Chemistry of [Et₄N][Mo^IV(SPh)(PPh₃)(mnt)₂] as an Analogue of Dissimilatory Nitrate Reductase with Its Inactivation on Substitution of Thiolate by Chloride

Abstract

Structural-functional analogue of the reduced site of dissimilatory nitrate reductase is synthesized as [Et4N][MoIV(SPh)(PPh3)(mnt)2].CH2Cl2 (1). PPh3 in 1 is readily dissociated in solution to generate the active site of the reduced site of dissimilatory nitrate reductase. This readily reacts with nitrate. The nitrate reducing system is characterized by substrate saturation kinetics. Oxotransfer to and from substrate has been coupled to produce a catalytic system, NO3- + PPh3 --> NO2- + OPPh3, where NO3- is the substrate for dissimilatory nitrate reductase. The corresponding chloro complex, [Et4N][MoIV(Cl)(PPh3)(mnt)2].CH2Cl2 (2), responds to similar PPh3 dissociation but is unable to react with nitrate, showing the indispensable role of thiolate coordination for such oxotransfer reaction. This investigation provides the initial demonstration of the ligand specificity in a model system similar to single point mutation involving site directed mutagenesis in this class of molybdoenzymes.

Pterin chemistry and its relationship to the molybdenum cofactor

“…Early examples among these models resulted from efforts to reproduce the inner coordination sphere of Mo, the spectroscopic features of Moco or to provide examples of substrate reactivity and mechanism. Following the identification of the dithiolene tether of molybdopterin for Mo, synthetic analog work was directed at dithiolene complexes, but these typically employed dithiolenes substituted by simple groups such as methyl [133,134], cyanide [135–137] or as part of a ring system (e.g., 1,2-benzenedithiolate, bdt) [138–140]. Only a few groups have tackled the problem of placing a pterin on the dithiolene chelate to access both essential components of molybdopterin.…”

The difference one ligand atom makes – An altered oxygen transfer reaction mechanism caused by an exchange of selenium for sulfur

“…In this particular case the selenium complex was the better oxo transfer catalyst compared to the sulfur complex although both performed less efficiently than other known molybdenum based oxo transfer catalysts [13][14][15][16][17][18] . The slowness of the reactions, however, provided the opportunity to investigate them in detail.…”

Synthesis, crystal structure and electrocatalysis of 1,2-ene dithiolate bridged diiron carbonyl complexes in relevance to the active site of [FeFe]-hydrogenases

“…This has been explained by an interaction of the metal d-orbitals with a combination of the filled sulfur p p orbitals and the arene p p orbitals, which acts to shield the change in electron density at the iron center as the oxidation state is changed, thus minimizing the changes in electron energies upon reduction. The importance of 1,2-ethylene-dithiolate in such model complexes can also be realized by the fact that "Nature" has used this ligand in the active site of Mo/W-oxotransferase redox enzymes because of its unique electronic property [39,40].…”