A Bioinspired Iron‐Molybdenum μ‐Nitrido Complex and Its Reactivity toward Ammonia Formation

Abstract

Multimetallic nitride species, especially those containing biologically related iron or molybdenum, are fundamentally important to understand the nitrogen reduction process catalysed by FeMo‐nitrogenase. However, until now, there remains no report about the construction of structurally well‐defined FeMo heteronuclear nitrido complex and its reactivity toward ammonia formation. Herein, a novel thiolate‐bridged FeIIMoVI complex featuring a bent Fe−N≡Mo fragment is synthesized and structurally characterized, which can be easily protonated to form a μ‐imido complex. Subsequently, through the proton‐coupled electron transfer (PCET) process, this imido species can smoothly convert into the μ‐amido complex, which can further undergo reductive protonation to afford the FeMo complex containing an ammine ligand. Overall, we present the first well‐defined {Fe(μ‐S)2Mo} platform that can give a panoramic picture for the late stage (N3−→NH2−→NH2−→NH3) of biological nitrogen reduction by the heterometallic cooperativity.

Unusual Hydrogenation Reactivities of a Thiolate-Bridged Dicobalt μ-Nitride Featuring a Bent {CoIII–N–CoIII} Core

“…Specifically, the Co–N bond distances of 1.7863(14) and 1.7837(14) Å in 3­[BPh 4 ] are very close to those measured for 2 , and the Co–N–Co bond angle slightly increases from 84.85(17)° in 2 to 89.02(6)° in 3­[BPh 4 ] . Both observations suggest that protonation of the nitrido group does not discernibly affect the Co–N–Co bonding, a similar situation observed for our previously reported FeMo μ-nitride . Relative to 2 , the longer Co–Co distance of 2.5028(3) Å in 3­[BPh 4 ] mainly arises from its larger Co–N–Co angle, since their Co–N bond lengths are nearly identical.…”

A thiolate-bridged ruthenium–molybdenum complex featuring terminal nitrido and bridging amido ligands derived from the N–H and N–N bond cleavage of hydrazine

“…The Mo1–N1 bond length is 1.6609(1) Å, which is analogous to those found in other Cp*Mo complexes containing a MoN triple bond. 33–35 In contrast, the Mo1–N2 distance is 2.0736(1) Å, which is significantly longer than that of Mo1–N1, indicating the different hybridization pattern of N2 from that of N1. Additionally, two H atoms bonded to N2 were also located in the Fourier difference map.…”

“…Subsequently, to construct heterometallic N x H y complexes, we conducted the reaction of 3 with one equivalent of hydrazine at room temperature but no transformation of 3 was observed. Therefore, we increased the amount of hydrazine; as shown in Scheme 2, treatment of 3 with eight equivalents of hydrazine at 60 °C afforded a new complex [Cp*Ru(μ-η 2 :η 1 -bdt) [33][34][35] In contrast, the Mo1-N2 distance is 2.0736(1) Å, which is significantly longer than that of Mo1-N1, indicating the different hybridization pattern of N2 from that of N1. Additionally, two H atoms bonded to N2 were also located in the Fourier difference map.…”

Strategies to achieve effective nitrogen activation

“…To date, the main challenge of NH 3 synthesis is the activation of nitrogen molecules which have an extremely strong N≡N bond with large bonding energy (945 kJ mol −1 ). In nature, iron–molybdenum enzymes (nitrogenase) can achieve nitrogen activation through iron–sulfur clusters with terminal molybdenum atoms: $$${{\rm{N}}}_{2}+16\,\text{ATP}+8\,{{\rm{H}}}^{+}+8\,{{\rm{e}}}^{-}\to 2\,{\text{NH}}_{3}+16\,\text{ADP}+{{\rm{H}}}_{2}+16\,{{\rm{H}}}_{x}{\text{PO}}_{4}^{n-},$$$where ATP and ADP represent adenosine triphosphate and adenosine diphosphate, respectively (Equation ) 34–36 . The mechanism of nitrogen activation is believed to be the coordination of N 2 molecules with the terminal metal center of FeMo nitrogenase.…”