Oxygen Atom Transfer Reactions with Molybdenum Cofactor Model Complexes That Contain a Tetradentate OSSO-Type Bis(phenolato) Ligand

Abstract

The catalytic activity of molybdenum complexes in oxidation state +IV, +V, and +VI stabilized by a tetradentate dithiaalkanediyl-2,2′-bis(phenolato) (OSSO)-type ligand was tested in the oxygen atom transfer (OAT) reaction from DMSO to PPh 3 . The molybdenum(IV) complexes [(OSSO)MoCl 2 ] (1a, b) were prepared from [MoCl 4 (NCMe) 2 ] and the corresponding bis(phenol) (OSSO)H 2 . The molybdenum(V) complexes [(OSSO)MoOCl] (2a, b) were obtained by salt metathesis either from MoOCl 4 or from MoOCl 3 with the corresponding bis(phenolate) salts [(OSSO)M 2 ] (M = Li, K). The reaction with MoOCl 4 proceeds via the intermediate [(OSSO)MoOCl 2 ] (A), which disproportionates into 2 and insoluble oligomers. Single crystal X-ray diffraction of 1a and 2b revealed octahedral cis-α-coordination of the metal center. EPR spectra of 2a and 2b show the characteristic signal of a molybdenum d 1 -spin system which is not coupled to the ligand. OAT reactions in the presence of 1−2 or of the bis(oxo) complex [(OSSO)MoO 2 ] (3) revealed that the molybdenum(IV) complex 1b exerts the high catalytic activity with complete conversion of PPh 3 to OPPh 3 within 30 min at 60 °C. The high catalytic activity of 1 compared to that of 2−3 is explained by the formation of the unstable intermediate A, which decomposes to 2 in the absence of PPh 3 .

Polar and nonpolar iron (II) complexes of isatin hydrazone derivatives as effective catalysts in oxidation reactions and their antimicrobial and anticancer activities

“…[ 44,63 ] The increase of the coordination number of Fe 2+ ion within the attached oxygen in C could promote its reactivity, which discussed and reported previously for Fe 2+ and MoO 2 2+ ‐species in the catalytic processes. [ 62,64 ] Within an oxygen transfer step for both Fe‐catalyst intermediates, the final product (RO) was extracted with the recyclability of the first intermediate (A). [ 51 ]…”

“…[44,63] The increase of the coordination number of Fe 2+ ion within the attached oxygen in C could promote its reactivity, which discussed and reported previously for Fe 2+ and MoO 2 2+ -species in the catalytic processes. [62,64] Within an oxygen transfer step…”

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

“…This means that researchers can establish new functional analogues by freely exploiting the huge variety of available chemical building blocks. The use of the dithiolene moiety is, hence, not a necessity, and bidentate [13][14][15][16][17][18], tridentate [19][20][21], or tetradentate [22][23][24] ligands with a mixture of oxygen, nitrogen, and sulfur coordination sites were introduced to replace the natural ligand system in functional analogues. Alter-natively, the metal ion may also be varied.…”

“…The molybdenum center can, for instance, be substituted by rhenium, due to the diagonal relationship between these two metals leading to an additional class of efficient OAT reagents [25][26][27][28][29]. Commonly, the examination of OAT reactivity includes natural and non-natural oxygen acceptors (organic phosphines, sulfite, selenite, arsenite) and oxygen donors (N-oxides, S-oxides), which still represent well-established, state-of-the-art approaches towards modelling either individual half reactions or entire OAT-only catalytic cycles when they are combined [21][22][23]27,[30][31][32][33][34]. This means that a reduced substrate and an oxidized substrate are mixed with the functional model complex, which is taking the oxygen atom from one substrate and delivering it to the other without passing through any PCET.…”

“…Additionally, trans-[MoO 2 (L10O)Cl] and cis-[MoO 2 (L3S)Cl] were catalytically active in DMF/d 6 -DMSO (1:1) with excess PPh 3 [19]. Besides the historically important scorpionate complexes, several other catalytic systems were shown to facilitate full OAT cycles while employing a broad range of ligands (Figure 11) [15,[20][21][22][23]108,109]. With the standard OAT benchmark catalysis introduced by Holm (vide supra), with S-oxides and PPh3 as substrates and with catalysts having specific modifications, the roles of metal centers (Mo vs. W) of donor atoms, and even of backbone substitution (second and outer coordination spheres) may be elucidated.…”