Experimental determination of redox cooperativity and electronic structures in catalytically active Cu–Fe and Zn–Fe heterobimetallic complexes

Karunananda, Malkanthi K.; Vázquez, Francisco X.; Ercan, E.; Bi, Wenli; Chattopadhyay, Soma; Shibata, Tomohiro; Mankad, Neal P.

doi:10.1039/c4dt01841a

Cited by 45 publications

(40 citation statements)

References 69 publications

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“…This interpretation was further supported by IR spectroscopy. The energies associated with the CO stretching modes in 1 (1910, 1840 cm −1 ) and 2 (1930, 1851 cm −1 ) are rather similar to those reported for other formally Fe 0 species, such as Cu−Fe (1914, 1849 cm −1 ) and Zn−Fe bonded complexes (1944, 1888 cm −1 ), and much lower than those for Cp(CO) 2 Fe−I (2038, 1988 cm −1 ).…”

Section: Methodssupporting

confidence: 77%

Structure and Magnetization Dynamics of Dy−Fe and Dy−Ru Bonded Complexes

et al. 2018

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We present an investigation of isostructural complexes that feature unsupported direct bonds between a formally trivalent lanthanide ion (Dy3+) and either a first‐row (Fe) or a second‐row (Ru) transition metal (TM) ion. The sterically rigid, yet not too bulky ligand PyCp22− (PyCp22−=[2,6‐(CH2C5H3)2C5H3N]2−) facilitates the isolation and characterization of PyCp2Dy−FeCp(CO)2 (1; d(Dy–Fe)=2.884(2) Å) and PyCp2Dy−RuCp(CO)2 (2; d(Dy–Ru)=2.9508(5) Å). Computational and spectroscopic studies suggest strong TM→Dy bonding interactions. Both complexes exhibit field‐induced slow magnetic relaxation with effectively identical energy barriers to magnetization reversal. However, in going from Dy−Fe to Dy−Ru bonding, we observed faster magnetic relaxation at a given temperature and larger direct and Raman coefficients, which could be due to differences in the bonding and/or spin–phonon coupling contributions to magnetic relaxation.

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Section: Methodssupporting

confidence: 77%

Structure and Magnetization Dynamics of Dy−Fe and Dy−Ru Bonded Complexes

et al. 2018

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“…Consistent with the formally BOA process, the [Fp] fragment is oxidized during the reaction. As we have noted before, 66,68 within the [Fp] fragment the redox chemistry is dominated by the CO ligands (Table 4) and Cp ligand, and the natural charge on Fe is relatively constant (between q = −1.17 and −1.00) throughout the reaction pathway. Regarding the CH 3 Cl molecule undergoing BOA, there is essentially no change in natural charge residing on the [CH 3 ] unit.…”

Section: ■ Results and Discussionmentioning

confidence: 91%

“…Subsequent spectroscopic and computational analyses of the starting point and end point of this methyl iodide reaction revealed that the Cu and Fe centers participate to a surprisingly limited extent in the redox changes in the formally BOA process, whereas the redox noninnocent CO ligands within the Fp group bear a large portion of the redox changes. 68 However, no information about the pathway for alkyl halide activation was probed in that study. Before embarking on reaction kinetics analysis, we first sought to establish that the BOA process occurs by a two-electron pathway rather than by a pathway involving radical intermediates.…”

Section: ■ Results and Discussionmentioning

confidence: 98%

Experimental and Computational Characterization of the Transition State for C–X Bimetallic Oxidative Addition at a Cu–Fe Reaction Center

et al. 2015

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The heterobimetallic complex (IPr)Cu-Fp (IPr = N,N′-bis(2,6-diisopropylimidazol-2-ylidene, Fp = FeCp(CO) 2 ) was identified previously as a nonprecious metal catalyst for C− H borylation. To better understand the nature of the bimetallic reaction pathways operative in this system, we have conducted a thorough mechanistic study of alkyl halide activation by the Cu− Fe heterobimetallic reaction center. Use of cyclopropylmethyl halide substrates as radical clocks established that alkyl halide activation occurs by a two-electron mechanism for alkyl bromides and chlorides but not iodides. Eyring analysis of the activation of benzyl chloride allowed for experimental determination of activation parameters, including a large and negative entropy of activation (ΔS ⧧ = −36 eu). A Hammett study with parasubstituted benzyl chlorides revealed a reaction constant of ρ = 1.6, indicating accumulation of negative charge in the transition state on the alkyl halide carbon. The Ru analogue, (IPr)Cu-Rp (Rp = RuCp(CO) 2 ), was found to react approximately 17−25 times more slowly with selected benzyl chlorides than (IPr)Cu-Fp, indicating that the relative nucleophilicities of the free metal carbonyl anions are predictive of the relative reactivities of their heterobimetallic counterparts. Synthesis and characterization of the new Ag and Au analogues, (IPr)Ag-Fp and (IPr)Au-Fp, are reported along with the observation that these more covalent congeners are significantly less reactive toward alkyl halides. DFT calculations were used to model a transition state for the Cu− Fe reaction, which was identified as stereoinvertive at the alkyl halide carbon. NBO calculations indicate crucial roles played by the CO ligands within the Fp group: they both act as redox noninnocent ligands and also provide structural templating to stabilize the transition state as the metal−metal bond breaks. ■ INTRODUCTIONThe mechanisms of oxidative addition (OA) and reductive elimination (RE) at single metal sites have been subject to intense study, in part due to their versatility in a wide range of important catalytic transformations. Analogous reactions of higher nuclearity, for example bimetallic oxidative addition (BOA) and bimetallic reductive elimination (BRE) at binuclear sites, are comparatively underexplored mechanistically, as well as for catalytic applications. 1−4 While many studies on BOA and BRE mechanisms have been reported with precious metals, 5−48 which are also typically capable of conducting single-site OA/RE chemistry, BOA and BRE pathways become particularly intriguing when they feature earth-abundant firstrow transition metals not usually associated with single-site OA/RE independently. 49 Mechanistic studies on such bimetallic pathways are more limited in number. 50−62 Our group recently reported that the heterobimetallic complex (IPr)Cu-Fp (IPr = N,N′-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene, Fp = FeCp(CO) 2 ) is a catalyst for the C−H borylation of arenes, 63 a reaction more typically conducted using single-site OA/RE cycling by Ir...

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“…[a] Entry Catalyst 1 st run After chronoamperometry [b] After chronopotentiometry [c] J280 (mA/cm 2 ) η10 (mV) J280 (mA/cm 2 ) η10 (mV) J280 (mA/cm 2 ) η10 (mV) the extraordinary WOC developed by Nature, that is the cuboidal Oxygen Evolving Complex, where a redox-inhert calcium ion has a key role in determining the activity of the manganese active sites. 85 Examples of cooperativity between Zn centers and other transition metals have been reported for some oxidation catalysts, 84,87 although further systematic studies would be necessary to draw definitive conclusions on the relationship between composition and catalytic properties of M-LDHs.…”

Section: Chronoamperometric and Chronopotentiometric Studiesmentioning

confidence: 99%