Cyanate Formation via Photolytic Splitting of Dinitrogen

Abstract

Light-driven N 2 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 N 2 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 N 2 and CO.

Formation of the N≡N Triple Bond from Reductive Coupling of a Paramagnetic Diruthenium Nitrido Compound

“…The two Ru–N···N angles are similar, at 112° and 117°, suggesting symmetric orbital interactions between the two nitrido compounds. Our finding of an out-of-plane zigzag TS geometry is particularly surprising considering that only planar zigzag TS geometries have been considered since Morokuma’s original proposal for N–N cleavage, ,,,,,,− with the exception of Schneider’s report of two out-of-plane zigzag TS geometries with M–N–N–M dihedral angles of 142° and 152° for the coupling of iridium nitrido complexes …”

“…Green ammonia synthesis − and direct ammonia fuel cells − are important enabling technologies for a zero-carbon Nitrogen Economy . − The basic chemical foundations for each of these catalytic technologies are reactions that cleave or form the extremely strong N–N triple bond in N 2 . − Recently, intriguing chemical systems have been developed in which transition metal complexes have been used to either split N 2 into metal-nitrido complexes − or to form N 2 via the union of two metal nitrides. − Despite these processes being the reverse of each other, differing transition state geometries were originally proposed for the N 2 cleavage and formation reactions (Scheme , top). Morokuma and co-workers first proposed the splitting of N 2 between two Mo centers as proceeding through a planar “zigzag” transition state with parallel nascent MoN units .…”

Molybdenum‐Mediated N2‐Splitting and Functionalization in the Presence of a Coordinated Alkyne

“…The activation barrier associated with the zig‐zag‐type [1b] transition state ( 1 TS , d N−N =1.64 Å, Δ G ≠ =26 kcal mol −1 relative to 3 6 , see Figure 3 ) is in line with the experimental observations, albeit at the upper Δ G limit. [16] Ultimately, two molecules of 2 are formed in an overall exergonic reaction (Δ G r =−19.8 kcal mol −1 relative to 3 6 ).…”

(n-Bu)4NBr-Promoted N2 Splitting to Molybdenum Nitride

“…These linear N 2 -bridged complexes were proposed as key intermediates to give corresponding nitrides via zigzag transition states. Based on these experimental evidences, 10 π-electron configuration in the π-MO manifold has been recognized as a crucial parameter for the productive N 2 -splitting. ,, For thermally stable complexes L n MN 2 ML n , N–N cleavage initiated via light or protonation were also well explored. ,,− Especially, Masuda and co-workers reported a chemical or electrochemical one-electron oxidation of [Mo­(depe) 2 (N 2 ) 2 ] (depe = Et 2 PCH 2 CH 2 PEt 2 ) to give the Mo nitride product . Overall, except for highly reductive Mo­(III) supported by amide or silanolate ligands demonstrating unprecedented reactivity, most widespread strategies for N 2 splitting often depend on redox reaction conditions (Scheme A).…”