C-H bond activation induced by thorium metallacyclopropene complexes: a combined experimental and computational study

Inter- and intramolecular C-H bond activations by thorium metallacyclopropene complexes were comprehensively studied. The reduction of [η⁵-1,2,4-(Me₃C)₃C₅H₂]₂ThCl₂ (1) with potassium graphite (KC₈) in the presence of internal alkynes (PhC[triple bond, length as m-dash]CR) yields the corresponding thorium metallacyclopropenes [η⁵-1,2,4-(Me₃C)₃C₅H₂]₂Th(η²-C₂Ph(R)) (R = Ph (2), Me (3), ⁱPr (4), C₆H₁₁ (5)). Complexes 3-5 derived from phenyl(alkyl)acetylenes are very reactive resulting in an intramolecular C-H bond activation of the 1,2,4-(Me₃C)₃C₅H₂ ligand. In contrast, no intramolecular C-H bond activation is observed for the diphenylacetylene derived complex 2, but it does activate α-C-H bonds in pyridine or carbonyl derivatives upon coordination. Density functional theory (DFT) studies complement the experimental studies and provide additional insights into the observed reactivity.