Low-coordinate cobalt-dinitrogen complex with high-spin configuration Ting-Yi Chen 1 , Weiying He 1,2 Serhiy Demeshko 1 , Sebastian Dechert 1 , Serena Debeer 2 and Franc Meyer 1 1 Georg-August-Universität Göttingen, Germany and 2 MPI-CEC, Germany Binding and activation of dinitrogen at metal ions is a key step in the fixation of this inert substrate into bioavailable N-containing compounds, most prominently in the industrial Haber-Bosch process and in the enzymatic NH 3 formation mediated by nitrogenase. In the latter, N 2 is reduced at low-coordinate high-spin iron ions at the central region of the oligometallic FeMo cofactor. Numerous synthetic complexes featuring coordinated N 2 have been reported with the aim of reductive N 2 functionalization, [1,2] and in this field cobalt is emerging as a particularly promising metal ion of the 3d series, after iron. However, low-coordinate high-spin cobalt/N 2 complexes remain rare. 3 In this work, we introduce a low-coordinate high-spin dicobalt/N 2 complex, {[(IAd)Co(C(TMS) 3 )] 2 (μ-N 2 )} ( 2 ), formed from the putative two-coordinate cobalt(I) complex [(IAd)Co(C(TMS) 3 )] ( 1 ) featuring a bulky N-heterocyclic carbene (NHC) ligand IAd. Strongly s-donating NHCs have recently been introduced as valuable ligands in cobalt/N 2 chemistry. 4 The structural and spectroscopic characterization of 2 as well as its N 2 binding equilibrium in solution will be discussed. Furthermore, synchrotron-based XAS Co-L 3,2 -edge and K-edge experiments accompanied by theoretical studies have been performed to understand the unusual electronic structure and nature of N 2 binding in this new system. References 1. Y. Nishibayashi, Dalton Trans. 2018, 47, 11290-11297. 2. F. Masero, M. A. Perrin, S. Dey, V. Mougel, Chem. Eur. J. 2021, 27, 3892-3928 3. K. Ding, A. W. Pierpont, W. W. Brennessel, G. Lukat-Rodgers, K. R. Rodgers, T. R. Cundari, E. Bill, P. L. Holland. J. Am. Chem. Soc. 2009, 131, 9471-9472. 4. Y. Gao, G. Li, L. Deng, J. Am. Chem. Soc. 2018, 140, 2239-2250.
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