Influence of the 5f Orbitals on the Bonding and Reactivity in Organoactinides: Experimental and Computational Studies on a Uranium Metallacyclopropene

The synthesis, structure, and reactivity of a uranium metallacyclopropene were comprehensively studied. Reduction of (η5-C5Me5)2UCl2 (1) with potassium graphite (KC8) in the presence of bis­(trimethylsilyl)­acetylene (Me3SiCCSiMe3) allows the first stable uranium metallacyclopropene (η5-C5Me5)2U­[η2-C2(SiMe3)2] (2) to be isolated. Magnetic susceptibility data confirm that 2 is a U­(IV) complex, and density functional theory (DFT) studies indicate substantial 5f orbital contributions to the bonding of the metallacyclopropene U-(η2-CC) moiety, leading to more covalent bonds between the (η5-C5Me5)2U2+ and [η2-C2(SiMe3)2]2– fragments than those in the related Th­(IV) compound. Consequently, very different reactivity patterns emerge, e.g., 2 can act as a source for the (η5-C5Me5)2U­(II) fragment when reacted with alkynes and a variety of heterounsaturated molecules such as imines, bipy, carbodiimide, organic azides, hydrazine, and azo derivatives.