Experimental and Computational Studies on an Actinide Metallacyclocumulene Complex

Reduction of (η5-C5Me5)2ThCl2 (1) with potassium graphite (KC8) in the presence of 1,4-diphenylbutadiyne (PhCCCCPh) yields the first actinide metallacyclocumulene, the thorium metallacyclopentatriene (η5-C5Me5)2Th­(η4-C4Ph2) (2). The structure and reactivity of 2 were investigated in detail; structural parameters and density functional theory (DFT) studies confirm the presence of a metallacyclopentatriene unit in 2. Furthermore, DFT computations also indicate a notable contribution of the 5f orbitals to the bonding of the metallacyclopentatriene Th–(η4-CCCC) moiety. While complex 2 shows no reactivity toward alkynes, it reacts with a variety of heterounsaturated molecules such as isothiocyanates, carbodiimides, aldehydes, ketones, nitriles, pyridines, and diazoalkane derivatives. DFT studies complement the experimental observations and provide additional insights. Furthermore, in comparison to group 4 metals, the thorium metallacyclopentatriene 2 exhibits distinctively different reactivity patterns.