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 [eta(5)-1,2,4-(Me3C)(3)C5H2](2)ThCl2 (1) with potassium graphite (KC8) in the presence of internal alkynes (PhC equivalent to CR) yields the corresponding thorium metallacyclopropenes [eta(5)-1,2,4-(Me3C)(3)C5H2](2)Th(eta(2)-C2Ph(R)) (R = Ph (2), Me (3), Pr-i (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)(3)C5H2 ligand. In contrast, no intramolecular C-H bond activation is observed for the diphenylacetylene derived complex 2, but it does activate a-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.