SYNTHESIS AND CHARACTERIZATION OF THORIUM TERT-BUTOXIDE COMPLEXES - X-RAY CRYSTAL-STRUCTURES OF TH(O-T-BU)4(PY)2 AND NATH2(O-T-BU)9

Two synthetic procedures have been employed for the preparation of thorium tert-butoxide complexes. Reaction of ThI4(THF)4 with 4 equiv of KO-t-Bu in THF/pyridine solution provides Th(O-t-Bu)4(py)2 (1) in moderate yield. Alcoholysis of the thorium metallacycle [{(Me3Si)2N}2Th(CH2SiMe2NSiMe3)] with >4 equiv of HO-t-Bu produces the dimeric alcoholate Th2(O-t-Bu)8(HO-t-Bu) (2) in 70% isolated yield. The coordinated alcohol in 2 is readily deprotonated by employing NaN(SiMe3)2 in hexane solution to provide hexane-soluble NaTh2(O-t-Bu)9 (3) in ca. 70% yield. Formation of the trimeric complex Th3O(O-t-Bu)10 (4) occurs upon addition of stoichiometric amounts of H2O to refluxing toluene solutions of 2. Compounds 1-4 have been characterized by elemental analysis, H-1 NMR, infrared spectroscopy, and, for 1 and 3, single-crystal X-ray diffraction. In 1, the Th atom is coordinated to four alkoxide and two pyridine ligands in a cis pseudo-octahedral fashion with average Th-O and Th-N distances of 2.182(6) and 2.752(7) angstrom, respectively. In 3, the NaTh2(O-t-Bu)9 unit is closely related to the well-known M3X11 cluster and is best described as NaTh2(mu3-O-t-Bu)2(mu2-O-t-Bu)3(O-t-Bu)4. Averaged Na-mu3-O and Na-mu2-O distances are 2.399(17) and 2.607(10) angstrom, respectively. Th-O distances are 2.155(8), 2.280(10), 2.464(7), and 2.491(7) angstrom for terminal, doubly bridging to sodium, doubly bridging to thorium, and triply bridging alkoxides, respectively. Crystal data for 1 (at 25-degrees-C): Monoclinic space group C2/c, with a = 12.656(3) angstrom, b = 15.326(3), c = 16.803(3) angstrom, beta = 96.43(3)-degrees, V = 3238.7(12) angstrom3, d(calc) = 1.363 g cm-3, and Z = 4. Crystal data for 3 (at 25-degrees-C): Orthorhombic space group Pnma, with a = 11. 170(2) angstrom, b = 25.408(5), c = 17.195(3) angstrom, V = 4880.1(16) angstrom3, d(calc) = 1.559 g cm-3, and Z = 4.