Microscopic Reactivity of Phenylferrate Ions toward Organyl Halides

Abstract

Despite its practical importance, organoiron chemistry remains poorly understood due to its mechanistic complexity. Here, we focus on the oxidative addition of organyl halides to phenylferrate anions in the gas phase. By mass-selecting individual phenylferrate anions, we can determine the effect of the oxidation state, the ligation, and the nuclearity of the iron complex on its reactions with a series of organyl halides RX. We find that Ph 2 Fe(I) À and other lowvalent ferrates are more reactive than Ph 3 Fe(II) À ; Ph 4 Fe(III) À is inert. The coordination of a PPh 3 ligand or the presence of a second iron center lower the reactivity. Besides direct crosscoupling reactions resulting in the formation of RPh, we also observe the abstraction of halogen atoms. This reaction channel shows the readiness of organoiron species to undergo radical-type processes. Complementary DFT calculations afford further insight and rationalize the high reactivity of the Ph 2 Fe(I) À complex by the exothermicity of the oxidative addition and the low barriers associated with this reaction step. At the same time, they point to the importance of changes of the spin state in the reactions of Ph 3 Fe(II) À .

Observation and Characterization of Single Elementary Reactions of Organometallics

“…Similar to the case of the Pd(0) complexes, the reactivity of phenylferrate ions Ph n Fe – , n = 2–4, and Ph 2 Fe(PPh 3 ) − toward organyl iodides RI decreased for the coordinatively more saturated species . Kinetic measurements with a customized quadrupole-ion trap furnished absolute bimolecular rate constants.…”

“…Similar to the case of the Pd(0) complexes, the reactivity of phenylferrate ions Ph n Fe − , n = 2−4, and Ph 2 Fe(PPh 3 ) − toward organyl iodides RI decreased for the coordinatively more saturated species. 58 Kinetic measurements with a customized quadrupole-ion trap furnished absolute bimolecular rate constants. Ph 2 Fe − reacted with all organyl iodides investigated and showed two different reaction channels: the direct transfer of an iodine atom to the iron center and the formal exchange of one phenyl group of the ferrate complex for an iodine atom (Scheme 12).…”

“…Quantum chemical calculations supported this interpretation and moreover suggested that the competing iodine-transfer channel can proceed from two different branching points (Scheme 12). 58 Tandem-mass spectrometry has also been used to examine the elementary step of reductive elimination. The analysis of this unimolecular reaction is particularly straightforward because it does not require the infusion of neutral substrate gases into the mass spectrometer and can be directly performed with commercial instruments suitable for gas-phase fragmentation experiments.…”

Electrospray-Ionization Mass Spectrometry for the Analysis and Quantification of Carbanions

“…Complexes containing, for example, the very basic Me − and Ph − can be detected by ESI-MS, whereas the free anions cannot. 98 This has been made use of for the in-situ monitoring of a Co(I)-based coordination polymerization of isoprene. The unique advantages of ESI-MS enabled the investigation of the active species and the discovery of a reversible propagation mechanism that might go unnoticed when relying on snapshots of the reaction products instead.…”

“…78 Complexation by transition metals can increase the stability instead. 98 Radical anions are encountered less often during synthetic chemistry when compared to carbanions. The possibility of spontaneous electron detachment is present whenever the EA of a neutral species is negative or only slightly positive.…”