Synthesis and Reactivity of a U(IV) Dibenzyne Complex

Reaction of UCl4 with 6 equiv of 2-Li-C6H4CH2NMe2 affords the U(IV) dibenzyne complex [Li]2[U(2,3-C6H3CH2NMe2)2(2-C6H4CH2NMe2)2] (1), which can be isolated as a dark blue solid in 40% yield. Complex 1 represents a rare example of a structurally characterized dibenzyne complex, and its solid-state metrical parameters suggest that the two benzyne ligands are best described with the dianionic metallacyclopropene resonance form. The reactivity of 1 with a variety of electrophiles and oxidants, including benzophenone, 1-azidoadamantane, and benzonitrile, was also explored. Reaction of 1 with 2 equiv of benzophenone affords the insertion product [Li][U(2-C6H3CH2NMe2-3-COPh2)2(2-C6H4CH2NMe2)] (3) as a red-orange solid in 61% yield, concomitant with formation of 1 equiv of 2-Li-C6H4CH2NMe2. Reaction of 1 with 2 equiv of PhCN also affords an insertion product, [Li][Li(Et2O)][U(2,3-C6H3CH2NMe2)(2-C6H3CH2NMe2-3-C(Ph)═N)(2-C6H4CH2NMe2)2] (4), as a green-brown crystalline solid in 21% yield. In an attempt to oxidize 1...