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Extremely Stable Thorium(IV) Dialkyl Complexes...
Journal article

Extremely Stable Thorium(IV) Dialkyl Complexes Supported by Rigid Tridentate 4,5-Bis(anilido)xanthene and 2,6-Bis(anilidomethyl)pyridine Ligands

Abstract

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 Li2[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 LiCH2SiMe3 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-dependent 1 J C,H coupling constants for ThCH 2 , 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. Bis-ligand complexes were not accessible with the XA2 platform, presumably due to increased ligand rigidity.

Authors

Cruz CA; Emslie DJH; Harrington LE; Britten JF; Robertson CM

Journal

Organometallics, Vol. 26, No. 3, pp. 692–701

Publisher

American Chemical Society (ACS)

Publication Date

January 1, 2007

DOI

10.1021/om060914f

ISSN

0276-7333

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