Rigid non-carbocyclic ancillary ligands in organothorium chemistry

Carlos A Cruz, McMaster University

Abstract

A new rigid, dianionic ligand, 4,5-bis(2,6-diisopropylanilido)-2,7-di- tert-butyl-9,9-dimethylxanthene {[XA2]}, has been designed for use in the chemistry of the actinides. Pro-ligand H2[XA 2] (1) was synthesized by the Hartwig-Buchwald coupling of 4,5-dibromo-2,7-di- tert-butyl-9,9-dimethylxanthene with 2,6-diisopropylaniline. ^ Stable alkali metal salts of the [XA2] ligand, K2(dme) 2[XA2] (2) and Na2(XA2] (3), were accessible by deprotonation of H2[XA 2] with KH or NaH in dme or toluene, respectively. The thermally unstable lithium salt of McConville's 2,6-bis(2,6-diisopropylanilidomethyl)pyridine {Li2[BDPP], 4} was isolated by deprotonation of pro-ligand H2[BDPP] with nBuLi or LiCH2SiMe 3 in hexanes at low temperature. ^ An alternative route to ((BDPP)ThCl2(dme)] (5) and [LTh(CH2SiMe3)2] (9 and 10) involved combination of two or four equivalents of LiCH2SiMe 3 with [ThCl4(dme)2], followed by addition of H2L. These reactions likely proceed by alkane elimination from dialkyl or tetraalkyl thorium intermediates. The solid-state structure of [(BDPP)Th(CH2SiMe3)2] (9) suggests the presence of α-agostic C-H-Th interactions for both alkyl groups. ^ Addition of two equivalents of PhCH2MgCl to [LThCl2(dme)] yielded solvent-free [LTh(CH2Ph)2] {L = {XA2] (12) and [BDPP] (13)]. The 1 JC-H coupling constants in both complexes {120 and 139 Hz for 12; 127 and 138 Hz for 13} are indicative of η1 and ηη2- or η3 -coordinated benzyl ligands in solution; polyhapto benzyl coordination was also observed in the solid state. ^ Reaction of [(XA2)Th(CH2Ph)2] ( 12) with either one or two equivalents of B(C6F5) 3 afforded the first non-carbocyclic actinide alkyl cation, [(XA 2)Th(CH2Ph)][PhCH2B(C6F5) 3] (21), and a rare example of an actinide dication, [(XA 2)Th][PhCH2B(C6F5)3] 2 (27). In both 21 and 27 the PhCH2B(C6F5)3 anion is η 6-coordinated to thorium. Reaction of neutral dialkyl complex [(XA 2)Th(CH2SiMe3)2] (9) with [Ph3C][B(C6F5)4] in benzene or toluene at room temperature resulted in the formation of [(XA2)Th(CH 2SiMe3)(η6-arene)][B(C6F 5)4] (arene = C6H6, 22; arene = C 7H8, 23). ^ Preliminary reaction studies with both neutral and cationic thorium complexes supported by the [BDPP] and [XA2] ancillary ligands demonstrated significant activity for olefin polymerization and hydroamination catalysis. Reactions of 9 and 10 with 4 atm. of hydrogen also suggest that the [BDPP] and [XA2] ligand frameworks may be suitable for the stabilization of thorium hydride complexes. (Abstract shortened by UMI.)^

Subject Area

Chemistry, Inorganic

Recommended Citation

Carlos A Cruz, "Rigid non-carbocyclic ancillary ligands in organothorium chemistry" (January 1, 2010). ETD Collection for McMaster University. Paper AAINR74669.
http://digitalcommons.mcmaster.ca/dissertations/AAINR74669