A Heterodimetallic Monomeric Complex with a Uranium-Cobalt Triple Bond

The crystal structure of heterodimetallic monomeric complexes featuring a U-M triple bond has been rarely reported. Here, we present an example of a heterodimetallic monomeric complex [(Trapen^CH2PPh2)U(Co)] (4) containing a U-Co triple bond, which was synthesized by the reaction of [(Trapen^CH2PPh2)U(Cl)] (2) or [(Trapen^CH2PPh2)U] (3) with CoCl₂ in the presence of KC₈. The crystal structure of 4 reveals a highly symmetrical geometry with a linear Co-U-N_amine axis line, and the U-Co bond length 2.1890(11) Å is slightly longer than the sum of the covalent triple-bond radii of uranium and cobalt (2.14 Å). The U-N_amine bond length (2.439(6) Å) is significantly shortened compared to that of precursors 2 and 3. The significant contraction of the U-N_amine bond demonstrates electronic reinforcement via the inverse trans-influence (ITI). Detailed computational investigations further support the existence of a U≡Co triple bond in 4, and the formal oxidation states of uranium and cobalt appear to be U(IV) and Co(-I). The low-temperature magnetic moments of 4 are approaching 2.1 μ_B, which is attributed to its near-doubly degenerate spin-orbit ground states in the pseudo-C_3v symmetry. Remarkably, 4 served as the catalyst for the hydroboration and dimerization of terminal alkynes under mild conditions.