DFT Study of the Reaction of a Two-Coordinate Iron(II) Dialkyl Complex with Molecular Oxygen

Abstract

DFT studies are reported of a monomeric iron dialkyl for which oxygen atom insertion into metal-methyl bonds occurs with O2: FeMe2 + O2 → Fe(OMe)2. Computation of the reaction coordinate implicates the intermediacy of Fe(III)-peroxo, Fe(VI)-dioxo, and Fe(IV)-oxo intermediates, connected by O2 oxidative addition and two methyl migration steps. Analysis of the reaction of O2 with d(6)-Fe(Me)2 indicates that oxy-insertion for this iron complex occurs with lower free energy barriers than competing homolytic/radical pathways, exploiting "spin-flip" processes via minimum energy crossing points (MECPs).

Solution and Gas‐Phase Reactivity of Me12Fe8− and Related Cluster Ions

“…Neidig and co‐workers had also noted the high sensitivity of Me 12 Fe 8 − toward air. Although the structure of [Fe 8 ,Me 12 ,O 2 ] − is unknown, the incorporation of highly electronegative oxygen atoms into the cluster is likely to stabilize its negative charge. Thus, [Fe 8 ,Me 12 ,O 2 ] − presumably has a particularly high ESI activity, which implies that even very small amounts of this species should give rise to a notable signal intensity.…”

“…Furthermore, the clusteri ons Me 13 Fe 8 À and [Fe 8 ,Me 12 ,O 2 ] À (Supporting Information, Figure S2) were detectedi nc onsiderably lower signal intensities. The observation of the former indicates that Me 12 Fe 8 À is not the only cluster ion produced from transmetalation under typical reaction conditions of ironcatalyzed cross-coupling.T he oxygen-containing species [Fe 8 ,Me 12 ,O 2 ] À presumably resulted from the reactiono f Me 12 Fe 8 À with traces of dioxygen present in the sample solution or the mass spectrometer.N eidig and co-workers had also noted the high sensitivity of Me 12 Fe 8 À towarda ir.A lthough the structure of [Fe 8 ,Me 12 ,O 2 ] À is unknown, [12] the incorporation of highly electronegative oxygen atoms into the clusteri sl ikely to stabilize its negative charge. Thus, [Fe 8 ,Me 12 ,O 2 ] À presumably has ap articularly high ESI activity,w hich implies that even very small amountso ft his species should give rise to an otable signal intensity.…”

“…The base peak of the obtained negative-ion mode ESI mass spectrum indeed showedt he expectedm ass shift of 36 uand could thus be unambiguously identified as (CD 3 ) 12 Fe 8 À (Supporting Information, Figures S10 and S11). Furthermore, the mononuclear complexes (CD 3 ) 3 Fe À and (CD 3 ) 4 Fe À as well as the cluster ion [Fe 8 ,(CD 3 ) 12 ,O 2 ] À (Supporting Information, Figure S12) were observed.…”

“…[5] Notwithstanding these discrepancies, the discussion focused almost completely on mononuclear complexes before Neidig and coworkers very recently proposed the involvement of small iron clusters as a" new paradigm …i nt his chemistry". [6] Studying the reactionso fF e III salts with MeMgBri nt etrahydrofuran (THF), these authors isolated and structurally characterized the unprecedented ionic cluster compound [MgCl(THF) 5 ] + [Me 12 Fe 8 ] À (Figure 1). [6,7] Spectroscopic investigations provided strong evidencet hat the Me 12 Fe 8 À cluster ion, thoughb eing highly thermolabile and air-sensitive, remained intact in solution.…”

Self-assembly of an Organometallic Fe9O6 Cluster from Aerobic Oxidation of (tmeda)Fe(CH2tBu)2

“…For iron-specific systems, Power has shown that Fe-aryl complexes exhibit formal O=O scission and O-atom insertion into M-Caryl bonds. 38,39 In an extensive DFT study on the related O2 reaction with the twocoordinate compound FeMe2, 40 Cundari reported that the O-atom insertion is calculated to proceed via initial formation of open-shell Fe III -(O2 -) species and eventual generation of dioxo intermediates (as seen in Cr oxidation chemistry reported by Theopold) 41 prior to O-atom insertion into the Fe-C bonds. Additionally, Chirik has shown that ferrous dialkyls are susceptible to Fe-C homolysis upon addition of π-acidic redox-active ligands, 42 suggesting that coordination of O2 could lead to the generation of free alkyl radicals.…”