The synthesis, structure, and reactivity of thorium oxo and sulfido metallocenes have been comprehensively studied. Heating of an equimolar mixture of the dimethyl metallocene [η⁵-1,2,4-(Me₃C)₃C₅H₂]₂ThMe₂ (2) and the bis-amide metallocene [η⁵-1,2,4-(Me₃C)₃C₅H₂]₂Th(NH-p-tolyl)₂ (3) in refluxing toluene results in the base-free imido thorium metallocene, [η⁵-1,2,4-(Me₃C)₃C₅H₂]₂Th═N(p-tolyl) (4), which is a useful precursor for the preparation of oxo and sulfido thorium metallocenes [η⁵-1,2,4-(Me₃C)₃C₅H₂]₂Th═E (E = O (5) and S (15)) by cycloaddition–elimination reaction with Ph₂C═E (E = O, S) or CS₂. The oxo metallocene 5 acts as a nucleophile toward alkylsilyl halides, while sulfido metallocene 15 does not. The oxo metallocene 5 and sulfido metallocene 15 undergo a [2 + 2] cycloaddition reaction with Ph₂CO, CS₂, or Ph₂CS, but they show no reactivity with alkynes. Density functional theory (DFT) studies provide insights into the subtle interplay between steric and electronic effects and rationalize the experimentally observed reactivity patterns. A comparison between Th, U, and group 4 elements shows that Th⁴⁺ behaves more like an actinide than a transition metal.

Kondo coupling of $f$ and conduction electrons is a common feature of $f$-electron intermetallics. Similar effects should occur in carbon ring systems (metallocenes). Evidence for Kondo coupling in $\mathrm{Ce}({\mathrm{C}}_8{\mathrm{H}}_8{)}_2$ (cerocene) and the ytterbocene $\mathrm{Cp}^{*}{}_2\mathrm{Yb}(\mathrm{bipy})$ is reported from magnetic susceptibility and $L_{\mathrm{III}}$-edge x-ray absorption spectroscopy. These well-defined systems provide a new way to study the Kondo effect on the nanoscale, should generate insight into the Anderson Lattice problem, and indicate the importance of this often-ignored contribution to bonding in organometallics.