Metal–Sulfur Compounds in N₂ Reduction and Nitrogenase-Related Chemistry

Abstract

Transition metal–sulfur (M–S) compounds are an indispensable means for biological systems to convert N2 into NH3 (biological N2 fixation), and these may have emerged by chemical evolution from a prebiotic N2 fixation system. With a main focus on synthetic species, this article provides a comprehensive review of the chemistry of M–S compounds related to the conversion of N2 and the structures/functions of the nitrogenase cofactors. Three classes of M–S compounds are highlighted here: multinuclear M–S clusters structurally or functionally relevant to the nitrogenase cofactors, mono- and dinuclear transition metal complexes supported by sulfur-containing ligands in N2 and N2H x (x = 2, 4) chemistry, and metal sulfide-based solid materials employed in the reduction of N2. Fair assessments on these classes of compounds revealed that our understanding is still limited in N2 reduction and related substrate reductions. Our aims of this review are to compile a collection of studies performed at atomic to mesoscopic scales and to present potential opportunities for elucidating the roles of metal and sulfur atoms in the biological N2 fixation that might be helpful for the development of functional materials.

Reactions of [Fe6C(CO)14(S)]2–: Cluster Growth, Redox, Sulfiding

“…The convertibility of [Fe 6 C(CO) 14 S] 2into clusters that more closely resemble FeMoco remains an intriguing but challenging opportunity. [5] One potential goal for future research could be the synthesis of Fe-C clusters with fewer CO ligands. The cluster [Co 6 C(S) 2 (CO) 12 ] 0 provides precedent not only for the increased degree of sulfiding but also for a trigonal prismatic M 6 C core, [20] as observed in FeMoco.…”

“…In practice, the purification entailed stirring a slurry of (Ph 4 P) 2 [5] in CH 2 Cl 2 /Et 2 O (1:5 to 1:10) in air at room temperature overnight. After removal of the yellow solution, the unreacted black residue of (Ph 4 P) 2 [5] was analyzed. The 13 C NMR spectrum of this fresh sample revealed only one carbide signal at 479.2 ppm.…”

“…[21] It appears, however, that in solution, [5] 2degrades to the parent cluster [Fe 6 C(CO) 16 ] 2-. Thus, single crystals of (Ph 4 P) 2 [5], which were analyzed by X-ray crystallography, cocrystallized with ≈ 10 % of (Ph 4 P) 2 [Fe 6 C(CO) 16 ] (Figure 3). As for [4] 2-, the structure of [5] 2can be described as the edge-fusion of an M 6 C octahedron and a M 3 S tetrahedron.…”

“…[4] As summarized in a recent review, the modeling of FeMoco remains of intense interest. [5] In place of carbide, some models employ organic carbon substituents. [6] With reference to FeMoco, we recently reported the synthesis of [Fe 6 C(CO) 14 (S)] 2-([1] 2-), which is the first Fe-C-S cluster.…”

“…Structure of the dianion in (Ph 4 P) 2[5] drawn at the 50 % probability level. Selected distances in ranked order[Å].…”