Geometric and redox flexibility of pyridine as a redox-active ligand that can reversibly accept one or two electrons.
Ontology highlight
ABSTRACT:
SUBMITTER: Lewis RA
PROVIDER: S-EPMC4169077 | biostudies-literature | 2014 Oct
REPOSITORIES: biostudies-literature
Publications
Geometric and redox flexibility of pyridine as a redox-active ligand that can reversibly accept one or two electrons.
Lewis Richard A RA MacLeod K Cory KC Mercado Brandon Q BQ Holland Patrick L PL
Chemical communications (Cambridge, England) 20141001 76
A low-coordinate iron(I) species can reversibly reduce pyridine, either by one electron to give a new C-C bond, or by two electrons to give a pyridine-derived bridge with an unprecedented μ-η(1):η(3) binding mode. ...[more]
Similar Datasets
Project description:The synthesis of the first example of a third-row metallocorrolazine characterized by single crystal X-ray diffraction is reported. This Re(V)(O) porphyrinoid complex shows an exclusively ligand-based reactivity with strong acids and oxidizing agents. The one-electron oxidized π-radical-cation complex is capable of H-atom abstraction.
| S-EPMC4679572 | biostudies-literature
Project description:Nature uses control of the secondary coordination sphere to facilitate an astounding variety of transformations. Similarly, synthetic chemists have found metal-ligand cooperativity to be a powerful strategy for designing complexes that can mediate challenging reactivity. In particular, this strategy has been used to facilitate two electron reactions with first row transition metals that more typically engage in one electron redox processes. While NNN pincer ligands feature prominently in this area, examples which can potentially engage in both proton and electron transfer are less common. Dihydrazonopyrrole (DHP) ligands have been isolated in a variety of redox and protonation states when complexed to Ni. However, the redox-state of this ligand scaffold is less obvious when complexed to metal centers with more accessible redox couples. Here, we synthesize a new series of Fe-DHP complexes in two distinct oxidation states. Detailed characterization supports that the redox-chemistry in this set is still primarily ligand based. Finally, these complexes exist as 5-coordinate species with an open coordination site offering the possibility of enhanced reactivity.
| S-EPMC9435867 | biostudies-literature
Project description:Pyridine activation by inexpensive iron catalysts has great utility, but the steps through which iron species can break the strong (105-111 kcal mol-1 ) C-H bonds of pyridine substrates are unknown. In this work, we report the rapid room-temperature cleavage of C-H bonds in pyridine, 4-tert-butylpyridine, and 2-phenylpyridine by an iron(I) species, to give well-characterized iron(II) products. In addition, 4-dimethylaminopyridine (DMAP) undergoes room-temperature C-N bond cleavage, which forms a dimethylamidoiron(II) complex and a pyridyl-bridged tetrairon(II) square. These facile bond-cleaving reactions are proposed to occur through intermediates having a two-electron reduced pyridine that bridges two iron centers. Thus, the redox non-innocence of the pyridine can play a key role in enabling high regioselectivity for difficult reactions.
| S-EPMC5266524 | biostudies-literature
Project description:Addition of biphenylene to the bis(imino)pyridine iron dinitrogen complexes, ((iPr)PDI)Fe(N(2))(2) and [((Me)PDI)Fe(N(2))](2)(?(2)-N(2)) ((R)PDI = 2,6-(2,6-R(2)-C(6)H(3)-N?CMe)(2)C(5)H(3)N; R = Me, (i)Pr), resulted in oxidative addition of a C-C bond at ambient temperature to yield the corresponding iron biphenyl compounds, ((R)PDI)Fe(biphenyl). The molecular structures of the resulting bis(imino)pyridine iron metallacycles were established by X-ray diffraction and revealed idealized square pyramidal geometries. The electronic structures of the compounds were studied by Mössbauer spectroscopy, NMR spectroscopy, magnetochemistry, and X-ray absorption and X-ray emission spectroscopies. The experimental data, in combination with broken-symmetry density functional theory calculations, established spin crossover (low to intermediate spin) ferric compounds antiferromagnetically coupled to bis(imino)pyridine radical anions. Thus, the overall oxidation reaction involves cooperative electron loss from both the iron center and the redox-active bis(imino)pyridine ligand.
| S-EPMC3777725 | biostudies-literature
Project description:Metal-organic coordination networks at surfaces, formed by on-surface redox assembly, are of interest for designing specific and selective chemical function at surfaces for heterogeneous catalysts and other applications. The chemical reactivity of single-site transition metals in on-surface coordination networks, which is essential to these applications, has not previously been fully characterized. Here, we demonstrate with a surface-supported, single-site V system that not only are these sites active toward dioxygen activation, but the products of that reaction show much higher selectivity than traditional vanadium nanoparticles, leading to only one V-oxo product. We have studied the chemical reactivity of one-dimensional metal-organic vanadium - 3,6-di(2-pyridyl)-1,2,4,5-tetrazine (DPTZ) chains with O2. The electron-rich chains self-assemble through an on-surface redox process on the Au(100) surface and are characterized by X-ray photoelectron spectroscopy, scanning tunneling microscopy, high-resolution electron energy loss spectroscopy, and density functional theory. Reaction of V-DPTZ chains with O2 causes an increase in V oxidation state from VII to VIV, resulting in a single strongly bonded (DPTZ2-)VIVO product and spillover of O to the Au surface. DFT calculations confirm these products and also suggest new candidate intermediate states, providing mechanistic insight into this on-surface reaction. In contrast, the oxidation of ligand-free V is less complete and results in multiple oxygen-bound products. This demonstrates the high chemical selectivity of single-site metal centers in metal-ligand complexes at surfaces compared to metal nanoislands.
| S-EPMC5887816 | biostudies-other
Project description:The synthesis of aluminum complexes with redox-active formazanate ligands is described. Salt metathesis using AlCl3 was shown to form a five-coordinate complex with two formazanate ligands, whereas organometallic aluminum starting materials yield tetrahedral mono(formazanate) aluminum compounds. The aluminum diphenyl derivative was successfully converted to the iodide complex (formazanate)AlI2, and a comparison of spectroscopic/structural data for these new complexes is provided. Characterization by cyclic voltammetry is supplemented by chemical reduction to demonstrate that ligand-based redox reactions are accessible in these compounds. The possibility to obtain a formazanate aluminum(I) carbenoid species by two-electron reduction was examined by experimental and computational studies, which highlight the potential impact of the nitrogen-rich formazanate ligand on the electronic structure of compounds with this ligand.
| S-EPMC6506801 | biostudies-literature
Project description:The cobalt complex [Co(III)N4H(Br)2](+) (N4H = 2,12-dimethyl-3,7,11,17-tetraazabicyclo-[11.3.1]-heptadeca-1(7),2,11,13,15-pentaene) was used for electrocatalytic CO2 reduction in wet MeCN with a glassy carbon working electrode. When water was employed as the proton source (10 M in MeCN), CO was produced (fCO= 45% ± 6.4) near the Co(I/0) redox couple for [Co(III)N4H(Br)2](+) (E1/2 = -1.88 V FeCp2(+/0)) with simultaneous H2 evolution (fH2= 30% ± 7.8). Moreover, we successfully demonstrated that the catalytically active species is homogeneous through the use of control experiments and XPS studies of the working glassy-carbon electrodes. As determined by cyclic voltammetry, CO2 catalysis occurred near the formal Co(I/0)redox couple, and attempts were made to isolate the triply reduced compound ("[Co(0)N4H]"). Instead, the doubly reduced ("Co(I)") compounds [CoN4] and [CoN4H(MeCN)](+) were isolated and characterized by X-ray crystallography. Their molecular structures prompted DFT studies to illuminate details regarding their electronic structure. The results indicate that reducing equivalents are stored on the ligand, implicating redox noninnocence in the ligands for H2 evolution and CO2 reduction electrocatalysis.
| S-EPMC4033636 | biostudies-literature
Project description:Octahedrally coordinated cobalt(II) complexes with a redox-active bisguanidine ligand and acac co-ligands were synthesized and their redox chemistry analysed in detail. The N-H functions in a bisguanidine ligand with partially alkylated guanidino groups form N-H⋅⋅⋅O hydrogen bonds with the acac co-ligands, thereby massively influencing the redox chemistry. For all complexes, the first one-electron oxidation is metal-centred, leading to CoIII complexes with neutral bisguanidine ligand units. Further one-electron oxidation is ligand-centred in the case of Co-bisguanidine complexes with fully alkylated guanidino groups, giving CoIII complexes with radical monocationic bisguanidine ligands. On the other hand, the hydrogen-bond strengthening upon oxidation of the Co-bisguanidine complex with partially alkylated guanidino groups initiates metal reduction (CoIII →CoII ) and two-electron oxidation of the guanidine ligand, providing the first example for the stimulation of redox-induced electron transfer by interligand hydrogen bonding.
| S-EPMC8252010 | biostudies-literature
Project description:Two homoleptic copper(II) complexes [Cu(L1)2 ] and [Cu(L2)2 ] with anionic redox-active ligands were synthesised, one with urea azine (L1) and the other with thio-urea azine (L2) ligands. One-electron oxidation of the complexes initiates an unprecedented redox-induced electron transfer process, leading to monocationic copper(I) complexes [Cu(L1)2 ]+ and [Cu(L2)2 ]+ with two oxidised ligands. While [Cu(L1)2 ]+ is best described as a CuI complex with two neutral radical ligands that couple antiferromagnetically, [Cu(L2)2 ]+ is a CuI complex with two clearly different ligand units in the solid state and with a magnetic susceptibility close to a diamagnetic compound. Further one-electron oxidation of the complex with L1 ligands results in a dication [Cu(L1)2 ]2+ , best described as a CuI complex with a twofold oxidised, monocationic ligand and a neutral radical ligand. The stability in at least three redox states, the accumulation of spin density at the ligands and the facile ligand-metal electron transfer make these complexes highly attractive for a variety of applications; here the catalytic aerobic oxidation of alcohols to aldehydes is tested.
| S-EPMC8596453 | biostudies-literature
Project description:A new bimetallic platform comprising a six-coordinate Fe(ONO)2 unit bound to an (ONO)M (M = Fe, Zn) has been discovered ((ONOcat)H3 = bis(3,5-di-tert-butyl-2-phenol)amine). Reaction of Fe(ONO)2 with either (ONOcat)Fe(py)3 or with (ONOq)FeCl2 under reducing conditions led to the formation of the bimetallic complex Fe2(ONO)3, which includes unique five- and six-coordinate iron centers. Similarly, the reaction of Fe(ONO)2 with the new synthon (ONOsq˙)Zn(py)2 led to the formation of the heterobimetallic complex FeZn(ONO)3, with a six-coordinate iron center and a five-coordinate zinc center. Both bimetallic complexes were characterized by single-crystal X-ray diffraction studies, solid-state magnetic measurements, and multiple spectroscopic techniques. The magnetic data for FeZn(ONO)3 are consistent with a ground state S = 3/2 spin system, generated from a high-spin iron(ii) center that is antiferromagnetically coupled to a single (ONOsq˙)2- radical ligand. In the case of Fe2(ONO)3, the magnetic data revealed a ground state S = 7/2 spin system arising from the interactions of one high-spin iron(ii) center, one high-spin iron(iii) center, and two (ONOsq˙)2- radical ligands.
| S-EPMC5530940 | biostudies-literature