Heterometallic Clusters with Uranium-Metal Bonds Supported by Double-Layer Nitrogen-Phosphorus Ligands

International audienceCONSPECTUS: Heterometallic clusters with M-M bonds have significantly interested chemists because of their attractive structures and synergistic effects in small-molecule activation and catalysis. However, reports of the isolation of heterometallic clusters with uranium-transition metal (U-TM) bonds remain very limited. In this Account, we describe our research in the construction of heterometallic molecular clusters with multiple U-TM single or multiple bonds supported by novel double-layer N-P ligands. Multimetallic synergistic catalysis and small-molecule activation with these species are also summarized. First, according to the hard-soft acid-base theory, we employed a three-armed N-P ligand, which can be used to construct heterometallic clusters with four or six U-Ni bonds. This strategy was also effective in the construction of complexes with direct rare earth metal-TM bonding. The similar two-armed N-P ligands also are effective platforms for the synthesis of heterometallic complexes with U-Ni, U-Pd, and U-Pt bonds. Second, a set of heterometallic clusters featuring U Rh, U Co, and U Fe triple bonds were constructed under routine experimental conditions. X-ray diffraction analysis of these clusters exhibits the shortest U-TM bond distance (1.9693(4) angstrom for the U Fe triple bond) in these complexes. Theoretical studies reveal that the nature of the triple bond is one covalent sigma bond and two TM -> U dative pi bonds. A large Wiberg bond index (WBI) of 2.93 and a significant degree of covalency for the U TM triple bonds were also found in these complexes. Third, these uranium complexes supported by the double-layer N-P ligands exhibit great potential in small-molecule activation. For instance, N-2 cleavage without an external reducing agent was achieved by a U(III)-P(III) synergistic six-electron reduction. The synergism between U(III) and P(III) enables the activation of other small molecules, such as O-2, P-4, and As-(nano)(0), and highlights the importance of the P atom in the double-layer N-P ligand for the activation of small molecules. A heterometallic cluster with U-Rh bonds can break the strong N N triple bond in N-2 in the presence of potassium graphite, suggesting a synergistic effect between U and Rh. This multimetallic synergistic effect was also observed in catalytic processes. A heterometallic cluster with U Co triple bonds shows excellent selectivity and activity in the hydroboration of a series of alkynes under mild conditions. These results lead to effective methods for the construction of heterometallic molecular clusters with U-TM single or multiple bonds and could promote the application of heterometallic clusters with U-TM bonds in catalysis and the activation of small molecules