Inorganic & Coordination Chemistry, Contributed Talk (15min)
IC-015

Cation assisted binding and cleavage of dinitrogen by uranium complexes

N. Jori1, R. Scopelliti1, I. Z̆ivković2, T. Rajeshkumar3, A. Sienkiewicz2,4, L. Maron3, M. Mazzanti1*
1Insititut des Sciences et Ingénierie Chimiques, EPFL, 2Laboratory for Quantum Magnetism, Institute of Physics, EPFL, 3Laboratoire de Physique et Chimie des Nano-objets, Institut National des Sciences Appliquées, Toulouse, 4ADSresonances Sàrl

Dinitrogen (N2) is a cheap and widely available molecule, however, its low reactivity complicates its use for the synthesis of high-added feedstocks. Notably, the industrial Haber-Bosch process uses N2 to synthesize ammonia (NH3), but requires harsh temperatures and pressures. Before the current Fe-based catalyst was implemented, uranium materials were reported to be highly effective in the transformation of N2 into NH3. Nevertheless, the N2chemistry of uranium remains underdeveloped, with only a few examples of molecular uranium complexes that are capable of cleaving N2 to nitridesupon addition of external reducing agent,[1-3] where uranium nitrides are considered important inrtermediates the Haber Bosch process. Recently, our group reported two bimetallic uranium(III) systems that were able to perform the four-electron reduction of N2.[4,5] Moreover, we found that the N2 bound in the bridging oxide system could be functionalized by addition of CO to yield a cyanamido complex, but the addition of acid or H2 resulted only in the release of N2.[5]

Here, we will present a series of alkali bound-oxo-bridged diuranium(III) complexes that provide a unique example of decreasing N2 binding affinity with increasing cation size. We will show spectroscopic, electrochemical, and computational data, suggesting that the decreased reactivity is due to sterics rather than electronic effects. We also show that weak N2 binding in ambient conditions does not prevent alkali assisted N2 cleavage to nitride. Furthermore, we will present the first example of Cs-assisted dinitrogen cleavage by a metal complex.

[1] I. Korobkov, S. Gambarotta and G. P. A. Yap, Angew. Chem. Int. Ed. Engl., 2002, 41, 3433-3436
[2] X. Q. Xin, I. Douair, Y. Zhao, S. Wang, L. Maron and C. Q. Zhu, J. Am. Chem. Soc., 2020, 142, 15004-15011
[3] N. Jori, L. Barluzzi, I. Douair, L. Maron, F. Fadaei-Tirani, I. Z̆ivković and M. Mazzanti, J. Am. Chem. Soc., 2021, 143, 11225-11234
[4] M. Falcone, L. Chatelain, R. Scopelliti, I. Z̆ivković and M. Mazzanti, Nature, 2017, 547, 332–335
[5] M. Falcone, L. Barluzzi, J. Andrez, F. Fadaei-Tirani, I. Z̆ivković, A. Fabrizio, C. Corminboeuf, K. Severin and M. Mazzanti, Nature Chem. 2019, 11, 154–160.