From a nanoparticular solid-state material to molecular organo-f-element-polyarsenides

Rare earth benzene tetraanion-bridged amidinate complexes

The benzene tetraanion-bridged rare earth inverse arene amidinate complexes [{Ln(κ1:η6-Piso)}2(μ-η6:η6-C6H6)] (2-Ln, Ln = Gd, Tb, Dy, Y; Piso = {(NDipp)2C t Bu}, Dipp = C6H3 iPr2-2,6) were prepared by the reduction of parent Ln(iii) bis-amidinate halide precursors [Ln(Piso)2X] (Ln = Tb, Dy; X = Cl, I) or [Ln(Piso)2I] (Ln = Gd, Y) with 3 eq. KC8 in benzene, or by the reaction of the homoleptic Ln(ii) complexes [Ln(Piso)2] (Ln = Tb, Dy) with 2 eq. KC8 in benzene. The arene exchange reaction of 2-Tb with toluene gave crystals of [{Tb(κ1:η6-Piso)}2(μ-η6:η6-C7H8)] (3-Tb), while no reactions were observed when C6D6 solutions of 2-Y were separately treated with biphenyl, naphthalene or anthracene. The reactivity study shows that 2-Y can behave as a four-electron reductant to reduce 1,3,5,7-cyclooctatetraene (COT). Complexes 2-Ln were characterized by single crystal X-ray diffraction, elemental analysis, SQUID magnetometry, UV-vis-NIR, ATR-IR, NMR, density functional theory (DFT) and ab initio calculations. These data consistently show that 2-Ln formally contain Ln(iii) centres with arene-capped inverse-sandwich Dipp-Ln(iii)-(C6H6)4--Ln(iii)-Dipp configurations, and DFT calculations on a model of 2-Y revealed strong Y-(C6H6)4- δ-bonding interactions between the filled π-orbitals of the benzene tetraanion and vacant 4d orbitals of the Y(iii) ions. A strong intermolecular coupling interaction between the two Tb(iii) centres in 2-Tb (J tot = -6.84 cm-1) was evidenced by a step in a magnetization vs. field plot of 2-Tb at ca. 3.4 T at 2 K, which we attribute to an anti-ferromagnetic transition of the magnetic moment; we also determined an exchange coupling constant J ex = -0.25(1) cm-1 for 2-Gd.

Neutral inverse-sandwich rare-earth metal complexes of the benzene tetraanion

Rare-earth metal complexes of the parent benzene tetraanion and neutral inverse-sandwich rare-earth metal arene complexes have remained elusive. Here, we report the first neutral inverse-sandwich rare-earth metal complexes of the parent benzene tetraanion supported by a monoanionic β-diketiminate (BDI) ligand. Reduction of the trivalent rare-earth metal diiodide precursors (BDI)MI2(THF) (BDI = HC(C(Me)N[C6H3-(3-pentyl)2-2,6])2; M = Y, 1-Y; M = Sm, 1-Sm) in benzene or para-xylene by potassium graphite yielded the neutral inverse-sandwich rare-earth metal arene complexes [(BDI)M(THF) n ]2(μ-η6,η6-arene) (M = Y, Sm; arene = benzene, 2-M; arene = para-xylene, 3-M). Single crystal X-ray diffraction, spectroscopic and magnetic characterization studies, together with density functional theory (DFT) calculations confirm that these neutral rare-earth metal arene complexes possess an [M3+-(arene)4--M3+] electronic structure with strong metal-arene δ interactions. The arene exchange reactivity shows that 2-Sm has higher stability than 3-Sm. Furthermore, 2-Sm can behave as a four-electron reductant to reduce unsaturated organic substrates. Particularly, while the reaction of 2-Sm with 1,3,5,7-cyclooctatetraene (COT) yielded (BDI)Sm(η8-COT) (4-Sm), 2-Sm reacted with 1,4-diphenylbutadiyne to afford (BDI)Sm(η4-C4Ph2) (5-Sm), the first rare-earth metallacyclopentatriene complex.

f-Element heavy pnictogen chemistry

The coordination and organometallic chemistry of the f-elements, that is group 3, lanthanide, and actinide ions, supported by nitrogen ligands, e.g. amides, imides, and nitrides, has become well developed over many decades. In contrast, the corresponding f-element chemisty with the heavier pnictogen analogues phosphorus, arsenic, antimony, and bismuth has remained significantly underdeveloped, due largely to a lack of suitable synthetic methodologies and also the inherent hard(f-element)-soft(heavier pnictogen) acid-base mismatch, but has begun to flourish in recent years. Here, we review complexes containing chemical bonds between the f-elements and heavy pnictogens from phosphorus to bismuth that spans five decades of endeavour. We focus on complexes whose identity has been unambiguously established by structural authentication by single-crystal X-ray diffraction with respect to their synthesis, characterisation, bonding, and reactivity, in order to provide a representative overview of this burgeoning area. By highlighting that much has been achieved but that there is still much to do this review aims to inspire, focus and guide future efforts in this area.