Platinum Group Metal Complexes Research Articles

Innovative electrochemical sensor based on platinum group metal complexes for determination of nitrite: Application for simultaneous detection of nitrite and tartrazine

In the context of this experimental study, new palladium and ruthenium complexes based on a symmetric ligand, named 2E-Peaemp ((3E,3’E)-3,3’-(((piperazine-1,4-diyl bis (ethane-2,1-diyl)) bis (azanediyl)) bis (ethan1-yl-1-ylidene)) bis (6-methyl-2H-pyran-2,4(3 H)-dione), and their hybrid compounds with carbon nanotubes were prepared and characterized. The sensors prepared using a cavity microelectrode (MEC) modified with a mixture of graphite (CG), carbon nanotubes (MWCNT) and the synthesized complexes (Pd-2E-Peaemp and Ru-2E-Peaemp) were applied to detect the pollutants such as Nitrites and Tartrazine separately and simultaneously in aqueous solutions and real samples (Tap water, wastewater and bottled commercial spring water). The detection limits (LODs) determined for nitrites and tartrazine are obtained using MEC/CG-MWCNT-Pd-2E-Peaemp electrode, and the electrochemical measurements demonstrated a sensitive and rapid response in the analysis of these species. LODs are 0.39 µM and 0.11 µM, respectively, within the concentration range of 0–909 µM for nitrites and 0–97 µM for tartrazine. This electrode modified by the palladium complex is also used to simultaneously detect nitrite and tartrazine analytes using the differential pulse voltammetry (DPV) technique, indicating that the proposed sensor can be an interesting alternative tool to measure these species in real samples. The application of this electrode in these natural environments reveals that the developed sensor can detect low concentrations of nitrite (NO2-; trace) without any interference from other ions substances as acetate (CH3COO-), borate (BO3−3), phosphate (PO4−3), dihydrogen ( 2 H+), sulfate (SO4−2), sodium (Na+), hydroxide (OH-), potasium (K+), chloride (Cl-), magnesium (I) ( Mg+), nitrate (NO3-), calcium (Ca2+), carbonate (CO3−2).

Beyond the First Coordination Sphere─Manipulating the Excited-State Landscape in Iron(II) Chromophores with Protons.

Molecular transition metal chromophores play a central role in light harvesting and energy conversion. Recently, earth-abundant transition-metal-based chromophores have begun to challenge the dominance of platinum group metal complexes in this area. However, the development of new chromophores with optimized photophysical properties is still limited by a lack of synthetic methods, especially with respect to heteroleptic complexes with functional ligands. Here, we demonstrate a facile and efficient method for the combination of strong-field carbenes with the functional 2,2'-bibenzimidazole ligand in a heteroleptic iron(II) chromophore complex. Our approach yields two isomers that differ predominantly in their excited-state lifetimes based on the symmetry of the ligand field. Deprotonation of both isomers leads to a significant red-shift of the metal-to-ligand charge transfer (MLCT) absorption and a shortening of excited-state lifetimes. Femtosecond transient absorption spectroscopy in combination with quantum chemical simulations and resonance Raman spectroscopy reveals the complex relationship between protonation and photophysical properties. Protonation is found to tip the balance between MLCT and metal-centered (MC) excited states in favor of the former. This study showcases the first example of fine-tuning of the excited-state landscape in an iron(II) chromophore through second-sphere manipulations and provides a new perspective to the challenge of excited-state optimizations in 3d transition metal chromophores.

Survey of Recent Trends of IB-IVB Metals and Their Compounds in Cancer Treatment

Metals from IB to IVB groups of the periodic table, because of their flexible oxidation states, natures of coordinated bioligands, and geometries upon complexation, display various properties and efficiency of metal-based cytotoxic drugs. Recent decades have witnessed remarkable progress in the synthesis and therapeutic application of numerous inorganic compounds in cancer investigations. The main potential therapeutic agents, such as the complexes of platinum group metals possessing antineoplastic activity have been broadly described previously in the literature and are beyond the space of this analysis. The key objective of the present study is to analyze the possible activity of IB-IVB group metals their coordination compounds against the cancer cell types. The increasing number of anticancer drug candidates among these metals proves this field offers a remarkably variation of novel opportunities for the synthesis of advanced new pharmaceutics with diverse and specific modes of action. Furthermore, the review provides forthcoming insights into prospective clinical scenarios for approaching treatment applications. That is why this field of research deserves more attention. It is expected that this review can serve as a guiding framework for future investigations in cancer chemotherapy.

Investigation of half-sandwich platinum group metal complexes featuring benzamide derived ligands and their diazido derivatives: Synthesis, molecular structures and biological studies

Benzamide derivative ligands L1 and L2 were synthesized and reactions of these ligands with metal dimers [Ru(p-cymene)Cl2]2 and [Cp*MCl2]2 (M = Rh/Ir) yielded a series of “piano-stool”-type neutral mononuclear metal-arene-benzamide complexes (1, 2, 3, 4, 5 and 6) of the general formula [(arene)M(κ1(N)L)Cl2] (where arene = p-cymene and Cp*, M = Ru, Rh and Ir and L = L1 and L2). Further treatment of the neutral complexes 1-6 with sodium azide in methanol resulted in the formation of diazido complexes 7, 8, 9 and 10. Crystallographic studies of the complexes 2, 5, 7 and 8 revealed the ligands coordinated to the metal centers through the nitrogen atom of thiazole/thiadiazole ring in a monodentate fashion. The complexes were characterized by NMR, FTIR, UV-Vis spectroscopy and ESI-mass spectrometry. All the ligands and metal complexes were screened for their antibacterial and antioxidant activities. Interestingly, it was observed that only the diazido complexes were active towards the Gram-positive Staphylococcus aureus bacterial strains, with activities more than the standard. Antioxidant study revealed that the compounds possess insignificant activities.

Imidazophenothiazine-Based Thermally Activated Delayed Fluorescence Materials with Ultra-Long-Lived Excited States for Energy Transfer Photocatalysis.

Triplet-triplet energy transfer (EnT) is a powerful activation pathway in photocatalysis that unlocks new organic transformations and improves the sustainability of organic synthesis. Many current examples, however, still rely on platinum-group metal complexes as photosensitizers, with associated high costs and environmental impacts. Photosensitizers that exhibit thermally activated delayed fluorescence (TADF) are attractive fully organic alternatives in EnT photocatalysis. However, TADF photocatalysts incorporating heavy atoms remain rare, despite their utility in inducing efficient spin-orbit-coupling, intersystem-crossing, and consequently a high triplet population. Here, we describe the synthesis of imidazo-phenothiazine (IPTZ), a sulfur-containing heterocycle with a locked planar structure and a shallow LUMO level. This acceptor is used to prepare seven TADF-active photocatalysts with triplet energies up to 63.9 kcal mol-1. We show that sulfur incorporation improves spin-orbit coupling and increases triplet lifetimes up to 3.64 ms, while also allowing for tuning of photophysical properties via oxidation at the sulfur atom. These IPTZ materials are applied as photocatalysts in five seminal EnT reactions: [2 + 2] cycloaddition, the disulfide-ene reaction, and Ni-mediated C-O and C-N cross-coupling to afford etherification, esterification, and amination products, outcompeting the industry-standard TADF photocatalyst 2CzPN in four of the five studied scenarios. Detailed photophysical and theoretical studies are used to understand structure-activity relationships and to demonstrate the key role of the heavy atom effect in the design of TADF materials with superior photocatalytic performance.

Half-Sandwich Type Platinum-Group Metal Complexes of C-Glucosaminyl Azines: Synthesis and Antineoplastic and Antimicrobial Activities

While platinum-based compounds such as cisplatin form the backbone of chemotherapy, the use of these compounds is limited by resistance and toxicity, driving the development of novel complexes with cytostatic properties. In this study, we synthesized a set of half-sandwich complexes of platinum-group metal ions (Ru(II), Os(II), Ir(III) and Rh(III)) with an N,N-bidentate ligand comprising a C-glucosaminyl group and a heterocycle, such as pyridine, pyridazine, pyrimidine, pyrazine or quinoline. The sugar-containing ligands themselves are unknown compounds and were obtained by nucleophilic additions of lithiated heterocycles to O-perbenzylated 2-nitro-glucal. Reduction of the adducts and, where necessary, subsequent protecting group manipulations furnished the above C-glucosaminyl heterocycles in their O-perbenzylated, O-perbenzoylated and O-unprotected forms. The derived complexes were tested on A2780 ovarian cancer cells. Pyridine, pyrazine and pyridazine-containing complexes proved to be cytostatic and cytotoxic on A2780 cells, while pyrimidine and quinoline derivatives were inactive. The best complexes contained pyridine as the heterocycle. The metal ion with polyhapto arene/arenyl moiety also impacted on the biological activity of the complexes. Ruthenium complexes with p-cymene and iridium complexes with Cp* had the best performance in ovarian cancer cells, followed by osmium complexes with p-cymene and rhodium complexes with Cp*. Finally, the chemical nature of the protective groups on the hydroxyl groups of the carbohydrate moiety were also key determinants of bioactivity; in particular, O-benzyl groups were superior to O-benzoyl groups. The IC50 values of the complexes were in the low micromolar range, and, importantly, the complexes were less active against primary, untransformed human dermal fibroblasts; however, the anticipated therapeutic window is narrow. The bioactive complexes exerted cytostasis on a set of carcinomas such as cell models of glioblastoma, as well as breast and pancreatic cancers. Furthermore, the same complexes exhibited bacteriostatic properties against multiresistant Gram-positive Staphylococcus aureus and Enterococcus clinical isolates in the low micromolar range.

Metal-organic frameworks as catalyst precursors in Catalytic Hydrogenation of Carbon Dioxide: Review

Catalytic hydrogenation of carbon dioxide to value-added chemicals is an attractive process to address both energy and environmental issues. Several approaches have been used to convert the greenhouse gas to useful products. This conversion has been done mainly through homogeneous catalytic systems of platinum group metal complexes. In recent years there has been a growing concern to design heterogeneous catalysts that are able to convert carbon dioxide to C1 products. The large surface area that metal-organic frameworks coupled with porosity make them better candidates for catalytic conversion of carbon dioxide to the desired products. Results from these studies indicate that metal-organic frameworks (MOFs) may answer both environmental and energy issues associated with the production of the greenhouse gas. This contribution will focus on the recent development in the design and application of MOFs in catalytic hydrogenation of carbon dioxide. Special emphases on tandem capture of carbon dioxide and hydrogen followed by subsequent hydrogenation of carbon dioxide in the presence of frustrated Lewis pairs functionalised MOF will be discussed.

Dithiocarbamate Complexes of Platinum Group Metals: Structural Aspects and Applications

The incorporation of dithiocarbamate ligands in the preparation of metal complexes is largely prompted by the versatility of this molecule. Fascinating coordination chemistry can be obtained from the study of such metal complexes ranging from their preparation, the solid-state properties, solution behavior as well as their applications as bioactive materials and luminescent compounds, to name a few. In this overview, the dithiocarbamate complexes of platinum-group elements form the focus of the discussion. The structural aspects of these complexes will be discussed based upon the intriguing findings obtained from their solid- (crystallographic) and solution-state (NMR) studies. At the end of this review, the applications of platinum-group metal complexes will be discussed.

Complexes of Platinum Group Metals with a Conformationally Locked Scorpionate in a Metal-Organic Framework: An Unusually Close Apical Interaction of Palladium(II).

We report synthetic strategies for installing platinum group metals (PGMs: Pd, Rh, Ir, and Pt) on a scorpionate-derived linker (TpmC*) within a metal-organic framework (MOF), both by room-temperature postsynthetic metalation and by direct solvothermal synthesis, with a wide range of metal loadings relevant for fundamental studies and catalysis. In-depth studies for the palladium adduct Pd(II)@Zr-TpmC* by density-functional-theory-assisted extended X-ray absorption fine structure spectroscopy reveals that the rigid MOF lattice enforces a close Pd(II)-Napical interaction between the bidentate palladium complex and the third uncoordinated pyrazole arm of the TpmC* ligand (Pd-Napical = 2.501 ± 0.067 Å), an interaction that is wholly avoided in molecular palladium scorpionates.

Half-sandwich platinum group metal complexes containing coumarin-N-acylhydrazone hybrid ligands: Synthesis and biological evaluation studies

A series of half-sandwich platinum group metal complexes containing coumarin-N-acylhydrazone ligands have been prepared. The metal precursors of the type [(p-cymene)RuCl2]2 and [Cp*MCl2]2 (M = Rh/Ir) and coumarin-N-acylhydrazone ligands (L1, L2 and L3) were reacted in the ratio of 1:2 (M:L), forming neutral bidentate (N ∩ O) complexes (1–9). The complexes are of the general formula [(arene)M{κ2(N∩O)L}Cl]. All these complexes have been characterized by analytical, spectroscopic and single-crystal X-ray diffraction studies. The complexes and ligands were then carried out for antibacterial, antioxidant and DNA binding studies. The results show that both ligands and complexes possess potent antibacterial and antioxidant properties.___________________________________________________________________________

Phosphorescent κ3 -(N^C^C)-Gold(III) Complexes: Synthesis, Photophysics, Computational Studies and Application to Solution-Processable OLEDs.

Efficient OLED devices have been fabricated using organometallic complexes of platinum group metals. Still, the high material cost and low stability represent central challenges for their application in commercial display technologies. Based on its innate stability, gold(III) complexes are emerging as promising candidates for high-performance OLEDs. Here, a series of alkynyl-, N-heterocyclic carbene (NHC)- and aryl-gold(III) complexes stabilized by a κ3 -(N^C^C) template have been prepared and their photophysical properties have been characterized in detail. These compounds exhibit good photoluminescence quantum efficiency (ηPL ) of up to 33 %. The PL emission can be tuned from sky-blue to yellowish green colors by variations on both the ancillary ligands as well as on the pincer template. Further, solution-processable OLED devices based on some of these complexes display remarkable emissive properties (ηCE 46.6 cd.A-1 and ηext 14.0 %), thus showcasing the potential of these motifs for the low-cost fabrication of display and illumination technologies.

Recent Advances in the Biological Investigation of Organometallic Platinum-Group Metal (Ir, Ru, Rh, Os, Pd, Pt) Complexes as Antimalarial Agents.

In the face of the recent pandemic and emergence of infectious diseases of viral origin, research on parasitic diseases such as malaria continues to remain critical and innovative methods are required to target the rising widespread resistance that renders conventional therapies unusable. The prolific use of auxiliary metallo-fragments has augmented the search for novel drug regimens in an attempt to combat rising resistance. The development of organometallic compounds (those containing metal-carbon bonds) as antimalarial drugs has been exemplified by the clinical development of ferroquine in the nascent field of Bioorganometallic Chemistry. With their inherent physicochemical properties, organometallic complexes can modulate the discipline of chemical biology by proffering different modes of action and targeting various enzymes. With the beneficiation of platinum group metals (PGMs) in mind, this review aims to describe recent studies on the antimalarial activity of PGM-based organometallic complexes. This review does not provide an exhaustive coverage of the literature but focusses on recent advances of bioorganometallic antimalarial drug leads, including a brief mention of recent trends comprising interactions with biomolecules such as heme and intracellular catalysis. This resource can be used in parallel with complementary reviews on metal-based complexes tested against malaria.

Professor Robert D. Gillard: Transition Metal Chemist 1936–2013: Part I

This first part of a two-part commemoration of the life and work of Robert D. Gillard begins with a biographical outline which provides a context for his chemical achievements. He was awarded a State Scholarship and after his National Service in the Royal Air Force he went up to St Edmund Hall, Oxford, to read Chemistry. There follows a chronological account of his career in Chemistry starting with his undergraduate days in Oxford, where a Part II project with Dr Harry Irving on alkaline earth and cobalt complexes proved seminal. His PhD research at Imperial College, London in the Geoffrey Wilkinson group broadened his experience into the then poorly developed chemistry of rhodium and other platinum group metal complexes. Gillard next went to Sheffield University as a Lecturer where he developed independent research while continuing to work on earlier topics. There followed a move to Canterbury as a Reader at the University of Kent. In his particularly productive seven years there with a large research group he widened his experience further, expanding his interests in such areas as the optical properties of transition metal complexes, considering biological and medical relevance, and increasing the range of metals and ligands he investigated. His subsequent time at Cardiff and then into retirement will be covered in the second part of this commemoration.

In vitro biological evaluation of half-sandwich platinum-group metal complexes containing benzothiazole moiety

Ligands containing benzothiazole moiety upon reaction with arene platinum group metal precursors in dry methanol yielded cationic complexes 1–9 having N∩N bonding mode. The general formulation of the complexes is presented as [(arene)M(κ2N∩N-L)Cl]+, where L = L1, L2 and L3, M = Ru, Rh and Ir, and arene = p-cymene and pentamethylcyclopentadiene (Cp*). All these complexes were characterized by various spectroscopic techniques and were found to be air-stable. The biological activity studies of these complexes and ligands such as antibacterial and cytotoxicity studies showed that complexes 5, 6 and 9 have the highest antibacterial activity and ligand L1 has the highest cytotoxicity activity.

Homo- and Hetero-Oligonuclear Complexes of Platinum Group Metals (PGM) Coordinated by Imine Schiff Base Ligands.

Chemistry of Schiff base (SB) ligands began in 1864 due to the discovery made by Hugo Schiff (Schiff, H., Justus Liebigs Ann. der Chemie 1864, 131 (1), 118–119). However, there is still a vivid interest in coordination compounds based on imine ligands. The aim of this paper is to review the most recent concepts on construction of homo- and hetero-oligonuclear Schiff base coordination compounds narrowed down to the less frequently considered complexes of platinum group metals (PGM). The combination of SB and PGM in oligonuclear entities has several advantages over mononuclear or polynuclear species. Such complexes usually exhibit better electroluminescent, magnetic and/or catalytic properties than mononuclear ones due to intermetallic interactions and frequently have better solubility than polymers. Various construction strategies of oligodentate imine ligands for coordination of PGM are surveyed including simple imine ligands, non-innocent 1,2-diimines, chelating imine systems with additional N/O/S atoms, classic N2O2-compartmental Schiff bases and their modifications resulting in acyclic fused ligands, macrocycles such as calixsalens, metallohelical structures, nano-sized molecular wheels and hybrid materials incorporating mesoionic species. Co-crystallization and formation of metallophilic interactions to extend the mononuclear entities up to oligonuclear coordination species are also discussed.

Insights to the strained thiocarbamate derivative complexes of platinum group metals induced by azide as a co-ligand: Characterization and biological studies

Halide bridged metal precursors of platinum group on reaction with thiocarbamate derivative ligands (L1 and L2) yielded a series of neutral mono-dentate complexes (1–6) formulated as [(arene)M(κ1(S)-L)Cl2] where, L = L1 and L2, M = Ru, Rh and Ir, arene = p-cymene, Cp∗. Structural studies revealed the ligands coordinated to the metal centers through the thione sulfur in a mono-dentate fashion. These neutral complexes (1–6) were further reacted with NaN3 in methanol which resulted in the formation of highly strained κ2(N,S) azido complexes (7–12). Further treatment of the azido complexes with diethyl acetylene dicarboxylate (DEAD) yielded in the case of rhodium and iridium triazolo complexes (13–16). All these complexes were characterized by various spectroscopic techniques. NMR analysis revealed the triazolo ring coordinated to the metal center via the central nitrogen. Besides the varied coordination of the complexes, these complexes as well as the ligands exhibited antibacterial activity against some bacterial strains under study as well as profound antioxidant potency.

Synthesis of half sandwich platinum group metal complexes containing pyridyl benzothiazole hydrazones: Study of bonding modes and antimicrobial activity

Pyridyl benzothiazole hydrazone derivatives containing ruthenium, rhodium and iridium complexes have been synthesized, characterized and evaluated for antimicrobial activity. Metal precursors of the type [(arene)RuCl2]2(arene = p-cymene, benzene), [Cp∗MCl2]2 (M = Rh/Ir) and pyridyl benzothiazole hydrazone ligands (L1 and L2) have been employed in this work. Complexes containing ligands L1 in 1:2 (M:L) ratio yielded only one type of cationic mononuclear complexes whereas ligand L2 in 1:2 (M:L) ratio yielded two types of cationic mononuclear complexes. In same manner ligand L2 in 1:1 (M:L) ratio also yielded two types of binuclear complexes with different modes of binding. All these complexes have been characterized by analytical, spectroscopic and single-crystal X-ray diffraction studies. Antibacterial studies of ligands and complexes have been carried out and were found to exhibit potent activity towards gram-positive and gram-negative bacteria.

Arene platinum group metal complexes containing imino-quinolyl ligands: synthesis and antibacterial studies

Imino-quinolyl Schiff-base ligands have been prepared by the condensation reaction of substituted 2-aminopyridine and quinoline-2-carbaldehyde. The reaction of [(arene)MCl2]2 with imino-quinolyl Schiff-base ligands leads to the formation of cationic complexes [(arene)M(L)Cl]+ (1–12). Single crystal X-ray diffraction studies were used to confirm the coordination mode and structures of these complexes. The molecular structures of these complexes revealed that they adopt characteristic three-legged piano stool geometry with the metal coordinating through a terminal chloride and imino-quinolyl ligands in a bidentate chelating NN′ fashion. The ligand coordinates to the metal center through the nitrogen of the quinoline and the imine nitrogen forming a five-membered metallacycle. These compounds were evaluated for their in vitro antibacterial activity by the agar well diffusion method against Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae strains. Results show that all the ligands and complexes inhibited the growth of bacteria.

Synthesis, structural and in-vitro functional studies of half-sandwich platinum group metal complexes having various bonding modes of benzhydrazone derivative ligands

Complexes 1–9 were synthesized by reacting metal precursors [(arene)MCl2]2 (arene = p-cymene, Cp*; M = Ru, Rh and Ir) and benzhydrazone derivative ligands L1, L2 and L3 which resulted in the formation of cationic complexes with PF6 as the counter ion. Ruthenium complexes exhibited N∩O bonding mode while rhodium and iridium complexes exhibited N∩N bonding mode with the migration of the NH proton to the adjacent CO (keto) group forming enol. Anti-bacterial activity studies (against Gram-positive and Gram-negative bacteria) as well as anti-cancer [HCT116 p53 wild type (p53+/+) and HCT116 p53 null (p53−/−)] were carried out for all the complexes as well as ligands where interestingly, ligand L2 and complex 5 showed high activity potency (in-vitro) for both biological studies. Amongst Ru, Rh and Ir, rhodium complexes showed more anticancer activity.

Mesoionic Carbene (MIC)-Catalyzed H/D Exchange at Formyl Groups

Summary H/D exchange at formyl groups is the most direct approach for the synthesis of deuterated aldehydes. Platinum-group metal complexes have been employed to catalyze this transformation, with significant substrate scope limitations. Although N-heterocyclic carbenes can also activate the C–H bond of aldehydes through the formation of Breslow intermediates, benzoin condensation and other C–C-bond-forming pathways have so far outpaced synthetically useful H/D exchange. Investigation of the reaction of aldehydes with 1,2,3-triazolylidenes has revealed the reversible formation of Breslow intermediates and the inhibition of the condensation steps in methanol solvent. 1,2,3-Triazolylidenes catalyze the H/D exchange of aryl, alkenyl, and alkyl aldehydes in high yields and deuterium incorporation levels using deuterated methanol as an affordable D source. The unique properties of these mesoionic carbenes (MICs) enable a streamlined preparation of deuterated synthetic intermediates and pharmacophores that are highly valuable as mechanistic and metabolic probes.