Testing the Push–Pull Hypothesis: Lewis Acid Augmented N₂ Activation at Iron

Abstract

We present a systematic investigation of the structural and electronic changes that occur in an Fe(0)–N2 unit (Fe(depe)2(N2); depe = 1,2-bis(diethylphosphino)-ethane) upon the addition of exogenous Lewis acids. Addition of neutral boranes, alkali metal cations, and an Fe2+ complex increases the N–N bond activation (Δ νNN up to 172 cm−1), decreases the Fe(0)–N2 redox potential, polarizes the N–N bond, and enables −N protonation at uncommonly anodic potentials. These effects were rationalized using combined experimental and theoretical studies.

Boron‐Catalyzed C−C Functionalization of Allyl Alcohols

“…[7] Tris(pentafluorophenyl)borane has also been used as an excellent activator for metallocene Ziegler-Natta catalysts. [13][14][15] Recently, it was also found by Szymczak [16] and Simonneau [17] that B(C 6 F 5 ) 3 can interact with N 2 containing transition complexes. [13][14][15] Recently, it was also found by Szymczak [16] and Simonneau [17] that B(C 6 F 5 ) 3 can interact with N 2 containing transition complexes.…”

Group 6 Transition‐Metal/Boron Frustrated Lewis Pair Templates Activate N2and Allow its Facile Borylation and Silylation

“…[12] While this paper was being written, Szymczak and co-workers reported, in av ery elegant but contextually different study,t hat adduct formation of 2 with the [(depe) 2 Fe(N 2 )] complex (depe = 1,2-bis(diethylphosphino)ethane) enhances activation of the dinitrogen ligand (Scheme 1, bottom). [13] We treated orange C 6 D 6 suspensions of 1 with 1equivalent of 2 at room temperature and immediately obtained dark green solutions.S pectroscopic analysis indicated the clean formation of new complexes 3, according to 1 H, 31 P, 19 Fand 11 BNMR spectroscopy (! 90 % NMR yield;S cheme 2).…”

“…Repeating these experiments on al arger scale in toluene or chloroben- zene,followed by addition of pentane caused precipitation of dark powders (see the Supporting Information for details) from which single crystals suitable for an X-ray diffraction study could be grown. [13] Compounds 3 Mo and 3 W can be viewed as zero-valent Group 6m etal/B(C 6 F 5 ) 3 TMFLP templates that activate dinitrogen. Themolecular structures of adducts 3 Mo and 3 W given in Figure 1a re quite similar.…”

Cationic silyldiazenido complexes of the Fe(diphosphine)2(N2) platform: structural and electronic models for an elusive first intermediate in N2fixation

“…1.748 (8) 8,15 Collectively these data correlate with an enhanced transfer of electron density from Fe into the NN fragment upon electrophilic attack at the terminal nitrogen (N β ), which results in an increased Fe-N bond order attendant with a reduction in the N-N bond order. Recently, the borane adduct Fe(depe) 2 (NN·B(C 6 F 5 ) 3 ) has been structurally verified, 16 which permits a valuable comparison between electrophiles of differing Lewis acidity upon the extent of electron transfer from Fe to N 2 , using the same parent system 1. The lower IR stretching frequencies 17 (Table 1; see ESI for full details), although with slightly more obtuse N-N-Si bond angles than those observed from X-ray diffraction data.…”

“…Using a Walsh-type analysis, it was shown that this interaction is optimised for a bent rather than linear N-N-B bond angle, as this maximises overlap between the B p-orbital and a lobe of the N 2 π* MO; for the B(C 6 F 5 ) 3 adduct this was experimentally determined to be 137.0(3)°. 16 The experimental and theoretical trends in N-N-R bond angles for the [Fe(PP) 2 …”