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

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, H 2 [XAd] ( 1 ), which upon deprotonation with excess KH or KCH 2 Ph in THF or dme generated [{K(THF) 3 } 2 (XAd)] ( 2a ) and [K 2 (XAd)(dme)] ( 2b ). Subsequent reaction of in situ generated 2a or 2b with [ThCl 4 (dme) 2 ] yielded [(XAd)ThCl 4 K 2 ]· x (dme) ( 3 ; x = 0.5-2), which reacted with 2 equiv. of LiCH 2 SiMe 3 or K[allyl TMS ] to afford the bis(hydrocarbyl) complexes [(XAd)Th(CH 2 SiMe 3 ) 2 (THF)] ( 4 ) and [(XAd)Th(η 3 -allyl TMS ) 2 ] { 5 ; allyl TMS = 1-(SiMe 3 )C 3 H 4 }. 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 CH 2 groups of 5 occurred on the NMR timescale, as a consequence of rapid π-σ-π hapticity changes. Additionally, low temperature 1 H and 13 C NMR spectroscopy indicates that 5 exists as a rapidly exchanging mixture of two isomers with C 1 and C 2 symmetry. Compounds 2a , 4 and 5 were crystallographically characterized. A rigid new pincer pro-ligand, 4,5-bis(1-adamantylamino)-2,7-di- tert -butyl-9,9-dimethylxanthene, is described, with deprotonation and complexation to afford thorium( iv ) chloro, alkyl, and allyl derivatives.