Divergent reactivity of U(iii) and U(ii) complexes with organoazides via isolable diazenylimido intermediates

Abstract

The chemistry of organoazides with metal complexes is ubiquitous in synthesis and catalysis. While many transition metal organoazide complexes have been isolated as key reaction intermediates, f-block metal organoazide complexes are extremely rare. Here, we report the isolation and characterization of U(V) and U(IV) diazenylimido complexes [(^AdTPBN₃)U(γ-N₃Ad)]^0/−1 (2/4), as the intermediates in the reactions of U(III) and U(II) precursors [(^AdTPBN₃)U]^0/−1 (1/5) with 1-adamantylazide (AdN₃). Moreover, 2 and 4 exhibit divergent reactivity: while 2 transforms to a U(IV) azido product (^AdTPBN₃)UN₃ (3) via C–N bond cleavage, 4 converts to a U(IV) imido complex [K(18-crown-6)(THF)₂][(^AdTPBN₃)UNAd] (6) through dinitrogen extrusion. Furthermore, reactivity with other organoazides has been found to depend on the oxidation states of uranium as well as the nature of organoazides. The reactions of 1 with benzylazide, tritylazide, and trimethylstannylazide exclusively yield 3. In contrast, the reaction of 1 with trimethylsilylazide (Me₃SiN₃) results in a mixture of 3 and a U(V) imido complex (^AdTPBN₃)UNSiMe₃ (8), whereas the reaction of 5 with Me₃SiN₃ leads to a sole U(III) azido product [K(18-crown-6)(THF)₂][(^AdTPBN₃)UN₃] (9). These results unveil unprecedented redox-switchable divergent reactivity of organoazides with metal complexes and provide new insights on uranium chemistry enabled by the tris(amido)arene framework.