Thorium(iv) alkyl and allyl complexes of a rigid NON-donor pincer ligand with flanking 1-adamantyl substituents

Abstract

Palladium-catalyzed coupling of 1-adamantylamine (2 equiv.) with 4,5-dibromo-2,7-di-tert-butyl-9,9-dimethylxanthene afforded the proligand 4,5-bis(1-adamantylamino)-2,7-di-tert-butyl-9,9-dimethylxanthene, H₂[XAd] (1), which upon deprotonation with excess KH or KCH₂Ph in THF or dme generated [{K(THF)₃}₂(XAd)] (2a) and [K₂(XAd)(dme)] (2b). Subsequent reaction of in situ generated 2a or 2b with [ThCl₄(dme)₂] yielded [(XAd)ThCl₄K₂]·x(dme) (3; x = 0.5–2), which reacted with 2 equiv. of LiCH₂SiMe₃ or K[allyl^TMS] to afford the bis(hydrocarbyl) complexes [(XAd)Th(CH₂SiMe₃)₂(THF)] (4) and [(XAd)Th(η³-allyl^TMS)₂] {5; allyl^TMS = 1-(SiMe₃)C₃H₄}. Dialkyl complex 4 was stable at 80 °C for at least 2.5 hours, but decomposed over 4.5 hours at 110 °C. Diallyl complex 5 was stable for hours at 85 °C, and suffered less than 5% decomposition after 10 minutes at 155 °C. At room temperature, averaging of the syn and anti protons of the allyl CH₂ groups of 5 occurred on the NMR timescale, as a consequence of rapid π–σ–π hapticity changes. Additionally, low temperature ¹H and ¹³C NMR spectroscopy indicates that 5 exists as a rapidly exchanging mixture of two isomers with C₁ and C₂ symmetry. Compounds 2a, 4 and 5 were crystallographically characterized.