Alkyl Radical Generation by an Intramolecular Homolytic Substitution Reaction between Iron(II) and Trialkylsulfonium Groups

Abstract

Intramolecular, homolytic substitution reactions between iron(II) species and various trialkylsulfonium groups were directly observed in the gas phase upon collision-induced dissociation. In spite of the notoriously low reduction potential of trialkylsulfonium species and the mismatched oxidation potential of iron(II), the reactions proceed at moderate collision energies, forming an alkyl radical as well as a thioether coordinated to the iron. In contrast to classical homolytic substitutions, the attacking radical is a "metalloradical", namely iron(II) that is oxidized to iron(III) during the reaction. With this process we demonstrate that the conceptually analogous, putative radical generation step in radical S-adenosyl methionine (SAM) enzymes is possible and plausible. Further, we show that this kind of reaction only occurs in constrained systems with a defined geometry. Combining experimental measurements with DFT studies and NBO analyses allowed us to gain insights into the reactivity and transition states of these systems. Based on our findings, we challenge the notion of a collinear transition state in the radical generation step of radical SAM enzymes and propose it to be bent instead.

Synthesis, Spectroscopic, and Structural Characterization of Organyl Disulfanides and a Tetrasulfanide

“…During our studies on homolytic substitution reactions in sulfonium groups, we stumbled upon a perthiolate species, namely, [PPh 4 ]­[PhS 2 ], as a reaction side product, inspiring the search for a clean synthesis and isolation of such compounds. Stirring of sodium thiophenolate with 1 equiv of tetraphenylphosphonium chloride and 1 equiv of elemental sulfur in acetonitrile (MeCN) for a few hours at room temperature (r.t.) under inert atmosphere formed a dark green solution.…”

“…During our studies on homolytic substitution reactions in sulfonium groups, 24 we stumbled upon a perthiolate species, namely, [PPh 4 ][PhS 2 ], as a reaction side product, inspiring the search for a clean synthesis and isolation of such compounds.…”

Synthesis, Isolation, and Characterization of a Phenylsulfane-Selenolate Compound

“…ESI-MS studies were conducted on a Thermo Finnigan TSQ Quantum instrument with a flow rate of 5 μL min –1 . The measurements were conducted at spray voltages from -3000 to -4000 V at a capillary temperature of 473 K. Argon was used as the collision gas in collision-induced dissociation (CID) experiments at a pressure of 0.1 mTorr …”

“…The measurements were conducted at spray voltages from -3000 to -4000 V at a capillary temperature of 473 K. Argon was used as the collision gas in collision-induced dissociation (CID) experiments at a pressure of 0.1 mTorr. 25 Computational Details. Full DFT studies were performed using the Gaussian 09d1 program.…”

Iron(II) and Copper(I) Control the Total Regioselectivity in the Hydrobromination of Alkenes

“…With these results in hand, we focused on the idea of reversing the reaction pathway toward the exclusive formation of the corresponding Markovnikov product. The existence of a putative amount of metalloradicals containing iron­(II), which are able to modulate the reactivity of S -adenosyl methionine systems, showed us that the presence of iron­(II) would act as a modulator in the outcome of the reaction. Moreover, iron­(II) catalysts are present in a wide number of radical processes, − making them an attractive alternative for modifying radical processes without altering their nature.…”