CHEMISTRY OF TRIVALENT CERIUM AND URANIUM METALLOCENES - REACTIONS WITH ALCOHOLS AND THIOLS

The trivalent cerium metallocene (Me3CC5H4)3Ce reacts with alcohols, HOR (R = CHMe2 or Ph), or thiols, HSR (R = CHMe2, or Ph), to give the dimers (Me3CC5H4)4Ce2 (µ-ER)2 as shown by X-ray crystallography for the isopropoxide and isopropylthiolate derivatives. Crystals of (Me3CC5H4)4Ce2(µ-OCHMe2)2 are monoclinic, P21/c with a = 11.962 (4) Å, b = 14.489 (5) Å, c = 12.384 (5) Å, β = 103.31 (3)°, and V = 2089 Å3; the structure was refined by full-matrix least-squares methods to a conventional R factor of 0.028, 2874 data, F2 > 2σ(F2). The Ce2O2 unit is planar, the geometry about the cerium atom is pseudotetrahedral, and the geometry is planar about the oxygen atom. Crystals of (Me3CC5H4)4Ce2(µ-SCHMe2)2 are also monoclinic, P21/n with a = 14.255 (9) Å, b = 13.585 (9) Å, c = 11.265 (7) Å, β = 96.02 (5)°, V = 2170 Å3; the structure was refined by full-matrix least-squares methods to a conventional R factor of 0.028, 2899 data, F2 > 2σ(F2). The Ce2S2 unit is planar, and the geometry about cerium is pseudotetrahedral though the geometry is pyramidal at sulfur so that the isopropyl groups are anti relative to the Ce2S2 ring. Methanol or water give an insoluble solid, presumably Ce(OMe)3 or Ce(OH)3, whereas HECMe3 (E = O or S) do not react with (Me3CC5H4)3Ce, but the thiol does react with the sterically less bulky metallocene (MeC5H4)3Ce(THF) (THF = tetrahydrofuran) to give (MeC5H4)4Ce2(µ-SCMe3)2. The pKa’s (H2O) of the organic acids generally predict the thermodynamic outcome of the proton-exchange reactions, though the latter set of experiments show that kinetic (i.e., steric) factors play a role. The uranium metallocene (Me3CC5H4)3U reacts with HSPh at low temperature to give isolable (Me3CC5H4)4U2(µ-SPh)2, which rearranges in solution to the monomeric, tetravalent species (Me3CC5H4)3USPh and unidentified material. The dimer intermediate cannot be detected with the sterically smaller metallocene (MeC5H4)3U(THF), as only (MeC5H4)3UER (ER = OMe, OCHMe2, OPh, and SCHMe2) are isolated. © 1990, American Chemical Society. All rights reserved.