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Severely Bent Dinitrogen Bridging in Highly Preorganized Dinuclear Cobalt Complexes Featuring an Intricate Electronic Structure

Year: 2025

Type: article

Abstract: High Resolution Image Download MS PowerPoint Slide Preorganized bimetallic complexes could open up new avenues of cooperative substrate activation and transformation of inert dinitrogen (N 2 ). While the most common structural motif in synthetic dinuclear N 2 complexes is a linear M–N–N–M unit, only a few examples of bent geometries reminiscent of the proposed N 2 binding modes in the Haber–Bosch process or the M-cluster of Nitrogenase have been reported. Exploiting the structural constraints imposed by a compartmental pyrazolato/β-diketiminato hybrid ligand platform (L 3̵– ), we here report a series of dicobalt(I) complexes [LCo 2 (N 2 )] − hosting N 2 within the preorganized bimetallic cleft with extremely acute Co-Ct N2 -Co angles of around 123.5° (Ct N2 is the N 2 centroid). A detailed electronic structure analysis using wave function methods shows that the ground state of diamagnetic [LCo 2 (N 2 )] − may not be a simple closed-shell singlet, but rather of multiconfigurational nature subject to spin–orbit coupling. Co–N–N–Co bending significantly decreases overlap of metal d-orbitals with the in-plane p(N) orbitals, yet the N 2 substrate is substantially more activated ( ν̃ NN ≈ 1900 cm –1 ) than in most Co I complexes with end-on bound N 2 or linear Co–N–N–Co arrangement; no coactivation by the alkali cation K + is observed for [LCo 2 (N 2 )] − . Reversible oxidation gives an unusual mixed-valent complex [LCo I Co II (N 2 )] in which the highly bent Co–N–N–Co core is retained. [LCo 2 (N 2 )][K(THF) 2 ] is found to cocrystallize with KBEt 3 H, indicating that the putative [LCo 2 (N 2 H)] 2– has a very low hydricity. In presence of KC 8 and Me 3 SiCl, complex [LCo 2 (N 2 )] − serves as (pre)catalyst for the reductive silylation of N 2 into N(SiMe 3 ) 3 . We discuss the implications of the highly exposed, “ cis -bent” N 2 unit for onward reactivity.

Source: JACS Au

DOI: 10.1021/jacsau.5c00129