A Combined Experimental and Theoretical Investigation of Arene-Supported Actinide and Ytterbium Tetraphenolate Complexes

Abstract

Modular tetraphenolate ligands tethered with a protective arene platform (para-phenyl or para-terphenyl) are used to support mononuclear An(IV) (An = Th, U) complexes with an exceptionally large and open axial coordination site at the metal. The base-free complexes and a series of neutral donor adducts were synthesized and characterized by spectroscopies and single-crystal Xray diffraction. Anionic Th(IV) -ate complexes with an additional axial aryloxide ligand were also synthesized and characterized. The para-phenyl-tethered mononuclear complexes exhibit rare An(IV)−arene interactions, and the An(IV)−arene distance broadly increases with axial donor strength. The para-terphenyl-tethered complexes have almost no interaction with the arene base, isolating the central metal cation. Computational analysis of the mononuclear complexes and their reduced analogues, and Yb(III) congeners, as well as the effect of additional donor ligand binding, seek to elucidate the electronic structure of the metal−arene interactions and establish whether they, or their reduced or oxidized counterparts, could function as molecular qubits.

Reduction of Thorium Tris(amido)arene Complexes: Reversible Double and Single C–C Couplings

“…The Th–C arene distances are in a narrow range of 2.952(4)–2.994(4) Å with an average of 2.976(4) Å, indicating that the anchoring arene is η 6 -bound to thorium. Notably, the Th–C centroid distance of 2.6283(4) Å is significantly shorter than that of the thorium­(IV) complex of neutral benzene [(XA 2 )­Th­(CH 2 SiMe 3 )­(η 6 -C 6 H 6 )]­[B­(C 6 F 5 ) 4 ] [2.9501(9) Å; XA 2 = 4,5-bis­(2,6-di- iso -propylanilido)-2,7-di- tert -butyl-9,9-dimethylxanthene] and close to the shortest Th–C centroid distance documented in the literature for thorium­(IV) neutral arene complexes [2.6199(14) Å in ( p TP)­Th­(N 3 SiMe 3 ); p Tp = para -xylenetetra­(3- tert -butyl-5-methyl-2-phenoxide)], suggesting nonnegligible thorium–arene interaction in 1 .…”

“…Compared to uranium, thorium–arene interactions are much less studied and thorium arene complexes are scarce. In 2003, Gambarotta and co-workers reported the synthesis of thorium complexes of naphthalene dianion and their reactivity as thorium­(II) synthons. , Later on, a handful of thorium­(IV) complexes with either inter- or intramolecular arene coordination were reported. ,− Notably, all attempts to reduce thorium­(IV) arene complexes led to ligand-based reduction with the formation of thorium­(IV) complexes of reduced arenes (Figure a). ,, Such reduction reactivity is in contrast to that of uranium­(IV) analogues, which usually result in uranium-centered reduction. ,, The different reactivity between thorium and uranium may be attributed to the facts that thorium­(IV) is more difficult to reduce than uranium­(IV) − and genuine thorium­(III) and thorium­(II) complexes are much rarer compared to their uranium­(III) and uranium­(II) counterparts. − Furthermore, a comparison between thorium and uranium inverse-sandwich arene complexes shows that thorium has less tendency to form δ-bonding interactions with arenes than uranium …”

Synthesis and comparison of iso-structural f-block metal complexes (Ce, U, Np, Pu) featuring η6-arene interactions

“…Turning to discussion of the 2 M and 3 M structures in the broader context of previously reported literature, the most noteworthy feature of these complexes is the metal-arene h 6interactions present. Examples of f-element interactions with formally neutral arenes for these metal ions are reported, with a handful of structurally veried reports for uranium, 30,36,41,42,46,47,[51][52][53]55,56,[78][79][80][81] six for cerium, [82][83][84][85][86][87] one for neptunium 21 and none for plutonium at the time of writing. It should be noted that this type of interaction is also known for several rare-earth and lanthanide compounds, though here we focus on comparisons to similar f-element complexes (Ce, U, Np).…”

“…[10][11][12][13][14][15][16][17][18][19][20][21][22][23] Of note, f-block metal complexes which contain metal-arene interactions have proven to be highly valuable for understanding bonding and the role of valence orbitals for lanthanides and actinides. [24][25][26][27][28][29][30][31][32] Among this class of molecules, those which feature neutral arene coordinating motifs are of particular interest as these may exhibit covalent participation of the metal in the form of p/d/4 type interactions. 31,[33][34][35][36][37] Such complexes have potential to provide new key insight into f-block bonding modes as has been the case in other areas of the periodic table; for example, the seminal discovery of bis(benzene)chromium, Cr(h 6 -C 6 H 6 ) 2 , by E. O. Fischer, which revolutionized the understanding of transition metal chemistry.…”