. The Ti–C(CO) and C–O bond lengths [2.050(8) and 1 .130(10)Å] are consistentwith the CO being bonded to titanium as in [Ti(cp)₂(CO)₂]. The Ti–C(C₂Ph₂) bond lengths [2.107(7) and 2.230(7)Å], together with the CC bond distance [1.285(10)Å] and CC–Ph deformation angles [I 38.8(7) and 145.8(7)°], suggest a metallocyclopropene structure for the titanium–diphenylacetylene interaction.