Structure and Properties of Carbonylbis(eta-cyclopentadienyl) (pi-diphenylacetylene)titanium: The First Titanium Complex containing a Two-carbon -Bonded Ligand

The reaction of [Ti(cp) 2(CO) 2] (cp = η-C 5H 5) with diphenylacetylene gives mononuclear [Ti(cp) 2(C 2Ph 2)(CO)] characterised by ν(CO) at 1 995 and ν(C≡C) 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 H 2. At >30 °C and in solutions of aromatic hydrocarbons it decomposes to [Ti(cp) 2(CO) 2] and [Ti(cp 2(CPh:CPh·CPh:CPh)]. Its stability in the solid state has allowed an X-ray structural analysis: orthorhombic, space group P2 12 12 1, 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 C 5H 5 rings and η-bonded to the diphenylacetylene ligand. The two 'eclipsed' C 5H 5 rings are bent back to make room in the horizontal (molecular) plane for a CO ligand and a 'σ,π'-bonded C 2Ph 2 molecule. The Ti-C(CO) and C-O bond lengths [2.050(8) and 1.130(10) Å] are consistent with the CO being bonded to titanium as in [Ti(cp) 2(CO) 2]. The Ti-C(C 2Ph 2) bond lengths [2.107(7) and 2.230(7) Å], together with the C=C bond distance [1.285(10) Å] and C≡C-Ph deformation angles [138.8(7) and 145.8(7)°], suggest a metallocyclopropene structure for the titanium-diphenylacetylene interaction