Recent developments in the homogeneous reduction of dinitrogen by molybdenum and iron

Abstract

The reduction of gaseous nitrogen (N2) is a challenge for industrial, biological and synthetic chemists, who want to understand the formation of ammonia (NH3) for agriculture and also want to form N-C and N-Si bonds for fine chemical synthesis. The iron-molybdenum active site of nitrogenase has inspired chemists to explore the ability of iron and molybdenum complexes to bring about transformations related to N2 reduction. This area of research has gained significant momentum, and the last two years have witnessed a number of significant advances in synthetic Fe-N2 and Mo-N2 chemistry. In addition, the identities of all atoms in the iron-molybdenum cofactor of nitrogenase have finally been elucidated, and the discovery of a carbide has generated new questions and targets for coordination chemists. This Perspective summarizes the recent work on iron and molydenum complexes, and highlights the opportunities for continued research.

Silylation of Dinitrogen Catalyzed by Hydridodinitrogentris(Triphenylphosphine)Cobalt(I)

“…In this context, most of the effort has been focused on molybdenum and iron systems [14][15][16][17][18]. Two major strategies for catalytic N2 activation by homogeneous systems were developed: reductive protonation to yield ammonia and reductive silylation to yield silylamines ( Figure 1).…”

Low‐Temperature N2 Binding to Two‐Coordinate L2Fe0 Enables Reductive Trapping of L2FeN2− and NH3 Generation

“…It is of interest to explore whether other donor ligands and geometries might expose similar reactivity patterns for Fe-N 2 species. [11,12] For example, Holland and co-workers recently reported a solution characterization of a 3-coordinate Fe complex with an N 2 ligand linearly bridged between Fe and a solvated Mg cation (D in Figure 1). [13,14] The N 2 ligand in this complex is highly activated.…”

Mechanisms for the Formation of NH3, N2H4, and N2H2 in the Protonation Reaction of Fe(DMeOPrPE)2N2 {DMeOPrPE = 1,2‐bis[bis(methoxypropyl)phosphino]ethane}

“…Thus, there is no conclusive mechanistic evidence that the short-lived purple intermediate (11) that forms in the reaction of 1 with acid lies along the pathway to hydrazine and ammonia. But, if it does then the pathway in Scheme 13, involving a bridging diazene species (13), is the likely pathway. This latter statement can be concluded with reasonable certainty because the Fe 0 atoms in Equation (2) are converted quantitatively to Fe II in the reaction, i.e., no Fe III is formed.…”

“…The monomeric and dinuclear species are in equilibrium, with the monomer being favored at low temperature. (13) The role of the purple intermediate in the formation of ammonia in Equation (2) is as yet uncertain. On the one hand, the transient purple color was always observed in any protonation reaction of Fe(DMeOPrPE) 2 N 2 (1) that successfully yielded ammonia [Equation (2) (11), generated by one of the methods in Scheme 11, was treated with 1 M TfOH under N 2 or Ar.…”

“…Accordingly, they have made significant advances in the coordination chemistry of iron-dinitrogen complexes and in the reduction of dinitrogen using homogeneous iron complexes. [13][14][15][16][17] Of particular interest to us was Leigh's report that the hydride ligand in transFe(dmpe) 2 (N 2 )H + [dmpe = 1,2-bis(dimethylphosphanyl)ethane] can be reductively deprotonated to yield the five-coordinate iron(0)-dinitrogen complex Fe(dmpe) 2 N 2 (Scheme 1). [18] Re-protonation of the Fe 0 product complex resulted in moderate yields of ammonia and small amounts of hydrazine (Scheme 1).…”