Metal Exchange Reactions Research Articles

(Invited) Metalation of Porphyrins on Surfaces in Liquid and Vacuum

Adsorption and metalation of porphyrins on metal single-crystal surfaces under ultrahigh vacuum has been studied extensively, but less is known about the adsorption behavior of porphyrins on oxide surfaces. On metal surfaces porphyrin molecules will react with coadsorbed metal atoms or the surface itself, producing the metalated molecules and coadsorbed hydrogen atoms, which subsequently combine and desorb as hydrogen molecules. Examples will be given of 5,10,15,20-tetraphenylporphyrin (2HTPP) on Cu(111). A similar reaction is also possible for oxide surfaces. As 2HTPP is adsorbed on MgO an ion-exchange reaction happens already at room temperature and the two aminic protons of the porphyrin molecule are exchanged with a Mg2+ ion from the oxide surface, producing MgTPP and, locally, Mg(OH)2. Examples will be given of adsorption on both single-crystal MgO(100) substrates and nanostructured powders. Examples will also be given of metalation of 2HTPP adsorbed on a Au(111) surface immersed in an aqueous zinc acetate solution, metal-exchange reactions with Cu2+ and unsuccessful attempts to demetalate the adsorbed metalloporphyrins in acidic solutions.

Complex formation of β-brominated tetraphenylporphyrins and metal exchange of their cadmium complexes with d-metal salts in dimethylformamide

Complex formation of zinc and copper(II) acetates with tetraphenylporphyrin, 2-bromo-5,10,15,20-tetraphenylporphyrin, 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrin, and 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphyrin in N,N-dimethylformamide has been studied. The rate constants determined in the study of the complex formation and the metal exchange reactions have been compared.

Tuning the electronic structure of thiolate-protected 25-atom clusters by co-substitution with metals having different preferential sites.

Trimetallic Au24-xAgxPd and tetrametallic Au24-x-yAgxCuyPd clusters were synthesized by the subsequential metal exchange reactions of dodecanethiolate-protected Au24Pd clusters. EXAFS measurements revealed that Pd, Ag, and Cu dopants preferentially occupy the center and edge sites of the core, and staple sites, respectively. Spectroscopic and theoretical studies demonstrated that the synergistic effects of multiple substitutions on the electronic structures are additive in nature.

The C[sbnd]N coupling reaction of bimetallic cations [MAu(CH)]+ (M = Pt, Ir, Os) with NH3

Bimetallic methylidyne cluster cations such as [MAu(CH)]+ (M=Pt, Ir, Os), featuring the combination of a less reactive (Au) and a more reactive (M) metal centers, exhibit very different reactivities with NH3. Density functional calculations confirm the direct CN coupling in all clusters, with the main products of PtAu/[CH2NH2]+ in the Pt system and [MAu(CNH2)]+ (M=Ir, Os)/H2 in the Ir and Os systems. Furthermore, for the first time, a feasible minor product reaction path leading to the direct formation of HCN has been located in both the Ir and Os systems. The great potential of regulating reaction pathways by designing bi- or multi-metallic catalysts is presented.

Iridium Complexes of the Conformationally Rigid IBioxMe4 Ligand: Hydride Complexes and Dehydrogenation of Cyclooctene

A method for accessing the formally 14 VE iridium(III) hydride fragment {Ir(IBioxMe4)2(H)2}+ (2), containing the conformationally rigid NHC ligand IBioxMe4, is reported. Hydrogenation of trans-[Ir(IBioxMe4)2(COE)Cl] (1) in the presence of excess Na[BArF4] leads to the formation of dimeric [{Ir(IBioxMe4)2(H)2}2Cl][BArF4] (3), which is structurally fluxional in solution and acts as a reservoir of monomeric 2 in the presence of excess halogen ion abstractor. Stable dihydride complexes trans-[Ir(IBioxMe4)2(2,2′-bipyridine)(H)2][BArF4] (4) and [Ir(IBioxMe4)3(H)2][BArF4] (5) were subsequently isolated through in situ trapping of 2 using 2,2′-bipyridine and IBioxMe4, respectively, and fully characterized. Using mixtures of 3 and Na[BArF4] as a latent source of 2, the reactive monomeric fragment’s reactivity was explored with excess ethylene and cyclooctene, and trans-[Ir(IBioxMe4)2(C2H4)2][BArF4] (6) and cis-[Ir(IBioxMe4)2(COD)][BArF4] (7) were isolated, respectively, through sacrificial hydrogenation of the alkenes. Complex 6 is notable for the adoption of a very unusual orthogonal arrangement of the trans-ethylene ligands in the solid state, which has been analyzed computationally using energy and charge decomposition (EDA-NOCV). The formation of 7 via transfer dehydrogenation of COE highlights the ability to partner IBioxMe4 with reactive metal centers capable of C–H bond activation, without intramolecular activation. Reaction of 7 with CO slowly formed trans-[Ir(IBioxMe4)2(CO)2][BArF4] (8), but the equivalent reaction with bis-ethylene 6 was an order of magnitude faster, quantifying the strong coordination of COD in 7.

ChemInform Abstract: Tuning the Properties of Copper‐Based Catalysts Based on Molecular in situ Studies of Model Systems

AbstractReview: 42 refs.

Tuning the properties of copper-based catalysts based on molecular in situ studies of model systems.

Studying catalytic processes at the molecular level is extremely challenging, due to the structural and chemical complexity of the materials used as catalysts and the presence of reactants and products in the reactor's environment. The most common materials used on catalysts are transition metals and their oxides. The importance of multifunctional active sites at metal/oxide interfaces has been long recognized, but a molecular picture of them based on experimental observations is only recently emerging. The initial approach to interrogate the surface chemistry of catalysts at the molecular level consisted of studying metal single crystals as models for reactive metal centers, moving later to single crystal or well-defined thin film oxides. The natural next iteration consisted in the deposition of metal nanoparticles on well-defined oxide substrates. Metal nanoparticles contain undercoordinated sites, which are more reactive. It is also possible to create architectures where oxide nanoparticles are deposited on top of metal single crystals, denominated inverse catalysts, leading in this case to a high concentration of reactive cationic sites in direct contact with the underlying fully coordinated metal atoms. Using a second oxide as a support (host), a multifunctional configuration can be built in which both metal and oxide nanoparticles are located in close proximity. Our recent studies on copper-based catalysts are presented here as an example of the application of these complementary model systems, starting from the creation of undercoordinated sites on Cu(111) and Cu2O(111) surfaces, continuing with the formation of mixed-metal copper oxides, the synthesis of ceria nanoparticles on Cu(111) and the codeposition of Cu and ceria nanoparticles on TiO2(110). Catalysts have traditionally been characterized before or after reactions and analyzed based on static representations of surface structures. It is shown here how dynamic changes on a catalyst's chemical state and morphology can be followed during a reaction by a combination of in situ microscopy and spectroscopy. In addition to determining the active phase of a catalyst by in situ methods, the presence of weakly adsorbed surface species or intermediates generated only in the presence of reactants can be detected, allowing in turn the comparison of experimental results with first principle modeling of specific reaction mechanisms. Three reactions are used to exemplify the approach: CO oxidation (CO + 1/2O2 → CO2), water gas shift reaction (WGSR) (CO + H2O → CO2 + H2), and methanol synthesis (CO2 + 3H2 → CH3OH + H2O). During CO oxidation, the full conversion of Cu(0) to Cu(2+) deactivates an initially outstanding catalyst. This can be remedied by the formation of a TiCuOx mixed-oxide that protects the presence of active partially oxidized Cu(+) cations. It is also shown that for the WGSR a switch occurs in the reaction mechanism, going from a redox process on Cu(111) to a more efficient associative pathway at the interface of ceria nanoparticles deposited on Cu(111). Similarly, the activation of CO2 at the ceria/Cu(111) interface allows its facile hydrogenation to methanol. Our combined studies emphasize the need of searching for optimal metal/oxide interfaces, where multifunctional sites can lead to new efficient catalytic reaction pathways.

Metal exchange reaction between Mg(II) and Cd(II) octa(4-bromophenyl)tetraazaporphyrinates with manganese(II) chloride in dimethylformamide

Reaction of metal exchange of Mg(II) and Cd(II) octa(4-bromophenyl)tetraazaporphyrinates with MnCl2 in dimethylformamide has been studied by means of spectrophotometry. Kinetic parameters of the reaction have been determined; the reaction stoichiometry mechanism has been suggested.

Study of the metal-exchange reaction between Cd(II) octa(4-bromophenyl)tetraazaporphyrinate and cobalt chloride in organic solvents

The metal-exchange reaction between Cd(II) octa(4-bromophenyl)tetraazaporphyrinate and cobalt chloride in dimethylformamide and dimethyl sulfoxide was studied by spectrophotometry. Kinetic parameters of the metal-exchange reaction were determined. A possible stoichiometric mechanism of the reaction was proposed. Cobalt(III) octa(4-bromophenyl)tetraazaporphyrinate was synthesized and characterized.

Preparation of an Ester-Containing Grignard Reagent by Halogen–Metal Exchange

In this experiment, students carry out a halogen–metal exchange reaction of methyl 2-iodobenzoate with isopropylmagnesium chloride in THF at 0 °C to afford 2-carbomethoxyphenylmagnesium chloride, which is treated with p-methoxybenzaldehyde to give a lactone (phthalide) product. This reaction introduces students to the modern method of preparation of Grignard and organolithium reagents by halogen–metal exchange rather than by using metallic magnesium or lithium, which is rarely done in a research laboratory. It also demonstrates that Grignard reagents bearing reactive functionality can be prepared and utilized in synthesis, although students are still often taught otherwise. The IR spectrum of the crude product provides semiquantitative information on the success of the reaction because the lactone product and starting material ester and aldehyde have very different carbonyl absorptions, demonstrating the power of this technique to distinguish between functional groups. The product can be purified by chrom...

Structural Studies of (rac)-BIPHEN Organomagnesiates and Intermediates in the Halogen–Metal Exchange of 2-Bromopyridine

Four lithium magnesiate complexes (2–5) containing the dianionic (rac)-BIPHEN ligand have been prepared and characterized using X-ray crystallography and NMR spectroscopy. (THF)3·Li2Mg{(rac)-BIPHEN}nBu2, 2, (THF)3·Li2Mg{(rac)-BIPHEN}(CH2SiMe3)2, 3, and (THF)2·Li2Mg{(rac)-BIPHEN}neoPe2, 4, have been prepared by complexation of the appropriate dialkylmagnesium compound with in situ prepared Li(rac)-BIPHEN in a mixture of hydrocarbon/THF. For all structures, the Mg centers are four-coordinate (and retain the alkyl groups); however, in 2 and 3 the two Li centers have different coordination spheres (one binding to one THF molecule, the other to two). The solid-state structures of 2 and 3 are essentially isostructural with that of 4 except that both Li atoms in this molecule have equivalent coordination spheres. The solution behaviors of these three molecules have been studied by 1H, 13C, and DOSY NMR spectroscopy. During the synthesis of 2, it was discovered that a (rac)-BIPHEN-rich (or n-butyl-free) lithium magnesiate, (THF)4Li2Mg{(rac)-BIPHEN}fo2, 2b, could be isolated. The lithium precursor to 2–5, (THF)4·Li4{(rac)-BIPHEN)}2, 1, has also been isolated. Within the molecular structure of this tetranuclear complex, there are three different Li coordination environments. Finally, 2 has already shown promise as a reagent in a halogen–metal exchange reaction with 2-bromopyridine. The structural chemistry at play in this reaction was probed by X-ray crystallography and NMR spectroscopy. The organometallic intermediate pyridyl-magnesiated 5, (THF)2·Li2Mg{(rac)-BIPHEN}(2-pyridyl)2, was isolated in high yield.

Fluorescent metal ion chemosensors via cation exchange reactions of complexes, quantum dots, and metal-organic frameworks.

Due to their wide range of applications and biological significance, fluorescent sensors have been an active research area in the past few years. In the present review, recent research developments on fluorescent chemosensors that detect metal ions via cation exchange reactions (transmetalation, metal displacement, or metal exchange reactions) of complexes, quantum dots, and metal-organic frameworks are described. These complex-based chemosensors might have a much better selectivity than the corresponding free ligands/receptors because of the shielding function of the filled-in metal ions. Moreover, not only the chemical structure of the ligands/receptors but also the identity of the central metal ions have a tremendous impact on the sensing performances. Therefore, sensing via cation exchange reactions potentially provides a new, simple, and powerful way to design fluorescent chemosensors.

Combining the Reactivity Properties of PCy3 and PtBu3 into a Single Ligand, P(iPr)(tBu)2. Reaction via Mono- or Bisphosphine Palladium(0) Centers and Palladium(I) Dimer Formation

Trialkylphosphine ligands are ubiquitous in catalysis. Via modulation of the steric bulk of these ligands, two central aspects that dictate reactivity and selectivity in catalysis can be controlled: i.e., the coordination sphere and favored oxidation state of the reactive metal center. Within this class of ligands, tricyclohexylphosphine (PCy3) and tri-tert-butylphosphine (PtBu3) are most widely used in catalysis. While the smaller PCy3 favors reactivity via Pd bisphosphine species with the test substrate 4-chlorophenyl triflate 1 and does not form dinuclear Pd(I) complexes upon oxidation of Pd(0), PtBu3 reacts via a monophosphine-ligated Pd complex with 1 and forms dinuclear Pd(I) complexes on oxidation. We herein report that the hybrid ligand P(iPr)(tBu)2, characterized by a cone angle that is between those of PCy3 and PtBu3, features all of these reactivity properties in a single scaffold. This is exemplified in chemoselectivity studies with test system 1, in which the site selectivity could be readily modulated. The novel Pd(I) dimer {[P(iPr)(tBu)2]PdI}2 has also been synthesized.

Metal exchange reaction of magnesium(II) octa(4-bromophenyl)tetraazaporphyrinate with copper and cobalt chlorides in dimethylformamide

Metal exchange reaction of magnesium(II) octa(4-bromophenyl)tetraazaporphyrinate with copper and cobalt chlorides in dimethylformamide has been studied by spectrophotometry measurements. Kinetic parameters of the metal exchange reaction have been determined. Possible stoichiometric mechanism of the reaction was proposed.

Metal exchange reaction of magnesium octaphenyltetraazaporphyrin with copper, cobalt, and zinc chlorides in DMSO and DMF

Metal exchange reaction of (octaphenyltetraazaporphyrinato)magnesium(II) with copper, cobalt, and zinc chlorides in dimethyl sulfoxide and dimethylformamide has been studied by spectrophotometry. Kinetic and thermodynamic parameters of the process have been determined, and a probable reaction mechanism has been proposed. Zinc(II), copper(II), cobalt(II), and cobalt(III) complexes of octaphenyltetraazaporphyrin have been isolated and characterized.

ChemInform Abstract: Generation of Arynes Triggered by Sulfoxide—Metal Exchange Reaction of ortho‐Sulfinylaryl Triflates.

ChemInformVolume 45, Issue 32 Preparative Organic Chemistry ChemInform Abstract: Generation of Arynes Triggered by Sulfoxide—Metal Exchange Reaction of ortho-Sulfinylaryl Triflates. Suguru Yoshida, Suguru Yoshida Inst. Biomater. Bioeng., Med. Dent. Univ., Chiyoda, Tokyo 101, JapanSearch for more papers by this authorKeisuke Uchida, Keisuke Uchida Inst. Biomater. Bioeng., Med. Dent. Univ., Chiyoda, Tokyo 101, JapanSearch for more papers by this authorTakamitsu Hosoya, Takamitsu Hosoya Inst. Biomater. Bioeng., Med. Dent. Univ., Chiyoda, Tokyo 101, JapanSearch for more papers by this author Suguru Yoshida, Suguru Yoshida Inst. Biomater. Bioeng., Med. Dent. Univ., Chiyoda, Tokyo 101, JapanSearch for more papers by this authorKeisuke Uchida, Keisuke Uchida Inst. Biomater. Bioeng., Med. Dent. Univ., Chiyoda, Tokyo 101, JapanSearch for more papers by this authorTakamitsu Hosoya, Takamitsu Hosoya Inst. Biomater. Bioeng., Med. Dent. Univ., Chiyoda, Tokyo 101, JapanSearch for more papers by this author First published: 24 July 2014 https://doi.org/10.1002/chin.201432027Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume45, Issue32August 12, 2014 RelatedInformation

Mechanochemistry with metallosupramolecular polymers.

The transduction of mechanical force into useful chemical reactions is an emerging design approach to impart soft materials with new functions. Here, we report that mechanochemical transductions can be achieved in metallosupramolecular polymers. We show that both reversible and irreversible reactions are possible and useful to create mechanically responsive materials that display new functions. The metallopolymer studied was a cross-linked network assembled from a europium salt and a telechelic poly(ethylene-co-butylene) with 2,6-bis(1'-methylbenzimidazolyl)pyridine (Mebip) ligands at the termini. The Eu(3+) complexes serve both as mechanically responsive binding motifs and as built-in optical probes that can monitor the extent of (dis)assembly due to their characteristic photoluminescent properties. Indeed, dose-dependent and reversible metal-ligand dissociation occurs upon exposure to ultrasound in solution. The absence of ultrasound-induced dissociation of a low-molecular weight model complex and in-depth studies of temperature effects confirm that the dissociation is indeed the result of mechanical activation. The influence of the strength of the metal-ligand interactions on the mechanically induced dissociation was also explored. Metallopolymers in which the Mebip ligands were substituted with more strongly coordinating dipicolinate (dpa) ligands do not dissociate upon exposure to ultrasound. Finally, we show that mechanochemical transduction in metallosupramolecular polymers is also possible in the solid state. We demonstrate mending of damaged objects through ultrasound as well as mechanochromic behavior based on metal-exchange reactions in metallopolymers imbibed with an auxiliary metal salt.

Tailoring Porphyrin (Nano)Structures

Many possibilities exist to modify the structure of porphyrins. These include variation of the central metal, N-substitution or modulation of the macrocyclic π-system. Recent years have seen a surge in π-annulated systems while a more established approach is the synthesis of nonplanar porphyrins via peripheral macrocycle interactions. Any of these strategies results in porphyrin systems with altered structure, conformation and physicochemical properties. What is lacking is true ‘conformational design’ of porphyrins, i.e., the use of the recent advances in organometallic chemistry in conjunction with structural studies to yield functional systems with predesigned conformations. Such an approach would aid development of new optical materials and catalysts.Similarly, an expanding body of studies on porphyrin nanomaterials on surfaces is beginning to reveal how surface/macrocycle interactions alter the chemical properties of porphyrins. Metallation and metal exchange reactions are possible and specific types of porphyrin nanostructures are now accessible via logical 2D synthesis on metal surfaces. Initial studies of porphyrin-graphene interactions indicate that a combination of tailor made porphyrins with specific macrocycle-surface interactions can yield functional nanomaterials.

Metal exchange reaction between magnesium octaphenyltetraazaporphyrinate and d-metals salts in dimethylformamide

Reaction of metal exchange between magnesium octaphenyltetraazaporphyrinate with copper and cobalt chlorides in dimethylformamide has been studied by spectrophotometry. Parameters of the reactions kinetics have been determined, and their mechanism has been suggested.

Optical Chemosensors Based on Transmetalation of Salen-Based Schiff Base Complexes

We report our systematic studies of novel, simple, selective, and sensitive optical (both colorimetric and fluorescent) chemosensors for detecting Al(3+) based on transmetalation reactions (metal displacement or exchange reactions) of a series of K(I), Ca(II), Zn(II), Cu(II), and Pt(II) complexes containing different ligands of salen-based Schiff bases. Both the chemical structure of the salen ligand and the identity of the central metal ion have a tremendous impact on the sensing performance, which is mainly determined by the stability constant of the complex. Moreover, the selectivities of the salen-complex-based chemosensors are much better than those of the corresponding free salen ligands because of the shielding function of the filled-in metal ion in the complex. Therefore, the present work potentially provides a new and simple way to design optical probes via complex-based transmetalation reactions.