Lanthanum Does Form Stable Molecular Compounds in the +2 Oxidation State

Abstract

Dedicated to Professor William J. Evans on the occasion of his 60th birthdayThe continuing quest for molecular complexes of lowoxidation-state lanthanides (other than the well-known samarium(II), europium(II), and ytterbium(II)) has produced significant achievements.[1] The majority of such compounds are derivatives of neodymium, dysprosium, and thulium, [2] obtained from the corresponding molecular iodides (often prepared in situ): [NdI 2 (thf) [2c,d] or by the reduction of an appropriate Ln III derivative. [2e,f] The present state of lanthanum, cerium, praseodymium, and gadolinium redox chemistry was described by S. A. Cotton: "None of these metals exhibits a stable + 2 state in any of its compounds and … they are unlikely to form stable compounds in this state." [3] Thus, the isolation of room-temperature-stable solid La II compounds is a very unexpected and significant breakthrough in the chemistry of lanthanides.Related to the subject of this study is a large group of inorganic materials: reduced or metal-rich rare-earth-metal halides, [4] including LaI 2 (featuring an extended structure with La 5d1 electrons delocalized on a conduction band), in which a lanthanum atom can be considered as being in the + 2 oxidation state.[4b] These compounds are better treated in a materials science context, where the metal valence [5,6] rather than the oxidation state is of primary importance.Previously [8] The latter featured redox ambiguity, which was also found in cerocene [9] and bis(pentalene)-cerium, [10] in which a metal-bound ligand had readily accessible adjacent oxidation states. For the binuclear arenebridged complexes, three different metal-ligand formal charge distributions are possible: Ln 2+

Reactivity and Properties of Metal Complexes Enabled by Flexible and Redox-Active Ligands with a Ferrocene Backbone

“…106 However, chemists never stopped pushing synthetic limits and, recently, low valent lanthanide chemistry has emerged as a fast developing field. [107][108][109] Recent advancements feature the synthesis and characterization of divalent lanthanide complexes for the complete lanthanide series, [110][111][112][113][114][115][116] reduced dinitrogen complexes, [117][118][119][120][121] reduced arene complexes, 26-29, 57, 122-126 and bimetallic reductive cleavage of aromatic C-H bonds. 40,44 Our group focused on the reduction chemistry of rare-earth metal complexes with non-innocent  ligands, followed by a small molecule activation study.…”

Rare Earth Arene-Bridged Complexes Obtained by Reduction of Organometallic Precursors

“…In 2008, Lappert isolated the first compound in a series of metal complexes with an ambiguous electronic structure: [K(18-crown-6)(Et2O)]([1,3-(Me3Si)2C5H3]3La) (Hitchcock et al, 2008). The authors proposed that it contains a lanthanum(II) ion.…”

Expanding the Chemistry of Molecular U2+ Complexes: Synthesis, Characterization, and Reactivity of the {[C5H3(SiMe3)2]3U}− Anion

“…(1)]. [1] Subsequently, as econd example was obtained by Meyer and co-workers in at ris(aryloxide)arene ligand environment by potassium reduction of [( Ad,Me ArO) 3 mes]U [Eq. (2)].…”

“…(2)]. [2] These reactionsa re variations of reductionse xamined with Cp'' 3 M[ Cp'' = C 5 H 3 (SiMe 3 ) 2 ; M = La [3] and Th [4] ]a nd with Cp' 3 Ln [5] to make new + 2i ons of the rare earth metals and thorium as depicted in Equation (3).…”

“…The reactivity/stability of 2 was of particular interest since 1 is so reactive that it is difficult to characterize its physical properties. Wer eport here that the reduction chemistry of Cp'' 3 Ul eads to new examples of U 2 + complexes.T he spectroscopic and magnetic properties of the new U 2 + complexes are described and compared to those of 1 and reactivity studies on both 1 and 2 are presented to allow further elaboration of the chemistryo fU 2 + .…”