Study of Molybdenum(4+) Quinoxalyldithiolenes As Models for the Noninnocent Pyranopterin in the Molybdenum Cofactor

Overview

Journal Inorg Chem

Specialty Chemistry

Date 2011 Sep 8

PMID 21894968

Citations 23

Authors

Kelly G Matz

Regina P Mtei

Rebecca Rothstein

Martin L Kirk

Sharon J Nieter Burgmayer

Affiliations

Soon will be listed here.

Abstract

A model system for the molybdenum cofactor has been developed that illustrates the noninnocent behavior of an N-heterocycle appended to a dithiolene chelate on molybdenum. The pyranopterin of the molybdenum cofactor is modeled by a quinoxalyldithiolene ligand (S(2)BMOQO) formed from the reaction of molybdenum tetrasulfide and quinoxalylalkyne. The resulting complexes TEA[Tp*MoX(S(2)BMOQO)] [1, X = S; 3, X = O; TEA = tetraethylammonium; Tp* = hydrotris(3,5-dimethylpyrazolyl)borate] undergo a dehydration-driven intramolecular cyclization within quinoxalyldithiolene, forming Tp*MoX(pyrrolo-S(2)BMOQO) (2, X = S; 4, X = O). 4 can be oxidized by one electron to produce the molybdenum(5+) complex 5. In a preliminary report of this work, evidence from X-ray crystallography, electronic absorption and resonance Raman spectroscopies, and density functional theory (DFT) bonding calculations revealed that 4 possesses an unusual asymmetric dithiolene chelate with significant thione-thiolate character. The results described here provide a detailed description of the reaction conditions that lead to the formation of 4. Data from cyclic voltammetry, additional DFT calculations, and several spectroscopic methods (IR, electronic absorption, resonance Raman, and electron paramagnetic resonance) have been used to characterize the properties of members in this suite of five Mo(S(2)BMOQO) complexes and further substantiate the highly electron-withdrawing character of the pyrrolo-S(2)BMOQO ligand in 2, 4, and 5. This study of the unique noninnocent ligand S(2)BMOQO provides examples of the roles that the N-heterocycle pterin can play as an essential part of the molybdenum cofactor. The versatile nature of a dithiolene appended by heterocycles may aid in modulating the redox processes of the molybdenum center during the course of enzyme catalysis.

Citing Articles

Advancing Our Understanding of Pyranopterin-Dithiolene Contributions to Moco Enzyme Catalysis.

Burgmayer S, Kirk M Molecules. 2023; 28(22).

PMID: 38005178 PMC: 10673323. DOI: 10.3390/molecules28227456.

Making Moco: A Personal History.

Burgmayer S Molecules. 2023; 28(21).

PMID: 37959716 PMC: 10649979. DOI: 10.3390/molecules28217296.

Protonation and Non-Innocent Ligand Behavior in Pyranopterin Dithiolene Molybdenum Complexes.

Gates C, Varnum H, Getty C, Loui N, Chen J, Kirk M Inorg Chem. 2022; 61(35):13728-13742.

PMID: 36000991 PMC: 10544801. DOI: 10.1021/acs.inorgchem.2c01234.

Resonance Raman spectroscopy of pyranopterin molybdenum enzymes.

Kirk M, Lepluart J, Yang J J Inorg Biochem. 2022; 235:111907.

PMID: 35932756 PMC: 10575615. DOI: 10.1016/j.jinorgbio.2022.111907.

Synthesis, Redox and Spectroscopic Properties of Pterin of Molybdenum Cofactors.

Colston K, Basu P Molecules. 2022; 27(10).

PMID: 35630801 PMC: 9146068. DOI: 10.3390/molecules27103324.

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