C-H ACTIVATION OF ARENES AND SUBSTITUTED ARENES BY THE YTTRIUM HYDRIDE (CP-ASTERISK-2YH)2 - COMPETITION BETWEEN CP-ASTERISK LIGAND METALATION, ARENE METALATION, AND H D EXCHANGE - MOLECULAR-STRUCTURES OF SK-2Y(MU-H)(MU-ETA(1),ETA(5)-CH2C5ME4)YCP-ASTERISK AND CP-ASTERISK-2Y(O-C6H4PPH2CH2)/

Several C-H activation reactions with (Cp2YH)2 (1) are reported. Ther molysis of 1 in n-octane, cyclohexane, or benzene leads to formation o f the thermodynamically favored product Cp2Y(mu-H)(mu-eta1,eta'-CH2C5 Me4)YCp(2). The molecular structure of 2 was determined by X-ray diff raction. The compound crystallizes in space group P1BAR with unit cell parameters a = 10.433(3) angstrom, b = 13.661(3) angstrom, c = 15.076 (5) angstrom, alpha = 113.76(3)-degrees, beta = 90.62(3)-degrees, gamm a = 100.45(2)-degrees. The unit cell contains two molecules of 2 (Z = 2) and one benzene molecule. Least-squares refinement based on 4240 re flections converged to R(F) = 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 tolue ne, a preference for H/D exchange on the para and meta positions was f ound. Metalation of benzene and toluene is possible when the hydrogen gas generated is removed quickly, leading to compounds Cp2YPh (3) and Cp2YCH2Ph (4), respectively. This process is much slower than the H/ D scrambling reaction, and formation of 2 competes. It is proposed tha t the H/D exchange with benzene and toluene and the formation of 3 and 4 proceed through different sigma-bond metathesis pathways. With arom atic molecules PhX (X = OMe, SMe, NMe2, CH2NMe2, PMe2, -PPh2=CH2, F, C l, Br), ortho-metalation of the phenyl group is the dominant reaction, although formation of 2 is also observed (X = NMe2, CH2NMe2). For hal obenzenes (X = F, Cl, Br) instantaneous reaction was observed but the products appeared to be complicated mixtures which could not be identi fied. Organic workup and analysis of the organic products showed that C-C coupling leading to biphenyl derivatives is taking place. The prod uct resulting from ortho-metalation of Ph3P=CH2, CP2y(o-C6H4-PPh2CH2) (10), crystallizes in space group P2(1)/n with unit cell parameters a = 13.449(2) angstrom, b = 16.522(2) angstrom, c 15.410(2) angstrom, b eta = 108.73(l)-degrees. The unit cell contains four molecules of 10 ( Z = 4). Least-squares refinement based on 5198 reflections converged t o R(F) = 0.043.