Structure and Reactivity of an Asymmetric Synthetic Mimic of Nitrogenase Cofactor

Abstract

The Mo nitrogenase catalyzes the ambient reduction of N to NH at its M-cluster site. A complex metallocofactor with a core composition of [MoFe S C], the M-cluster, can be extracted from the protein scaffold and used to facilitate the catalytic reduction of CN , CO, and CO into hydrocarbons in the isolated state. Herein, we report the synthesis, structure, and reactivity of an asymmetric M-cluster analogue with a core composition of [MoFe S ]. This analogue, referred to as the Mo-cluster, is the first synthetic example of an M-cluster mimic with Fe and Mo positioned at opposite ends of the cluster. Moreover, the ability of the Mo-cluster to reduce C substrates to hydrocarbons suggests the feasibility of developing nitrogenase-based biomimetic approaches to recycle C waste into fuel products.

Activation of CO2 by Vanadium Nitrogenase

“…These newer studies employ organic proton sourcess uch as 2,6-dimethylpyridinium and triethylammonium salts under buffering conditions and use the strong reductant Sm II I 2 to drive catalytic substrate reduction. [100,102,103] The use of Sm II I 2 as ar eductant in organic chemistry has been well-studied, althought he redox potential of this powerful electron source is highly sensitive to its coordinating ligands. [104,105] Based on the observed formation of ad istinct Sm II I 2 species in the nitrogenase cofactor experiments, aD MF-coordinated Sm II I 2 complex is believed to be formed in situ.…”

“…[104,105] Based on the observed formation of ad istinct Sm II I 2 species in the nitrogenase cofactor experiments, aD MF-coordinated Sm II I 2 complex is believed to be formed in situ. [100,102,103] The reduction potential of Sm II I 2 in THF has been determined to be À0.89 Vv s. SCE; [106] however,t he dielectric constant and dipole moment of DMF is similart ot he ligand 1,3-dimethyltetrahydropyrimidin-2(1H)-one (DMPU) and is therefore expected to render the solution reduction potential closertoa pproximately À1.5 Vv s. SCE. [105,107,108] Using these improved reduction conditions, the Fischer-Tropsch-like hydrogenation of CO 2 with V-cluster can be accomplished.…”

“…More recent experiments have improved upon this methodology by using lower cluster loading and performing the reactions in organic solvent, namely mixtures of N , N ‐dimethylformamide (DMF) and tetrahydrofuran (THF). These newer studies employ organic proton sources such as 2,6‐dimethylpyridinium and triethylammonium salts under buffering conditions and use the strong reductant Sm II I 2 to drive catalytic substrate reduction . The use of Sm II I 2 as a reductant in organic chemistry has been well‐studied, although the redox potential of this powerful electron source is highly sensitive to its coordinating ligands .…”

“…The use of Sm II I 2 as a reductant in organic chemistry has been well‐studied, although the redox potential of this powerful electron source is highly sensitive to its coordinating ligands . Based on the observed formation of a distinct Sm II I 2 species in the nitrogenase cofactor experiments, a DMF‐coordinated Sm II I 2 complex is believed to be formed in situ . The reduction potential of Sm II I 2 in THF has been determined to be −0.89 V vs. SCE; however, the dielectric constant and dipole moment of DMF is similar to the ligand 1,3‐dimethyltetrahydropyrimidin‐2(1 H )‐one (DMPU) and is therefore expected to render the solution reduction potential closer to approximately −1.5 V vs. SCE …”

Synthetic Analogues of Nitrogenase Metallocofactors: Challenges and Developments

“…Establishing this type of heterometallic asymmetry is challenging for synthetic inorganic chemists in general, but the recent preparation of [Cp*Mo IV Fe 5 S 9 (SH)] 3− ( 7 , Figure , Cp*=η 5 ‐pentamethylcyclopentadienyl) by Tanifuji et al. provides a means to realize such structural features . Previous work by the Tatsumi group showed the utility of the synthon [Cp*MS 3 ] − (M=Mo VI , W VI ) to assemble metal–sulfur clusters, whereby the coordinatively saturated Mo atom could be installed with its primary coordination sphere preassembled .…”