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.