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Nitrogen Fixation, Nitride, N2 Splitting, Photochemistry, Carbonylation
Abstract:
Light-driven N2 cleavage into molecular nitrides is an
attractive strategy for synthetic nitrogen fixation. However, suitable
platforms are rare. Furthermore, the development of catalytic
protocols via this elementary step suffers from poor understanding
of N−N photosplitting within dinitrogen complexes, as well as of the
thermochemical and kinetic framework for coupled follow-up
chemistry. We here present a tungsten pincer platform, which
undergoes fully reversible, thermal N2 splitting and reverse nitride
coupling, allowing for experimental derivation of thermodynamic and
kinetic parameters of the N−N cleavage step. Selective N−N splitting
was also obtained photolytically. DFT computations allocate the
productive excitations within the {WNNW} core. Transient absorption spectroscopy shows ultrafast repopulation of the electronic
ground state. Comparison with ground-state kinetics and resonance Raman data support a pathway for N−N photosplitting via a
nonstatistically vibrationally excited ground state that benefits from vibronically coupled structural distortion of the core. Nitride
carbonylation and release are demonstrated within a full synthetic cycle for trimethylsilylcyanate formation directly from N2 and CO.
