Mono(pentamethylcyclopentadienyl)thorium Chemistry: Synthesis, Structural Characterization, and Reactivity of Aryloxide and Alkyl Derivatives

Abstract

Reaction of ThBr4(THF)4 with 1 equiv of Cp*MgBr(THF) (Cp* = η-C5Me5) produces the mono(pentamethylcyclopentadienyl) complex Cp*ThBr3(THF)3 (1). Treatment of 1 with 1 or 2 equiv of KOAr (Ar = 2,6-t-Bu2C6H3) 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 Me3SiCH2MgCl leads to isolation of the bis(alkyl) complex Cp*Th(OAr)(CH2SiMe3)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-BuCMe2CH2)(OAr)(OPPh3) (7). In the presence of 1 equiv of [HNMe2Ph][B(C6F5)4], 4 is found to catalyze the hydrogenation of 1-hexene and also the polymerization of ethylene. Compounds 1−7 have been characterized by 1H 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) Å, respectively. Cp*Th(OAr)(CH2SiMe3)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) Å. Th−Cp*centroid and Th−O distances are very similar to those found in 3, at 2.53(1) and 2.186(6) Å, respectively. Cp*Th(OC6H3-t-BuCMe2CH2)(OAr)(OPPh3) (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)°). The Th−C distance to the tert-butyl methylene group is 2.521(12) Å, while Th−O distances to the aryloxide and triphenylphosphine oxide ligands are 2.199(7) (av) and 2.445(7) Å, respectively.