Affiliation: | 1. Clausius-Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms-Universität, Wegelerstraße 12, 53115 Bonn, Germany;2. Clausius-Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms-Universität, Wegelerstraße 12, 53115 Bonn, Germany These authors contributed equally to this work. Co-first authors. Contribution: Data curation (equal), Formal analysis (equal), Investigation (equal), Software (equal);3. Georg-August-Universität Göttingen, Institut für Anorganische Chemie, Tammannstraße 4, 37077 Göttingen, Germany;4. Clausius-Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms-Universität, Wegelerstraße 12, 53115 Bonn, Germany Contribution: Investigation (supporting), Methodology (equal) |
Abstract: | Transition-metal nitrides/nitrenes are highly promising reagents for catalytic nitrogen-atom-transfer reactivity. They are typically prepared in situ upon optically induced N2 elimination from azido precursors. A full exploitation of their catalytic potential, however, requires in-depth knowledge of the primary photo-induced processes and the structural/electronic factors mediating the N2 loss with birth of the terminal metal-nitrogen core. Using femtosecond infrared spectroscopy, we elucidate here the primary molecular-level mechanisms responsible for the formation of a unique platinum(II) nitrene with a triplet ground state from a closed-shell platinum(II) azide precursor. The spectroscopic data in combination with quantum-chemical calculations provide compelling evidence that product formation requires the initial occupation of a singlet excited state with an anionic azide diradical ligand that is bound to a low-spin d8-configured PtII ion. Subsequent intersystem crossing generates the Pt-bound triplet azide diradical, which smoothly evolves into the triplet nitrene via N2 loss in a near barrierless adiabatic dissociation. Our data highlight the importance of the productive, N2-releasing state possessing azide ππ* character as a design principle for accessing efficient N-atom-transfer catalysts. |