927674-72-4Relevant articles and documents
Extremely stable thorium(IV) dialkyl complexes supported by rigid tridentate 4,5-bis(anilido)xanthene and 2,6-bis(anilidomethyl)pyridine ligands
Cruz, Carlos A.,Emslie, David J. H.,Harrington, Laura E.,Britten, James F.,Robertson, Craig M.
, p. 692 - 701 (2008/10/09)
A new NON-donor ligand, 4,5-bis(2,6-diisopropylanilino)-2,7-di-tert-butyl- 9,9-dimethylxanthene (H2[XA2], 1), was prepared by palladium-catalyzed coupling of 2,6-diisopropylaniline with the appropriate dibromoxanthene precursor. Stable K2(dme)2[XA2] (2) and Na2[XA2] (3) salts were accessible by deprotonation of H2[XA2] with KH in dme or NaH in toluene. The thermally unstable lithium salt of McConville's 2,6-bis(2,6- diisopropylanilidomethyl)pyridine ligand (Li2[BDPP], 4) was isolated by deprotonation with nBuLi or LiCH2SiMe3 in hexanes at low temperature. Reaction of [ThCl4(dme)2] with Li 2[BDPP] or M2(dme)n[XA2] resulted in the formation of pentagonal bipyramidal [LThCl2(dme)] complexes (L = BDPP, 5; XA2, 6). Subsequent reaction of 5 or 6 with LiCH 2SiMe2 gave base- and salt-free dialkyl complexes, [LTh(CH2SiMe3)2] (L = BDPP, 7; XA2, 8), which are stable for days in solution at 90 and 70°C, respectively. Complexes 5, 7, and 8 were also accessible by initial combination of 2 or 4 equiv of LiCH2SiMe3 with [ThCl4(dme) 2], followed by addition of H2L. These reactions likely proceed by alkane elimination, but dialkyl or tetraalkyl thorium intermediates were not identified. The X-ray crystal structure of 8 suggests the presence of α-agostic C-H-Th interactions for both alkyl groups. In solution, 7 and 8 exhibit temperature-dependent1JC,H coupling constants for ThCH2, demonstrating the presence of α-agostic interactions which become increasingly favored at lower temperature. Reaction of 5 with Li2[BDPP] at 0°C or 7 with H2[BDPP] at 100°C resulted in the formation of extremely sterically encumbered [Th(BDPP) 2] (9), which adopts a highly distorted six-coordinate geometry with the four anilido groups arranged in an approximate tetrahedron around thorium. Bisligand complexes were not accessible with the XA2 platform, presumably due to increased ligand rigidity.