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Nitrogen is fundamental to all of life and many industrial processes. The interchange of nitrogen oxidation states in the industrial production of ammonia, nitric acid, and other commodity chemicals is largely powered by fossil fuels. A key goal of contemporary research in the field of nitrogen chemistry is to minimize the use of fossil fuels by developing more efficient heterogeneous, homogeneous, photo-, and electrocatalytic processes or by adapting the enzymatic processes underlying the natural nitrogen cycle. These approaches, as well as the challenges involved, are discussed in this Review.

Bimetallic transition metal complexes with site-specific redox properties offer a versatile platform for understanding electron polarization, intramolecular electron transfer processes, and customizing electronic and magnetic properties that might impact reactivity and catalyst design. Inspired by the dissymmetric nickel sites in the Acetyl CoA Synthase (ACS) Active Site, three new bimetallic Ni(N2S2)-Ni(S2C2R2) complexes based on Ni(N2S2) metalloligand donor synthons, Nid, in mimicry of the nickel site distal to the redox-active iron sulfur cluster of ACS, and nickel dithiolene receiver units, designated as Nip, the nickel proximal to the 4Fe4S cluster, were combined to explore the influence of ligand environment on electronic structure and redox properties of each unit. The combination of synthons gave a matrix of three S-bridged dinickel complexes, characterized by X-ray crystallography, and appropriate spectroscopies. Computational modeling is connected to the electronic characteristics of the nickel donor and receiver units. This study demonstrated the intricacies of identifying sites of electrochemical redox processes, within multi-metallic systems containing non-innocent ligands. [ABSTRACT FROM AUTHOR]

With the goal of generating hetero‐redox levels on metals as well as on nitric oxide (NO), metallodithiolate (N2S2)CoIII(NO−), N2S2 = N,N‐ dibenzyl‐3,7‐diazanonane‐1,9‐dithiolate, is introduced as ligand to a well‐characterized labile [Ni0(NO)+] synthon. The reaction between [Ni0(NO+)] and [CoIII(NO−)] has led to a remarkable electronic and ligand redistribution to form a heterobimetallic dinitrosyl cobalt [(N2S2)NiII∙Co(NO)2]+ complex with formal two electron oxidation state switches concomitant with the nickel extraction or transfer as NiII into the N2S2 ligand binding site. To date, this is the first reported heterobimetallic cobalt dinitrosyl complex. [ABSTRACT FROM AUTHOR]

Three- vs. two-carbon N-to-N connectors give rise to monomeric, tetrahedral N2S2Co(II) (μeff = 4.24 BM) or dimeric [(N2S2)Co(II)]2 (diamagnetic) complexes, respectively. Differences in the derivative products of the Lewis acid receivers, W0(CO)3 and W0(CO)4, illustrate nucleophilicity of the thiolate sulfur lone pairs in each case, as well as their structural control. [ABSTRACT FROM AUTHOR]

A Ni(meso-daco) [where mese-daco= mercaptoethyl)(sulfinatoethyl)diazacyclooctane] (Ni-2) complex of W[(CO).sub.5] was isolated to compare its donor ability to the analogous ([[nu].sup.1]-Ni-1)W[(CO).sub.5] adduct (where Ni-1 is Ni(bme-daco) and (bme-daco)=bis(mercaptoethyl)-diazacycloethyl)sulfinatoethyl)diazacyclooctane]. It was shown that modification of the thiolate S to sulfinate could serve as a block to bidentate coordination that prevails in the nickel dithiolato complexes without significantly altering the monodentate ligation and donor ability of such metalloligands.

The synthesis of Ni[N.sub.2][S.sub.2] metalloligands, including the solid-phase synthesis of resin-bound Ni[(CGC).sup.2-], and sulfur-based derivatization with W[(CO).sub.5] and Rh[(CO).sub.2.sup.+] are carried out and described. Through comparison to analogous well characterized, solution-phase complexes, Attenuated Total Reflectance FTIR spectroscopy establishes the presence of unique heterobimetalic complexes both in solution and immobilized on resin beads.

The synthesis of the metallodithiolate derivate of tungsten pentacarbonyl from the reaction of photogenerated W(CO)(sub 5)THF and Ni-1* ((1,5-bis(2-mercapto-2-methylpropane)-1,5-diazacycloctanato)nickel(II) is described along with its crystal structure. The studies demonstrate that, although ring-opening is a rather facile process, the once formed pentacarbonyl derivative is extremely stable toward further W-S bond cleavage.

The physical properties and structures of a series of six complexes of the type (NiN2S2)W(CO)4 are used to establish electronic and steric parameters for square planar NiN2S2 complexes as bidentate, S-donor ligands. It is found that there is little difference in donor abilities of the five neutral ligands, while the dianionic ligand transfers more electron density onto the W(CO)4 moiety, and the spatial orientations of the ligands remain fixed with respect to the W(CO)4 moiety.

A series of tetragonally distorted square pyramids of formula N2S2M(NO) (M = Fe, Co) is prepared and characterizes by v(NO) IR and EPR spectroscopies, magnetism and elestrochemical properties, as well as solid-state crystal structure determinations. The v(NO) IR frequencies and the

Species competent for H2 production are generated using the [Fe]H2ase active site as a guide for the preparation of synthetic electrocatalysts. This study explored CO exchange with the hydrophilic PTA ligand whose effect is to facilitate the electrocatalysis of H2 production by ca. 0.1 to 0.2V.

The N-protonated bimercaptoethanediazacyclooctane serves as a bidentate dithiolate ligand to oxidized Fe(NO)(sub 2) mimicking Cys-X-Cys binding of Fe(NO)(sub 2) to proteins or thio-biomolecule. These molecules are useful for in vivo studies of NO degradation of iron-sulfur clusters in ferredoxins.