Abstract
A MoIV mono-oxido bis-dithiolene complex, [MoO(mohdt)2]2− (mohdt = 1-methoxy-1-oxo-4-hydroxy-but-2-ene-2,3-bis-thiolate) was synthesized as a structural and functional model for molybdenum oxidoreductase enzymes of the DMSO reductase family. It was comprehensively characterized by inter alia various spectroscopic methods and employed as an oxygen atom transfer (OAT) catalyst. The ligand precursor of mohdt was readily prepared by a three-step synthesis starting from dimethyl-but-2-ynedioate. Crystallographic and 13C-NMR data support the rationale that by asymmetric substitution the electronic structure of the ene-dithio moiety can be fine-tuned. The MoIVO bis-dithiolene complex was obtained by in situ reaction of the de-protected ligand with the metal precursor complex trans-[MoO2(CN)4]4−. The catalytic oxygen atom transfer mediated by the complex was investigated by the model OAT reaction from DMSO to triphenylphosphine with the substrate transformation being monitored by 31P NMR spectroscopy. [MoO(mohdt)2]2− was found to be catalytically active reaching 93% conversion, albeit with a rather low reaction rate (reaction time 56 h). The observed overall catalytic activity is comparable to those of related complexes with aromatic dithiolene ligands despite the novel ligand being aliphatic in nature and originally perceived to perform more swiftly. The respective results are rationalized with respect to a potential intermolecular interaction between the hydroxyl and ester functions together with the electron-withdrawing functional groups of the dithiolene ligands of the molybdenum mono-oxido complex and equilibrium between the active monomeric MoIVO and MoVIO2 and the unreactive dimeric MO3 species.
Highlights
Molybdenum dependent enzymes are essential contributors to the life of nearly every known organism on earth being it an ancient archaeon, a plant or a mammal which includes the modern human being (Mendel, 2007; Edwards et al, 2015)
The synthetic route to dithiolene ligand precursors 1–4 along with the complexation reaction are displayed in Scheme 2
The unsymmetrically substituted dithiolene ligand is subject to a push-pull effect modulating its electronic structure
Summary
Molybdenum dependent enzymes are essential contributors to the life of nearly every known organism on earth being it an ancient archaeon, a plant or a mammal which includes the modern human being (Mendel, 2007; Edwards et al, 2015). Defects in the maturation of the molybdenum cofactors (Figure 1), which can occur at different stages of the respective multistep biosynthesis, cause diseases (e.g., isolated sulfite oxidase deficiency: iSOD) due to the non-functioning of the molybdenum enzymes. This has consequences such as brain damage, motor retardation, convulsions etc. Understanding exactly what makes Moco unstable and what makes it catalytically active is of great interest for those aiming at developing an artificial cofactor which might be used as a respective drug in the future This constitutes the motivation for our group and for the study discussed in the following as one of many approaches. A moiety including molybdenum and one or two dithiolene ligands (representing molybdopterin— MPT; see Figure 1) is one of the most common motives in molybdenum cofactor bio-inorganic chemistry (Rajagopalan, 1997; Schulzke and Samuel, 2011)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
