Mono(pentamethylcyclopentadienyl)thorium chemistry: Synthesis, structural characterization, and reactivity of aryloxide and alkyl derivatives

Reaction of ThBr4(THF)(4) with 1 equiv of Cp*MgBr(THF) (Cp* = eta-C(5)Me(5)) produces the mono(pentamethylcyclopentadienyl) complex Cp*ThBr3(THF)(3) (1). Treatment of 1 with 1 or 2 equiv of KOAr (Ar = 2,6-t-Bu(2)C(6)H(3)) yields the mono- and bis(aryloxide) species Cp*ThBr2(OAr)(THF) (2) and Cp*ThBr(OAr)(2) (3), respectively, Alkylation of 2 with 2 equiv of Me(3)SiCH(2)MgCl leads to isolation of the bis(alkyl) complex Cp*Th(OAr)(CH(2)SiMe(3))(2) (4), while 3 reacts with 1 equiv of MeMgBr to form the mono(alkyl) derivative Cp*ThMe(OAr)2 (5). 4 reacts with dihydrogen to produce the trimeric thorium dihydride [Cp*ThH2(OAr)](3) (6), while thermolysis of 4 in the presence of triphenylphosphine oxide leads to the isolation of the metallacyclic species Cp*Th(OC6H3-t-BuCMe(2)CH(2))(OAr)(O=PPh(3)) (7). In the presence of 1 equiv of [HNMe(2)Ph][B(C6F5)(4)], 4 is found to catalyze the hydrogenation of l-hexene and also the polymerization of ethylene. Compounds 1-7 have been characterized by H-1 NMR and IR spectroscopy, by microanalysis, and, in the case of 3, 4, and 7, by single-crystal X-ray diffraction studies. Cp*ThBr(OAr)(2)(3) exhibits a somewhat distorted three-legged piano-stool geometry with Th-Cp*(centroid), Th-O, and Th-Br distances of 2.57(1), 2.16(1) (av), and 2.821(2) Angstrom, respectively. Cp*Th(OAr)(CH(2)SiMe(3))(2) (4) also displays a three-legged piano-stool geometry with Th-C distances to the alkyl groups of 2.460(9) and 2.488(12) Angstrom. Th-Cp*(centroid) and Th-O distances are very similar to those found in 3, at 2.53(1) and 2.186(6) Angstrom, respectively. Cp*Th(OC6H3-t-BuCMe(2)CH(2))(OAr)(O = PPh(3)) (7) features a distorted trigonal bipyramidal geometry about the metal center, with the Cp* ligand and the oxygen atom of the cyclometalated aryloxide ligand occupying axial sites (Cp*(centroid)-Th-O = 168.3(3)degrees). The Th-C distance to the tert-butyl methylene group is 2.521(12) Angstrom, while Th-O distances to the aryloxide and triphenylphosphine oxide ligands are 2.199(7) (av) and 2.445(7) Angstrom, respectively.