Arene-Bridged Dithorium Complexes: Inverse Sandwiches Supported by a δ Bonding Interaction

Abstract

A series of arene-bridged dithorium complexes was synthesized via the reduction by potassium graphite of a Th(IV) precursor in the presence of arenes. All these compounds adopt an inverse-sandwich structure, with the arene bridging two thorium centers in a μ-η 6 ,η 6 -mode. Structural and spectroscopic data support the assignment of two Th(IV) ions and an arene tetraanion, which is an aromatic structure according to Huckel's rule. Arene exchange reactions revealed that the stability of the corresponding compounds follows the series naphthalene ≪ toluene < benzene ≈ biphenyl. Reactivity studies showed that they function as fourelectron reductants capable to reduce anthracene, cyclooctatetraene, alkynes, and azobenzene, while a mononuclear thorium anthracene complex could reduce benzene. Density functional theory calculations unveiled that the bonding interactions consist of δ bonds between thorium 6d and 5f orbitals and arene π* orbitals, showing a significant covalent character, able to stabilize highly reduced arene ligands.

Selective Coupling of Lanthanide Metallacyclopropenes and Nitriles via Azametallacyclopentadiene and η2-Pyrimidine Metallacycle

“…A direct comparison of the bonding shows a more reactive M–C bond in 2a than that of 2c , consistent with the different reactivity between 2a and 2c . Moreover, this Lu–C sp2 bond in 2a is even more polarized than the M–C sp2 bonds in all other reported metallacyclopropenes. − …”

“…Metallacyclopropenes have long been targeted by organometallic and coordination chemists because of the intrinsic interest in their structure, reactivity, and synthetic and catalytic applications . Although transition, main-group, and actinide metallacyclopropenes have been extensively studied, their analogues of rare-earth metals (Sc, Y, and lanthanides) have remained elusive due to the synthetic difficulty and high reactivity . Initially, the reduction of diphenylacetylene by divalent Cp* 2 Sm (Cp* = C 5 Me 5 ) was tried to afford a μ-η 1 :η 1 -(PhCCPh) 2– -bridged disamarium­(III) complex, instead of a samarium metallacyclopropene .…”

Actinide arene-metalates: ion pairing effects on the electronic structure of unsupported uranium–arenide sandwich complexes

“…34 These complexes have provided valuable electronic insight into actinide bonding, particularly with respect to d-interactions, while enabling rich redox chemistry and other novel reactivity patterns such as the C-H borylation of arenes. [34][35][36][37][38][39][40][41][42][43][44][45][46] For example, U(O-2,6-t Bu 2 C 6 H 3 ) 3 reacts with benzene in the presence of HBBN (HBBN ¼ 9-bora- 9-bicylononane) 47 and U(k 1 :h 6 48 where the uranium-arene bonds are enforced through intramolecular ligand tethering. Interestingly, it has been predicted by means of density functional theory (DFT) that uranium-arene complexes may also provide access to the unknown U(I) oxidation state.…”

Reactivity of Lutetacyclopropene toward Benzyl, Benzoyl, and Trimethylsilyl Nitriles Affording Diversified Lutetium Complexes

“…In contrast to the metallacyclopropenes of early transition metals, main group elements, and actinides, rare-earth metallacyclopropenes have been neglected for many years . Until 2019, our group prepared the first series of rare-earth metallacyclopropenes from the chloride precursors of rare-earth metals, potassium graphite (KC 8 ), and alkynes .…”