Throughout the previous ten years many scientists took inspiration from natural molybdenum and tungsten-dependent oxidoreductases to build functional active site analogues. These studies not only led to an ever more detailed mechanistic understanding of the biological template, but also paved the way to atypical selectivity and activity, such as catalytic hydrogen evolution. This review is aimed at representing the last decade’s progress in the research of and with molybdenum and tungsten functional model compounds. The portrayed systems, organized according to their ability to facilitate typical and artificial enzyme reactions, comprise complexes with non-innocent dithiolene ligands, resembling molybdopterin, as well as entirely non-natural nitrogen, oxygen, and/or sulfur bearing chelating donor ligands. All model compounds receive individual attention, highlighting the specific novelty that each provides for our understanding of the enzymatic mechanisms, such as oxygen atom transfer and proton-coupled electron transfer, or that each presents for exploiting new and useful catalytic capability. Overall, a shift in the application of these model compounds towards uncommon reactions is noted, the latter are comprehensively discussed.

Heteroleptic molybdenum complexes bearing 1,5‐diaza‐3,7‐diphosphacyclooctane (P₂N₂) and non‐innocent dithiolene ligands were synthesized and electrochemically characterized. The reduction potentials of the complexes were found to be fine‐tuned by a synergistic effect identified by DFT calculations as ligand‐ligand cooperativity via non‐covalent interactions. This finding is supported by electrochemical studies combined with UV/Vis spectroscopy and temperature‐dependent NMR spectroscopy. The observed behavior is reminiscent of enzymatic redox modulation using second ligand sphere effects.

The synthesis of an alkene is reported which is concurrently twisted (twist angle = 86.6(8)°), push–pull (dipole moment = 7.48 D), and electron-rich (E_1/2 = −1.45 V and −0.52 V vs. Fc/Fc⁺) in nature, comprising a unique trinity combination for the alkene class of compounds. Subsequently, this newly synthesized alkene-motif was used as a donor for the synthesis of a zwitterionic boron-containing π-conjugated compound (dipole moment = 12.17 D) through an intramolecular charge transfer process exploiting the π-conjugated donor–acceptor system.

Triazolylidene ligands belong to a class of N-heterocyclic carbenes of growing chemical interest. Their precursors are readily available using Click chemistry and, therefore, highly modular for tuning their electronic characteristics. Due to their notable donor properties, these ligands are particularly suitable for modulating the electronic properties of the central ions of their complexes. Here, a bidentate bistriazolylidene which is a particularly strong donor ligand is combined with a low valent molybdenum(0) center and four carbon monoxide molecules as co-ligands. The novel complex exhibits characteristic electrochemical and IR-spectroscopic behavior. An X-ray structural analysis provides metrical details which are not entirely in agreement with spectroscopic data, likely going back to crystal packing effects. In comparison with precursor and ligand SCXRD data, notable geometrical changes induced by the coordination of the ligand to the metal can be observed. The analyses strongly support the bistriazolylidene ligand as being a particularly good donor of electron density towards the central metal. Potentially, these findings may support, in the future, the design of potent catalysts for the reductive activation of small molecules.

Among the many structural model complexes for the molybdenum and tungsten dependent oxidoreductases, none are specifically highlighted as being water stable and water soluble, and only very few may have such potential. Herein, complex salts with potassium cations and bisdithiolene oxido molybdate or tungstate anions are described, which were designed to be water‐tolerant and soluble in purely aqueous medium. Four different routes to water‐soluble complexes of the type K ₂ [MOx(dt) ₂ ] (M = Mo, W; dt = ene‐1,2‐dithiolate, x  = 1, 2) are presented, the applicability of which depends on the varied, distinct ligand precursors. The crystal structures of the salts are examined in detail, with particular attention to cation–anion interactions, alongside an analysis of the corresponding infrared spectra to support structural interpretations and interaction characteristics.