Gas-phase synthesis and structure of thorium benzyne complexes

Abstract

The thorium benzyne complex (η2-C6H4)ThCl3– was synthesized in the gas phase through consecutive decarboxylation and dehydrochlorination from the (C6H5CO2)ThCl4– precursor upon collision-induced dissociation. Theoretical calculations suggest that (η2-C6H4)ThCl3– exhibits a...

Dual-Ligand Strategy for the Preparation of Gas-Phase Uranyl(VI) Benzyne Complexes from Uranyl(VI) Benzoates

“…Both the C 6 H 4 moiety and chlorine atom reside in the equatorial plane of uranyl with a slightly bent [O�U�O] 2+ unit (164.5°). The six C−C bonds with comparable lengths (1.39−1.40 Å) in the C 6 H 4 moiety are indicative of the dianionic resonance form of the benzyne ligand, 11,12,31,32 which supports the VI oxidation state of uranium in (η 2 -C 6 H 4 )UO 2 Cl − , and agrees well with its reactivity toward water as discussed above. The two U VI −C benzyne bond lengths of 2.352 and 2.381 Å are close to the U IV −C benzyne distances (2.340−2.473 Å) reported in the monobenzyne and dibenzyne complexes of uranium(IV).…”

“…Therefore, it is neither thermodynamically nor kinetically favorable to form the benzyne complex in comparison to the formation of UO 2 Cl 2 – . In the case of thorium, which was studied at the same B3LYP level, the precursor has to overcome an energy barrier of 61.9 kcal/mol that is comparable to that for the formation of the uranyl benzyne complex prior to the formation of the thorium benzyne complex, but the energy required for C 6 H 5 radical loss to give ThCl 4 – is 73.8 kcal/mol, much higher than that in the uranium case. Such difference in the C 6 H 5 radical loss pathway is due to the formation of ThCl 4 – with an uncommon III oxidation state for thorium, which contrasts the more easily accessible pentavalent UO 2 Cl 2 – .…”

“…This is also consistent with the reactivity of early transitionmetal benzyne complexes, 5,7 as well as the reactivity of the thorium benzyne complex. 11 DFT calculations were employed to obtain a detailed understanding of the geometrical and electronic structures of the benzyne complex, and the result of (C 6 H 5 )UO 2 Cl − is also listed for comparison. As displayed in Figure 3, the benzyne complex (η 2 -C 6 H 4 )UO 2 Cl − exhibits a singlet ground state with C s symmetry, which lies 14.2 kcal/mol below the triplet state.…”

“…A more polarized U V −C aryl bond is found for the (C 6 H 5 )UO 2 Cl − complex with the contribution of uranium reduced by 9%. Of note, the U 5f orbital contributes 31.1% to the U VI −C benzyne bond, more than the contribution of Th 5f orbital (18.3%) to the Th IV −C benzyne bond in (η 2 -C 6 H 4 )ThCl 3 − , 11 indicating that the 5f orbitals play a significant role in stabilizing the uranium benzyne linkage. It is worth noting that the thorium benzyne complex (η 2 -C 6 H 4 )ThCl 3 − was generated via liberation of a HCl molecule from (C 6 H 5 )ThCl 4 − .…”

“…The recently reported thorium benzyne complex (η 2 -C 6 H 4 )ThCl 3 – was synthesized via consecutive decarboxylation and dehydrochlorination of (C 6 H 5 CO 2 )ThCl 4 – in the gas phase, and this procedure can be applied to a wide range of substituted benzoic acids except those with electron-withdrawing groups at the ortho -position . As the other common actinide element, uranium, the first isolable uranium(IV) monobenzyne complex [Li][U(η 2 -C 6 H 3 CH 2 NMe 2 )(C 6 H 4 CH 2 NMe 2 ) 3 ] and the dibenzyne complex [Li] 2 [U(η 2 -C 6 H 3 CH 2 NMe 2 ) 2 (C 6 H 4 CH 2 NMe 2 ) 2 ] were obtained using a chelating arylamine ligand (2-Li-C 6 H 4 CH 2 NMe 2 ) as a sacrificial base for deprotonation of the uranium-bound aryl ligand, and their insertion reactivities toward electrophiles such as benzophenone and benzonitrile were demonstrated. , However, attempts to synthesize the uranium(VI) benzyne complexes using a variety of oxidants, including 1-azidoadamantane, Me 3 SiN 3 , I 2 , AgPF 6 , [Fc][PF 6 ], S 8 , and PhSSPh, were unsuccessful and ended up with the uranium(IV) insertion products or intractable mixtures, indicating the much higher reactivity or internal instability of the benzyne complexes of uranium(VI) compared to that of uranium(IV).…”