Activation of ammonia and hydrazine by electron rich Fe(ii) complexes supported by a dianionic pentadentate ligand platform through a common terminal Fe(iii) amido intermediate

Abstract

Synopsis: a highly reactive Fe(iii)–NH2 complex is generated via activation of ammonia or hydrazine in reactions of relevance to fundamental steps in ammonia oxidation processes mediated by an abundant, first row transition metal.

Uncovering Redox Non-innocent Hydrogen-Bonding in Cu(I)-Diazene Complexes

“…NMR line shape simulation of this AA′XX′ system provides coupling constants 1 J NH = −64 Hz, 2 J NH = 1 Hz, 1 J NN = 10 Hz, and 3 J HH = 23 Hz (Figure S11). The vicinal 3 J HH coupling is within the range of reported in previously characterized diazene complexes ( 3 J HH = 21–30 Hz). ,, Moreover, other diamagnetic C 2 -symmetric 15 N-labeled diazene complexes such as [(B 2 Pz 4 Py)­Fe]­(μ-N 2 H 2 ) and [PhBP CH 2 Cy 3 ]­Fe­(OAc)} 2 (μ-N 2 H 2 ) also exhibit characteristic AA′XX′ signals in 1 H NMR spectra.…”

“…The trends in ν­(NN) vibrational frequencies across this series underscore the need for an alternative to traditional H-bonding in which the strongest H-bond acceptor in 2d would lead to the largest difference in ν­(NN) from 3 that lacks any H-bond acceptor. We also note that the ν­(NN) frequencies observed across the 2a – 2d series (1419–1398 cm –1 ) in comparison to 3 (1353 cm –1 ) span a significant portion of known diazene ligand ν­(NN) frequencies, which range from 1321 cm –1 for an electron-rich [(B 2 Pz 4 py)­Fe] 2 (μ-N 2 H 2 ) complex to 1419 cm –1 for 2a . In particular, complexes 2a – 2d in conjunction with 3 illustrate the ability to dramatically tune the degree of NN activation through second-sphere interactions.…”

“…Known transition metal diazene complexes reveal a range of N 2 H 2 coordination motifs (Figure ). − Since the lifetime of free diazene is so short in solution (aqueous N 2 H 2 decay: k = 2.2 × 10 4 M –1 s –1 at 25 °C), isolable metal-diazene complexes enable the study of N 2 H 2 and the effects of coordination at metal centers by a wide variety of spectroscopic and other direct methods. − …”

A guide to secondary coordination sphere editing

“…90 This represents an attractive alternative to the H-bonding methods of stabilization noted above and provides opportunities for the study of intermediates that are relevant to the nitrogen cycle. [91][92][93][94][95] Lewis acid SCSs are often installed post metal coordination to avoid quenching of the ligand lone pairs. Exemplar of this notion, Szymczak and co-workers showed that iron could be coordinated to a pyridine(dicarbene) pincer ligand and subsequently hydroborated.…”

Nitride protonation and NH3 binding versus N–H bond cleavage in uranium nitrides

“…The irreversible binding of NH 3 , or its reactivity with the metal complex, may also constitute an important disadvantage in catalyst design. Despite the inherent stability of the N–H bonds in NH 3 , activation under mild conditions can occur through ligand–metal cooperation, 9 where the presence of basic ligands can result in the redox-neutral heterolysis of NH 3 and subsequent ligand protonolysis. Facile N–H activation of NH 3 via metal–ligand cooperative addition was also reported in one instance for a uranium complex.…”