Fe4 Cluster and a Buckled Macrocycle Complex from the Reduction of [(dmgBF2)2Fe(L)2] (L = MeCN, tBuiNC)

Rose, Michael J.; Winkler, Jay R.; Gray, Harry B.

doi:10.1021/ic202253v

Cited by 6 publications

(7 citation statements)

References 29 publications

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“… a Values given in Volts vs Fc + /Fc in acetonitrile. Values in parentheses are experimental from ref (shifted from SCE with −0.38 V) for Fe and ref for Ni. b Protonation occurs at the O–H–O bridge. c E 1/2 (M II/I ) for complexes 5-Fe and 1-Ni in acetonitrile were the references for Fe and Ni complexes, respectively, and agree with experiment by construction. d Experimental value is E p (Ni II/I ) with three equivalents of p -cyanoanilinium …”

Section: Results and Discussionmentioning

confidence: 99%

“…Optimizations were performed with two axial solvent ligands for Co II and Fe II , one solvent ligand for Co I , Fe I , and Co III H, and no solvent ligands for Ni II and Ni I . These choices were based on the experimental crystal structures ,,, and by optimizations of each complex with varying numbers of solvent ligands to determine how many ligands could be bound in stable configurations. Additional computational details are provided in the Supporting Information.…”

Section: Methodsmentioning

confidence: 99%

“…Cobalt diglyoxime catalysts evolve hydrogen in protic solutions both photochemically and electrochemically at modest overpotentials. − While Co(dmgH) 2 (dmg = dimethylglyoxime) has been shown to degrade in acidic solutions, Co(dmgBF 2 ) 2 is much more acid resistant and has been studied extensively. − Increased stability in acidic solutions can also be achieved by replacing one or both O–H–O bridges of Co(dmgH) 2 with propane, forming the diimine-dioxime complex Co(DO)(DOH)pn or Co(TIM), respectively [(DOH)(DOH)pn = N 2 ,N 2′ -propanediylbis(2,3-butanedione-2-imine-3-oxime) and TIM = 2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene]. In addition to cobalt complexes, nickel and iron H 2 evolution catalysts have also been studied. − …”

Section: Introductionmentioning

confidence: 99%

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Effects of Ligand Modification and Protonation on Metal Oxime Hydrogen Evolution Electrocatalysts

Solis

Hammes‐Schiffer

2013

Inorg. Chem.

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The design of hydrogen-evolving electrocatalysts that operate at modest overpotentials is important for solar energy devices. The M(II/I) reduction potential for metal diimine-dioxime and diglyoxime electrocatalysts is often related to the overpotential required for hydrogen evolution. Herein the impact of ligand modification and protonation on the M(II/I) reduction potentials for cobalt, nickel, and iron diimine-dioxime and diglyoxime complexes is investigated with computational methods. The calculations are consistent with experimental data available for some of these complexes and additionally provide predictions for complexes that have not yet been synthesized. The calculated pKa's imply that ligand protonation is likely to occur at the O-H-O bridge but not at other ligand sites for these complexes. Moreover, the calculations imply that a ligand-protonated Co(III)-hydride intermediate is formed along the H2 production pathway for catalysts containing an O-H-O bridge in the presence of sufficiently strong acid. The calculated M(II/I) reduction potentials indicate that the anodic shift due to protonation of the O-H-O bridge is greater than that due to replacing the O-H-O bridge with an O-BF2-O bridge for cobalt and nickel but not for iron complexes. Experiments suggest degradation for complexes with two O-H-O bridges and alternative mechanisms for certain iron complexes with two O-BF2-O bridges. Asymmetric cobalt, nickel, and strongly electron withdrawing substituted iron diimine-dioxime and diglyoxime complexes containing a single O-H-O bridge are proposed to be effective hydrogen evolution electrocatalysts with relatively low overpotentials in acetonitrile and water. These insights are important for the design of efficient aqueous-based hydrogen-evolving catalysts.

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Section: Results and Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effects of Ligand Modification and Protonation on Metal Oxime Hydrogen Evolution Electrocatalysts

Solis

Hammes‐Schiffer

2013

Inorg. Chem.

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“…Thus, these studies suggest that asymmetric cobaloxime complexes containing a single O–H–O bridge may be effective H 2 evolution electrocatalysts with relatively low overpotentials. These experimental and theoretical studies were performed in both water and acetonitrile, and metal oximes with nickel and iron centers were also investigated. ,,− Overall, these calculations provide insight into the relative effects of ligand modification and protonation, as well as metal substitutions, in two different solvents. Such insights are useful for the design of more effective catalysts for H 2 production.…”

Section: Cobaloximes For H2 Productionmentioning

confidence: 99%

Proton-Coupled Electron Transfer in Molecular Electrocatalysis: Theoretical Methods and Design Principles

2014

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Molecular electrocatalysts play an essential role in a wide range of energy conversion processes. The objective of electrocatalyst design is to maximize the turnover frequency and minimize the overpotential for the overall catalytic cycle. Typically, the catalytic cycle is dominated by key proton-coupled electron transfer (PCET) processes comprised of sequential or concerted electron and proton transfer steps. Theoretical methods have been developed to investigate the mechanisms, thermodynamics, and kinetics of PCET processes in electrocatalytic cycles. Electronic structure methods can be used to calculate the reduction potentials and pKa's and to generate thermodynamic schemes, free energy reaction pathways, and Pourbaix diagrams, which indicate the most stable species under certain conditions. These types of calculations have assisted in identifying the thermodynamically favorable mechanisms under specified experimental conditions, such as acid strength and overpotential. Such calculations have also revealed linear correlations among the thermodynamic properties, which can be used to predict the impact of modifying the ligands, substituents, or metal centers. The thermodynamic properties can be tuned with electron-withdrawing or electron-donating substituents. Ligand modification can exploit the role of noninnocent ligands. For example, ligand protonation typically decreases the overpotential. Calculations of rate constants for electron and proton transfer, as well as concerted PCET, have assisted in identifying the kinetically favorable mechanisms under specified conditions. The concerted PCET mechanism is thought to lower the overpotential required for catalysis by avoiding high-energy intermediates. Rate constant calculations have revealed that the concerted mechanism involving intramolecular proton transfer will be favored by designing more flexible ligands that facilitate the proton donor-acceptor motion while also maintaining a sufficiently short equilibrium proton donor-acceptor distance. Overall, theoretical methods have assisted in the interpretation of experimental data and the design of more effective molecular electrocatalysts.

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“…Currently there appear to be no structurally characterised complexes of the exact (Z)-but-2-ene-2,3-diamide ligand for any metal system, [13a] making the structure unique. However the oxidised neutral form of the ligand (HN=C(Me)ÀC(Me)=NH, glyimine) has recently been trapped in an Fe II complex, [26] whilst the derived anionic ligand À N= C(Me)ÀC(Me)=N À is quite well knowni nabridgingr ole in an E configuration, [27] In addition, the free E dianion has been characterised as the counter ion foraruthenium complex. [28] Attempts at aD Mm etal synthesis between activated Yb metal and DippFormH in CH 3 CN failed to produce [Yb(Dipp-Form) 2 (CH 3 CN) 3 ]( Yb5 a).…”

Section: Oxidation Of [Yb(dfform) 2 (Thf) 3 ](Yb3)mentioning

confidence: 99%

Enhancing the Value of Free Metals in the Synthesis of Lanthanoid Formamidinates: Is a Co‐oxidant Needed?

Deacon

Junk

Werner

2015

Chemistry A European J

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Treatment of N,N'-bis(aryl)formamidines (ArFormH), N,N'-bis(2,6-difluorophenyl)formamidine (DFFormH) or N,N'-bis(2,6-diisopropylphenyl)formamidine (DippFormH), with europium metal in CH3 CN is an efficient synthesis of the divalent complexes: [{Eu(DFForm)2 (CH3 CN)2 }2 ] (Eu1) or [Eu(DippForm)2 (CH3 CN)4 ] (Eu2). The synthetic method was extended to ytterbium, but the metal required activation by addition of Hg(0) . With DFFormH in CH3 CN, [{Yb(DFForm)2 (CH3 CN)}2 ] (Yb1) was obtained in good yield, and [Yb(DFForm)2 (thf)3 ] (Yb3) was obtained from a synthesis in CH3 CN/THF. Thus, this synthetic method completely circumvents the use of either salt metathesis, or redox transmetallation/protolysis (RTP) protocols to prepare divalent rare-earth formamidinates. Heating Yb1 in PhMe/C6 D6 resulted in decomposition to trivalent products, including one from a CH3 CN activation process. For a synthetic comparison, divalent ytterbium DFForm and DippForm complexes were synthesised by RTP reactions between Yb(0) , Hg(R)2 (R=Ph, C6 F5 ), and ArFormH in THF, leading to the isolation of either [Yb(DFForm)2 (thf)3 ] (Yb3), or the first five coordinate rare-earth formamidinate complex [Yb(DippForm)2 (thf)] (Yb4 b), and, from adjustment of the stoichiometry, trivalent [Yb(DFForm)3 (thf)] (Yb6). Oxidation of Yb3 with benzophenone (bp), or halogenating agents (TiCl4 (thf)2 , Ph3 CCl, C2 Cl6 ) gave [Yb(DFForm)3 (bp)] or [Yb(DFForm)2 Cl(thf)2 ], respectively. Furthermore, the structural chemistry of divalent ArForm complexes has been substantially broadened. Not only have the highest and lowest coordination numbers for divalent rare-earth ArForm complexes been achieved in Eu2 and Yb4 b, respectively, but also dimeric Eu1 and Yb1 have highly unusual ArForm bridging coordination modes, either perpendicular μ-1κ(N:N'):2κ(N:N') in Eu1, or the twisted μ-1κ(N:N'):2κ(N':F') DFForm coordination in Yb1, both unprecedented in divalent rare-earth ArForm chemistry and in the wider divalent rare-earth amidinate field.

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Fe₄ Cluster and a Buckled Macrocycle Complex from the Reduction of [(dmgBF₂)₂Fe(L)₂] (L = MeCN, ^tBuⁱNC)

Cited by 6 publications

References 29 publications

Effects of Ligand Modification and Protonation on Metal Oxime Hydrogen Evolution Electrocatalysts

Effects of Ligand Modification and Protonation on Metal Oxime Hydrogen Evolution Electrocatalysts

Proton-Coupled Electron Transfer in Molecular Electrocatalysis: Theoretical Methods and Design Principles

Enhancing the Value of Free Metals in the Synthesis of Lanthanoid Formamidinates: Is a Co‐oxidant Needed?

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