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1.
Chemistry ; : e202401280, 2024 May 13.
Artigo em Inglês | MEDLINE | ID: mdl-38739534

RESUMO

4- and 5-coordinate zinc thiolate complexes supported either by bis(carboxamide)pyridine frameworks or by substituted tris(pyrazolyl)borate ligands react with elemental sulfur (S8) following two distinct pathways. Some zinc thiolate moieties insert sulfur atoms to form zinc polysulfanide complexes, while others reduce sulfur and oxidize the thiolate. Here, we compare the effects of ligand electronics, strain, and sterics for selecting the respective reaction pathway. These results show that chelating and electron-deficient thiolate ligands better stabilize persistent zinc-bound polysulfanide species.

2.
Inorg Chem ; 62(5): 2128-2134, 2023 Feb 06.
Artigo em Inglês | MEDLINE | ID: mdl-36701811

RESUMO

Irradiation of cobalt metallocenes at the ligand-to-metal charge transfer energies results in the labilization of the cyclopentadienyl-cobalt bond and radical release. The cyclopentadienyl radical is detected by electron paramagnetic resonance (EPR) spectroscopy using a spin trap and can also be chemically trapped using hydrogen-atom-donating reagents. This reaction presents a new photochemical method of generating new cobalt complexes or of forming cyclopentadienyl cobalt(I) species that are active for catalytic [2 + 2 + 2] cyclotrimerization reactions. More importantly, these results also show that cobaltocene should not be considered as a photostable redox reagent under many conditions, including those relevant to photovoltaics or photocatalysis.

3.
J Am Chem Soc ; 144(45): 20630-20640, 2022 11 16.
Artigo em Inglês | MEDLINE | ID: mdl-36326496

RESUMO

A zinc dithiolate complex supported by a [N3S2] ligand was studied as a model for zinc-mediated thiolate-disulfide exchange, enabling isolation of a zinc-bound mixed-disulfide intermediate. Solution-phase characterization of this zinc-disulfide complex indicates an interaction between the zinc center and the disulfide moiety that results in activation of the S-S bond for subsequent reactions. Comparison of this reaction with disulfide exchange by a previously prepared zinc tetrasulfanido complex demonstrates that sulfane sulfur (S0) acts as an efficient thiolate trapping agent, that is, polysulfanide anions are much less basic than thiolates. The resulting polysulfanide anions also exhibit decreased nucleophilicity compared to the parent thiolate anions. Alkylation kinetics comparisons between the zinc dithiolate and zinc tetrasulfanido complexes indicate attenuation of zinc-bound thiolate nucleophilicity by sulfane. These results suggest a general interplay between zinc, sulfane, and thiol/thiolate reactivity that can significantly impact biological redox processes.


Assuntos
Enxofre , Zinco , Zinco/química , Enxofre/química , Compostos de Sulfidrila/química , Dissulfetos
4.
Inorg Chem ; 60(7): 4269-4277, 2021 Apr 05.
Artigo em Inglês | MEDLINE | ID: mdl-33502193

RESUMO

Characterizing the surfaces of colloidal semiconductor nanocrystals (NCs) remains a key challenge for understanding and controlling their physical properties and chemical behavior. For this reason, the development of new methods to study NC surfaces is of great interest. In this paper, we report the use of (Me3Si)2Fe(CO)4 and Et3SiCo(CO)4 as reagents for functionalizing CdSe NC surfaces with organometallic metal tetracarbonyl fragments. This method avoids NC surface reduction and can achieve high metal carbonyl surface densities. Surface reduction or oxidation, as well as changes to the surface stoichiometry, was shown to shift the metal carbonyl CO stretching frequencies, making these surface-bound metal carbonyl fragments useful spectroscopic reporters of NC surface chemistry. Normal coordinate analysis was used on the metal carbonyl CO stretching vibrations to study the electronic influence of the CdSe NCs on the transition-metal center of the metal carbonyl fragments. These studies demonstrate the utility of organometallic spectroscopic reporters in studying the surface chemistry of NCs.

5.
Nano Lett ; 19(11): 7770-7774, 2019 11 13.
Artigo em Inglês | MEDLINE | ID: mdl-31596596

RESUMO

Organometallic surface functionalization of colloidal CdSe and CdS nanocrystals using iron tetracarbonyl moieties is demonstrated to enable study of in situ colloidal nanocrystal surface redox chemistry. Spectroscopic measurements of the surface-bound metal carbonyl C-O stretches were used to elucidate the coordination environments and local symmetry of surface sites. The C-O stretching frequencies of these fragments were correlated to the electric field induced by nanocrystal surface charges and shift in energy upon surface reduction or oxidation. These measurements revealed that CdSe nanocrystals can accumulate multiple surface electrons under supra-band gap photoexcitation, a process likely relevant to photoactivated nanocrystal processes such as photobrightening. These surface charges are stable for hours and decay extremely slowly under anaerobic conditions.

6.
Inorg Chem ; 58(16): 10501-10507, 2019 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-31247870

RESUMO

Zinc thiolate bonds are intriguing targets of study because of their redox noninnocence and prevalence in bioinorganic sites. A five-coordinate zinc dithiolate complex [Et4N]2[LZn] (H4L = N,N'-di(2-sulfhydrylphenyl)-pyridine-2,6-dicarboxamide) was synthesized to study the oxidative reactivity of zinc thiolate bonds. Multiple chemically reversible reactions of the zinc thiolate bonds were identified. Oxidation of [Et4N]2[LZn] with iodine resulted in structural rearrangement to a bimetallic disulfide-bridged complex. In contrast, the addition of elemental sulfur to [Et4N]2[LZn] resulted in the insertion of a neutral S3 fragment into the Zn-thiolate bond to selectively form an unusual monometallic tetrasulfanido complex. When oxidized, this tetrasulfanido compound rearranged to form a bimetallic trisulfide-bridged complex. The observed diversity of zinc thiolate reactivity, particularly with sulfur, is likely important in biological contexts.


Assuntos
Complexos de Coordenação/química , Compostos de Sulfidrila/química , Sulfetos/química , Enxofre/química , Zinco/química , Modelos Moleculares , Estrutura Molecular , Oxirredução
7.
Inorg Chem ; 58(4): 2336-2345, 2019 Feb 18.
Artigo em Inglês | MEDLINE | ID: mdl-30730725

RESUMO

The modulation of the reactivity of metal oxo species by redox inactive metals has attracted much interest due to the observation of redox inactive metal effects on processes involving electron transfer both in nature (the oxygen-evolving complex of Photosystem II) and in heterogeneous catalysis (mixed-metal oxides). Studies of small-molecule models of these systems have revealed numerous instances of effects of redox inactive metals on electron- and group-transfer reactivity. However, the heterometallic species directly involved in these transformations have rarely been structurally characterized and are often generated in situ. We have previously reported the preparation and structural characterization of multiple series of heterometallic clusters based on Mn3 and Fe3 cores and described the effects of Lewis acidity of the heterometal incorporated in these complexes on cluster reduction potential. To determine the effects of Lewis acidity of redox inactive metals on group transfer reactivity in structurally well-defined complexes, we studied [Mn3MO4], [Mn3MO(OH)], and [Fe3MO(OH)] clusters in oxygen atom transfer (OAT) reactions with phosphine substrates. The qualitative rate of OAT correlates with the Lewis acidity of the redox inactive metal, confirming that Lewis acidic metal centers can affect the chemical reactivity of metal oxo species by modulating cluster electronics.

8.
J Am Chem Soc ; 138(35): 11105-8, 2016 09 07.
Artigo em Inglês | MEDLINE | ID: mdl-27518320

RESUMO

Understanding the structural and compositional origins of midgap states in semiconductor nanocrystals is a longstanding challenge in nanoscience. Here, we report a broad variety of reagents useful for photochemical reduction of colloidal CdSe quantum dots, and we establish that these reactions proceed via a dark surface prereduction step prior to photoexcitation. Mechanistic studies relying on the specific properties of various reductants lead to the proposal that this surface prereduction occurs at oxidized surface selenium sites. These results demonstrate the use of small-molecule inorganic chemistries to control the physical properties of colloidal QDs and provide microscopic insights into the identities and reactivities of their localized surface species.


Assuntos
Compostos de Cádmio/química , Pontos Quânticos/química , Compostos de Selênio/química , Selênio/química , Alquilação , Coloides , Oxirredução , Propriedades de Superfície
9.
J Am Chem Soc ; 138(13): 4310-3, 2016 Apr 06.
Artigo em Inglês | MEDLINE | ID: mdl-26978480

RESUMO

A potentiometric method for measuring redox potentials of colloidal semiconductor nanocrystals (NCs) is described. Fermi levels of colloidal ZnO NCs are measured in situ during photodoping, allowing correlation of NC redox potentials and reduction levels. Excellent agreement is found between electrochemical and optical redox-indicator methods. Potentiometry is also reported for colloidal CdSe NCs, which show more negative conduction-band-edge potentials than in ZnO. This difference is highlighted by spontaneous electron transfer from reduced CdSe NCs to ZnO NCs in solution, with potentiometry providing a measure of the inter-NC electron-transfer driving force. Future applications of NC potentiometry are briefly discussed.


Assuntos
Pontos Quânticos , Compostos de Cádmio/química , Transporte de Elétrons , Nanopartículas/química , Nanoestruturas/química , Oxirredução , Potenciometria , Compostos de Selênio/química , Semicondutores , Óxido de Zinco/análise
10.
Inorg Chem ; 55(12): 6095-9, 2016 Jun 20.
Artigo em Inglês | MEDLINE | ID: mdl-27281290

RESUMO

Inspired by the ferromagnetic coupling in the cubane model CaMn(IV)3O4 of the oxygen-evolving complex of photosystem II, 3d-4f mixed-metal DyMn3O4 clusters were prepared for investigation of the magnetic properties. For comparison, YMn(IV)3O4 and YMn(IV)2Mn(III)O4 clusters were investigated as well and showed ferromagnetic interactions, like the calcium analogue. DyMn(IV)3O4 displays single-molecule-magnet properties, while the one-electron-reduced species (DyMn(IV)2Mn(III)O4) does not, despite the presence of a Mn(III) center with higher spin and single-ion anisotropy.


Assuntos
Manganês/química , Espectroscopia de Ressonância de Spin Eletrônica , Oxirredução
11.
Proc Natl Acad Sci U S A ; 110(25): 10084-8, 2013 Jun 18.
Artigo em Inglês | MEDLINE | ID: mdl-23744039

RESUMO

Understanding the effect of redox-inactive metals on the properties of biological and heterogeneous water oxidation catalysts is important both fundamentally and for improvement of future catalyst designs. In this work, heterometallic manganese-oxido cubane clusters [MMn3O4] (M = Sr(2+), Zn(2+), Sc(3+), Y(3+)) structurally relevant to the oxygen-evolving complex (OEC) of photosystem II were prepared and characterized. The reduction potentials of these clusters and other related mixed metal manganese-tetraoxido complexes are correlated with the Lewis acidity of the apical redox-inactive metal in a manner similar to a related series of heterometallic manganese-dioxido clusters. The redox potentials of the [SrMn3O4] and [CaMn3O4] clusters are close, which is consistent with the observation that the OEC is functional only with one of these two metals. Considering our previous studies of [MMn3O2] moieties, the present results with more structurally accurate models of the OEC ([MMn3O4]) suggest a general relationship between the reduction potentials of heterometallic oxido clusters and the Lewis acidities of incorporated cations that applies to diverse structural motifs. These findings support proposals that one function of calcium in the OEC is to modulate the reduction potential of the cluster to allow electron transfer.


Assuntos
Compostos de Manganês/química , Manganês/química , Óxidos/química , Fotossíntese , Água/química , Cálcio/química , Catálise , Química Bioinorgânica , Eletroquímica , Transporte de Elétrons , Modelos Moleculares , Oxirredução , Complexo de Proteína do Fotossistema II/química
12.
J Am Chem Soc ; 137(34): 11163-9, 2015 Sep 02.
Artigo em Inglês | MEDLINE | ID: mdl-26263400

RESUMO

Electronically doped colloidal semiconductor nanocrystals offer valuable opportunities to probe the new physical and chemical properties imparted by their excess charge carriers. Photodoping is a powerful approach to introducing and controlling free carrier densities within free-standing colloidal semiconductor nanocrystals. Photoreduced (n-type) colloidal ZnO nanocrystals possessing delocalized conduction-band (CB) electrons can be formed by photochemical oxidation of EtOH. Previous studies of this chemistry have demonstrated photochemical electron accumulation, in some cases reaching as many as >100 electrons per ZnO nanocrystal, but in every case examined to date this chemistry maximizes at a well-defined average electron density of ⟨Nmax⟩ ≈ (1.4 ± 0.4) × 10(20) cm(-3). The origins of this maximum have never been identified. Here, we use a solvated redox indicator for in situ determination of reduced ZnO nanocrystal redox potentials. The Fermi levels of various photodoped ZnO nanocrystals possessing on average just one excess CB electron show quantum-confinement effects, as expected, but are >600 meV lower than those of the same ZnO nanocrystals reduced chemically using Cp*2Co, reflecting important differences between their charge-compensating cations. Upon photochemical electron accumulation, the Fermi levels become independent of nanocrystal volume at ⟨N⟩ above ∼2 × 10(19) cm(-3), and maximize at ⟨Nmax⟩ ≈ (1.6 ± 0.3) × 10(20) cm(-3). This maximum is proposed to arise from Fermi-level pinning by the two-electron/two-proton hydrogenation of acetaldehyde, which reverses the EtOH photooxidation reaction.


Assuntos
Aldeídos/química , Nanoestruturas/química , Óxido de Zinco/química , Coloides/química , Elétrons , Etanol/química , Hidrogenação , Oxirredução , Processos Fotoquímicos , Semicondutores
13.
Polyhedron ; 84: 103-110, 2014 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-30393421

RESUMO

A binucleating bis(N-heterocyclic carbene) ligand was designed as a means to coordinate and proximally constrain two transition metal centers. Using an imidazopyridine-based NHC afforded a framework structurally related to previously reported para-terphenyl diphosphines. Bimetallic copper, cobalt, and nickel complexes supported by this framework were synthesized and structurally characterized. Strong interactions between the metal centers and the central arene were observed in all nickel complexes. Dinickel(0) complexes of this ligand framework were found to react with CO2 to form a dicarbonyl-bridged dinickel(0) product, demonstrating facile CO2 reduction.

14.
Chem Sci ; 15(19): 7332-7341, 2024 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-38756819

RESUMO

Sulfur-containing anions (e.g. thiolates, polysulfides) readily exchange in solution, making control over their solution speciation and distribution challenging. Here, we demonstrate that different redox-inactive alkali, alkaline earth, and transition metals (Li+, Na+, K+, Mg2+, Ca2+, Zn2+, and Cd2+) shift the equilibria of sulfur catenation or sulfur reduction/oxidation between thiolate, polysulfanide, and polysulfide anions in acetonitrile solution. The thermodynamic factors that govern these equilibria are examined by identification of intermediate metal thiolate and metal polysulfide species using a combination of NMR spectroscopy, electronic absorption spectroscopy, and mass spectrometry. Electrochemical measurements demonstrate that the metal cation of the electrolyte modulates both sulfur reduction and thiolate oxidation potentials. DFT calculations suggest that the changes in equilibria are driven by stronger covalent interactions between polysulfide anions and more highly charged cations.

15.
J Am Chem Soc ; 135(3): 1073-82, 2013 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-23241061

RESUMO

The oxygen-evolving complex (OEC) of photosystem II contains a Mn(4)CaO(n) catalytic site, in which reactivity of bridging oxidos is fundamental to OEC function. We synthesized structurally relevant cuboidal Mn(3)MO(n) complexes (M = Mn, Ca, Sc; n = 3,4) to enable mechanistic studies of reactivity and incorporation of µ(3)-oxido moieties. We found that Mn(IV)(3)CaO(4) and Mn(IV)(3)ScO(4) were unreactive toward trimethylphosphine (PMe(3)). In contrast, our Mn(III)(2)Mn(IV)(2)O(4) cubane reacts with this phosphine within minutes to generate a novel Mn(III)(4)O(3) partial cubane plus Me(3)PO. We used quantum mechanics to investigate the reaction paths for oxygen atom transfer to phosphine from Mn(III)(2)Mn(IV)(2)O(4) and Mn(IV)(3)CaO(4). We found that the most favorable reaction path leads to partial detachment of the CH(3)COO(-) ligand, which is energetically feasible only when Mn(III) is present. Experimentally, the lability of metal-bound acetates is greatest for Mn(III)(2)Mn(IV)(2)O(4). These results indicate that even with a strong oxygen atom acceptor, such as PMe(3), the oxygen atom transfer chemistry from Mn(3)MO(4) cubanes is controlled by ligand lability, with the Mn(IV)(3)CaO(4) OEC model being unreactive. The oxidative oxide incorporation into the partial cubane, Mn(III)(4)O(3), was observed experimentally upon treatment with water, base, and oxidizing equivalents. (18)O-labeling experiments provided mechanistic insight into the position of incorporation in the partial cubane structure, consistent with mechanisms involving migration of oxide moieties within the cluster but not consistent with selective incorporation at the site available in the starting species. These results support recent proposals for the mechanism of the OEC, involving oxido migration between distinct positions within the cluster.


Assuntos
Cálcio/química , Manganês/química , Oxigênio/química , Teoria Quântica , Escândio/química , Água/química , Marcação por Isótopo , Oxirredução
16.
Inorg Chem ; 52(24): 13833-48, 2013 Dec 16.
Artigo em Inglês | MEDLINE | ID: mdl-24328344

RESUMO

Artificial photosynthesis has emerged as an important strategy toward clean and renewable fuels. Catalytic oxidation of water to O2 remains a significant challenge in this context. A mechanistic understanding of currently known heterogeneous and biological catalysts at a molecular level is highly desirable for fundamental reasons as well as for the rational design of practical catalysts. This Award Article discusses recent efforts in synthesizing structural models of the oxygen-evolving complex of photosystem II. These structural motifs are also related to heterogeneous mixed-metal oxide catalysts. A stepwise synthetic methodology was developed toward achieving the structural complexity of the targeted active sites. A geometrically restricted multinucleating ligand, but with labile coordination modes, was employed for the synthesis of low-oxidation-state trimetallic species. These precursors were elaborated to site-differentiated tetrametallic complexes in high oxidation states. This methodology has allowed for structure-reactivity studies that have offered insight into the effects of different components of the clusters. Mechanistic aspects of oxygen-atom transfer and incorporation from water have been interrogated. Significantly, a large and systematic effect of redox-inactive metals on the redox properties of these clusters was discovered. With the pKa value of the redox-inactive metal-aqua complex as a measure of the Lewis acidity, structurally analogous clusters display a linear dependence between the reduction potential and acidity; each pKa unit shifts the potential by ca. 90 mV. Implications for the function of the biological and heterogeneous catalysts are discussed.


Assuntos
Complexos de Coordenação/química , Manganês/química , Modelos Moleculares , Oxigênio/metabolismo , Cálcio/química , Catálise , Oxigênio/química , Difração de Raios X
17.
Chem Sci ; 14(45): 13080-13089, 2023 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-38023529

RESUMO

The participation of the surfaces of colloidal semiconductor nanocrystal quantum dots (QDs) in QD-mediated photocatalytic reactions is an important factor that distinguishes QDs from other photosensitizers (e.g. transition metal complexes or organic dyes). Here, we probe nucleophilic and radical reactivity of surface sulfides and selenides of metal chalcogenide (CdSe, CdS, ZnSe, and PbS) QDs using chemical reactions and NMR spectroscopy. Additionally, the high sensitivity of EPR spectroscopy is adapted to study these surface-centered reactions through the use of spin traps like 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) under photoexcitation and thermal conditions. We demonstrate that DMPO likely adds to CdSe QD surfaces under thermal conditions by a nucleophilic mechanism in which the surface chalcogenides add to the double bond, followed by further oxidation of the surface-bound product. In contrast, CdS QDs more readily form surface sulfur-centered radicals that can perform reactions including alkene isomerization. These results indicate that QD surfaces should be an important consideration for the design of photocatalysis beyond simply tuning QD semiconductor band gaps.

18.
Dalton Trans ; 51(25): 9611-9615, 2022 Jun 27.
Artigo em Inglês | MEDLINE | ID: mdl-35695261

RESUMO

ZnII and FeII chloride complexes of a di(methylthiazolidinyl)pyridine ligand were deprotonated to form the corresponding thiolate complexes supported by redox-active iminopyridine moieties. The thiolate donor groups are nucleophilic and reactive toward oxidants, electrophiles, and protons, while the pendant thiazolidine rings are available for hydrogen bonding. Anion exchange with the weakly-coordinating triflate anion resulted in self-assembly of the iminopyridine complexes to form a trimeric [M3S3] cluster. Hydrogen bonding closely associates anions with this trimetallic core.


Assuntos
Complexos de Coordenação , Ânions , Cristalografia por Raios X , Ligantes , Estrutura Molecular
19.
Chem Commun (Camb) ; 57(93): 12488-12491, 2021 Nov 23.
Artigo em Inglês | MEDLINE | ID: mdl-34747957

RESUMO

Nucleophilic 1,2-aminothiol compounds readily reduce typically-insoluble elemental sulfur to polysulfides in both water and nonpolar organic solvents. The resulting anionic polysulfide species are stabilized through hydrogen-bonding interactions with the proximal amine moieties. These interactions can facilitate sulfur transfer to alkenes.


Assuntos
Compostos de Sulfidrila/química , Sulfetos/química , Enxofre/química , Aminas/química , Ligação de Hidrogênio , Oxirredução , Solventes/química , Água/química
20.
Dalton Trans ; 49(45): 16305-16311, 2020 Nov 25.
Artigo em Inglês | MEDLINE | ID: mdl-32427258

RESUMO

A zinc tetrasulfanido complex supported by a bis(carboxamide)pyridine ligand framework has been synthesized by the insertion of elemental sulfur into the zinc-S(thiolate) bond of a zinc dithiolate complex ([LZn]2-). This paper reports on sulfur transfer reactions of this polysulfanido complex ([1]2-) and compares this behavior to known reactions of metal polysulfido complexes. Complex [1]2- was demonstrated to be in exchange with [LZn]2- and free elemental sulfur in solution. Although triphenylphosphine abstracts sulfur from [1]2- to form [LZn]2-, complex [LZn]2- can abstract sulfur from the zinc polysulfido complex (TMEDA)ZnS6 (TMEDA = N,N,N',N'-tetramethylethylenediamine). The tetrasulfanido complex [1]2- can also transfer sulfur to dimethyl acetylenedicarboxylate to form a zinc dithiolene complex. These studies demonstrate that the zinc complex with a tetrasulfanido moiety can undergo similar reactions as metal complexes with purely inorganic polysulfido groups, although the final metal-containing products are different.

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