This contribution describes thorium hydrocarbyl and hydride chemistry based upon the chelating (CH3)2Si[(CH3)4C5] 22- ligand (Me2SiCp″22-). Precursor Me2Si(Cp″H)2 can be prepared by reaction of SiCl4 with 2 equiv of Li(CH3)4C5, followed by methylation (CH3Li) and methanolic workup. Subsequent reaction with n-C4H9Li in 1,2-dimethoxyethane yields Me2Si(Cp″Li)2·2DME. The dilithium salt undergoes reaction with ThCl4 to yield Me2SiCp″2ThCl2·2LiCl·2pME, which, in turn, can be alkylated with lithium reagents to produce crystalline, thermally stable Me2SiCp″2ThR2 complexes where R = CH2Si(CH3)3, CH2C(CH3)3, C6H5, n-C4H9, and CH2C6H5. The Me2SiCp″2Th[CH2Si(CH3) 3]2 complex crystallizes in the monoclinic space group P21/m - C2h2 with two molecules in a unit cell of dimensions (20 ± 1°C) a = 11.960 (5) Å, b = 11.270 (5) Å, c = 12.395 (6) Å, and β = 99.32 (4)°. Least-squares refinement led to a value for the conventional R index (on F) of 0.076 for 2586 independent reflections having I > 3σ(I). The molecular structure consists of monomeric Me2SiCp′2Th[CH2Si(CH3) 3]2 units with η5-Cp″ coordination and ∠ (ring centroid)-Th-(ring centroid) = 118.4°. There is considerable dispersion in the Th-C(ring) distances. The Th[CH2Si(CH3)3]2 ligation is highly distorted, with Th-C-Si angles of 123.7 (14)° and 149.5 (12)°, accompanied by corresponding Th-C distances of 2.54 (2) and 2.48 (2) Å, respectively. The thorium coordination sphere is more "open" than that in Cp′2Th[CH2Si(CH3)3] 2. Hydrogenolysis of the dialkyl yields the dimeric hydride Me2SiCp″Th(μ-H)4ThCp″2SiMe 2, which crystallizes in the monoclinic space group P21/n with four molecules in a unit cell of dimensions (20 ± 1°C) a = 10.965 (2) Å, b = 19.843 (5) Å, c = 18.759 (3) Å, and β = 90.39 (2)°. Least-squares refinement led to a value for the conventional R index (on F) of 0.075 for 3298 independent reflections having I > 3σ(I). The dimer exhibits approximate C2 symmetry with (ring centroid)-Th-(ring centroid) angles of 118.1° and 117.7°. The Th-Th distance is 3.632 (2) Å which suggests, in combination with infrared spectral data, a Th(μ-H)4Th structure. The above hydride catalyzes the hydrogenation of 1-hexene at a rate ca. 103 faster than (Cp′2ThH2)2. For trans-2-hexene, hydrogenation catalyzed by the ring-bridged hydride is ca. 30 times more rapid than by (Cp2′ThH2)2.
|Number of pages||11|
|Publication status||Published - 1988|
ASJC Scopus subject areas
- Inorganic Chemistry
- Organic Chemistry