Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 21
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Inorg Chem ; 2020 Jul 08.
Artigo em Inglês | MEDLINE | ID: mdl-32639726

RESUMO

Metal-ligand cooperativity (MLC) relies on chemically reactive ligands to assist metals with small-molecule binding and activation, and it has facilitated unprecedented examples of catalysis with metal complexes. Despite growing interest in combining ligand-centered chemical and redox reactions for chemical transformations, there are few studies demonstrating how chemically engaging redox active ligands in MLC affects their electrochemical properties when bound to metals. Here we report stepwise changes in the redox activity of model Ru complexes as zero, one, and two BH3 molecules undergo MLC binding with a triaryl noninnocent N2S2 ligand derived from o-phenylenediamine (L1). A similar series of Ru complexes with a diaryl N2S2 ligand with ethylene substituted in place of phenylene (L2) is also described to evaluate the influence of the o-phenylenediamine subunit on redox activity and MLC. Cyclic voltammetry (CV) studies and density functional theory (DFT) calculations show that MLC attenuates ligand-centered redox activity in both series of complexes, but electron transfer is still achieved when only one of the two redox-active sites on the ligands is chemically engaged. The results demonstrate how incorporating more than one multifunctional reactive site could be an effective strategy for maintaining redox noninnocence in ligands that are also chemically reactive and competent for MLC.

2.
Chemistry ; 2020 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-32291835

RESUMO

Invited for the cover of this issue is the group of Evamarie Hey-Hawkins at the University of Leipzig and colleagues at the University of Stuttgart and University of Regensburg. The image depicts the reported complexes as three similar flowers growing from one common branch representing the ligand. Read the full text of the article at 10.1002/chem.202000226.

3.
Chemistry ; 2020 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-32022973

RESUMO

2,4,6-Tris(1-diphenylphosphanyl-1'-ferrocenylene)-1,3,5-triazine (1) coordinates all three coinage metal(I) ions in a 1:1 tridentate coordination mode. The C3 -symmetric coordination in both solid state and solution is stabilised by an uncommon cation-π interaction between the triazine core and the metal cation. Intramolecular dynamic behaviour was observed by variable-temperature NMR spectroscopy. The borane adduct of 1, 1BH3 , displays four accessible oxidation states, suggesting complexes of 1 to be intriguing candidates for redox-switchable catalysis. Complexes 1Cu, 1Ag, and 1Au display a more complicated electrochemical behaviour, and the electrochemical mechanism was studied by temperature-resolved UV/Vis spectroelectrochemistry and chemical oxidation.

4.
Inorg Chem ; 58(23): 16256-16266, 2019 Dec 02.
Artigo em Inglês | MEDLINE | ID: mdl-31710221

RESUMO

The deprotonation of 1-(1H-benzimidazol-2-yl)-3-methylbenzimidazolium hexafluorophosphate (2MeH2[PF6]) and 1-(1H-benzimidazol-2-yl)-3-isopropylbenzimidazolium hexafluorophosphate (2iPrH2[PF6]) with potassium tert-butoxide in THF afforded the benzimidazolium-benzimidazolates 2MeH and 2iPrH. The "instant carbene" behavior of these conjugated mesomeric betaines was demonstrated by trapping their carbenic tautomers 2'MeH and 2'iPrH with elemental sulfur and selenium, which afforded the corresponding thio- and selenourea derivatives 2'MeHE and 2'iPrHE (E = S, Se). The treatment of 2MeH and 2iPrH with nickelocene furnished the nickel(II) complexes [NiCp(2'Me)] and [NiCp(2'iPr)], which contain an anionic C,Namido-chelating NHC ligand. The electronic structure and redox behavior of the nickel(II) chelates were investigated, as well as those of the closely related chelates [NiCp(1'Me)] and [NiCp(1'iPr)] derived from the corresponding imidazolium-benzimidazolates 1MeH and 1iPrH. According to DFT calculations, the highest occupied molecular orbital (HOMO) is located over the NiCp moiety and the π system of the chelate ligand with a large contribution from the (benz-)imidazolate moiety. Cyclic voltammetry revealed a reversible oxidation to the monocation [NiCp(L)]+ (E1/2 = 0.315, 0.222, 0.396, 0.265 V vs ferrocene/ferrocenium for L = 1'Me, 1'iPr, 2'Me, 2'iPr, respectively) in CH2Cl2/0.1 M n-Bu4N[B(ArF)4] (B(ArF)4- = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate), and isosbestic behavior was found in UV-vis-NIR spectroelectrochemical experiments. The different redox potentials reflect the different donor/acceptor properties of the NHC part of the chelate ligands, with 1'iPr being the strongest and 2'Me the weakest net electron donor. The EPR spectroscopic signature of [NiCp(2'Me)]+ in CH2Cl2/0.1 M n-Bu4N[B(ArF)4] at 100 K is consistent with a chelate-ligand-based radical with strong spin-orbit coupling to the Ni center. In contrast, the EPR spectra of [NiCp(1'Me)]+, [NiCp(1'iPr)]+, and [NiCp(2'iPr)]+ indicate that these monocations are best described as NiIII complexes, the comparatively higher contribution of the NiIII(L) vs the NiII(L•+) valence tautomer being supported by the results of open-shell DFT calculations.

6.
J Am Chem Soc ; 141(30): 12029-12043, 2019 Jul 31.
Artigo em Inglês | MEDLINE | ID: mdl-31268701

RESUMO

Enzymes are Nature's polyfunctional catalysts tailor-made for specific biochemical synthetic transformations, which often proceed with almost perfect stereocontrol. From a synthetic point of view, artificial catalysts usually offer the advantage of much broader substrate scopes, but stereocontrol is often inferior to that possible with natural enzymes. A particularly difficult synthetic task in asymmetric catalysis is to overwrite a pronounced preference for the formation of an inherently favored diastereomer; this requires a high level of stereocontrol. In this Article, the development of a novel artificial polyfunctional catalyst type is described, in which an imidazolium-aryloxide betaine moiety cooperates with a Lewis acidic metal center (here Cu(II)) within a chiral catalyst framework. This strategy permits for the first time a general, highly enantioselective access to the otherwise rare diastereomer in the direct 1,4-addition of various 1,3-dicarbonyl substrates to ß-substituted nitroolefins. The unique stereocontrol by the polyfunctional catalyst system is also demonstrated with the highly stereoselective formation of a third contiguous stereocenter making use of a diastereoselective nitronate protonation employing α,ß-disubstituted nitroolefin substrates. Asymmetric 1,4-additions of ß-ketoesters to α,ß-disubstituted nitroolefins have never been reported before in literature. Combined mechanistic investigations including detailed spectroscopic and density functional theory (DFT) studies suggest that the aryloxide acts as a base to form a Cu(II)-bound enolate, whereas the nitroolefin is activated by H-bonds to the imidazolium unit and the phenolic OH generated during the proton transfer. Detailed kinetic analyses (RPKA, VTNA) suggest that (a) the catalyst is stable during the catalytic reaction, (b) not inhibited by product and (c) the rate-limiting step is most likely the C-C bond formation in agreement with the DFT calculations of the catalytic cycle. The robust catalyst is readily synthesized and recyclable and could also be applied to a cascade cyclization.

8.
Inorg Chem ; 58(3): 1742-1745, 2019 Feb 04.
Artigo em Inglês | MEDLINE | ID: mdl-30652870

RESUMO

Hexacarbonyldiiron bridged by a 1,1'-dithiolatoferrocene, [Fe(C5H4S)2{Fe(CO)3}2] (1), was synthesized, and the electrochemistry showed reversible oxidation at the Fe(C5H4S)2 site and quasi-reversible reduction at the hexacarbonyldiiron site. Spectroelectrochemical techniques showed reduction-induced ligand isomerization, where the thiolate ligand went from bridging to terminal and one carbon monoxide ligand moved to a quasi-bridging position; this mechanism was further supported by cyclic voltammetry simulation and density functional theory calculations. Complex 1 showed electrocatalytic activity toward hydrogen-evolving reaction.

9.
Chemistry ; 25(10): 2396-2406, 2019 Feb 18.
Artigo em Inglês | MEDLINE | ID: mdl-30238642

RESUMO

Ligands with 1,1'-bis(donor)ferrocene motif are capable of a wide range of binding modes, including the trans chelation mode in which there is a Fe-M interaction (κ3 -D,Fe,D), in the form of a dative Fe→TM bond (TM=transition metal). This Minireview will explore the nature of this Fe-TM interaction thorough select examples as well as how to characterize a Fe→TM dative bond using physical, computational, and spectroscopic techniques.

10.
Dalton Trans ; 47(37): 12873-12878, 2018 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-30167603

RESUMO

The electronic structure of recently reported diaurum (AuIAuI and XAuII-AuIIX) complexes, containing two methylferrocenyloxazoline ligands are described. Oxidations occurred at the methylferrocenyl and the monocation complex containing AuIAuI bridge was valence localized while the AuII-AuII complex was valence delocalized, i.e., Fe2.5+/Fe2.5+. These findings were supported by electrochemical, and spectroscopic measurements and further supported by computational analysis (DFT).

11.
Chem Sci ; 9(5): 1221-1230, 2018 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-29675167

RESUMO

Tetraoxolene radical-bridged lanthanide SMM systems were prepared for the first time by reduction of the respective neutral compounds. Magnetic measurements reveal the profound influence of the radical center on magnetic behavior. Strong magnetic couplings are revealed in the radical species, which switch on SMM behavior under zero applied field for DyIII and TbIII compounds. HFEPR spectra unravel the contributions of the magnetic coupling and the magnetic anisotropy. For GdIII this results in much more accurate magnetic coupling parameters with respect to bulk magnetic measurements.

12.
Inorg Chem ; 56(23): 14688-14696, 2017 12 04.
Artigo em Inglês | MEDLINE | ID: mdl-29144131

RESUMO

Recently we had reported the noninnocent behavior of 1,1'-bis(diphenylphosphino)ferrocene (dppf) in Fe(CO)3dppf [Ringenberg et al., Inorg. Chem., 2017, 56, 7501]. Moving to the left in the periodic table, HMn(CO)3(dRpf) where dRpf = dppf (1H) and 1,1'-bis(diisopropylphosphino)ferrocene (dippf) (2H) were synthesized. The hydride ligand was removed by protonation with [(Et2O)2H][B(ArF)4] ([B(ArF)4]- = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate), resulting in the rapid evolution of H2 followed by the formation of an Fe→Mn interaction. The reaction mechanism was determined by in situ IR experiments which show that directly following protonation both [1]+ and [2]+ offer an open manganese coordination site that allows for the formation of an intramolecular Fe→Mn dative bond. This process is significantly faster for [2]+ than for [1]+. The reduction chemistry as studied by cyclic voltammetry (CV) reveals that both complexes change from a distorted octahedral coordination with an Fe→Mn interaction to an open square-pyramidal configuration which is more stable for [1]0 than [2]0. Reoxidation of this square-pyramidal species proceeds more reversibly for 2 versus 1 due to the faster ferrocene ligand reorganization. The electrochemical mechanism was studied by in situ spectroscopic techniques, e.g., IR, UV-vis-NIR (near IR), and EPR spectroelectrochemistry (SEC) as well as by CV simulation. The new complexes described offer an exciting platform for the development of electrocatalysts for the reduction of CO2 to CO, or for proton reduction (2H+ + 2e- → H2).

13.
Inorg Chem ; 56(13): 7501-7511, 2017 Jul 03.
Artigo em Inglês | MEDLINE | ID: mdl-28598145

RESUMO

The tricarbonyliron (TCFe) complexes Fe(CO)3(dppf) and Fe(CO)3(dppp), where dppf = 1,1'-bis(diphenylphosphino)ferrocene and dppp = 1,3-bis(diphenylphosphino)propane, exhibit redox activity that induces configurational isomerization. The presence of the ferrocenyl (Fc) group stabilizes higher oxidized forms of TCFe. Using spectroelectrochemistry (IR, UV-vis, Mössbauer, and EPR) and computational analysis, we can show that the Fc in the backbone of the dppf ligand tends to form a weak dative bond to the electrophilic TCFeI and TCFeII species. The open shell TCFeI intermediate was stabilized by the distribution of spin between the two Fe centers (Fc and TCFe), whereas lacking the Fc moiety resulted in highly reactive TCFeI species. The [Fe(CO)3(dppf)]+ cation adopts two possible configurations, square-pyramidal (without an Fe-Fe interaction) and trigonal-bipyramidal (containing an Fe-Fe interaction). The two configurations are in equilibrium with the trigonal-bipyramidal configuration being enthalpically favored (ΔH = -7 kJ mol-1). There is an entropic penalty (ΔS = -20 J mol-1) due to tilting of the Cp (cyclopentadienide) rings of the dppf moieties by ∼8°. Additionally, the terminal iron hydride [FeH(CO)3(dppf)]BF4 was formed by protonation with a strong acid (HBF4·Et2O).

14.
Dalton Trans ; 46(16): 5143-5146, 2017 Apr 19.
Artigo em Inglês | MEDLINE | ID: mdl-28350025

RESUMO

The complexes [CpNi(DAB)]BF4, Cp = cyclopentadienyl, DAB = substituted 1,4-diaza-1,3-butadienes, undergo two reduction processes. EPR spectroscopically active Ni(i) intermediates were observed despite the potential redox activity of the DAB ligands and these reduced species catalyse the conversion of electrons and protons (from acetic acid) into dihydrogen.

15.
Chemistry ; 23(8): 1770-1774, 2017 Feb 03.
Artigo em Inglês | MEDLINE | ID: mdl-27943431

RESUMO

The compounds [Fe(CO)3 (dRpf)]n+ , n=0, 1, 2 and dRpf=1,1'-bis(dicyclohexylphosphino)ferrocene ([1]n+ ) or 1,1'-bis(diisopropylphosphino)ferrocene ([2]n+ ), were obtained as two-step reversible redox systems by photolytic and redox reactions. The iron-iron distance decreases from about 4 Što about 3 Šon oxidation, which takes place primarily at the tricarbonyliron moiety. Whereas ferrocene oxidation is calculated to occur only in excited states, the near infrared absorptions of the mixed-valent monocations are due to an unprecedented "inverse" inter-valence charge transfer from the electron-rich iron(II) in the ferrocene backbone to the electron-deficient tricarbonyliron(I). Protonation of complex 1 results in the formation of the structurally characterized hydride [1H]BF4 , which reacts with acetone to form the dication, 12+ , and isopropanol. While the hydride [2H]BF4 was found to be unstable, protonation of 2 in acetone resulted in the clean formation of 22+, formally a hydrogen transfer.

16.
Chem Commun (Camb) ; 51(94): 16806-9, 2015 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-26435029

RESUMO

Oxidation of Au(I) in the presence of Fe(II) allowed for the synthesis of unique dinuclear ferrocenyl Au(II) complexes via the first reported enantiopure planar chiral ferrocenyl Au(I) complex. (Spectro)electrochemical studies show that oxidation at Fe(II) is favoured, but DFT studies suggest that the energy differences for oxidation of one or the other metal should be quite small.

17.
Inorg Chem ; 53(14): 7241-7, 2014 Jul 21.
Artigo em Inglês | MEDLINE | ID: mdl-24992155

RESUMO

Triarylborane Lewis acids bind [Fe2(pdt)(CO)4(CN)2](2-) [1](2-) (pdt(2-) = 1,3-propanedithiolate) and [Fe2(adt)(CO)4(CN)2](2-) [3](2-) (adt(2-) = 1,3-azadithiolate, HN(CH2S(-))2) to give the 2:1 adducts [Fe2(xdt)(CO)4(CNBAr3)2](2-). Attempts to prepare the 1:1 adducts [1(BAr3)](2-) (Ar = Ph, C6F5) were unsuccessful, but related 1:1 adducts were obtained using the bulky borane B(C6F4-o-C6F5)3 (BAr(F)*3). By virtue of the N-protection by the borane, salts of [Fe2(pdt)(CO)4(CNBAr3)2](2-) sustain protonation to give hydrides that are stable (in contrast to [H1](-)). The hydrides [H1(BAr3)2](-) are 2.5-5 pKa units more acidic than the parent [H1](-). The adducts [1(BAr3)2](2-) oxidize quasi-reversibly around -0.3 V versus Fc(0/+) in contrast to ca. -0.8 V observed for the [1](2-/-) couple. A simplified synthesis of [1](2-), [3](2-), and [Fe2(pdt)(CO)5(CN)](-) ([2](-)) was developed, entailing reaction of the diiron hexacarbonyl complexes with KCN in MeCN.


Assuntos
Boranos/química , Cianetos/química , Hidrogenase/química , Proteínas com Ferro-Enxofre/química , Domínio Catalítico , Ligação de Hidrogênio , Modelos Moleculares , Espectrofotometria Infravermelho
18.
Angew Chem Int Ed Engl ; 51(41): 10228-34, 2012 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-22996755

RESUMO

Nature's use of redox-active moieties combined with 3d transition-metal ions is a powerful strategy to promote multi-electron catalytic reactions. The ability of these moieties to store redox equivalents aids metalloenzymes in promoting multi-electron reactions, avoiding high-energy intermediates. In a biomimetic spirit, chemists have recently developed approaches relying on redox-active moieties in the vicinity of metal centers to catalyze challenging transformations. This approach enables chemists to impart noble-metal character to less toxic, and cost effective 3d transitional metals, such as Fe or Cu, in multi-electron catalytic reactions.

19.
Chem Commun (Camb) ; 47(44): 12065-7, 2011 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-21959544

RESUMO

Incorporation of a biotinylated Hoveyda-Grubbs catalyst within (strept)avidin affords artificial metalloenzymes for the ring-closing metathesis of N-tosyl diallylamine in aqueous solution. Optimization of the performance can be achieved either by chemical or genetic means.


Assuntos
Biotina/química , Metaloproteínas/síntese química , Rutênio/química , Estreptavidina/química , Compostos Alílicos/química , Aminas/química , Biotinilação , Catálise
20.
Chem Commun (Camb) ; 47(30): 8470-6, 2011 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-21603692

RESUMO

Artificial metalloenzymes result from combining a catalytically active organometallic moiety with a macromolecular host. The resulting hybrid catalysts combine attractive features of both homogeneous and enzymatic systems. Herein we summarize the recent progress in this emerging field and outline the challenges ahead.


Assuntos
Enzimas/química , Metaloproteínas/química , Modelos Moleculares , Catálise , Complexos de Coordenação/química , Complexos de Coordenação/metabolismo , DNA/química , DNA/metabolismo , Enzimas/metabolismo , Metaloproteínas/metabolismo , Oxirredução , Pirazinas/química , Pirazinas/metabolismo , Rutênio/química , Fosfato de Sitagliptina , Estereoisomerismo , Triazóis/química , Triazóis/metabolismo
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA