Rapid, Covalent Addition of Phosphine to Dithiolene in a Molybdenum Tris(dithiolene). A New Structural Model for Dimethyl Sulfoxide Reductase

Theoretical Understanding of Reactions of Rhenium and Ruthenium Tris(thiolate) Complexes with Unsaturated Hydrocarbons: Noninnocent Nature of the Ligand, Mechanism, and Origin of Differential Reactivity

In retrospect to the complexity induced by the noninnocent ligands in identifying the transition metal's oxidation state and correlating the ligand's noninnocence with reactivity, the reactions of alkene/alkyne addition to rhenium/ruthenium tris(thiolate) complexes are particularly good cases for shedding light on the chemistry of the dppbt ligand, including its noninnocent nature, ligand-centered mechanism, and origin of differential reactivity. Density functional theory (DFT) combined with the high-level ab initio calculations performed herein demonstrates that, upon alkene/alkyne addition, the orbital symmetry properly regulates the reaction to form ligand-centered cis-interligand dithioethers as the most favorable pathway. The neutral and cationic Re and Ru dithioethers are revealed via DFT calculations to be in a low-spin ground state; on the contrary, high-level ab initio methods confirm that the dicationic Re-dithioethers exhibit obvious multireference character with antiferromagnetic coupling between Re-d_yz and S1-p_y. The metal-stabilized thiyl radicals play a pivotal role in delivering the reactivity of [RuL₃]⁺ and [ReL₃]^+/2+ toward alkene/alkyne rather than [ReL₃], where [RuL₃]⁺ and [ReL₃]^+/2+ present significant radical characters on ligand S2, yet neutral [ReL₃] has little such feature, from which differential reactivity arises. Faster styrene addition to Ru tris(thiolate) in contrast to Re tris(thiolate) has been properly interpreted using DFT calculations with major products assigned. The deeper understanding gained in this work would illuminate further experimental exploration in adding alkene/alkyne to other metal-stabilized thiyl radicals.

Inspired by Nature-Functional Analogues of Molybdenum and Tungsten-Dependent Oxidoreductases

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.

Deoxygenation of mono-oxo bis(dithiolene) Mo and W complexes by protonation

Protonation-assisted deoxygenation of a mono-oxo molybdenum center has been observed in many oxotransferases when the enzyme removes an oxo group to regenerate a substrate binding site. Such a reaction is reported here with discrete synthetic mono-oxo bis(dithiolene) molybdenum and tungsten complexes, the chemistry of which had been rarely studied because of the instability of the resulting deoxygenated products. An addition of tosylic acid to an acetonitrile solution of [Mo(IV)O(S2C2Ph2)2](2-) (1) and [W(IV)O(S2C2Ph2)2](2-) (2) results in the loss of oxide with a concomitant formation of novel deoxygenated complexes, [M(MeCN)2(S2C2Ph2)2] (M = Mo (3), W (4)), that have been isolated and characterized. Whereas protonation of 1 exclusively produces 3, two different reaction products can be generated from 2; an oxidized product, [WO(S2C2Ph2)2](-), is produced with 1 equiv of acid while a deoxygenated product, [W(MeCN)2(S2C2Ph2)2] (4), is generated with an excess amount of proton. Alternatively, complexes 3 and 4 can be obtained from photolysis of [Mo(CO)2(S2C2Ph2)2] (5) and [W(CO)2(S2C2Ph2)2] (6) in acetonitrile. A di- and a monosubstituted adducts of 3, [Mo(CO)2(S2C2Ph2)2] (5) and [Mo(PPh3)(MeCN)(S2C2Ph2)2] (7) are also reported.