Organometallic Fragments Research Articles

A hierarchical assembly strategy for near-infrared photothermal conversion: unconventional heterogeneous metalla[2]catenanes.

Herein, we report a hierarchical assembly strategy for constructing heterogeneous half-sandwich organometallic D–A (D = π-donor, A = π-acceptor) interlocked structures, and their application in near-infrared (NIR) photothermal conversion. Thienothiophene and diketopyrrolopyrrole groups were selected as the D and A units, leading to two homogeneous metalla[2]catenanes with D–D–D–D and A–A–A–A stacks, respectively. By the ordered secondary assembly of homogeneous metalla[2]catenanes, two unprecedented heterogeneous D–A metalla[2]catenanes comprising an unusual mixed D–A–D–D and unconventional D–A–A–A stacks were realized by the combination of multiple noncovalent interactions, as all demonstrated by a detailed X-ray crystallographic study. Benefiting from the mixed D–A stacking modes, NIR absorption of heterogeneous D–A metalla[2]catenanes is significantly enhanced in contrast to homogeneous metalla[2]catenanes. Thanks to the enhanced NIR absorption and the fluorescence quenching effect from half-sandwich organometallic fragments, heterogeneous D–A metalla[2]catenanes displayed high-performance NIR photothermal conversion properties (η = 27.3%).

Solvent free synthesis of ferrocene based rhodamine – hydrazone molecular probe with improved bioaccumulation for sensing and imaging applications

Functionalization of ferrocenyl hydrazone with rhodamine based tag using solid state synthetic method led to the formation of molecules containing both, fluorescent active and electroactive fragments, [(η5-C5H5)Fe{(η5-C5H4)C(R)NNC(O)-X}] (R = CH3, H; X = Rhodamine-6G). The molecules showed selective metal ion sensing and switching behavior with distinct interaction and influence from the organometallic fragment. The sensing behavior was explored within bacterial strain and THP-1 cancer cell lines to understand the subcellular distribution of heavy metal ions and their potential in applications related to bioimaging, uptake and bioremediation activities. The study showed significant intracellular metal recognition and bioaccumulation characteristics and understanding towards ferrocene based signaling behavior upon oxidation.

Ruthenium-Cyclopentadienyl Bipyridine-Biotin Based Compounds: Synthesis and Biological Effect.

Prospective anticancer metallodrugs should consider target-specific components in their design in order to overcome the limitations of the current chemotherapeutics. The inclusion of vitamins, which receptors are overexpressed in many cancer cell lines, has proven to be a valid strategy. Therefore, in this paper we report the synthesis and characterization of a set of new compounds [Ru(η5-C5H5)(P(C6H4R)3)(4,4'-R'-2,2'-bpy)]+ (R = F and R' = H, 3; R = F and R' = biotin, 4; R = OCH3 and R' = H, 5; R = OCH3 and R' = biotin, 6), inspired by the exceptional good results recently obtained for the analogue bearing a triphenylphosphane ligand. The precursors for these syntheses were also described following modified literature procedures, [Ru(η5-C5H5)(P(C6H4R)3)2Cl], where R is -F (1) or -OCH3 (2). The structure of all compounds is fully supported by spectroscopic and analytical techniques and by X-ray diffraction studies for compounds 2, 3, and 5. All cationic compounds are cytotoxic in the two breast cancer cell lines tested, MCF7 and MDA-MB-231, and much better than cisplatin under the same experimental conditions. The cytotoxicity of the biotinylated compounds seems to be related with the Ru uptake by the cells expressing biotin receptors, indicating a potential mediated uptake. Indeed, a biotin-avidin study confirmed that the attachment of biotin to the organometallic fragment still allows biotin recognition by the protein. Therefore, the biotinylated compounds might be potent anticancer drugs as they show cytotoxic effect in breast cancer cells at low dose dependent on the compounds' uptake, induce cell death by apoptosis and inhibit the colony formation of cancer cells causing also less severe side effects in zebrafish.

Mössbauer Spectroscopy and Theoretical Studies of Iron Bimetallic Complexes Showing Electrocatalytic Hydrogen Evolution.

Mössbauer spectroscopy and density functional theory (DFT) calculations are reported for the mononuclear Fe-nitrosyl complex [Fe( N, N'-bis(2-mercaptoethyl)-1,4-diazacycloheptane)NO] {[Fe(bme-dach)(NO)] (1)} and the series of dithiolate-bridged dinuclear complexes M-Fe(CO)Cp [M = Fe(bme-dach)(NO) (1-A), Ni(bme-dach) (2-A), and Co(bme-dach)(NO) (3-A)], in which M is a metallo-ligand to Fe(CO)Cp+ (Fe'Cp). The latter is an organometallic fragment in which Fe is coordinated by one CO and one cyclopentadienyl ligand. Complexes 1-A and 2-A were previously shown to have electrocatalytic hydrogen evolution activity. Mononuclear {Fe-NO}7 complex 1, with overall spin of 1/2, has an isomer shift of 0.23(2) mm/s [Δ EQ = 1.37(2) mm/s] and magnetic hyperfine couplings of {-38 T, -26.8 T, 8.6 T}. In complexes 2-A and 3-A, Fe'(CO)Cp+ has a diamagnetic ground state and δ = 0.33(2) mm/s (Δ EQ ≈ 1.78 mm/s), consistent with a low-spin FeII site. In contrast, in complex 1-A, M = Fe(bme-dach)(NO) (i.e., complex 1) the magnetic hyperfine interactions of both metallo-ligand, M, and low-spin Fe'Cp are perturbed and Fe'Cp exhibits small magnetic hyperfine interactions, although its isomer shift and quadrupole splittings are largely unaltered. The DFT calculations for 1-A are in agreement with the paramagnetism observed for the Fe'(CO)Cp+ iron site.

Luminescent dinuclear rhenium(I)[sbnd]PNA conjugates for microRNA-21 targeting: Synthesis, chemico-physical and biological characterization

Two different luminescent rhenium complexes, having the general formula [Re2(μ-Cl)2(CO)6(μ-1,2-diazine)] and containing two different diazine ligands, namely 4-(pyridazin-4-yl)-butanoic acid (Re-1) and 8-(5-methylpyridazin-4-yl)-octanoic acid (Re-2), were prepared. Exploiting the presence of the carboxylic acid moieties, both complexes were further covalently linked to a 20-mer oligomer (PNA1), bearing a nucleobase sequence complementary to that of mature miR-21–5p (5′-TCAACATCAGTCTGATAAGCTA-3′), as well as to a 20-mer oligomer (PNA2) used as a negative control bearing the sequence 5′-GTGTAACACGTCCTATACGCC-3’. The resulting four Re-PNA conjugates were characterized and used to target miR-21 in the DU145 prostate cancer cell line. The conjugation with PNA did not perturb the photoluminescence behavior of the organometallic fragments: emission from 3MLCT excited states, centered in a range between 580 and 610 nm, was observed, with satisfactory photoluminescence quantum yields (Φ = ca. 0.03–0.01, in aerated water/acetonitrile solution 1/1). Experiments of cell uptake, performed with living prostate cancer cells showed that the length of the aliphatic linker between the rhenium complex and the PNA sequence, strongly affects the cellular localization.

Homo- and heterobimetallic azines derived from ferrocene and cyrhetrene: Synthesis, structural characterization and electrochemical studies

A new series of asymmetrical heterobimetallic azines [(η5-C5H5)Fe{(η5-C5H4)C(R) = NNC(R1)-(η5-C5H4)Re(CO)3}] (1–3) and symmetrical homobimetallic cyrhetrenyl azines [{(η5-C5H4)C(R) = N}Re(CO)3]2 (4, 5) have been synthesized and were spectroscopically characterized by FT-IR, NMR, EI-MS and cyclic voltammetry. The molecular structures of 1 and 4 were determined using single-crystal X-ray diffraction technique. Based on the oxidation potential of the ferrocenyl units and the high degree of planarity of the [(C5H4)C(H) = NNC(H)-(C5H4)] system in complex 1, we inferred electronic communication between the electron-withdrawing cyrhetrenyl groups through the π-conjugated azine bridge. The compounds display an (E,E)-configuration about the >CN- bond, an s-trans conformation for the NN bond and an anti-conformation for the two organometallic fragments.

Synthesis and characterization of the first cyrhetrenyl-appended calix[4]arene macrocycle and its application as an electrochemical sensor for the determination of Cu(II) in bivalve mollusks using square wave anodic stripping voltammetry

An electrochemical sensor for the determination of Cu(II) in bivalve mollusks using a glassy carbon electrode modified with p-tert-butylcalix [4]arene-bis-cyrhetrenylimine (Cy2(Calix [4])) by square wave anodic stripping voltammetry (SWASV) has been developed. The organometallic compound was synthesized from cyrhetrene-carboxaldehyde and 25,26-bis-(2-aminoethoxy)-26,28-dihydrocalix [4]arene through a condensation reaction. Metalloligand (Cy2(Calix [4])) was characterized by FT-IR and 1H-13C 2D NMR spectroscopies and monocrystal X-ray diffraction and was obtained as a single isolated isomer (E). The optimum chemical and electrochemical conditions for the modified electrode were optimized and the methodology was applied in different samples of bivalve mollusks with satisfactory results. A cooperative effect between the organometallic fragment and the calixarene macrocycle improves the preconcentration capacity of the electrochemical sensor, creating a new opportunity to perform rapid and sensitive analyses in the detection of copper in marine resources.

"Doping" of Polyyne with an Organometallic Fragment Leads to Highly Conductive Metallapolyyne Molecular Wire.

Exploration of highly conductive molecules is essential to achieve single-molecule electronic devices. The present paper describes the results on single-molecule conductance study of polyyne wires doped with the organometallic Ru(dppe)2 fragment, X-(C≡C) n-Ru(dppe)2-(C≡C) n-X. The metallapolyyne wires end-capped with the gold fragments (X = AuL) are subjected to single-molecule conductance measurements with the STM break junction technique, which reveal the high conductance (10-3-10-2 G0; n = 2-4) with the low attenuation factor (0.25 Å-1) and the low contact resistance (33 kΩ). A unique "'doping'" effect of Ru(dppe)2 fragment was found to lead to the high performance as suggested by the hybrid density functional theory-nonequilibrium green function calculation.

Neutral Bis(imino)-1,4-dihydropyridinate and Cationic Bis(imino)pyridine σ-Alkylzinc(II) Complexes as Hydride Exchange Systems: Classic Organometallic Chemistry Meets Ligand-Centered, Biomimetic Reactivity

The 1,4-dihydropyridinate complex [(4-Bn-HBIP)Zn(Bn)], readily available through the highly selective reaction of a 2,6-bis(imino)pyridine ligand with dibenzylzinc, contains two distinct reactive centers. One of them is the σ-organometallic benzylzinc moiety, which reacts with weak protic acids (e.g., water and methanol) to release the free dihydropyridine ligand. In contrast, the reaction with p-tolualdehyde, a mild electrophile, does not involve the benzylzinc but the 1,4-dihydropyridinate fragment. Even a strong electrophile such as B(C6F5)3 selectively removes the hydrogen atom from the C4 position of the heterocyclic ring but leaves intact the organometallic fragment, to afford the ionic complex [(4-Bn-BIP)Zn(Bn)]+[HB(C6F5)3]−. The hydride donor capacity of the dihydropyridinate ligand is strongly reminiscent of the widespread pyridine-based cofactors (e.g., NADH/NAD+), one of the most common redox exchange molecules in biologic chemistry. In order to investigate the reversibility of the hydride exch...

Influence of highly basic phosphine ligand on the reactivity and hydrolysis of P4 and P4S3 supported by ruthenium fragments

Substitution of PPh3 in [RuCp(PPh3)2Cl] with highly basic PMe3 gave a remarkable change in the reactivity towards P4 and unexpectedly only the bimetallic complex cation [{RuCp(PMe3)2}2(μ,η1:1-P4)]2+ (3) was formed which was characterized by NMR spectroscopy and single crystal X-ray diffraction analysis. The equimolar reaction between the synthon [RuCp(PMe3)2]+ and the mixed cage P4S3 is highly selective quantitatively yielding only the product with η1-Pbasal coordination to ruthenium. On the other hand, the related [RuCp(PPh3)2]+ cation gave a 2:1 mixture of mono-η1-Pbasal and bimetallic complex. The solid state structure of [RuCp(PMe3)2(η1-Pbasal-P4S3)]+ (4) was solved by X-ray diffraction and represents the first example of X-ray structure of intact P4S3 coordinated to a mononuclear ruthenium organometallic fragment. Hydrolysis of the P4 ligand in 3 resulted mainly in two products, i.e. free H3PO3 and the diphosphane complex cation [{RuCp(PMe3)2}2(μ,η1:1-P2H4)]2+ (9), while in the presence of methanol two mononuclear complexes [RuCp(PMe3)2{P(OH)3}]+ (8) and [RuCp(PMe3)2{P(OCH3)3}]+ (10) in (2:1) ratio were selectively formed.

Predicting the DNP-SENS efficiency in reactive heterogeneous catalysts from hydrophilicity.

Identification of surfaces at the molecular level has benefited from progress in dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP SENS). However, the technique is limited when using highly sensitive heterogeneous catalysts due to secondary reaction of surface organometallic fragments (SOMFs) with stable radical polarization agents. Here, we observe that in non-porous silica nanoparticles (NPs) (dparticle = 15 nm) some DNP enhanced NMR or SENS characterizations are possible, depending on the metal-loading of the SOMF and the type of SOMF substituents (methyl, isobutyl, neopentyl). This unexpected observation suggests that aggregation of the nanoparticles occurs in non-polar solvents (such as ortho-dichlorobenzene) leading to (partial) protection of the SOMF inside the interparticle space, thereby preventing reaction with bulky polarization agents. We discover that the DNP SENS efficiency is correlated with the hydrophilicity of the SOMF/support, which depends on the carbon and SOMF concentration. Nitrogen sorption measurements to determine the BET constant (CBET) were performed. This constant allows us to predict the aggregation of silica nanoparticles and consequently the efficiency of DNP SENS. Under optimal conditions, CBET > 60, we found signal enhancement factors of up to 30.

Surface organometallic chemistry in heterogeneous catalysis.

The broad challenges of energy and environment have become a main focus of research efforts to develop more active and selective catalytic systems for key chemical transformations. Surface organometallic chemistry (SOMC) is an established concept, associated with specific tools, for the design, preparation and characterization of well-defined single-site catalysts. The objective is to enter a catalytic cycle through a presumed catalytic intermediate prepared from organometallic or coordination compounds to generate well defined surface organometallic fragments (SOMFs) or surface coordination fragments (SCFs). These notions are the basis of the "catalysis by design" strategy ("structure-activity" relationship) in which a better understanding of the mechanistic aspects of the catalytic process led to the improvement of catalyst performances. In this review the application of SOMC strategy for the design and preparation of catalysts for industrially relevant processes that are crucial to the energy and environment is discussed. In particular, the focus will be on the conversion of energy-related feedstocks, such as methane and higher alkanes that are primary products of the oil and gas industry, and of their product of combustion, CO2, whose efficient capture and conversion is currently indicated as a top priority for the environment. Among the main topics related to energy and environment, catalytic oxidation is also considered as a key subject of this review.

Novel organometallic chalcones functionalized with a crown ether fragment as optical ion chemosensors

We previously reported the synthesis and characterization of new organometallic chalcones derived from ferrocene, cyrhetrene and cymantrene functionalized with a benzo‐15‐crown‐5 fragment. The ferrocene and cyrhetrene chalcones have been investigated as chemosensors for metal ions with optical response in acetonitrile. Several metal ions were selected considering the diameter of the cavity and the charge‐to‐radius ratio of the cation. The stoichiometry of the complexes was determined using Job's method. It was found that Na+ and Ca2+ complexes have a 1:1 stoichiometry while a 2:1 (metaloligand‐to‐cation) stoichiometry was determined for Ba2+ and Pb2+ complexes. The association constants were calculated according to the stoichiometry of the complex and the results showed that they are directly affected by the electron‐withdrawing nature of the organometallic fragment. Moreover, complexes of ferrocenyl chalcone have larger association constants than those of the cyrhetrenyl analogue. This experimental observation is consistent with the electronic properties of the ferrocenyl fragment.

Tris(perfluoroalkyl)germylethynyl derivatives of biphenyl containing ferrocenyl donor group: Structure, spectra, and photoinduced intramolecular electron transfer

Ferrocenyl derivatives with perfluorinated organometallic fragments are prospective sensitizers for photovoltaic devices which can provide higher stability and resistance to oxidation in comparison with the known analogs. For the development of the photovoltaic devices based on such molecules, the estimates of probabilities of photoinduced electron transfer both inside the molecule and from the molecule to the internal semiconductor electrode are required. In this work, the structural, electronic, spectral and radiative parameters of trialkylgermyl (alkyl = Me, n-C3H7, CF3, n-C3F7) derivatives of 4,4′-diethynylbiphenyl containing ferrocenyl donor group are considered. The spectral and radiative parameters of these compounds were calculated using the TD-DFT theory with the B3LYP, PBE0, BHandHLYP и CAM-B3LYP functionals. For all the molecules, the probabilities of photoinduced electron transfer to the outer molecular fragments inside the sensitizer are estimated on the basis of direct analysis of charge redistributions in the excited states.

New cyrhetrenyl and ferrocenyl sulfonamides: Synthesis, characterization, X-ray crystallography, theoretical study and anti-Mycobacterium tuberculosis activity

A new series of cyrhetrenyl and ferrocenyl sulfonamides were designed, synthesized and characterized. The reactions of organometallic amines (P2 and P3) with the corresponding arylsulfonyl chlorides produced cyrhetrenyl (2a-c) and ferrocenyl (3a-c) sulfonamide derivatives. All the compounds were characterized by conventional spectroscopic techniques (FT-IR, 1H and 13C NMR and mass spectrometry). The proposed molecular structures of 2a and 3a were confirmed by single-crystal X-ray crystallography. Theoretical calculations at the DFT level were also carried out as an approximation to rationalize the influences of the electronic natures of the organometallic fragments into the sulfonamide skeleton. All the complexes were screened in vitro against Mycobacterium tuberculosis and exhibited only modest activities in the micromolar range.

Organometallic Chalcones Functioning as Radical Traps: Observations on the Solvated Electron Reduction and the C·H2OH and C·H2Cl Addition Processes. A Time-Resolved, Mechanistic Study.

The pulse radiolysis method was used to investigate reactions between organometallic chalcones derived from ferrocene, cyrhetrene, and cymantrene substituted with a phenyl (R1) or a 4'-benzo-15-crown-5 (B1) moiety and the solvated electron e-sol and two radicals. The principal spectroscopic transformations resolved with the e-sol reactions reveal that the chalcone compounds react under a diffusion controlled condition. The chromophore in the reaction product is the radical anion chalcone, -C(═O)CH═CH-. The kinetics of the redox processes are consistent with the formation of the radical anion in a first step, followed by an E/Z isomerization reaction in the second step. The rate of the E/Z isomerization reaction is dependent on the chalcone substituent. Reactions with C·H2OH and C·H2Cl radicals are strongly affected by the nature of the organometallic fragment. The transient spectra for the reactions between C·H2OH and C·H2Cl radicals with the phenyl-substituted chalcone show weak, broad absorption bands at λob < 400 nm. Only the ferrocenyl derivatives showed an intense absorption band with λmax = 350 nm. The C-centered radicals react with organometallic chalcones with lifetimes less than or equal to a few microseconds, and the products are assigned as adducts of the C-centered radicals to the chalcone.

Thiomaltol-Based Organometallic Complexes with 1-Methylimidazole as Leaving Group: Synthesis, Stability, and Biological Behavior.

Thiomaltol, a potential S,O-coordinating molecule, has been utilized for the complexation of four different organometallic fragments, yielding the desired RuII , OsII , RhIII , and IrIII complexes having a "piano-stool" configuration. In addition to the synthesis of these compounds with a chlorido leaving group, the analogous 1-methylimidazole derivatives have been prepared, giving rise to thiomaltol-based organometallics with enhanced stability under physiological conditions. The organometallic compounds have been characterized by NMR spectroscopy, elemental analysis, and X-ray diffraction analysis. Their behavior in aqueous solution and their interactions with certain amino acids have been studied by ESI mass spectrometry. Their pH-dependent stability has been investigated by 1 H NMR in aqueous solution, and their cytotoxicity against three different cancer cell lines has been investigated. Furthermore, their capacity as topoisomerase IIα inhibitors as well as their effect on the cell cycle distribution and reactive oxygen species (ROS) generation have been elucidated.

Pentacene- and BODIPY-Containing trans-Bis(ethynyl)bis(phosphine)platinum(II) Organometallic Polymers: A DFT Point of View

The effect of the polymer dimension and the nature of the end-group of oligomer models containing pentacence ([pen]) and BODIPY ([BOD]) alternating with the organometallic fragment trans-bis(trialkylphosphine)platinum(II) ([Pt]), i.e. ([Ar] n–[Pt] m)x with [Ar] = C≡C–[pen]–C≡C, C≡C–[BOD]–C≡C, and 1 < x < 4, on their structures and optical properties were investigated by means of DFT and TDDFT (B3LYP) calculations. For sake of reduction of computation size for the oligomers, the trialkylphosphine was set to PMe3 instead of the commonly encountered PBu3 in the experimental articles. Two specific aspects were addressed. Firstly, a series of computations were performed in a systematic manner in order to find the best conditions for these calculations (namely the choice of basis sets and solvent fields), due to the large size of the oligomer models. Secondly, the effect of the oligomer size and nature of the terminal unit of ([Ar] n–[Pt] m)x, namely C≡C–[pen]–C≡CH or C≡C–[BOD]–C≡CH and [Pt]–Cl, on the structure and electronic properties have also been examined. These calculations indicate that the nature of end-groups has a little impact on the properties mentioned above for the alternating ((C≡C–[BOD]–C≡C) n–[Pt] m)x oligomers, but some minor effects are noted for the (C≡C–[pen]–C≡C)-containing species. Noteworthy, the evolution of the properties, notably the position of the lowest energy electronic transition, shows no significant evolution above 3 units. This computational result indicates the limitation of the electronic communication across the polymer chains. The lowest energy electronic states are all mainly ππ* located in the [Ar] fragment. Consequently, this work was limited to 4 units only.

Thomas F. Fässler

Thomas F. Fässler

Catalysis by Design: Well-Defined Single-Site Heterogeneous Catalysts.

Heterogeneous catalysis, a field important industrially and scientifically, is increasingly seeking and refining strategies to render itself more predictable. The main issue is due to the nature and the population of catalytically active sites. Their number is generally low to very low, their "acid strengths" or " redox properties" are not homogeneous, and the material may display related yet inactive sites on the same material. In many heterogeneous catalysts, the discovery of a structure-activity reationship is at best challenging. One possible solution is to generate single-site catalysts in which most, if not all, of the sites are structurally identical. Within this context and using the right tools, the catalyst structure can be designed and well-defined, to reach a molecular understanding. It is then feasible to understand the structure-activity relationship and to develop predictable heterogeneous catalysis. Single-site well-defined heterogeneous catalysts can be prepared using concepts and tools of surface organometallic chemistry (SOMC). This approach operates by reacting organometallic compounds with surfaces of highly divided oxides (or of metal nanoparticles). This strategy has a solid track record to reveal structure-activity relationship to the extent that it is becoming now quite predictable. Almost all elements of the periodical table have been grafted on surfaces of oxides (from simple oxides such as silica or alumina to more sophisticated materials regarding composition or porosity). Considering catalytic hydrocarbon transformations, heterogeneous catalysis outcome may now be predicted based on existing mechanistic proposals and the rules of molecular chemistry (organometallic, organic) associated with some concepts of surface sciences. A thorough characterization of the grafted metal centers must be carried out using tools spanning from molecular organometallic or surface chemistry. By selection of the metal, its ligand set, and the support taken as a X, L ligands in the Green formalism, the catalyst can be designed and generated by grafting the organometallic precursor containing the functional group(s) suitable to target a given transformation (surface organometallic fragments (SOMF)). The choice of these SOMF is based on the elementary steps known in molecular chemistry applied to the desired reaction. The coordination sphere necessary for any catalytic reaction involving paraffins, olefins, and alkynes also can thus be predicted. Only their most complete understanding can allow development of catalytic reactions with the highest possible selectivity, activity, and lifetime. This Account will examine the results of SOMC for hydrocarbon transformations on oxide surfaces bearing metals of group 4-6. The silica-supported catalysts are exhibiting remarkable performances for Ziegler-Natta polymerization and depolymerization, low temperature hydrogenolysis of alkanes and waxes, metathesis of alkanes and cycloalkanes, olefins metathesis, and related reactions. In the case of reactions involving molecules that do not contain carbon (water-gas shift, NH3 synthesis, etc.) this single site approach is also valid but will be considered in a later review.