Alasdair Formanuik

Actinide covalency measured by pulsed electron paramagnetic resonance spectroscopy

Our knowledge of actinide chemical bonds lags far behind our understanding of the bonding regimes of any other series of elements. This is a major issue given the technological as well as fundamental importance of f-block elements. Some key chemical differences between actinides and lanthanides-and between different actinides-can be ascribed to minor differences in covalency, that is, the degree to which electrons are shared between the f-block element and coordinated ligands. Yet there are almost no direct measures of such covalency for actinides. Here we report the first pulsed electron paramagnetic resonance spectra of actinide compounds. We apply the hyperfine sublevel correlation technique to quantify the electron-spin density at ligand nuclei (via the weak hyperfine interactions) in molecular thorium(III) and uranium(III) species and therefore the extent of covalency. Such information will be important in developing our understanding of the chemical bonding, and therefore the reactivity, of actinides.

Concomitant Carboxylate and Oxalate Formation From the Activation of CO2 by a Thorium(III) Complex

Abstract Improving our comprehension of diverse CO2 activation pathways is of vital importance for the widespread future utilization of this abundant greenhouse gas. CO2 activation by uranium(III) complexes is now relatively well understood, with oxo/carbonate formation predominating as CO2 is readily reduced to CO, but isolated thorium(III) CO2 activation is unprecedented. We show that the thorium(III) complex, [Th(Cp′′)3] (1, Cp′′={C5H3(SiMe3)2‐1,3}), reacts with CO2 to give the mixed oxalate‐carboxylate thorium(IV) complex [{Th(Cp′′)2[κ2‐O2C{C5H3‐3,3′‐(SiMe3)2}]}2(μ‐κ2:κ2‐C2O4)] (3). The concomitant formation of oxalate and carboxylate is unique for CO2 activation, as in previous examples either reduction or insertion is favored to yield a single product. Therefore, thorium(III) CO2 activation can differ from better understood uranium(III) chemistry.

A structural investigation of heteroleptic lanthanide substituted cyclopentadienyl complexes

The substituted cyclopentadienyl group 1 transfer agents KCp′′, KCp′′′ and KCptt (Cp′′ = {C5H3(SiMe3)2-1,3}−; Cp′′′ = {C5H2(SiMe3)3-1,2,4}−; Cptt = {C5H3(tBu)2-1,3}−) were prepared by modification of established procedures and the structure of [K(Cp′′)(THF)]∞·THF (1) was obtained. KCp′′ and KCptt were reacted variously with [Ln(I)3(THF)4] (Ln = La, Ce) in 2 : 1 stoichiometries to afford monomeric [La(Cp′′)2(I)(THF)] (2a·THF) and the dimeric complexes [La(Cp′′)2(μ-I)]2 (2a), [Ce(Cp′′)2(μ-I)]2 (2b) and [Ce(Cptt)2(μ-I)]2 (3). KCp′′′ was reacted with [Ce(I)3(THF)4] to afford the mono-ring complex [Ce(Cp′′′)(I)2(THF)2] (4), regardless of the stoichiometric ratio of the reagents. Complex 4 was reacted with [KN(SiMe3)2] to yield [Ce(Cp′′′)2(I)(THF)] (5), [Ce(Cp′′′){N(SiMe3)2}2] (6) and [Ce{N(SiMe3)2}3] by ligand scrambling. Complexes 1–6 have all been structurally authenticated and are variously characterised by other physical methods.