Physicochemical properties of near-linear Ln(II) bis-silylamide complexes (Ln = Sm, Eu, Tm, Yb)

Conrad Goodwin, Nicholas Chilton, Gianni F. Vettese, Eufemio Moreno Pineda, Iain Crowe, Joseph W. Ziller, William J. Evans, David Mills

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    Following our report of the first near-linear lanthanide (Ln) complex, [Sm(N††)2] (1), herein we present the synthesis of [Ln(N††)2] [N†† = {N(SiiPr3)2}–; Ln = Eu (2), Tm (3) and Yb (4)], thus achieving approximate uniaxial geometries for a series of “traditional” Ln(II) ions. Experimental evidence, together with calculations performed on a model of 4, indicate that dispersion forces are important for the stabilization of the near-linear geometries of 1-4. The isolation of 3 under a dinitrogen atmosphere is noteworthy, given that “[Tm(N′′)(μ-N′′)]2” (N′′ = {N(SiMe3)2}–) has not previously been structurally authenticated and reacts rapidly with N2(g) to give [{Tm(N′′)¬2}2(μ-η2:η2-N2)]. Complexes 1-4 have been characterized as appropriate by single crystal XRD, magnetic measurements, electrochemistry, and multinuclear NMR, EPR, and electronic spectroscopy, along with computational methods for 3 and 4. The remarkable geometries of monomeric 1-4 lead to interesting physical properties, which complement and contrast with comparatively well understood dimeric [Ln(N′′)(μ-N′′)]2 complexes. EPR spectroscopy of 3 shows that the near-linear geometry stabilizes mJ states with oblate spheroid electron density distributions, validating our previous suggestions. Cyclic voltammetry experiments carried out on 1-4 did not yield Ln(II) reduction potentials, so a reactivity study of 1 was performed with selected substrates in order to benchmark the Sm(III)→Sm(II) couple. The separate reactions of 1 with TEMPO (2,2,6,6-tetramethyl-piperidinyl-1-oxy), azobenzene and benzophenone gave crystals of [Sm(N††)2(TEMPO)] (5), [Sm(N††)2(N2Ph2)] (6) and [Sm(N††){μ-OPhC(C6H5)CPh2O-κ-O,O′}]2 (7), respectively. The isolation of 5-7 shows that the Sm(II) center in 1 is still accessible despite having two bulky N†† moieties, and that the N-donor atoms are able to deviate further from linearity or ligand scrambling occurs in order to accommodate another ligand in the Sm(III) coordination spheres of the products.
    Original languageEnglish
    JournalInorganic Chemistry
    Issue number20
    Early online date23 May 2016
    Publication statusPublished - 2016


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