C-H Activation of Arenes and Substituted Arenes by the Yttrium Hydride (Cp*2YH)2:Competition between Cp* Ligand Metalation, Arene Metalation, and H/D Exchange. Molecular Structures of Cp*2Y(μ-H)(μ-η1,η5-CH2C5Me4)YCp* and Cp*2Y(o-C6H4PPh2CH2)

Several C-H activation reactions with (Cp*2YH)2 (1) are reported. Thermolysis of 1 in n-octane, cyclohexane, or benzene leads to formation of the thermodynamically favored product Cp*2Y(μ-H)(μ-η1,η5-CH2C5Me4)YCp* (2). The molecular structure of 2 was determined by X-ray diffraction. The compound crystallizes in space group P1 with unit cell parameters a = 10.433(3) Å, b = 13.661(3) Å, c = 15.076(5) Å, α = 113.76(3)°, β = 90.62(3)°, γ = 100.45(2)°. The unit cell contains two molecules of 2 (Z = 2) and one benzene molecule. Least-squares refinement based on 4240 reflections converged to RF = 0.065. With deuterated aromatic solvents fast H/D exchange takes place between the solvent and hydride ligands of 1, without intermediate metalation of solvent molecules. For toluene, a preference for H/D exchange on the para and meta positions was found. Metalation of benzene and toluene is possible when the hydrogen gas generated is removed quickly, leading to compounds Cp*2YPh (3) and Cp*2YCH2Ph (4), respectively. This process is much slower than the H/D scrambling reaction, and formation of 2 competes. It is proposed that the H/D exchange with benzene and toluene and the formation of 3 and 4 proceed through different σ-bond metathesis pathways. With aromatic molecules PhX (X = OMe, SMe, NMe2, CH2NMe2, PMe2, -PPh2=CH2, F, Cl, Br), ortho-metalation of the phenyl group is the dominant reaction, although formation of 2 is also observed (X = NMe2, CH2NMe2). For halobenzenes (X = F, Cl, Br) instantaneous reaction was observed but the products appeared to be complicated mixtures which could not be identified. Organic workup and analysis of the organic products showed that C-C coupling leading to biphenyl derivatives is taking place. The product resulting from ortho-metalation of Ph3P=CH2, Cp*2Y(o-C6H4PPh2CH2) (10), crystallizes in space group P21/n with unit cell parameters a = 13.449(2) Å, b = 16.522(2) Å, c 15.410(2) Å, β = 108.73(1)°. The unit cell contains four molecules of 10 (Z = 4). Least-squares refinement based on 5198 reflections converged to RF = 0.043