Two Exceptional Homoleptic Iron(IV) Tetraalkyl Complexes

Casitas, Alicia; Rees, Julian A.; Goddard, Richard; Bill, Eckhard; DeBeer, Serena; Fürstner, Alois

doi:10.1002/ange.201612299

Cited by 18 publications

(7 citation statements)

References 78 publications

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“…The detected organoferrate(IV) complexes presumably result from redox disproportionation reactions as well. Fürstner and co-workers had also suggested such an origin for the neutral tetraalkyliron species they had observed . In those cases, even sterically demanding adamantyl groups apparently participated in redox disproportionation reactions.…”

Section: Discussionmentioning

confidence: 85%

“…For R = p -F-C 6 H 4 , the mass spectrum showed the full series of Ph n Fe(III)R 4– n – complexes ( n = 0–4, Figure S33), whereas only ferrates containing mainly or exclusively the electron-poor aryl group R were detected for R = p -CF 3 -C 6 H 4 and p -CN-C 6 H 4 (Figures S34 and S35). In the case of R = p -CF 3 -C 6 H 4 , we also found Ph n Fe(IV)R 5– n – complexes ( n = 0 and 1), which represent rare examples of organoiron(IV) species …”

Section: Resultsmentioning

confidence: 99%

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Oxidation States, Stability, and Reactivity of Organoferrate Complexes

et al. 2018

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We have applied a combination of electrospray-ionization mass spectrometry, electrical conductivity measurements, and Mössbauer spectroscopy to identify and characterize the organoferrate species R Fe formed upon the transmetalation of iron precursors (Fe(acac), FeCl, FeCl, Fe(OAc)) with Grignard reagents RMgX (R = Me, Et, Bu, Hex, Oct, Dec, MeSiCH, Bn, Ph, Mes, 3,5-(CF)-CH; X = Cl, Br) in tetrahydrofuran. The observed organoferrates show a large variety in their aggregation (1 ≤ m ≤ 8) and oxidation states (I to IV), which are chiefly determined by the nature of their organyl groups R. In numerous cases, the addition of a bidentate amine or phosphine changes the distributions of organoferrates and affects their stability. Besides undergoing efficient intermolecular exchange processes, several of the probed organoferrates react with organyl (pseudo)halides R'X (R' = Et, Pr, Bu, Ph, p-Tol; X = Cl, Br, I, OTf) to afford heteroleptic complexes of the type RFeR'. Gas-phase fragmentation of most of these complexes results in reductive eliminations of the coupling products RR' (or, alternatively, of R). This finding indicates that iron-catalyzed cross-coupling reactions may proceed via such heteroleptic organoferrates RFeR' as intermediates. Gas-phase fragmentation of other organoferrate complexes leads to β-hydrogen eliminations, the loss of arenes, and the expulsion of organyl radicals. The operation of both one- and two-electron processes is consistent with previous observations and contributes to the formidable complexity of organoiron chemistry.

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Section: Discussionmentioning

confidence: 85%

Section: Resultsmentioning

confidence: 99%

Oxidation States, Stability, and Reactivity of Organoferrate Complexes

et al. 2018

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“…Indirect evidence suggests that alkoxide ligands render the disproportionation reaction of Mo(IV), leading to the formation of [Mo(O t Bu) 5 ], remarkably facile, even though [MoCl 4 (THF) 2 ] was also found to be intrinsically unstable toward decay into Mo(III) and Mo(V) in CH 2 Cl 2 solution at ambient temperature. The question whether the increased reaction rate in the presence of tert- butoxide has to do with the formation of the dinuclear complex [( t BuO) 3 Mo≡Mo(O t Bu) 3 ] as a particularly favorable low-valent product of the disproportionation process or if stabilization of [Mo(O t Bu) 5 ] itself by dispersive forces within the ligand sphere 58 , 59 plays any significant role will be the subject of future studies.…”

Section: Discussionmentioning

confidence: 99%

Isolation of a Homoleptic Non-oxo Mo(V) Alkoxide Complex: Synthesis, Structure, and Electronic Properties of Penta-tert-Butoxymolybdenum

et al. 2020

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Treatment of [MoCl 4 (THF) 2 ] with MO t Bu (M = Na, Li) does not result in simple metathetic ligand exchange but entails disproportionation with formation of the well-known dinuclear complex [( t BuO) 3 Mo≡Mo(O t Bu) 3 ] and a new paramagnetic compound, [Mo(O t Bu) 5 ]. This particular five-coordinate species is the first monomeric, homoleptic, all-oxygen-ligated but non-oxo 4d 1 Mo(V) complex known to date; as such, it proves that the dominance of the Mo=O group over (high-valent) molybdenum chemistry can be challenged. [Mo(O t Bu) 5 ] was characterized in detail by a combined experimental/computational approach using X-ray diffraction; UV/vis, MCD, IR, EPR, and NMR spectroscopy; and quantum chemistry. The recorded data confirm a Jahn–Teller distortion of the structure, as befitting a d 1 species, and show that the complex undergoes Berry pseudorotation. The alkoxide ligands render the disproportionation reaction, leading the formation of [Mo(O t Bu) 5 ] to be particularly facile, even though the parent complex [MoCl 4 (THF) 2 ] itself was also found to be intrinsically unstable; remarkably, this substrate converts into a crystalline material, in which the newly formed Mo(III) and Mo(V) products cohabitate the same unit cell.

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“…In this connection the thermochemical properties of molecules, the catalytic characteristics of large molecules, the stabilities of branched alkanes, and the π−π or σ−π attractions between hydrocarbon systems could be significantly modified by London dispersion effects. 18 The recent synthesis of Fe(cyclohexyl) 4 by Furstner and coworkers 19 having a structure with 24 β-hydrogen atoms demonstrates that stabilization by London dispersion effects can even override decomposition of homoleptic metal alkyls by β-hydrogen elimination.…”

Section: Introductionmentioning

confidence: 90%

Dispersion Effects in Stabilizing Organometallic Compounds: Tetra-1-norbornyl Derivatives of the First-Row Transition Metals as Exceptional Examples

Wan

et al. 2019

J. Phys. Chem. A

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In 1972 Bower and Tennett first synthesized a series of tetra-1-norbornyl derivatives, (nor) 4 M, of the first-row transition metals from titanium to cobalt. These were found to be exceptionally stable for homoleptic metal alkyls containing only metal−carbon σ-bonds. The theoretical energies for the dissociation of 1-norbornyl ligands from these unusually high oxidation state organometallics through the reactions (nor) 4 M → (nor) 3 M + nor • and (nor) 4 M → (nor) 2 M + nor-nor indicate that dispersion effects play an important role in determining their exceptional stability. Thus, all of the (nor) 4 M (M = Ti to Cu) derivatives are viable with respect to 1-norbornyl radical dissociation when the London dispersion effect is considered. However, (nor) 4 Cu becomes disfavored if the dispersion correction is ignored. Thus, the stability of the (nor) 4 M molecules is seen to arise from the favorable combination of steric and dispersion force effects of the four 1-norbornyl groups tetrahedrally disposed around the metal atom and maximizing the dispersion attraction between them in a spherical hydrocarbon structure with a central metal atom. The tri-1-norbornyl derivatives (nor) 3 M appear be disfavored with respect to disproportionation into (nor) 4 M + (nor) 2 M. This is consistent with the experimental syntheses of the (nor) 4 M (M = Cr to Co) derivatives with the metal in the +4 oxidation by reactions with 1norbornyllithium with metal halides in the +2 or +3 metal oxidation states. Both the OPBE method and the BPW91 method predict high-spin states for the d 2 and d 3 complexes (nor) 4 Cr and (nor) 4 Mn but low-spin states for (nor) 4 Fe and (nor) 4 Co, consistent with experiment.

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Two Exceptional Homoleptic Iron(IV) Tetraalkyl Complexes

Cited by 18 publications

References 78 publications

Oxidation States, Stability, and Reactivity of Organoferrate Complexes

Oxidation States, Stability, and Reactivity of Organoferrate Complexes

Isolation of a Homoleptic Non-oxo Mo(V) Alkoxide Complex: Synthesis, Structure, and Electronic Properties of Penta-tert-Butoxymolybdenum

Dispersion Effects in Stabilizing Organometallic Compounds: Tetra-1-norbornyl Derivatives of the First-Row Transition Metals as Exceptional Examples

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