## Abstract

This contribution describes thorium hydrocarbyl and hydride chemistry based upon the chelating (CH_{3})_{2}Si[(CH_{3})_{4}C_{5}]_{2}^{2}-ligand (Me_{2}SiCp“_{2}^{2~}). Precursor Me_{2}Si(Cp“H)_{2} can be prepared by reaction of SiCl_{4}with 2 equiv of Li(CH_{3})_{4}C_{5}, followed by methylation (CH_{3}Li) and methanolic workup. Subsequent reaction with n-C_{4}HgLi in 1, 2-dimethoxyethane yields Me_{2}Si(Cp^{“}Li)_{2}-2DME. The dilithium salt undergoes reaction with ThCl_{4}to yield Me_{2}SiCp”_{2}ThCl_{2}-2LiCl.2DME, which, in turn, can be alkylated with lithium reagents to produce crystalline, thermally stable Me_{2}SiCp^{“}_{2}ThR_{2}complexes where R = CH_{2}Si(CH_{3})_{3}, CH_{2}C(CH_{3})_{3}, C_{6}H_{6}, M-c_{4}H_{9}, and CHoC_{6}H_{5}. The Me_{2}SiCp”_{2}Th[CH_{2}Si(CH_{3})_{3}]_{2} complex crystallizes in the monoclinic space group P2_{1}/m—C_{2/l}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 Me_{2}SiCp”_{2}Th[CH_{2}Si(CH_{3})_{3}]_{2} units with η^{5}-Cp” coordination and ∠(ring centroid)-Th-(ring centroid) = 118.4°. There is considerable dispersion in the Th-C(ring) distances. The Th[CH_{2}Si(CH_{3})_{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) A, respectively. The thorium coordination sphere is more “open” than that in Cp'_{2}Th[CH_{2}Si(CH_{3})_{3}]_{2}. Hydrogenolysis of the dialkyl yields the dimeric hydride Me_{2}SiCp''_{2}Th(M-H)_{4}ThCp“_{2}SiMe_{2}, which crystallizes in the monoclinic space group P2_{1}/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 C_{2}symmetry with (ring centroid)-Th-(ring centroid) angles of 118.1° and 117.7°. The Th-Th distance is 3.632 (2) A which suggests, in combination with infrared spectral data, a Th(μ-H)_{4}Th structure. The above hydride catalyzes the hydrogenation of 1-hexene at a rate ca. 10^{3} faster than (Cp'_{2}ThH_{2})_{2}. For trans-2-hexene, hydrogenation catalyzed by the ring-bridged hydride is ca. 30 times more rapid than by (Cp_{2}'ThH_{2})_{2}.

Original language | English (US) |
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Pages (from-to) | 1828-1838 |

Number of pages | 11 |

Journal | Organometallics |

Volume | 7 |

Issue number | 8 |

DOIs | |

State | Published - Aug 1988 |

## ASJC Scopus subject areas

- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry