Testing the Polynuclear Hypothesis: Multielectron Reduction of Small Molecules by Triiron Reaction Sites

Abstract

High-spin trinuclear iron complex (tbsL)Fe3(thf) ([tbsL]6− = [1,3,5- C6H9(NPh-o-NSitBuMe2)3]6−) (S = 6) facilitates 2 and 4e− reduction of NxHy type substrates to yield imido and nitrido products. Reaction of hydrazine or phenylhydrazine with (tbsL)Fe3(thf) yields triiron µ3-imido cluster (tbsL)Fe3(µ3-NH) and ammonia or aniline, respectively. (tbsL)Fe3(µ3-NH) has a similar zero-field 57Fe Mössbauer spectrum compared to previously reported [(tbsL)Fe3(µ3-N)]NBu4, and can be directly synthesized by protonation of the anionic triiron nitrido with lutidinium tetraphenylborate. Deprotonation of the triiron parent imido (tbsL)Fe3(µ3-NH) with lithium bis(trimethylsilyl)amide results in regeneration of the triiron nitrido complex capped with a thf-solvated Li cation [(tbsL)Fe3(µ3-N)]Li(thf)3. The lithium capped nitrido, structurally similar to the pseudo C3-symmetric triiron nitride with a tetrabutylammonium counter cation, is rigorously C3-symmetric featuring intracore distances of Fe–Fe 2.4802(5) Å, Fe–N(nitride) 1.877(2) Å, and N(nitride)–Li 1.990(6) Å. A similar 2e− reduction of 1,2-diphenylhydrazine by (tbsL)Fe3(thf) affords (tbsL)Fe3(µ3-NPh) and aniline. The solid state structure of (tbsL)Fe3(µ3-NPh) is similar to the series of µ3-nitrido and -imido triiron complexes synthesized in this work with average Fe–Nimido and Fe–Fe bond lengths of 1.941(6) Å and 2.530(1) Å, respectively. Reductive N=N bond cleavage of azobenzene is also achieved in the presence of (tbsL)Fe3(thf) to yield triiron bisimido complex (tbsL)Fe3(µ3-NPh)(µ2-NPh), which has been structurally characterized. Ligand redox participation has been ruled out and, therefore, charge balance indicates that the bisimido cluster has undergone a 4e− metal based oxidation resulting in an (FeIV)(FeIII)2 formulation. Cyclic voltammograms of the series of triiron clusters presented herein demonstrate that oxidation states up to (FeIV)(FeIII)2 (in the case of [(tbsL)Fe3(µ3-N)]NBu4) are electrochemically accessible. These results highlight the efficacy of high-spin, polynuclear reaction sites to cooperatively mediate small molecule activation.

Topological insights in polynuclear Ni/Na coordination clusters derived from a schiff base ligand

“…These entities are of great interest for their aesthetically beautiful structures [2][3][4], unexpected transformations [5][6][7] and potential applications in magnetism [8][9][10], luminescence [11][12][13][14][15], catalysis [16][17][18], etc. Paramagnetic transition metal CCs are of intense interest and have attracted a vast amount of attention since the discovery that some CCs behave as single-molecule magnets (SMMs) [19][20][21].…”

Bifunctional Catalysts for CO2 Reduction

“…9 Furthermore, the resulting nitride product is cathodically shifted from the all-ferrous starting material, a result of anionic nitride ligand and the metals coming into closer proximity. 10 We hypothesized that moving from iron to cobalt would increase the basicity of the trinuclear core and make atom and group-transfer processes even more facile. To probe this we investigated the reactivity of .…”

Nature's masterclass

“…For example, his group demonstrated that a trinuclear iron complex can catalyse reductions of nitrogen compounds, such as hydrazine, requiring two or four electrons. 3 The ultimate goal would be to find a simple molecular catalyst that mimics the nitrogenase reaction, which requires six electrons for each nitrogen molecule to be split.…”