Physicochemical Properties of Near-Linear Lanthanide(II) Bis(silylamide) Complexes (Ln = Sm, Eu, Tm, Yb)

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

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Abstract

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), Yb (4)], thus achieving approximate uniaxial geometries for a series of “traditional” LnII ions. Experimental evidence, together with calculations performed on a model of 4, indicates that dispersion forces are important for 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 X-ray diffraction, magnetic measurements, electrochemistry, multinuclear NMR, electron paramagnetic resonance (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 LnII reduction potentials, so a reactivity study of 1 was performed with selected substrates in order to benchmark the SmIII → SmII couple. The separate reactions of 1 with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), azobenzene, and benzophenone gave crystals of [Sm(N††)2(TEMPO)] (5), [Sm(N††)2(N2Ph2)] (6), and [Sm(N††){μ-OPhC(C6H5)CPh2O-κO,O′}]2 (7), respectively. The isolation of 5–7 shows that the SmII 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 SmIII coordination spheres of the products.
Original languageEnglish
Pages (from-to)10057-10067
Number of pages11
JournalInorganic Chemistry
Volume55
Issue number20
Early online date23 May 2016
DOIs
Publication statusPublished - 17 Oct 2016

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