A Unique Organolanthanide Cluster Containing Bulky Cyclooctatetraenyl Ligands

Triple Inverse Sandwich versus End-On Diazenido: Bonding Motifs across a Series of Rhenium-Lanthanide and -Actinide Complexes

While synthesizing a series of rhenium-lanthanide triple inverse sandwich complexes, we unexpectedly uncovered evidence for rare examples of end-on lanthanide dinitrogen coordination for certain heavy lanthanide elements as well as for uranium. We begin our report with the synthesis and characterization of a series of trirhenium triple inverse sandwich complexes with the early lanthanides, Ln[(μ-η5:η5-Cp)Re(BDI)]3(THF) (1-Ln, Ln = La, Ce, Pr, Nd, Sm; Cp = cyclopentadienide, BDI = N,N'-bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate). However, as we moved across the lanthanide series, we ran into an unexpected result for gadolinium in which we structurally characterized two products for gadolinium, namely, 1-Gd (analogous to 1-Ln) and a diazenido dirhenium double inverse sandwich complex Gd[(μ-η1:η1-N2)Re(η5-Cp)(BDI)][(μ-η5:η5-Cp)Re(BDI)]2(THF)2 (2-Gd). Evidence for analogues of 2-Gd was spectroscopically observed for other heavy lanthanides (2-Ln, Ln = Tb, Dy, Er), and, in the case of 2-Er, structurally authenticated. These complexes represent the first observed examples of heterobimetallic end-on lanthanide dinitrogen coordination. Density functional theory (DFT) calculations were utilized to probe relevant bonding interactions and reveal energetic differences between both the experimental and putative 1-Ln and 2-Ln complexes. We also present additional examples of novel end-on heterobimetallic lanthanide and actinide diazenido moieties in the erbium-rhenium complex (η8-COT)Er[(μ-η1:η1-N2)Re(η5-Cp)(BDI)](THF)(Et2O) (3-Er) and uranium-rhenium complex [Na(2.2.2-cryptand)][(η5-C5H4SiMe3)3U(μ-η1:η1-N2)Re(η5-Cp)(BDI)] (4-U). Finally, we expand the scope of rhenium inverse sandwich coordination by synthesizing divalent double inverse sandwich complex Yb[(μ-η5:η5-Cp)Re(BDI)]2(THF)2 (5-Yb), as well as base-free, homoleptic rhenium-rare earth triple inverse sandwich complex Y[(μ-η5:η5-Cp)Re(BDI)]3 (6-Y).

New kind of electride sandwich complexes based on the cyclooctatetraene ligand M12(η8-C8H8)2M22 (M1 = Na, K and M2 = Ca, Mg): a theoretical study

In the present study, the electronic structures of a series of binuclear sandwich complexes based on the cyclooctatetraene ligand M¹₂(η⁸-C₈H₈)₂M²₂ (M¹ = Na, K and M² = Ca, Mg) are studied theoretically. Each cyclooctatetraene ligand binds with the metal in the η⁸ binding mode. The M²-M² bond length agrees well with the reported bimetallic covalent Ca₂ and Mg₂ bond lengths. The Wiberg bond index (WBI) also indicates the presence of covalent M²-M² bonds, which gives additional stability to the complex. A non-nuclear attractor (NNA) is found in-between the M²-M² bond and the negative Laplacian of the electron density is found at the NNA. Noncovalent interaction (NCI) plot shows that electron density is localized at the M²-M² bond. Based on the performed analysis, we have concluded that the designed sandwich complexes are electrides. We herein report, for the first time, the electride sandwich complexes of the cyclooctatetraene ligand. Due to the presence of a diffuse electron system, the electride complexes exhibit higher values of the static second hyperpolarizability within the range of 2.6 × 10⁵ to 1.4 × 10⁶ a.u. Among the studied complexes, M¹₂(η⁸-C₈H₈)₂Ca₂ exhibit a higher value of static second hyperpolarizability.

Nanoscale Organolanthanum Clusters: Nuclearity-Directing Role of Cyclopentadienyl and Halogenido Ligands

Tetramethylaluminato/halogenido(X) ligand exchange reactions in half-sandwich complexes [CpR La(AlMe4 )2 ] are feasible in non-coordinating solvents and provide access to large coordination clusters of the type [CpR LaX2 ]x . Incomplete exchange reactions generate the hexalanthanum clusters [CpR 6 La6 X8 (AlMe4 )4 ] (CpR =Cp*=C5 Me5 , X=I; CpR =Cp'=C5 H4 SiMe3 , X=Br, I). Treatment of [Cp*La(AlMe4 )2 ] with two equivalents Me3 SiI gave the nonalanthanum cluster [Cp*LaI2 ]9 , while the exhaustive reaction of [Cp'La(AlMe4 )2 ] with the halogenido transfer reagents Me3 GeX and Me3 SiX (X=I, Br, Cl) produced a series of monocyclopentadienyl rare-earth-metal clusters with distinct nuclearity. Depending on the halogenido ion size the homometallic clusters [Cp'LaCl2 ]10 and [Cp'LaX2 ]12 (X=Br, I) could be isolated, whereas different crystallization techniques led to the aggregation of clusters of distinct structural motifs, including the desilylated cyclopentadienyl-bridged cluster [(μ-Cp)2 Cp'8 La8 I14 ] and the heteroaluminato derivative [Cp'10 La10 Br18 (AlBr2 Me2 )2 ]. The use of the Cp' ancillary ligand facilitates cluster characterization by means of NMR spectroscopy.

One ligand fits all: lanthanide and actinide sandwich complexes comprising the 1,4-bis(trimethylsilyl)cyclooctatetraenyl (=COT′′) ligand

Twelve new lanthanide and actinide sandwich complexes containing the 1,4-bis(trimethylsilyl)cyclooctatetraenyl ligand (COT′′) have been prepared and structurally characterized by X-ray diffraction.

Unprecedented bending and rearrangement of f-element sandwich complexes induced by superbulky cyclooctatetraenide ligands

The use of the superbulky cyclooctatetraenide dianion ligand [C(8)H(6)(SiPh(3))(2)](2-) (= COT(BIG)) in organo-f-element chemistry leads to unprecedented effects such as the formation of a significantly bent anionic Ce(III) sandwich complex, a novel cerocene formed by sterically induced SiPh(3) group migration, as well as the first example of a bent uranocene.