Dioxo-Molybdenum(VI) and Mono-oxo-Molybdenum(IV) Complexes Supported by New Aliphatic Dithiolene Ligands:  New Models with Weakened MoO Bond Characters for the Arsenite Oxidase Active Site

Abstract

The cis-dioxo-molybdenum(VI) complexes, [MoO2(L(H))2]2- (1b), [MoO2(L(S))(2)]2- (2b), and [MoO2(L(O))2]2- (3b) (L(H) = cyclohexene-1,2-dithiolate, L(S) = 2,3-dihydro-2H-thiopyran-4,5-dithiolate, and L(O) = 2,3-dihydro-2H-pyran-4,5-dithiolate), with new aliphatic dithiolene ligands were prepared and investigated by infrared (IR) and UV-vis spectroscopic and electrochemical methods. The mono-oxo-molybdenum(IV) complexes, [MoO(L(H))2]2- (1a), [MoO(L(S))2]2- (2a), and [MoO(L(O))2]2- (3a), were further characterized by X-ray crystal structural determinations. The IR and resonance Raman spectroscopic studies suggested that these cis-dioxo molybdenum(VI) complexes (1b-3b) had weaker Mo=O bonds than the common Mo(VI)O2 complexes. Complexes 1b-3b also exhibited strong absorption bands in the visible regions assigned as charge-transfer bands from the dithiolene ligands to the cis-MoO2 cores. Because the oxygen atoms of the cis-Mo(VI)O2 cores are relatively nucleophilic, these complexes were unstable in protic solvents and protonation might occur to produce Mo(VI)O(OH), as observed with the oxidized state of arsenite oxidase.

Syntheses and properties of a new series of tetrathiafulvalene derivatives incorporating fused ethyleneoxymethylene and ethylenethiomethylene units, and their charge–transfer complexes

“…2.5. Synthesis of donors 6,7-Dihydro-4H-1, 3-dithiolo[4,5-c]pyran-2-one [10 (X = O)] and 6,7-dihydro-4H-1, 3-dithiolo[4,5-c]thiopyran-2-one [11 (X = S)] were prepared according to the literature [5]. Compound 10 (X = O) could be easily recrystallized from ethanol and further purified by sublimation at 100 C in vacuum (10 À2 Torr), and then characterized by 1 H and 13 Donor 4 was synthesized by a cross-coupling reaction as follows.…”

“…In this work, we have synthesized new TTF derivatives 1-9 (Graphical abstract) containing one oxygen or one sulfur atom in the six-membered ring. 1,3-Dithiole derivatives containing EOM and ETM, 10 (X = O) and 11 (X = S) (Scheme 1), have been reported in the literature [5] in which 10 (X = O) was described as being too insoluble to be measured by 1 H NMR spectra. However, we were able to characterize it by both 1 H and 13 C NMR spectroscopy.…”

Molybdenum and Tungsten Oxidoreductase Models

“…Later, the Sugimoto group was able to synthesise and structurally characterise a smaller pyrandi-thiolene molybdenum model complex ( Figure 3b) and could show that there were differences between this and related complexes, in which the oxygen was substituted by carbon or sulfur, with respect to spectroscopic and electrochemical properties, again supporting an electronic finetuning of the active-site metal by such a ligand system. [13] General difficulties in modelling mpt-bound molybdenum and tungsten are firstly the complicated and so far not achieved synthesis of a ligand containing really all features of mpt and the instability of the free natural cofactor, indicating that this will also be a problem with a synthetic cofactor addressing every functional group of mpt. Accordingly, our next step in this respect was primarily of a theoretical nature aimed at ascertaining what really needs to be mimicked in order to produce a mpt model that is the most economic to synthesise but the most accurate with respect to the electronic and geometric properties of the molecules.…”

New bis(pyranodithiolene) tungsten(IV) and (VI) complexes as chemical analogues of the active sites of tungsten enzymes

“…Recently, we have synthesized 5-coordinate Mo IV O and 6-coordinate Mo VI O 2 complexes of pyranodithiolene and crystallographically characterized the former complex, (Et 4 N) 2 [Mo IV O(pyranodithiolene) 2 ] [11]. On the other hand, Garner and Joule's group has reported di-cobalt complex of pyrano-tetrahydroquinoxaline dithiolene [12].…”

“…1 shows the crystal structure of 1a. 1a is isomorphous with (Et 4 N) 2 [Mo IV O(L 0 ) 2 ] [11]. The tungsten center is coordinated with one terminal oxo and four sulfur atoms from the two pyranodithiolenes, L 0 , and adopts a squarepyramidal structure.…”