Insertion reactions of isocyanides and nitriles into unsupported iron-aryl bonds: the synthesis of a dimeric iron(II) homoleptic iminoacyl complex

Klose, Alain; Solari, Euro; Ferguson, Richard; Floriani, Carlo; Chiesi‐Villa, Angiola; Rizzoli, Corrado

doi:10.1021/om00031a006

Cited by 37 publications

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“…We recently reported the synthesis of a hexaamine ligand scaffold, MeC(CH 2 NHPh-o-NH 2 ) 3 ( H LH 6 ), that readily binds three divalent metal ions within a proximal trigonal planar arrangement (e.g., ( H L)Fe 3 (PMe 2 R) 3 ). 18 The metal complexes are formed via a transamination reaction from an organometallic precursor (e.g., Fe 2 (Mes) 4 ; Mes = 2,4,6-Me 3 C 6 H 2 ), 20 wherein the two amine groups on each o-phenylenediamine arm of the ligand are both deprotonated to give the formally hexa-anionic ligand [ H L] 6À . Formation of the trinuclear complexes requires the presence of a strong σ-donating tertiary phosphine (e.g., PMe 2 R, R = Me, Ph) to bind each of the metal centers.…”

Section: Resultsmentioning

confidence: 99%

[(^HL)₂Fe₆(NCMe)_m]ⁿ⁺ (m = 0, 2, 4, 6; n = −1, 0, 1, 2, 3, 4, 6): An Electron-Transfer Series Featuring Octahedral Fe₆ Clusters Supported by a Hexaamide Ligand Platform

2011

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Using a trinucleating hexaamide ligand platform, the all-ferrous hexanuclear cluster ((H)L)(2)Fe(6) (1) is obtained from reaction of 3 equiv of Fe(2)(Mes)(4) (Mes = 2,4,6-Me(3)C(6)H(2)) with 2 equiv of the ligand ((H)L)H(6). Compound 1 was characterized by X-ray diffraction analysis, (57)Fe Mössbauer, SQUID magnetometry, mass spectrometry, and combustion analysis, providing evidence for an S=6 ground state and delocalized electronic structure. The cyclic voltammogram of [((H)L)(2)Fe(6)](n+) in acetonitrile reveals a rich redox chemistry, featuring five fully reversible redox events that span six oxidation states ([((H)L)(2)Fe(6)](n+), where n=-1→4) within a 1.3 V potential range. Accordingly, each of these species is readily accessed chemically to provide the electron-transfer series [((H)L)(2)Fe(6)(NCMe)(m)][PF(6)](n) (m=0, n=-1 (2); m=2, n=1 (3); m=4, n=2 (4); m=6, n=3 (5); m=6, n=4 (6)). Compounds 2-6 were isolated and characterized by X-ray diffraction, (57)Fe Mössbauer and multinuclear NMR spectroscopy, and combustion analysis. Two-electron oxidation of the tetracationic cluster in 6 by 2 equiv of [NO](+) generates the thermally unstable hexacationic cluster [((H)L)(2)Fe(6)(NCMe)(m)](6+), which is characterized by NMR and (57)Fe Mössbauer spectroscopy. Importantly, several stepwise systematic metrical changes accompany oxidation state changes to the [Fe(6)] core, namely trans ligation of solvent molecules and variation in Mössbauer spectra, spin ground state, and intracluster Fe-Fe separation. The observed metrical changes are rationalized by considering a qualitative, delocalized molecular orbital description, which provides a set of frontier orbitals populated by Fe 3d electrons.

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Section: Resultsmentioning

confidence: 99%

[(^HL)₂Fe₆(NCMe)_m]ⁿ⁺ (m = 0, 2, 4, 6; n = −1, 0, 1, 2, 3, 4, 6): An Electron-Transfer Series Featuring Octahedral Fe₆ Clusters Supported by a Hexaamide Ligand Platform

2011

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“…Fe 2 (Mes) 4 (Mes = 2,4,6-Me 3 C 6 H 2 ) was prepared by a modified version of a previously reported method (see the Supporting Information). 14 ( H L) 2 Fe 6 and its oxidized acetonitrile adducts [( H L) 2 Fe 6 (NCMe) m ][PF 6 ] n ( m = 4, n = 2 ( 1 ); m = 6, n = 3 ( 2 ); m = 6, n = 4 ( 3 )) were prepared according to the methodology previously reported by our laboratory. 11a All other reagents were purchased from commercial vendors and used without further purification.…”

Section: Methodsmentioning

confidence: 99%

Ligand Field Strength Mediates Electron Delocalization in Octahedral [(^HL)₂Fe₆(L′)_m]ⁿ⁺ Clusters

2015

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To assess the impact of terminal ligand binding on a variety of cluster properties (redox delocalization, ground-state stabilization, and breadth of redox state accessibility), we prepared three electron-transfer series based on the hexanuclear iron cluster [(HL)2Fe6(L′)m]n+ in which the terminal ligand field strength was modulated from weak to strong (L′ = DMF, MeCN, CN). The extent of intracore M–M interactions is gauged by M–M distances, spin ground state persistence, and preference for mixed-valence states as determined by electrochemical comproportionation constants. Coordination of DMF to the [(HL)2Fe6] core leads to weaker Fe–Fe interactions, as manifested by the observation of ground states populated only at lower temperatures (<100 K) and by the greater evidence of valence trapping within the mixed-valence states. Comproportionation constants determined electrochemically (Kc = 104–108) indicate that the redox series exhibits electronic delocalization (class II–III), yet no intervalence charge transfer (IVCT) bands are observable in the near-IR spectra. Ligation of the stronger σ donor acetonitrile results in stabilization of spin ground states to higher temperatures (~300 K) and a high degree of valence delocalization (Kc = 102– 108) with observable IVCT bands. Finally, the anionic cyanide-bound series reveals the highest degree of valence delocalization with the most intense IVCT bands (Kc = 1012–1020) and spin ground state population beyond room temperature. Across the series, at a given formal oxidation level, the capping ligand on the hexairon cluster dictates the overall properties of the aggregate, modulating the redox delocalization and the persistence of the intracore coupling of the metal sites.

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“…Diiron complexes offer a limited number of examples of isocyanide insertion despite the fact that CNR insertion into the Fe-C of mononuclear complexes is a known possibility, well investigated also in its mechanistic aspects [57,58]. Floriani et al reported on the reaction of the diiron complex [Fe 2 Mes 4 ] (Mes = 2,4,6-Me 3 C 6 H 2 ) with CN t Bu, in THF at 0 • C, leading to the formation of the bridging iminoacyl complex 7 as a result of isocyanide insertion into the Fe-aryl bond (Scheme 4) [59,60].…”

Section: Insertion Reactions Involving Isocyanides In Diiron Complexesmentioning

confidence: 99%

Bond Forming Reactions Involving Isocyanides at Diiron Complexes

et al. 2019

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The versatility of isocyanides (CNR) in organic chemistry has been tremendously enhanced by continuous advancement in transition metal catalysis. On the other hand, the urgent need for new and more sustainable synthetic strategies based on abundant and environmental-friendly metals are shifting the focus towards iron-assisted or iron-catalyzed reactions. Diiron complexes, taking advantage of peculiar activation modes and reaction profiles associated with multisite coordination, have the potential to compensate the lower activity of Fe compared to other transition metals, in order to activate CNR ligands. A number of reactions reported in the literature shows that diiron organometallic complexes can effectively assist and promote most of the “classic” isocyanide transformations, including CNR conversion into carbyne and carbene ligands, CNR insertion, and coupling reactions with other active molecular fragments in a cascade sequence. The aim is to evidence the potential offered by diiron coordination of isocyanides for the development of new and more sustainable synthetic strategies for the construction of complex molecular architectures.

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Insertion reactions of isocyanides and nitriles into unsupported iron-aryl bonds: the synthesis of a dimeric iron(II) homoleptic iminoacyl complex

Cited by 37 publications

References 0 publications

[(^HL)₂Fe₆(NCMe)_m]ⁿ⁺ (m = 0, 2, 4, 6; n = −1, 0, 1, 2, 3, 4, 6): An Electron-Transfer Series Featuring Octahedral Fe₆ Clusters Supported by a Hexaamide Ligand Platform

[(^HL)₂Fe₆(NCMe)_m]ⁿ⁺ (m = 0, 2, 4, 6; n = −1, 0, 1, 2, 3, 4, 6): An Electron-Transfer Series Featuring Octahedral Fe₆ Clusters Supported by a Hexaamide Ligand Platform

Ligand Field Strength Mediates Electron Delocalization in Octahedral [(^HL)₂Fe₆(L′)_m]ⁿ⁺ Clusters

Bond Forming Reactions Involving Isocyanides at Diiron Complexes

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Insertion reactions of isocyanides and nitriles into unsupported iron-aryl bonds: the synthesis of a dimeric iron(II) homoleptic iminoacyl complex

Cited by 37 publications

References 0 publications

[(HL)2Fe6(NCMe)m]n+ (m = 0, 2, 4, 6; n = −1, 0, 1, 2, 3, 4, 6): An Electron-Transfer Series Featuring Octahedral Fe6 Clusters Supported by a Hexaamide Ligand Platform

[(HL)2Fe6(NCMe)m]n+ (m = 0, 2, 4, 6; n = −1, 0, 1, 2, 3, 4, 6): An Electron-Transfer Series Featuring Octahedral Fe6 Clusters Supported by a Hexaamide Ligand Platform

Ligand Field Strength Mediates Electron Delocalization in Octahedral [(HL)2Fe6(L′)m]n+ Clusters

Bond Forming Reactions Involving Isocyanides at Diiron Complexes

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[(^HL)₂Fe₆(NCMe)_m]ⁿ⁺ (m = 0, 2, 4, 6; n = −1, 0, 1, 2, 3, 4, 6): An Electron-Transfer Series Featuring Octahedral Fe₆ Clusters Supported by a Hexaamide Ligand Platform

[(^HL)₂Fe₆(NCMe)_m]ⁿ⁺ (m = 0, 2, 4, 6; n = −1, 0, 1, 2, 3, 4, 6): An Electron-Transfer Series Featuring Octahedral Fe₆ Clusters Supported by a Hexaamide Ligand Platform

Ligand Field Strength Mediates Electron Delocalization in Octahedral [(^HL)₂Fe₆(L′)_m]ⁿ⁺ Clusters