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1.
Mononuclear metal–dioxygen species are key intermediates that are frequently observed in the catalytic cycles of dioxygen activation by metalloenzymes and their biomimetic compounds. In this work, a side‐on cobalt(III)–peroxo complex bearing a macrocyclic N‐tetramethylated cyclam (TMC) ligand, [CoIII(15‐TMC)(O2)]+, was synthesized and characterized with various spectroscopic methods. Upon protonation, this cobalt(III)–peroxo complex was cleanly converted into an end‐on cobalt(III)–hydroperoxo complex, [CoIII(15‐TMC)(OOH)]2+. The cobalt(III)–hydroperoxo complex was further converted to [CoIII(15‐TMC‐CH2‐O)]2+ by hydroxylation of a methyl group of the 15‐TMC ligand. Kinetic studies and 18O‐labeling experiments proposed that the aliphatic hydroxylation occurred via a CoIV–oxo (or CoIII–oxyl) species, which was formed by O? O bond homolysis of the cobalt(III)–hydroperoxo complex. In conclusion, we have shown the synthesis, structural and spectroscopic characterization, and reactivities of mononuclear cobalt complexes with peroxo, hydroperoxo, and oxo ligands.  相似文献   

2.
High‐valent cobalt‐oxo intermediates are proposed as reactive intermediates in a number of cobalt‐complex‐mediated oxidation reactions. Herein we report the spectroscopic capture of low‐spin (S=1/2) CoIV‐oxo species in the presence of redox‐inactive metal ions, such as Sc3+, Ce3+, Y3+, and Zn2+, and the investigation of their reactivity in C? H bond activation and sulfoxidation reactions. Theoretical calculations predict that the binding of Lewis acidic metal ions to the cobalt‐oxo core increases the electrophilicity of the oxygen atom, resulting in the redox tautomerism of a highly unstable [(TAML)CoIII(O.)]2? species to a more stable [(TAML)CoIV(O)(Mn+)] core. The present report supports the proposed role of the redox‐inactive metal ions in facilitating the formation of high‐valent metal–oxo cores as a necessary step for oxygen evolution in chemistry and biology.  相似文献   

3.
Terminal oxo complexes of late transition metals are frequently proposed reactive intermediates. However, they are scarcely known beyond Group 8. Using mass spectrometry, we prepared and characterized two such complexes: [(N4Py)CoIII(O)]+ ( 1 ) and [(N4Py)CoIV(O)]2+ ( 2 ). Infrared photodissociation spectroscopy revealed that the Co?O bond in 1 is rather strong, in accordance with its lack of chemical reactivity. On the contrary, 2 has a very weak Co?O bond characterized by a stretching frequency of ≤659 cm?1. Accordingly, 2 can abstract hydrogen atoms from non‐activated secondary alkanes. Previously, this reactivity has only been observed in the gas phase for small, coordinatively unsaturated metal complexes. Multireference ab‐initio calculations suggest that 2 , formally a cobalt(IV)‐oxo complex, is best described as cobalt(III)‐oxyl. Our results provide important data on changes to metal‐oxo bonding behind the oxo wall and show that cobalt‐oxo complexes are promising targets for developing highly active C?H oxidation catalysts.  相似文献   

4.
Dioxygen activation pathways on the (001) surfaces of cobalt ferrite, CoFe2O4, were investigated computationally using density functional theory and the hybrid Perdew-Burke-Ernzerhof exchange-correlation functional (PBE0) within the periodic electrostatic embedded cluster model. We considered two terminations: the A-layer exposing Fe2+ and Co2+ metal sites in tetrahedral and octahedral positions, respectively, and the B-layer exposing octahedrally coordinated Co3+. On the A-layer, molecular oxygen is chemisorbed as a superoxide on the Fe monocenter or bridging a Fe−Co cation pair, whereas on the B-layer it is adsorbed at the most stable anionic vacancy. Activation is promoted by transfer of electrons provided by the d metal centers onto the adsorbed oxygen. The subsequent dissociation of dioxygen into monoatomic species and surface reoxidation have been identified as the most critical steps that may limit the rate of the oxidation processes. Of the reactive metal-O species, [FeIII−O]2+ is thermodynamically most stable, while the oxygen of the Co−O species may easily migrate across the A-layer with barriers smaller than the associative desorption.  相似文献   

5.
The first 4π‐electron resonance‐stabilized 1,3‐digerma‐2,4‐diphosphacyclobutadiene [LH2Ge2P2] 4 (LH=CH[CHNDipp]2 Dipp=2,6‐iPr2C6H3) with four‐coordinate germanium supported by a β‐diketiminate ligand and two‐coordinate phosphorus atoms has been synthesized from the unprecedented phosphaketenyl‐functionalized N‐heterocyclic germylene [LHGe‐P=C=O] 2 a prepared by salt‐metathesis reaction of sodium phosphaethynolate (P≡C?ONa) with the corresponding chlorogermylene [LHGeCl] 1 a . Under UV/Vis light irradiation at ambient temperature, release of CO from the P=C=O group of 2 a leads to the elusive germanium–phosphorus triply bonded species [LHGe≡P] 3 a , which dimerizes spontaneously to yield black crystals of 4 as isolable product in 67 % yield. Notably, release of CO from the bulkier substituted [LtBuGe‐P=C=O] 2 b (LtBu=CH[C(tBu)N‐Dipp]2) furnishes, under concomitant extrusion of the diimine [Dipp‐NC(tBu)]2, the bis‐N,P‐heterocyclic germylene [DippNC(tBu)C(H)PGe]2 5 .  相似文献   

6.
A series of heterobimetallic complexes containing three‐center, two‐electron Au−H−Cu bonds have been prepared from addition of a parent gold hydride to a bent d10 copper(I) fragment. These highly unusual heterobimetallic complexes represent a missing link in the widely investigated series of neutral and cationic coinage metal hydride complexes containing Cu−H−Cu and M−H−M+ moieties (M=Cu, Ag). The well‐defined heterobimetallic hydride complexes act as precatalysts for the conversion of CO2 into HCO2Bpin with HBpin as the reductant. The selectivity of the heterobimetallic complexes for the catalytic production of a formate equivalent surpasses that of the parent monomeric Group 11 complexes.  相似文献   

7.
Transition metal complexes with terminal oxo and dioxygen ligands exist in metal oxidation reactions, and many are key intermediates in various catalytic and biological processes. The prototypical oxo‐metal [(OC)5Cr? O, (OC)4Fe? O, and (OC)3Ni? O] and dioxygen‐metal carbonyls [(OC)5Cr? OO, (OC)4Fe? OO, and (OC)3Ni? OO] are studied theoretically. All three oxo‐metal carbonyls were found to have triplet ground states, with metal‐oxo bond dissociation energies of 77 (Cr? O), 74 (Fe? O), and 51 (Ni? O) kcal/mol. Natural bond orbital and quantum theory of atoms in molecules analyses predict metal‐oxo bond orders around 1.3. Their featured ν(MO, M = metal) vibrational frequencies all reflect very low IR intensities, suggesting Raman spectroscopy for experimental identification. The metal interactions with O2 are much weaker [dissociation energies 13 (Cr? OO), 21 (Fe? OO), and 4 (Ni? OO) kcal/mol] for the dioxygen‐metal carbonyls. The classic parent compounds Cr(CO)6, Fe(CO)5, and Ni(CO)4 all exhibit thermodynamic instability in the presence of O2, driven to displacement of CO to form CO2. The latter reactions are exothermic by 47 [Cr(CO)6], 46 [Fe(CO)5], and 35 [Ni(CO)4] kcal/mol. However, the barrier heights for the three reactions are very large, 51 (Cr), 39 (Fe), and 40 (Ni) kcal/mol. Thus, the parent metal carbonyls should be kinetically stable in the presence of oxygen. © 2014 Wiley Periodicals, Inc.  相似文献   

8.
We report that the formation of μ‐oxo diferric compounds from O2 and FeCl2 complexes within the tris(2‐pyridylmethyl)amine series (N. K. Thallaj et al. Chem. Eur. J., 2008 , 14, 6742–6753) involves coordination of O2 to the metal centre and that this reaction occurs following initial dissociation of the bound equatorial chloride anion. We also report evidence of the formation of a reduced form of dioxygen by an inner‐sphere mechanism, thus leading to modification of the ligand. The solid‐state structures of [FeCl2L] complexes (L1=mono(α‐pivalamidopyridylmethyl)bis(2‐pyridylmethyl)amine, L2=mono(α‐pivalesteropyridylmethyl)bis(2‐pyridylmethyl)amine, L3=bis(α‐pivalamidopyridylmethyl)mono(2‐pyridylmethyl)amine are described, and spectroscopic data support the structural retention in solution. In [FeCl2L3], the two amide hydrogen atoms stabilise the equatorial chloride anion in such a way that its exchange by a weak ligand is impossible: [FeCl2L3] is perfectly oxygen‐stable. In [FeCl2L2], the equatorial chloride anion is completely free to move and coordination of O2 can take place. The reaction product with [FeCl2L2] is a μ‐oxo diferric complex in which the ester function has been transformed into a phenol group. This conversion can be seen as a hydrolysis reaction in basic medium, hence supporting the initial formation of a reduced form of dioxygen in the medium. Complex [FeCl2L1] exhibits a very weak reactivity with O2, in line with a semistabilised equatorial chloride counteranion.  相似文献   

9.
Synthesis of small‐molecule Cu2O2 adducts has provided insight into the related biological systems and their reactivity patterns including the interconversion of the CuII2(μ‐η22‐peroxo) and CuIII2(μ‐oxo)2 isomers. In this study, absorption spectroscopy, kinetics, and resonance Raman data show that the oxygenated product of [(BQPA)CuI]+ initially yields an “end‐on peroxo” species, that subsequently converts to the thermodynamically more stable “bis‐μ‐oxo” isomer (Keq=3.2 at ?90 °C). Calibration of density functional theory calculations to these experimental data suggest that the electrophilic reactivity previously ascribed to end‐on peroxo species is in fact a result of an accessible bis‐μ‐oxo isomer, an electrophilic Cu2O2 isomer in contrast to the nucleophilic reactivity of binuclear CuII end‐on peroxo species. This study is the first report of the interconversion of an end‐on peroxo to bis‐μ‐oxo species in transition metal‐dioxygen chemistry.  相似文献   

10.
The open‐chain polyether‐bridged flexible ligand 1,2‐bis[2‐(1H‐1,3‐imidazol‐1‐ylmethyl)phenoxy]ethane (L) has been used to create two two‐dimensional coordination polymers under hydrothermal reaction of L with CdII or CoII, in the presence of benzene‐1,4‐dicarboxylic acid (H2bdc). In poly[[(μ2‐benzene‐1,4‐dicarboxylato){μ‐1,2‐bis[2‐(1H‐1,3‐imidazol‐1‐ylmethyl)phenoxy]ethane}cadmium(II)] dihydrate], {[Cd(C8H4O4)(C22H22N4O2)]·2H2O}n, (I), and the cobalt(II) analogue {[Co(C8H4O4)(C22H22N4O2)]·2H2O}n, (II), the CdII and CoII cations are six‐coordinated by four carboxylate O atoms from two different bdc2− dianions in a chelating mode and two N atoms from two distinct L ligands. The metal ions, bdc2− dianions and L ligands each sit across crystallographic twofold axes. The bdc2− coordination mode and the coordinating orientation of the L ligand play an important role in constructing the novel two‐dimensional framework. Complexes (I) and (II) are threefold interpenetrated two‐dimensional frameworks; their structures are almost isomorphous, while the bond lengths, angles and hydrogen bonds are different in (I) and (II).  相似文献   

11.
Many iron‐containing enzymes involve metal–oxygen oxidants to carry out O2‐dependent transformation reactions. However, the selective oxidation of C? H and C?C bonds by biomimetic complexes using O2 remains a major challenge in bioinspired catalysis. The reactivity of iron–oxygen oxidants generated from an FeII–benzilate complex of a facial N3 ligand were thus investigated. The complex reacted with O2 to form a nucleophilic oxidant, whereas an electrophilic oxidant, intercepted by external substrates, was generated in the presence of a Lewis acid. Based on the mechanistic studies, a nucleophilic FeII–hydroperoxo species is proposed to form from the benzilate complex, which undergoes heterolytic O? O bond cleavage in the presence of a Lewis acid to generate an FeIV–oxo–hydroxo oxidant. The electrophilic iron–oxygen oxidant selectively oxidizes sulfides to sulfoxides, alkenes to cis‐diols, and it hydroxylates the C? H bonds of alkanes, including that of cyclohexane.  相似文献   

12.
Reactions between the 1,3‐diphosphete complex [Cp′′′Co(η4‐P2C2tBu2)] ( 1 ) and Ag[Al{OC(CF3)3}4] (Ag[pftb]) were carried out under different conditions. In CH2Cl2, the unprecedented 1,2‐diphosphete isomerization product [Ag2{Cp′′′Co(μ,η411‐1,2‐P2C2tBu2)}2{Cp′′′Co(μ,η41‐1,2‐P2C2tBu2)}2]⋅2[pftb] ( 2 ) could be isolated. In diffusion experiments of 1 in n‐hexane with Ag[pftb] in CH2Cl2, the triphosphacobaltocenium complex [Cp′′′Co(η5‐P3C2tBu2)][pftb] ( 4 ) and the phosphirenylium complex [Cp′′′Co(η3‐PC2tBu2)][pftb] ( 5 ) were obtained, showing a ring expansion and a ring contraction, respectively, under mild conditions. Moreover, addition of pyridine to the Ag complex 2 led to the new 1,2‐diphosphete complex [Cp′′′Co(η4‐1,2‐P2C2tBu2)] ( 3 ). Compound 3 is also formed by thermolysis of 1 , making it a promising method for this type of isomerization. 1,2‐Diphosphete complexes like 3 are thermodynamically more stable but also synthetically more elusive than their 1,3‐isomer counterparts.  相似文献   

13.
In the title compound, [Mn(C5H2N2O4)(H2O)2]n, the MnII ion has a distorted octahedral geometry and the 4‐oxido‐2‐oxo‐1,2‐dihydropyrimidine‐5‐carboxylate (Hiso2−) anion acts as a μ34‐bridging ligand. Two oxo O atoms from different Hiso2− ligands bridge two MnII ions, forming centrosymmetric dinuclear building blocks. Each dinuclear building block interacts with another four by the coordination of the oxide groups and carboxylate O atoms, producing a two‐dimensional framework in the ab plane. Hydrogen bonds further extend the two‐dimensional sheets into a three‐dimensional supramolecular framework.  相似文献   

14.
N‐Heterocyclic carbene based pincer ligands bearing a central silyl donor, [CSiC], have been envisioned as a class of strongly σ‐donating ligands that can be used for synthesizing electron‐rich transition‐metal complexes for the activation of inert bonds. However, this type of pincer ligand and complexes thereof have remained elusive owing to their challenging synthesis. We herein describe the first synthesis of a CSiC pincer ligand scaffold through the coupling of a silyl–NHC chelate with a benzyl–NHC chelate induced by one‐electron oxidation in the coordination sphere of a cobalt complex. The monoanionic CSiC ligand stabilizes the CoI dinitrogen complex [(CSiC)Co(N2)] with an unusual coordination geometry and enables the challenging oxidative addition of E−H bonds (E=C, N, O) to CoI to form CoIII complexes. The structure and reactivity of the cobalt(I) complex are ascribed to the unique electronic properties of the CSiC pincer ligand, which provides a strong trans effect and pronounced σ‐donation.  相似文献   

15.
N‐Heterocyclic carbene based pincer ligands bearing a central silyl donor, [CSiC], have been envisioned as a class of strongly σ‐donating ligands that can be used for synthesizing electron‐rich transition‐metal complexes for the activation of inert bonds. However, this type of pincer ligand and complexes thereof have remained elusive owing to their challenging synthesis. We herein describe the first synthesis of a CSiC pincer ligand scaffold through the coupling of a silyl–NHC chelate with a benzyl–NHC chelate induced by one‐electron oxidation in the coordination sphere of a cobalt complex. The monoanionic CSiC ligand stabilizes the CoI dinitrogen complex [(CSiC)Co(N2)] with an unusual coordination geometry and enables the challenging oxidative addition of E−H bonds (E=C, N, O) to CoI to form CoIII complexes. The structure and reactivity of the cobalt(I) complex are ascribed to the unique electronic properties of the CSiC pincer ligand, which provides a strong trans effect and pronounced σ‐donation.  相似文献   

16.
Iron cations are essential for the high activity of nickel and cobalt‐based (oxy)hydroxides for the oxygen evolution reaction, but the role of iron in the catalytic mechanism remains under active investigation. Operando X‐ray absorption spectroscopy and density functional theory calculations are used to demonstrate partial Fe oxidation and a shortening of the Fe?O bond length during oxygen evolution on Co(Fe)OxHy. Cobalt oxidation during oxygen evolution is only observed in the absence of iron. These results demonstrate a different mechanism for water oxidation in the presence and absence of iron and support the hypothesis that oxidized iron species are involved in water‐oxidation catalysis on Co(Fe)OxHy.  相似文献   

17.
The synthesis and characterization of (tBuPBP)Ni(OAc) ( 5 ) by insertion of carbon dioxide into the Ni−C bond of (tBuPBP)NiMe ( 1 ) is presented. An unexpected CO2 cleavage process involving the formation of new B−O and Ni−CO bonds leads to the generation of a butterfly-structured tetra-nickel cluster (tBuPBOP)2Ni4(μ-CO)2 ( 6 ). Mechanistic investigation of this reaction indicates a reductive scission of CO2 by O-atom transfer to the boron atom via a cooperative nickel-boron mechanism. The CO2 activation reaction produces a three-coordinate (tBuP2BO)Ni-acyl intermediate ( A ) that leads to a (tBuP2BO)−NiI complex ( B ) via a likely radical pathway. The NiI species is trapped by treatment with the radical trap (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) to give (tBuP2BO)NiII2-TEMPO) ( 7 ). Additionally, 13C and 1H NMR spectroscopy analysis using 13C-enriched CO2 provides information about the species involved in the CO2 activation process.  相似文献   

18.
Thermal activation of molecular oxygen is observed for the late‐transition‐metal cationic complexes [M(H)(OH)]+ with M=Fe, Co, and Ni. Most of the reactions proceed via insertion in a metal? hydride bond followed by the dissociation of the resulting metal hydroperoxide intermediate(s) upon losses of O, OH, and H2O. As indicated by labeling studies, the processes for the Ni complex are very specific such that the O‐atoms of the neutrals expelled originate almost exclusively from the substrate O2. In comparison to the [M(H)(OH)]+ cations, the ion? molecule reactions of the metal hydride systems [MH]+ (M=Fe, Co, Ni, Pd, and Pt) with dioxygen are rather inefficient, if they occur at all. However, for the solvated complexes [M(H)(H2O)]+ (M=Fe, Co, Ni), the reaction with O2 involving O? O bond activation show higher reactivity depending on the transition metal: 60% for the Ni, 16% for the Co, and only 4% for the Fe complex relative to the [Ni(H)(OH)]+/O2 couple.  相似文献   

19.
Mononuclear MnIII–peroxo and dinuclear bis(μ‐oxo)MnIII2 complexes that bear a common macrocyclic ligand were synthesized by controlling the concentration of the starting MnII complex in the reaction of H2O2 (i.e., a MnIII–peroxo complex at a low concentration (≤1 mM ) and a bis(μ‐oxo)MnIII2 complex at a high concentration (≥30 mM )). These intermediates were successfully characterized by various physicochemical methods such as UV–visible spectroscopy, ESI‐MS, resonance Raman, and X‐ray analysis. The structural and spectroscopic characterization combined with density functional theory (DFT) calculations demonstrated unambiguously that the peroxo ligand is bound in a side‐on fashion in the MnIII–peroxo complex and the Mn2O2 diamond core is in the bis(μ‐oxo)MnIII2 complex. The reactivity of these intermediates was investigated in electrophilic and nucleophilic reactions, in which only the MnIII–peroxo complex showed a nucleophilic reactivity in the deformylation of aldehydes.  相似文献   

20.
The sterically demanding β‐diketiminate ligand Ldmp [Ldmp = HC{(CMe)N(dmp)}2, dmp = C6H3‐2,6‐Me2] was used to stabilize various gallium complexes in the formal oxidation states +II and +III. The reaction of in situ generated [LdmpLi] with gallium chloride affords [LdmpGaCl2] ( 1 ), which was used as starting complex to synthesize a variety of gallium(III) compounds [LdmpGaX2] [X = F ( 2 ), I ( 3 ), H ( 4 ), and Me ( 5 )]. Synthesis of the dinuclear complex [LdmpGaI]2 ( 6 ), with gallium in the formal oxidation state +II was accomplished by converting “GaI” with in situ generated [LdmpLi] in toluene. All compounds were characterized by elemental analyses, NMR spectroscopy, LIFDI‐TOF‐MS, and single‐crystal X‐ray diffraction. Additionally DFT calculations were performed for analysis of the bonding in 6 .  相似文献   

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