Cationic Thorium Alkyl Complexes of Rigid NON- and NNN-Donor Ligands: π-Arene Coordination as a Persistent Structural Motif

Abstract

Reaction of the neutral dialkyl complex [(XA2)Th(CH2SiMe3)2] {1; XA2 = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene} with [CPh3][B(C6F5)4] in benzene or toluene at room temperature resulted in the formation of [(XA2)Th(CH2SiMe3)(η6-arene)][B(C6F5)4] {arene = C6H6 (5) and toluene (5B)}, which were characterized by 1H, 13C, and 2D NMR spectroscopy and by X-ray crystallography (for 5). In close analogy, reaction of [(XA2)Th(CH2Ph)2] (3) with [CPh3][B(C6F5)4] in toluene at room temperature resulted in the formation of 1 equiv of Ph3CCH2R (R = Ph) and precipitation of an insoluble orange-brown oil, which upon layering with hexanes yielded crystals of [(XA2)Th(η2-CH2Ph)(η6-C6H5Me)][B(C6F5)4] (6). NMR investigation of the reactions of 1 and 3 with substoichiometric amounts of [CPh3][B(C6F5)4] provided no evidence for dinuclear monocation formation. By contrast, reaction of [(BDPP)Th(CH2Ph)2] {4; BDPP = 2,6-bis(2,6-diisopropylanilidomethyl)pyridine} with 0.5 equiv of [CPh3][B(C6F5)4] resulted in the precipitation of an insoluble oil containing a mixture of a mononuclear and a dinuclear cation; the dinuclear cation was identified as [(BDPP)Th(η2-CH2Ph)(μ-η1:η6-CH2Ph)Th(η1-CH2Ph)(BDPP)][B(C6F5)4] (7) by X-ray crystallography. Reaction of complex 3 with B(C6F5)3 resulted in the formation of [(XA2)Th(η1-CH2Ph)][η6-PhCH2B(C6F5)3] (9), which was characterized in solution by NMR spectroscopy. Complexes 5, 5B, and 6 are rare examples of arene solvent-separated ion pairs, complex 9 exists as a tight contact ion pair, and dinuclear 7 exhibits a unique benzyl ligand bridging mode. The structures of cations 5−7 and 9 highlight a pronounced tendency for these systems to engage in arene π-coordination.

Divergent reactivity of [(κ3-L)ThCl2(dme)] with Grignard reagents: Alkylation, ancillary ligand transfer to magnesium, and halide exchange caught in the act

“…The composition of 3 also highlights the compatibility of magnesium alkyls with certain metal halides; both bridging and terminal. In contrast to the reaction of 1 with MeMgBr, reactions of 1 and [(XA 2 ) ThCl 2 (dme)] (2) with PhCH 2 MgCl provided the expected dibenzyl complexes, [LTh(CH 2 Ph) 2 ] [L ¼ BDPP (4) and XA 2 (5); previously reported] under most reaction conditions [15,18]. However, addition of PhCH 2 MgCl to 1 at À78 C and warming to room temperature after 5 min yielded a significant amount of [(XA 2 )Mg(dme)] (6), the product of ancillary ligand transfer from thorium to magnesium.…”

“…in toluene), the expected dialkyl products, [LTh(CH 2 Ph) 2 ] [L ¼ BDPP (4) and XA 2 (5); previously reported] were obtained in high yield (Scheme 3) [15,18]. However, the reaction to form 5 is best performed: (a) with addition of PhCH 2 MgCl at 20 C, or (b) with addition of PhCH 2 MgCl at À78 C, followed by stirring at 0 C for 3 h. If the addition of PhCH 2 MgCl to 2 was performed at À78 C, and the reaction was allowed to warm to room temperature after 5 minutes, a substantial amount (30e50%) of a new product, [(XA 2 ) Mg(dme)] (6), was formed in addition to complex 5 (Scheme 4) [49].…”

“…Our research has focused on the rigid, planar and tridentate BDPP [2,6-bis(2,6-diisopropylanilidomethyl) pyridine] [21] and XA 2 [4,5-bis(2,6-diisopropylanilido)-2,7-di-tertbutyl-9,9-dimethylxanthene] [14] dianions ( Fig. 1) [22], and reaction of Li 2 [14] and [LTh(CH 2 Ph) 2 ] [L ¼ BDPP (4) and XA 2 (5)] from which the first examples of non-cyclopentadienyl thorium alkyl cations were prepared [15,18]. However, caution is drawn to the expected outcome in reactions with PhCH 2 MgCl (vide infra).…”

“…of 1) [16]. In this work, the reactions of [LThCl 2 (dme)] [L ¼ BDPP (1) or XA 2 (2)] with MeMgBr and PhCH 2 MgCl [15,18] are discussed, and the unexpected products [{(BDPP)ThX(m-X) 2 Mg(OEt 2 )(m-Me)} 2 ] (X ¼ Br 0.73e0.87 /Cl 0.13e0.27 ; 3) and [(XA 2 )Mg(dme)] (6) are reported. Grignard reagents are commonly employed for the alkylation of d-and f-block metal halide complexes, especially when there exists the potential for reduction or ate-complex formation with more aggressive alkylating agents (e.g.…”

Computational study of An–X bonding (An = Th, U; X = p-block-based ligands) in pyrrolic macrocycle-supported complexes from the quantum theory of atoms in molecules and bond energy decomposition analysis

“…The organometallic chemistry of the early actinides has been the focus of significant attention for a number of years [1][2][3][4][5][6][7][8][9][10] and, in particular, covalency in the f-block has been the subject of much debate both experimentally and theoretically. [11][12][13] Traditional wisdom holds that there may be significant covalency in the bonding in transition metal and early actinide complexes, although the lanthanides and later actinides are generally more ionic in character.…”