A Chlorine‐Centered Cluster of Composition [(Me 3 Si) 2 NC(NCy) 2 SmCl 2 ] 5 (thf) 2 and a Comparison with the Heavier Ytterbium Congener [(Me 3 Si) 2 NC(NCy) 2 YbCl 2 ] 2 (LiCl) 2 (thf) 4

Structural Diversity and Multielectron Reduction Reactivity of Samarium(II) Iodido-β-diketiminate Complexes Dependent on Tetrahydrofuran Content

The molecular structures of complexes [Sm(Nacnac)I(thf)_n] (Nacnac = HC(C(Me)Ndipp)₂^-, dipp = 2,6-diisopropylphenyl, thf = tetrahydrofuran) depending on the number of thf ligands are studied. The complete removal of thf from a known complex [Sm(Nacnac)I(thf)₂] leads to a tetranuclear product [Sm(Nacnac)I]₄ (4). The partial removal of thf results in mixtures of dinuclear [Sm₂(Nacnac)₂I₂(thf)] (2), trinuclear [Sm₃(Nacnac)₃I₃(thf)] (3), and tetranuclear [Sm₄(Nacnac)₄I₄(thf)₂] (4*) complexes and 4, depending on the conditions. The reaction of solvent-free SmI₂ with 1 equiv of K(Nacnac) results mainly in [Sm(Nacnac)₂] (1), while the interaction of 4 with certain amounts of thf allows obtaining pure 2 and 3 (with the admixture of 4*). Complex 4* is the exact dimer of 2, and both compounds are stable in solutions. Reactions with 3 and 4 as reductants are studied. 4 is oxidized by I₂ to stoichiometrically yield two products, mixed-valent tetranuclear [Sm₄(Nacnac)₄I₅] (5) and binuclear [Sm(Nacnac)I₂]₂ (6) complexes. In the reaction of 4 with ⁿBu₃PTe, a trinuclear complex [Sm₃(Nacnac)₃(μ-I)₃(μ₃-E)₂] (8, E = I or Te) is formed in small amounts, with the formation of 6 as the second product. 3 serves as a two-electron reductant in the reaction with ⁿBu₃PTe to yield a trinuclear complex [Sm₃(Nacnac)₃I₃(μ-Te₂)] (7). Complexes 2, 4, 4*, 5, 6, and 8 possess a unique flat Sm_xI_y core of heavy atoms, which is assumed to be a consequence of the Nacnac ligand geometry.

Alternative (κ1-N:η6-arene vs.κ2-N,N) coordination of a sterically demanding amidinate ligand: are size and electronic structure of the Ln ion decisive factors?

The amine elimination reaction of equimolar amounts of ansa-bis(amidine) C₆H₄-1,2-{NC(tBu)NH(2,6-iPr₂C₆H₃)}₂ (L¹H) and [(Me₃Si)₂N]₂Yb(THF)₂ affords a bis(amidinate) Yb^II complex [C₆H₄-1,2-{NC(tBu)N(2,6-iPr₂C₆H₃)}₂]Yb(THF) (1) in 68% yield. Complex 1 features a rather rare η¹-amido:η⁶-arene coordination of both amidinate fragments to the Yb^II ion, resulting in the formation of a bent bis(arene) structure. Oxidation of 1 by I₂ regardless of the molar ratio of reagents (2 : 1 or 1 : 1) leads to the formation of the Yb^III species [{(2,6-iPr₂C₆H₃)[double bond, length as m-dash]NC(tBu)NH}-C₆H₄-1,2-{NC(tBu)N(2,6-iPr₂C₆H₃)}]YbI₂(THF)₂ (2) in which only one amidinate fragment is coordinated to the ytterbium ion in κ²-N,N'-chelating coordination mode, while the second NCN fragment is protonated in the course of the reaction and is not bound to the metal ion. The outcome of the salt metathesis reaction of LaCl₃ with lithium amidinates [C₆H₄-1,2-{NC(tBu)N(2,6-R₂C₆H₃)}₂Li₂] (R = Me, iPr) is proven to be strongly affected by the substituent 2,6-R₂C₆H₃ on the amidinate nitrogens. When R = iPr, the salt metathesis reaction occurs smoothly and results in the formation of an ate-chloro-amidinate complex [C₆H₄-1,2-{NC(tBu)N(2,6-iPr₂C₆H₃)}₂]La(μ²-Cl)Li(THF)(μ²-Cl)₂Li(THF)₂ (3) in which the La^III ion is coordinated by both amidinate fragments in a "classic"κ²-N,N'-chelating fashion. In the case of R = Me, the reaction requires prolonged heating for completion. Moreover, the salt metathesis reaction is accompanied by the fragmentation of the ligand and affords a trinuclear chloro-amidinate complex [C₆H₄-1,2-{NC(tBu)N(2,6-Me₂C₆H₃)}₂]La{[(tBu)C(N-2,6-Me₂C₆H₃)₂]La(THF)}₂(μ²-Cl)₄(μ³-Cl)₂ (4) containing one dianionic ansa-bis(amidinate) and two monoanionic [(tBu)C(N-2,6-Me₂C₆H₃)₂] amidinate fragments. DFT calculations are conducted to determine the factor that governs this change in coordination mode and, in particular, the effect of the metal oxidation state.