FORMATION OF BIMETALLIC, TRIMETALLIC, AND PENTAMETALLIC YTTRIUM METHOXIDE AND METHOXIDE OXIDE COMPLEXES FROM REACTIONS OF ALKALI-METAL METHOXIDES WITH BIS(CYCLOPENTADIENYL)YTTRIUM CHLORIDE

The superficially simple metathetical reaction of (C5H5)2YCl(THF) with alkali-metal methoxides has been found to form a variety of products and product mixtures depending on reaction conditions. (C5H5)2YCl(THF) reacts with NaOMe to form [(C5H5)2Y(mu-OMe)]2 (1) in 80-95% yield depending on the method of isolation of the product. 1 can be generated analogously from KOMe in up to 75% yield depending on reaction conditions and the source of KOMe. The primary byproduct in KOMe reactions, which ran be isolated in up to 20% yield, was identified as the trimetallic anion {[(C5H5)2Y(mu-OMe)]2[(C5H5)2Y](mu-3-O)}-(2). The yield of 2 can be increased to as high as 70% by varying the reaction conditions and the (C5H5)2YCl(THF) to KOMe stoichiometry. Me2O has been isolated as a byproduct in this oxide-forming reaction. The previously characterized pentametallic complex (C5H5)5Y5(mu-OMe)4(mu-3-OMe)4(mu-5-O) (3) is also formed in this reaction system. 3 can be obtained in high yield from the reaction of (C5H5)YCl2(THF)3, generated in situ, with 2 equiv of NaOMe in THF at reflux or from the reaction of (C5H5)2YCl(THF) and MeOH-solvated KOMe. Other cyclopentadienyl alkoxide products are also formed in these reactions, and the product mixtures are highly dependent upon the particular alkali-metal alkoxide used, its method of preparation, the reaction time and temperature, reagent concentrations, and workup procedure. The direct formation of the polymetallic products from 1 and methoxide reagents has been investigated and further shows the complexity of this system. Crystallographic data have been obtained on 1-3 as well as the (trimethylsilyl)cyclopentadienyl analogue of 1 [(C5H4SiMe3)2Y(mu-OMe)]2 (4) and its chloride precursor [(C5H4SiMe3)2Y(mu-Cl)]2 (5). Complexes 1, 4, and 5 are comprised of (C5H4R)2Y (R = H, SiMe3) bent metallocene units bridged by methoxide or chloride ligands. In 2, three (C5H5)2Y bent metallocene units define a triangle with two sides bridged by methoxide groups. Near the third side in the interior of the triangle and coplanar with the yttrium atoms is a mu-3-oxide ligand. 2 crystallized with the countercation {[(THF)3Na]2(mu-C5H5)} in which a bridging C5H5 group is sandwiched between two Na(THF)3 moieties. [(C5H5)2Y(mu-OMe)]2 crystallized from toluene in space group P1BAR with unit cell dimensions a = 16.747 (11) angstrom, b = 27.351 (14) angstrom, c = 8.404 (4) angstrom, alpha = 90.00 (4)-degrees, beta = 109.49 (4)-degrees, gamma = 90.05 (5)-degrees, V = 3629 (3) angstrom3, and Z = 6 for D(calcd) = 1.14 g cm-3. {[(C5H5)2Y)]3(OMe)2O}{[(THF)3Na]2(C5H5)} crystallized from THF in space group Pnam with unit cell dimensions a = 18.854 (6) angstrom, b = 15.803 (3) angstrom, c = 22.355 (8) angstrom, and Z = 4 for D(calcd) = 1.28 g cm-3. [(C5H4SiMe3)2Y(mu-Ome)]2 crystallized from benzene with two molecules of benzene in the lattice in space group C2/c with unit cell dimensions a = 24.930 (3) angstrom, b = 13.735 (2) angstrom, c = 14.764 (2) angstrom, beta = 91.90 (1)-degrees, V = 5052 (1) angstrom3, and Z = 4 for D(calcd) = 1.24 g cm-3. Least-squares refinement based on 3653 observed reflections led to a final R(F) value of 5.3%. [(C5H4SiMe3)2Y(mu-Cl)]2 crystallized from benzene in space group P1BAR with a = 8.676 (2) angstrom, b = 9.763 (2) angstrom, c = 12.487 (2) angstrom, alpha = 70.38 (1)-degrees, beta = 76.69 (1)-degrees, gamma = 88.67 (1)-degrees, V = 967.7 (3) angstrom3, and Z = 1 for D(calcd) = 1.37 g cm-3. Least-squares refinement of the model based on 3285 reflections converged to a final R(F) = 4.3%.