Identification of Oxidation State +1 in a Molecular Uranium Complex

Abstract

The concept of oxidation state plays a fundamentally important role in defining the chemistry of the elements. In the f block of the periodic table, well-known oxidation states in compounds of the lanthanides include 0, +2, +3 and +4, and oxidation states for the actinides range from +7 to +2. Oxidation state +1 is conspicuous by its absence from the f-block elements. Here we show that the uranium­(II) metallocene [U­(η5-C5 i Pr5)2] and the uranium­(III) metallocene [IU­(η5-C5 i Pr5)2] can be reduced by potassium graphite in the presence of 2.2.2-cryptand to the uranium­(I) metallocene [U­(η5-C5 i Pr5)2]− (1) (C5 i Pr5 = pentaisopropylcyclopentadienyl) as the salt of [K­(2.2.2-cryptand)]+. An X-ray crystallographic study revealed that 1 has a bent metallocene structure, and theoretical studies and magnetic measurements confirmed that the electronic ground state of uranium­(I) adopts a 5f3(7s/6d z 2 )1(6d x 2–y 2 /6d xy )1 configuration. The metal–ligand bonding in 1 consists of contributions from uranium 5f, 6d, and 7s orbitals, with the 6d orbitals engaging in weak but non-negligible covalent interactions. Identification of the oxidation state +1 for uranium expands the range of isolable oxidation states for the f-block elements and potentially signposts a synthetic route to this elusive species for other actinides and the lanthanides.

Isolation of C1 through C4 derivatives from CO using heteroleptic uranium(iii) metallocene aryloxide complexes

“…Actinides are large, electropositive metals which do not possess the ability to back bond to CO in a similar manner to transition metals 9 and uranium can span oxidation states of +1 to +6, giving a rich redox chemistry. [10][11][12] The quest for CO reductive coupling reactions began in the 1800s with Liebig and Gmelin reporting that CO reacts with molten potassium to produce (C 5 O 5 ) 2− and (C 6 O 6 ) 2− dianions. 13,14 Since then, other s-block [15][16][17][18][19][20][21][22] as well as p-block [23][24][25][26][27][28][29] complexes have been used for CO reduction over the years.…”

Structure and bonding patterns in heterometallic organometallics with linear Ln–Pd–Ln motifs

“…Consequently, rare-earth-based materials are important assets for technology, 3,4 especially that which use their magnetic and optical properties. [5][6][7][8] Recently, the field has strongly evolved with breakthrough reports of record magnetic properties for Dy 9,10 and Er, 11 unusual tetravalent oxidation states for Tb and Pr, [12][13][14] divalent [15][16][17][18] and monovalent 19 for U, and intermediate valence states in 4f-elements. [20][21][22] Among these singularities, Kempe reported unsupported metal-metal bonds between 4f elements and transition metals as molecular mimics for intermetallic compounds, which constitute rare examples of lanthanide ions in direct interaction with other metals.…”

Thorium- and Uranium-Mediated C–H Activation of a Silyl-Substituted Cyclobutadienyl Ligand

“…Organometallic sandwich and half-sandwich compounds of the lanthanides and actinides have played a central role in the development of f-block chemistry. Applications of these compounds range from catalysis, − small-molecule and other bond activation chemistry, − and, more recently, single-molecule magnetism − to fundamental questions related to electronic structure and chemical bonding. − The most popular ligands in f-element organometallic chemistry are cyclopentadienyl (Cp), cyclo-octatetraenyl (COT), and their numerous substituted derivatives. This popularity stems largely from the availability of ligand precursors and the ease with which substituents can be introduced, which allows the steric, electronic, and solubility properties of their f-element complexes to be modified for a particular purpose.…”