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 (PhCCR) 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.