title: Physicochemical Properties of Near-Linear Lanthanide(II) Bis(silylamide) Complexes (Ln = Sm, Eu, Tm, Yb).
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" LnIIions. 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″)]2complexes. EPR spectroscopy of 3 shows that the near-linear geometry stabilizes mJstates with oblate spheroid electron density distributions, validating our previous suggestions. Cyclic voltammetry experiments carried out on 1-4 did not yield LnIIreduction potentials, so a reactivity study of 1 was performed with selected substrates in order to benchmark the SmIII→ SmIIcouple. 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 SmIIcenter 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 SmIIIcoordination spheres of the products.
authors.affiliation: School of Chemistry, The University of Manchester , Oxford Road, Manchester M13 9PL, U.K.
authors.forename: Conrad A P
authors.initials: CA
authors.lastname: Goodwin
authors.affiliation: School of Chemistry, The University of Manchester , Oxford Road, Manchester M13 9PL, U.K.
authors.forename: Nicholas F
authors.initials: NF
authors.lastname: Chilton
authors.affiliation: School of Chemistry, The University of Manchester , Oxford Road, Manchester M13 9PL, U.K.
authors.forename: Gianni F
authors.initials: GF
authors.lastname: Vettese
authors.affiliation: School of Chemistry, The University of Manchester , Oxford Road, Manchester M13 9PL, U.K.
authors.forename: Eufemio
authors.initials: E
authors.lastname: Moreno Pineda
authors.affiliation: Photon Science Institute and School of Electrical and Electronic Engineering, The University of Manchester , Oxford Road, Manchester M13 9PL, U.K.
authors.forename: Iain F
authors.initials: IF
authors.lastname: Crowe
authors.affiliation: Department of Chemistry, University of California , Irvine, California 92697-2025, United States.
authors.forename: Joseph W
authors.initials: JW
authors.lastname: Ziller
authors.affiliation: School of Chemistry, The University of Manchester , Oxford Road, Manchester M13 9PL, U.K.
authors.forename: Richard E P
authors.initials: RE
authors.lastname: Winpenny
authors.affiliation: Department of Chemistry, University of California , Irvine, California 92697-2025, United States.
authors.forename: William J
authors.initials: WJ
authors.lastname: Evans
authors.affiliation: School of Chemistry, The University of Manchester , Oxford Road, Manchester M13 9PL, U.K.
authors.forename: David P
authors.initials: DP
authors.lastname: Mills