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A Density Functional Theory Study of the Hydrogenation of N2 Mediated by a Bimetallic Scandium Complex: H2 Activation
1Centre of New Technologies, University of Warsaw, Warszawa, Poland.
Abstract:
The utilization of early transition-metal platforms offers a promising avenue for dinitrogen activation, a key step in developing molecular alternatives for catalytic ammonia synthesis. Herein, we present a density functional theory study exploring N2 activation and functionalization mediated by an ansa-half-sandwich scandium complex. A thermodynamic evaluation of the bimetallic association of the (C5H4SiMe2NtBu)Sc monomer with N2 revealed the formation of a singlet side-on [(C5H4SiMe2NtBu)Sc]2(μ-η2:η2-N2) complex as the global minimum. Electronic properties and an orbital analysis confirmed the effective reduction to a diazenido fragment. Motivated by this finding, the reactivity toward dihydrogen was explored. The energy profile for the hydrogenation of the diazenido moiety resulted in a limiting activation barrier of 31 kcal mol-1, leading to a hydrazido species [(C5H4SiMe2NtBu)Sc]2(μ-N2H2) with a favourable driving force. Addition of a second equivalent of H2 resulted in the [(C5H4SiMe2NtBu)Sc]2(H)(μ-N2H3) complex, characterized by a protonated hydrazido and a Sc-hydride. This comprehensive mechanistic insight maps out the sequential hydrogenation capabilities of ansa-scandium platforms, defining key electronic factors and reactivity bottlenecks that encourage further developments toward the synthesis of NxHy species from the elemental constituents.
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