Unexpected Reaction Promoted by NH+···O=Mo Hydrogen Bonds in Nonpolar Solvents

Okamura, Taka‐aki; Yamada, T.; Hasenaka, Yuki; Onitsuka, Kiyotaka

doi:10.1002/ejic.201600081

Cited by 7 publications

(9 citation statements)

References 60 publications

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“…Bulky ligands are useful in bioinorganic chemistry to realize the active site and hydrophobic environment of metalloenzymes. We recently developed novel ligands containing bulky hydrophobic acylamino groups ((4- t -BuC 6 H 4 ) 3 CCONH = Ar 3 CCONH) and synthesized model compounds of enzymes. − These compounds formed intramolecular NH···X (X = O, S) hydrogen bonds and exhibited good solubility in nonpolar solvents, e.g., toluene, thus elucidating the regulating mechanism of the activity at the active site of enzymes.…”

Section: Introductionsupporting

confidence: 90%

Snapshot of Oxidation of Thiolate by Diiodine: Stabilization of Intermediate by NH···S Hydrogen Bonds

et al. 2017

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Ordinary thiolate (RS) reacts with diiodine (I) to afford an intermediate sulfenyl iodide (RSI) by releasing I; RSI is readily converted to disulfide (RSSR) by a disproportionation reaction. In the case of thiolate ArS containing very bulky acylamino groups forming NH···S hydrogen bonds, the crystal of the intermediate, [ArS-I-I], was obtained under usual conditions, and the structure was determined by X-ray diffraction analysis. The results show that the intramolecular NH···S hydrogen bonds stabilized the intermediate [ArS-I-I], consistent with theoretical calculations.

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Section: Introductionsupporting

confidence: 90%

Snapshot of Oxidation of Thiolate by Diiodine: Stabilization of Intermediate by NH···S Hydrogen Bonds

et al. 2017

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“…The dimerization may benefit from the presence of ester and hydroxyl functions on the dithiolene which constitute excellent functionalities for hydrogen bonding, which potentially results in close proximity of the catalytic centers even in solution. Previously, the presence of hydrogen bonding potential, in particular for intramolecular hydrogen bonding was perceived to be beneficial for catalysis (Oku et al, 1997; Okamura et al, 2016a,b). However, in this case it appears to be rather detrimental.…”

Section: Results and Discusionmentioning

confidence: 99%

An Asymmetrically Substituted Aliphatic Bis-Dithiolene Mono-Oxido Molybdenum(IV) Complex With Ester and Alcohol Functions as Structural and Functional Active Site Model of Molybdoenzymes

et al. 2019

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A Mo IV 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 13 C-NMR data support the rationale that by asymmetric substitution the electronic structure of the ene-dithio moiety can be fine-tuned. The Mo IV O bis-dithiolene complex was obtained by in situ reaction of the de-protected ligand with the metal precursor complex trans -[MoO 2 (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 31 P 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 Mo IV O and Mo VI O 2 and the unreactive dimeric M O 3 species.

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Section: Introductionmentioning

confidence: 99%

“…In addition to involvement of protons in CEPT and removals of tightly bound terminal oxo ligands, contributions of hydrogen-bonding interactions to structures and properties of molybdenum-oxo and analogous complexes were also demonstrated in model systems [38–50]. In a few cases, such interactions were capable of directly facilitating OAT reactions mediated by molybdenum compounds [40, 42, 44, 47, 50]. For example, pyridinium (HPyr + ) cation was previously found to be hydrogen-bonded to the Mo=O moiety of [HPyr] 2 [Mo IV O(mnt) 2 ] complex [42], which lengthens the Mo=O bond by 0.04 Ǻ. Interestingly, [HPyr] 2 [Mo IV O(mnt) 2 ] complex was more reactive towards oxidation by trimethylamine N-oxide, compared to [NEt 4 ] 2 [Mo IV O(mnt) 2 ] complex [42].…”

Section: Introductionmentioning

confidence: 99%

“…For example, pyridinium (HPyr + ) cation was previously found to be hydrogen-bonded to the Mo=O moiety of [HPyr] 2 [Mo IV O(mnt) 2 ] complex [42], which lengthens the Mo=O bond by 0.04 Ǻ. Interestingly, [HPyr] 2 [Mo IV O(mnt) 2 ] complex was more reactive towards oxidation by trimethylamine N-oxide, compared to [NEt 4 ] 2 [Mo IV O(mnt) 2 ] complex [42]. Unfortunately, most of these examples exhibited a meager rate enhancement of less than 10-fold [40, 44, 47, 50]. In addition, detailed mechanistic evaluations of these systems have not been carried out to pinpoint which elementary step(s) of OAT reactions is/are accelerated by acids or hydrogen-bonding interactions.…”

Section: Introductionmentioning

confidence: 99%

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Acid-facilitated product release from a Mo(IV) center: relevance to oxygen atom transfer reactivity of molybdenum oxotransferases

Talipov

Dong

et al. 2017

J Biol Inorg Chem

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We report that pyridinium ions (HPyr) accelerate the conversion of [Tp*MoOCl(OPMe)] (1) to [Tp*MoOCl(NCCH)] (2) by 10-fold, affording 2 in near-quantitative yield; Tp* = hydrotris(3,5-dimethyl-1-pyrazolyl)borate. This novel reactivity and the mechanism of this reaction were investigated in detail. The formation of 2 followed pseudo-first-order kinetics, with the observed pseudo-first-order rate constant (k ) linearly correlated with [HPyr]. An Eyring plot revealed that this HPyr-facilitated reaction has a small positive value of ∆S indicative of a dissociative interchange (I) mechanism, different from the slower associative interchange (I) mechanism in the absence of HPyr marked with a negative ∆S . Interestingly, log(k) was found to be linearly correlated to the acidity of substituted pyridinium ions. This novel reactivity is further investigated using combined DFT and ab initio coupled cluster methods. Different reaction pathways, including I, I, and possible alternative routes in the absence or presence of HPyr, were considered, and enthalpy and free energies were calculated for each pathway. Our computational results further underscored that the I route is energetically favored in the presence of HPyr, in contrast with the preferred I-NNO pathway in the absence of HPyr. Our computational results also revealed molecular-level details for the HPyr-facilitated I route. Specifically, HPyr initially becomes hydrogen-bonded to the oxygen atom of the Mo(IV)-OPMe moiety, which lowers the activation barrier for the Mo-OPMe bond cleavage in a rate-limiting step to dissociate the OPMe product. The implications of our results were discussed in the context of molybdoenzymes, particularly the reductive half-reaction of sulfite oxidase.

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Unexpected Reaction Promoted by NH+···O=Mo Hydrogen Bonds in Nonpolar Solvents

Cited by 7 publications

References 60 publications

Snapshot of Oxidation of Thiolate by Diiodine: Stabilization of Intermediate by NH···S Hydrogen Bonds

Snapshot of Oxidation of Thiolate by Diiodine: Stabilization of Intermediate by NH···S Hydrogen Bonds

An Asymmetrically Substituted Aliphatic Bis-Dithiolene Mono-Oxido Molybdenum(IV) Complex With Ester and Alcohol Functions as Structural and Functional Active Site Model of Molybdoenzymes

Acid-facilitated product release from a Mo(IV) center: relevance to oxygen atom transfer reactivity of molybdenum oxotransferases

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