Parent Complex Research Articles

A Cell Membrane Targeting Molybdenum-Iodine Nanocluster: Rational Ligand Design toward Enhanced Photodynamic Activity.

The development of singlet oxygen photosensitizers, which target specific cellular organelles, constitutes a pertinent endeavor to optimize the efficiency of photodynamic therapy. Targeting of the cell membrane eliminates the need for endocytosis of drugs that can lead to toxicity, intracellular degradation, or drug resistance. In this context, we utilized copper-free click chemistry to prepare a singlet oxygen photosensitizing complex, made of a molybdenum-iodine nanocluster stabilized by triazolate apical ligands. In phosphate-buffered saline, the complex formed nanoaggregates with a positive surface charge due to the protonatable amine function of the apical ligands. These nanoaggregates targeted cell membranes and caused an eminent blue-light phototoxic effect against HeLa cells at nanomolar concentrations, inducing apoptotic cell death, while having no dark toxicity at physiologically relevant concentrations. The properties of this complex were compared to those of a negatively charged parent complex to highlight the dominant effect of the nature of apical ligands on biological properties of the nanocluster. These two complexes also exerted (photo)antibacterial effects on several pathogenic strains in the form of planktonic cultures and biofilms. Overall, we demonstrated that the rational design of apical ligands toward cell membrane targeting leads to enhanced photodynamic efficiency.

Cases of intervention refusal encountered by public health nurses in Japan and characteristics of their support\u2013 qualitative analysis of described mother-child and elderly cases

BackgroundThe purpose of this study is to clarify the actual situation of the cases and the characteristics of support, focusing on mothers and their children, and elderly persons among the cases of intervention refusal encountered by public health nurses (PHNs) in Japan.MethodsThe data were descriptions of intervention refusal cases that were freely described by PHNs working for prefectural and municipal governments in questionnaire surveys nationwide. The characteristics of the cases and the support were categorized according to the situation of the case, and the number of descriptions was summarized and interpreted.ResultsThe results revealed that interventions involving mothers and children were refused in most of by mother or parents. The refusals were related to child abuse, parental mental illness, obsessiveness, and complex backgrounds. The actual status of intervention refusal in elderly persons, interventions are frequently refused by elderly persons themselves in the case of self-neglect and by family members living with the elderly in the case of abuse. The refusals were related to mental disorders or dementia and living alone. In both cases, PHNs provided support in collaboration with multi-disciplinary and multi-agencies, and attempts were made to alleviate the situation of refusal to intervene, from detecting cases through contact during home visits and in other settings, and by coordinating with appropriate team members as required.ConclusionsIt is suggested that PHNs need to acquire practical skills depending on the characteristics of the case to cope with critical situations throughout the process of engagement.

Applicability of Reddish-Orange Light Emitting Samarium (III) Complexes for Biomedical and Multifunctional Optoelectronic Devices

Six crimson samarium (III) complexes based on β-ketone carboxylic acid and ancillary ligands were synthesized by adopting the grinding technique. All synthesized complexes were investigated via elemental analysis, infrared, UV-Vis, NMR, TG/DTG and photoluminescence studies. Optical properties of these photostimulated samarium (III) complexes exhibit reddish-orange luminescence due to 4G5/2 → 6H7/2 electronic transition at 606nm of samarium (III) ions. Further, energy bandgap, color purity, CIE color coordinates, CCT and quantum yield of all complexes were determined accurately. Replacement of water molecules by ancillary ligands enriched these complexes (S2-S6) with decay time, quantum yield, luminescence, energy bandgap and biological properties than parent complex (S1). Interestingly, these efficient properties of complexes may find their applications in optoelectronics and lighting systems. In addition to these, the antioxidant and antimicrobial assays were also investigated to explore the applications in biological assays.

End-On Copper(I) Superoxo and Cu(II) Peroxo and Hydroperoxo Complexes Generated by Cryoreduction/Annealing and Characterized by EPR/ENDOR Spectroscopy.

In this report, we investigate the physical and chemical properties of monocopper Cu(I) superoxo and Cu(II) peroxo and hydroperoxo complexes. These are prepared by cryoreduction/annealing of the parent [LCuI(O2)]+ Cu(I) dioxygen adducts with the tripodal, N4-coordinating, tetradentate ligands L = PVtmpa, DMMtmpa, TMG3tren and are best described as [LCuII(O2•-)]+ Cu(II) complexes that possess end-on (η1-O2•-) superoxo coordination. Cryogenic γ-irradiation (77 K) of the EPR-silent parent complexes generates mobile electrons from the solvent that reduce the [LCuII(O2•-)]+ within the frozen matrix, trapping the reduced form fixed in the structure of the parent complex. Cryoannealing, namely progressively raising the temperature of a frozen sample in stages and then cooling back to low temperature at each stage for examination, tracks the reduced product as it relaxes its structure and undergoes chemical transformations. We employ EPR and ENDOR (electron-nuclear double resonance) as powerful spectroscopic tools for examining the properties of the states that form. Surprisingly, the primary products of reduction of the Cu(II) superoxo species are metastable cuprous superoxo [LCuI(O2•-)]+ complexes. During annealing to higher temperatures this state first undergoes internal electron transfer (IET) to form the end-on Cu(II) peroxo state, which is then protonated to form Cu(II)-OOH species. This is the first time these methods, which have been used to determine key details of metalloenzyme catalytic cycles and are a powerful tools for tracking PCET reactions, have been applied to copper coordination compounds.

Co-crystallisation as a modular approach to the discovery of spin-crossover materials.

Herein we present co-crystallisation as a strategy for materials discovery in the field of switchable spin crossover (SCO) systems. Using [Fe(3-bpp)2]·2A (where 3-bpp = 2,6-bis(pyrazol-3-yl)pyridine, A = BF4−/PF6−) as a starting point, a total of 11 new cocrystals have been synthesised with five different dipyridyl coformers. Eight of these systems show spin crossover behaviour, and all show dramatically different switching properties from the parent complex. The cocrystals have been studied by variable temperature single-crystal X-ray diffraction and SQUID magnetometry to develop structure–property relationships. The supramolecular architecture of the cocrystals depends on the properties of the coformer. With linear, rigid coformer molecules leading to 1D supramolecular hydrogen-bonded chains, while flexible coformers form 2D sheets and bent coformers yield 3D network structures. The SCO behaviour of the cocrystals can be modified through changing the coformer and thus co-crystallisation presents a rapid, facile and highly modular tool for the discovery of new switchable materials. The wider applicability of this strategy to the design of hybrid multifunctional materials is also discussed.

Novel bioinspired diiron core complexes with rigid chelating diphosphine ligands for highly efficient catalytic phenol hydroxylation

Hydroquinone (HQ) and catechol (CAT) are the important raw materials in the chemical industry, which can be produced through a direct catalytic hydroxylation process using hydrogen peroxide as an oxidant. Herein, we report two novel diiron core complexes (μ-budt)Fe2(CO)5(DPEphos) (1) and (μ-budt)Fe2(CO)5(Xantphos) (2) supported by rigid heterocyclic xanthene-like diphosphine ligands which exhibit high selectivity and activity in phenol hydroxylation. The structures of complexes 1 and 2 were characterized by FT-IR, UV–vis, 1H NMR, 31P-NMR, X-ray crystallography, while the catalytic products were tested by using HPLC. The FT-IR and UV–vis spectra reveal that two diphosphine ligands exhibit similar impacts on the structure of parent complex (μ-budt)Fe2(CO)6 [budt = SCH(CH3)CH2CH2)S]. Despite the similarity of ligands’ impact on the structure of the parent complex, the catalytic behavior was strongly influenced by the electronic and steric effects. The factors influencing the catalytic activity were optimized, including catalyst dosage, phenol/ H2O2 molar ratio, reaction temperature, and time. Under the optimal conditions, 1 exhibits great catalytic performance with 57.7% phenol conversion and 49.6% DHB yield, both of which are remarkable. The mechanism of phenol hydroxylation using 1 as a catalyst was also proposed. Hydroxyl radicals (•OH) were generated in the catalytic reaction, as demonstrated by electron spin resonance (ESR).

An NHC-Stabilized H2 GeBH2 Precursor for the Preparation of Cationic Group 13/14/15 Hydride Chains.

The synthesis, characterization and reactivity studies of the NHC‐stabilized complex IDipp ⋅ GeH2BH2OTf (1) (IDipp=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) are reported. Nucleophilic substitution of the triflate (OTf) group in 1 by phosphine or arsine donors provides access to the cationic group 13/14/15 chains [IDipp ⋅ GeH2BH2ERR1R2]+ (2 E=P; R, R1=H; R2=tBu; 3 E=P; R=H; R1, R2=Ph; 4 a E=P; R, R1, R2=Ph; 4 b E=As; R, R1, R2=Ph). These novel cationic chains were characterized by X‐ray crystallography, NMR spectroscopy and mass spectrometry. Moreover, the formation of the parent complexes [IDipp ⋅ GeH2BH2PH3][OTf] (5) and [IDipp ⋅ GeH3][OTf] (6) were achieved by reaction of 1 with PH3. Accompanying DFT computations give insight into the stability of the formed chains with respect to their decomposition.

Synthesis, optical and structural characterisation of ZnS nanoparticles derived from Zn(ii) dithiocarbamate complexes

Abstract Zinc sulphide nanoparticles represented as ZnS1, ZnS2 and ZnS3 have been prepared from Zn(ii) N-methyl-N-ethanoldithiocarbamate (1) complex and its 2,2′-bipyridine (2) and 1,10′-phenanthroline (3) adducts, respectively. Both the parent complex (1) and the adducts (2) and (3) were characterised by spectroscopic techniques and elemental analysis. In the solid state, the structures of complexes (1) and (2) were established using single-crystal X-ray analysis. Complex (1) possessed a distorted trigonal bipyramidal geometry about the zinc centre, whilst forming a dimer via bidentate bridging coordination between two opposite dithiocarbamate motifs. On the other hand, complex (2) formed a trigonal prismatic geometry about the Zn centre with a ZnS4N2 chromophore. The decomposition of the complexes in hexadecylamine afforded spherical-shaped ZnS nanoparticles of the cubic sphalerite crystal phase. The transmission electron microscopy (TEM) micrographs showed that the average particles size of ZnS1, ZnS2 and ZnS3 were 2.63, 5.27 and 6.52 nm, respectively. In the optical study, the estimated bandgap energies were found in the range between 4.34 and 4.08 eV, which indicated a blue shift when compared with the bandgap energy of bulk ZnS.

Bio-inspired nitrogen oxide (NOx) interconversion reactivities of synthetic heme Compound-I and Compound-II intermediates

Dioxygen activating heme enzymes have long predicted to be powerhouses for nitrogen oxide interconversion, especially for nitric oxide (NO) oxidation which has far-reaching biological and/or environmental impacts. Lending credence, reactivity of NO with high-valent heme‑oxygen intermediates of globin proteins has recently been implicated in the regulation of a variety of pivotal physiological events such as modulating catalytic activities of various heme enzymes, enhancing antioxidant activity to inhibit oxidative damage, controlling inflammatory and infectious properties within the local heme environments, and NO scavenging. To reveal insights into such crucial biological processes, we have investigated low temperature NO reactivities of two classes of synthetic high-valent heme intermediates, Compound-II and Compound-I. In that, Compound-II rapidly reacts with NO yielding the six-coordinate (NO bound) heme ferric nitrite complex, which upon warming to room temperature converts into the five-coordinate heme ferric nitrite species. These ferric nitrite complexes mediate efficient substrate oxidation reactions liberating NO; i.e., shuttling NO2− back to NO. In contrast, Compound-I and NO proceed through an oxygen-atom transfer process generating the strong nitrating agent NO2, along with the corresponding ferric nitrosyl species that converts to the naked heme ferric parent complex upon warmup. All reaction components have been fully characterized by UV–vis, 2H NMR and EPR spectroscopic methods, mass spectrometry, elemental analyses, and semi-quantitative determination of NO2− anions. The clean, efficient, potentially catalytic NOx interconversions driven by high-valent heme species presented herein illustrate the strong prospects of a heme enzyme/O2/NOx dependent unexplored territory that is central to human physiology, pathology, and therapeutics.

Enhancing the efficiency of near-infrared iridium (III) complexes-based OLEDs by auxiliary ligand functionalization

In order to enhance the charge balance of organic near infrared (NIR) electroluminescent devices, an ancillary ligand of pic-SCz which was covalently linking the bipolar group SCz (composed of PS (S) and tBuCz (Cz)) to pic (SCz=3,6-di-tert-butyl-9-(4-(phenylsulfonyl)phenyl)-9H-carbazole; PS = phenyl sulfone; tBuCz = 3,6-di-tert-butylcarbazole; pic= 2-picolinic acid) was developed for iridium (III) complex (TPA-BTz-Iq)2Ir(pic-SCz). Compared with parent complex (TPA-BTz-Iq)2Irpic, the photophysical and electroluminescent properties of (TPA-BTz-Iq)2Ir(pic-SCz) were improved by introducing Cz as hole transporting unit and PS as electron transporting unit. In phosphorescent organic light emitting devices (OLEDs), using (TPA-BTz-Iq)2Ir(pic-SCz) as the luminescent dopant, we obtained a maximum external quantum efficiency (EQEmax) of 0.95% at the wavelength of 712 nm. This is 3.28 times as much as that of (TPA-BTz-Iq)2Irpic (EQEmax is 0.29% at 712 nm).

Solid-state and solution characterizations of [(TMPA)Cu(II)(SO3)] and [(TMPA)Cu(II)(S2O3)] complexes: Application to sulfite and thiosulfate fast detection

Sulfite (SO32−) and thiosulfate (S2O32−) ions are used as food preservative and antichlor agent respectively. To detect low levels of such anions we used Cu(II) complex of the Tris-Methyl Pyridine Amine (TMPA) ligand, denoted L. Formation of [LCu(SO3)] (1) and [LCu(S2O3)] (2) in solution were monitored using UV–Vis, EPR and cyclic voltammetry, while the solid-state X-ray structures of both complexes were solved. In addition, we also evaluated the pH range in which the complexes are stable, and the anions binding affinity values for the [LCu(solvent)]2+ (3) parent complex. As a matter of illustration, we determined the sulfite content in a commercial crystal sugar.

A Ruthenium(II) Water Oxidation Catalyst Containing a pH-Responsive Ligand Framework.

The synthesis of a new RuII-based water oxidation catalyst is presented, in which a nitrophenyl group is introduced into the backbone of dpp via a pH-sensitive imidazole bridge (dpp = 2,9-di-(2′-pyridyl)-1,10-phenanthroline). This modification had a pronounced effect on the photophysical properties and led to the appearance of a significant absorption band around 441 nm in the UV–vis spectrum upon formation of the monoprotonated species under neutral conditions. Theoretical investigations could show that the main contributions to this band arise from transitions involving the imidazole and nitrophenyl motif, allowing us to determine the pKa value (6.8 ± 0.1) of the corresponding, twofold protonated conjugated acid. In contrast, the influence of the nitrophenyl group on the electrochemical properties of the catalytic center was negligible. Likewise, the catalytic performance of Ru(dppip-NO2) and its parent complex Ru(dpp) was comparable over the entire investigated pH range (dppip-NO2 = 2-(4-nitrophenyl)-6,9-di(pyridin-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline). This allowed the original catalytic properties to be retained while additionally featuring a functionalized ligand scaffold, which provides further modification opportunities as well as the ability to report the pH of the catalytic solution via UV–vis spectroscopy.

Synthesis, characterization, and antimicrobial activity investigations of ruthenium (II)–bipyridine complexes of ciprofloxacin derivatives

AbstractA series of ruthenium (II) complexes derived from the reaction between cis‐bis (2,2′‐bipyridine) dichloro ruthenium (II) dihydrate and enaminone derivatives of ciprofloxacin were synthesized and fully characterized using elemental analysis, cyclic voltammetry and different spectroscopic techniques (Uv–vis, FTIR, NMR, mass spectroscopy, and X‐ray photoelectron spectrometry (XPS)). The isolated compounds were tested for their antibacterial and antifungal activities against gram‐negative and gram‐positive bacteria. The FTIR data revealed that ciprofloxacin derivatives act as bidentate ligands through the pyridone carbonyl and the carboxylate oxygen atom. The UV–visible data showed that the charge transfer CT band is blue shifted upon the coordination of the ciprofloxacin derivatives compared to the CT band of the parent complex. The XPS results revealed the characteristic peaks of Ru3p3/2and Ru3p1/2as well as Ru3d5/2and Ru3d3/2, which confirmed the assembly of the ruthenium (II) ciprofloxacin derivative complexes. Cyclic voltammetry data showed that the ciprofloxacin enaminone derivatives have a similar reduction potential for the Ru (II)/Ru (III) redox couple, and it revealed that the coordination of the ruthenium (II) ion altered the redox property of the ligands and enhanced their electron transfer rate. The electrochemical and the UV–visible results suggest that the ciprofloxacin derivative ligands are‐acceptor ligands. Further, the complexes showed higher antibacterial activities than the parent ciprofloxacin antibiotic and did not show antifungal activities among the tested fungi strains.

Synthesis and redox properties of heterobimetallic Re(bpyCrown-M)(CO)3Cl complexes, where M = Na+, K+, Ca2+, and Ba2+

The operational electrochemical potential of a molecular electrocatalyst is typically pinned to the reduction potential of the parent complex. The predominant strategy for minimizing the overpotential is to modify the ligand with electron withdrawing functional groups to anodically shift the reduction potential. However, these changes often result in decreased catalytic rates. Re(bpy)(CO)3Cl is a well-known electrocatalyst for selective CO2 reduction to CO. In this work, the synthesis of Re(bpyCrown-M)(CO)3Cl is described, where bpyCrown-M is a bipyridine ligand containing a cyclic ether cavity, and M is a Na+, K+, Ca2+, or Ba2+ ion encapsulated within that cavity. Addition of these cations results in anodic shifts in reduction potential, and the magnitude of the shifts correlate with overall cationic charge. However, electrolysis under catalytic conditions for CO2 reduction results in precipitation of carbonate salts, diminishing overall catalytic activity.

Cationic Cycloheptatrienyl Cyclopentadienyl Manganese Sandwich Complexes: Tromancenium Explored with High-Power LED Photosynthesis.

In this contribution, we revisit the neglected and forgotten cationic, air-stable, 18-valence electron, heteroleptic sandwich complex (cycloheptatrienyl)(cyclopentadienyl)manganese, which was reported independently by Fischer and by Pauson about 50 years ago. Using advanced high-power LED photochemical synthesis, an expedient rapid access to the parent complex and to functionalized derivatives with alkyl, carboxymethyl, bromo, and amino substituents was developed. A thorough study of these “tromancenium” salts by a range of spectroscopic techniques (1H/13C/55Mn-NMR, IR, UV–vis, HRMS, XRD, XPS, EPR), cyclic voltammetry (CV), and quantum chemical calculations (DFT) shows that these manganese sandwich complexes are unique metallocenes with quite different chemical and physical properties in comparison to those of isoelectronic cobaltocenium salts or (cycloheptatrienyl)(cyclopentadienyl) sandwich complexes of the early transition metals. Electrochemically, all tromancenium ions undergo a chemically partially reversible oxidation and a chemically irreversible reduction at half-wave or peak potentials that respond to the substituents at the Cp deck. As exemplarily shown for the parent tromancenium ion, the product generated during the irreversible reduction process reverts at least partially to the starting material upon reoxidation. Quantum-chemical calculations of the parent tromancenium salt indicate that metal–ligand bonding is distinctly weaker for the cycloheptatrienyl ligand in comparison to that of the cyclopentadienyl ligand. Both the HOMO and the LUMO are metal and cycloheptatrienyl-ligand centered, indicating that chemical reactions will occur either metal-based or at the seven-membered ring, but not on the cyclopentadienyl ligand.

A red-orange carbazole-based iridium(III) complex: Synthesis, thermal, optical and electrochemical properties and OLED application

A novel heteroleptic iridium(III) acetylacetonate (acac) complex, (L-5-CHO)2Ir(acac) (3b), was synthesised from 2-(9’-hexylcarbazole-3’-yl)-5-formylpyridine (L-5-CHO) (1b). The complex 3b was determined to be thermally and electrochemically stable. The photoluminescence properties of the compound were studied, with a dichloromethane solution of 3b giving structureless emission at 662 nm, showing that the formyl group red-shifted the emission by 151 nm compared to the parent complex. Complex 3b was also shown to possess a moderate photoluminescence quantum yield (67%) and a short emission lifetime (τ = 280 ns). Organic light-emitting diodes (OLEDs) were fabricated with a solution-processed emissive layer (EML) consisting of poly(N-vinylcarbazole) (PVK), 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD) and iridium complex (3b). The OLEDs containing complex 3b showed red-orange electroluminescence (EL) at 624 nm. The influence of the host materials was studied and the best performance was achieved with both PVK and PBD in the emissive layer, with the resulting OLEDs exhibiting a current efficiency of 0.84 cd/A, a power efficiency of 0.20 lm/W, and an external quantum efficiency (EQE) of 0.66% at a brightness of 2548 cd/m2.

Molecular Alignment of Homoleptic Iridium Phosphors in Organic Light-Emitting Diodes.

The orientation of facial (fac) tris-cyclometalated iridium complexes in doped films prepared by vacuum deposition is investigated by altering the physical shape and electronic asymmetry in the molecular structure. Angle-dependent photoluminescence spectroscopy and Fourier-plane imaging microscopy show that the orientation of roughly spherical fac-tris(2-phenylpyridyl)iridium (Ir(ppy)3 ) is isotropic, whereas complexes that are oblate spheroids, fac-tris(mesityl-2-phenyl-1H-imidazole)iridium (Ir(mi)3 ) and fac-tris((3,5-dimethyl-[1,1'-biphenyl]-4-yl)-2-phenyl-1H-imidazole)iridium (Ir(mip)3 ), have a net horizontal alignment of their transition dipole moments. Optical anisotropy factors of 0.26 and 0.15, respectively, are obtained from the latter complexes when doped into tris(4-(9H-carbazol-9-yl)phenyl)amine host thin films. The horizontal alignment is attributed to the favorable van der Waals interaction between the oblate Ir complexes and host material. Trifluoromethyl groups substituted on one polar face of the Ir(ppy)3 and Ir(mi)3 complexes introduce chemical asymmetries in the molecules at the expense of their oblate shapes. The anisotropy factors of films doped with these substituted derivatives are lower relative to the parent complexes, indicating that the fluorinated patches reinforce horizontal alignment during deposition. High efficiencies obtained from organic light emitting diodes prepared using the Ir dopants is attributed, in part, to improved outcoupling of electroluminescence brought about by molecular alignment.

Electrochemical and Photophysical Study of Homoleptic and Heteroleptic Methylated Ru(II) Bis‐terpyridine Complexes

AbstractIn this study, we investigate the impact of N‐methylation on the electronic and photophysical properties of both homoleptic and heteroleptic Ru(II) bis‐terpyridine complexes based on the recently reported ligand 4’‐(4‐bromophenyl)‐4,4’’’ : 4’’,4’’’’‐dipyridinyl‐2,2’ : 6’,2’’‐terpyridine (Bipytpy), with pyridine substituents in the 4‐ and 4’’‐position. The first reduction of the methylated complexes takes place at the pyridinium site and is observed as multi‐electron process. Following N‐methylation, the complexes exhibit higher luminescence quantum yields and longer excited‐state lifetimes. Interestingly, the photophysical properties of the heteroleptic and homoleptic complexes are rather similar. TD‐DFT calculations support the experimental results. Furthermore, the complexes are tested as photosensitizers for photocatalytic hydrogen production, as the parent complex 1 [Ru(Bipytpy)(Tolyltpy)](PF6)2 (Tolyltpy: 4′‐tolyl‐2,2′ : 6′,2′’‐terpyridine) was recently shown to be active and highly stable under photocatalytic conditions. However, the methylated complexes reported herein are inactive as photosensitizers under the chosen conditions, presumably due to loss of the methyl groups, converting them to the non‐methylated parent complexes.

Redox Reaction between an Oxo-Bridged Diiron Complex and Hydrazine: A Kinetic Study

Objective: Mechanistic investigation of the reaction between the complex ion [FeIII 2(μ-O)(phen)4(H2O)2]4+ (1) (phen = 1,10-phenanthroline) and its hydrolytic derivatives [FeIII 2(μ-O)(phen)4(H2O)(OH)]3+ (1a) and [FeIII 2(μ-O)(phen)4(OH)2]2+ (1b) which coexist in rapid equilibria in the range pH = 3.00 to pH = 5.00 (pKa1 = 3.71 ± 0.03, pKa2 = 5.28 ± 0.07) with N2H5 + ion to produce [Fe(phen)3]2+ has been covered in this study. Methods: Rise in absorbance of the product with time was measured and rates have been determined using initial rate methods. Dependence of rate on pH and concentration of N2H5 + are studied in detail. Results: In the presence of excess phenanthroline, the reaction follows simple first-order exponential profile. Interestingly, in the absence of any added phenanthroline, the reaction becomes faster and the reaction profile changes to nearly linear with curvature near the end of the reaction. Slight autocatalytic nature has been observed only for the slower reactions. The observed rate constants obtained using initial rate method show first-order dependence on the concentration of N2H5 +. An increase in rate with increasing pH has been noticed. The plot of rate versus 1/[H+] shows saturation beginning near pH 4.6, suggesting that the mono-deprotonated form of the complex (i.e. 1a) is the active oxidant in this pH range. Conclusion: Presumably, the reaction becomes faster in the absence of added phenanthroline because ligand dissociation from the parent complex becomes facilitated when there is no external phenanthroline ligand present. This produces a coordinatively unsaturated Fe(III) species which is a faster oxidant.

Effect of the 2-R-Allyl and Chloride Ligands on the Cathodic Paths of [Mo(η3-2-R-allyl)(α-diimine)(CO)2Cl] (R = H, CH3; α-diimine = 6,6'-Dimethyl-2,2'-bipyridine, Bis(p-tolylimino)acenaphthene).

The new, formally Mo(II) complexes [Mo(η3-2-R-allyl)(6,6′-dmbipy)(CO)2Cl] (6,6′-dmbipy = 6,6′-dimethyl-2,2′-bipyridine; 2-R-allyl = allyl for R = H, 2-methallyl for R = CH3) and [Mo(η3-2-methallyl)(pTol-bian)(CO)2Cl] (pTol-bian = bis(p-tolylimino)acenaphthene) share, in this rare case, the same structural type. The effect of the anionic π-donor ligand X (Cl– vs NCS–) and the 2-R-allyl substituents on the cathodic behavior was explored. Both ligands play a significant role at all stages of the reduction path. While 2e–-reduced [Mo(η3-allyl)(6,6′-dmbipy)(CO)2]− is inert when it is ECE-generated from [Mo(η3-allyl)(6,6′-dmbipy)(CO)2(NCS)], the Cl– ligand promotes Mo–Mo dimerization by facilitating the nucleophilic attack of [Mo(η3-allyl)(6,6′-dmbipy)(CO)2]− at the parent complex at ambient temperature. The replacement of the allyl ligand by 2-methallyl has a similar effect. The Cl–/2-methallyl ligand assembly destabilizes even primary radical anions of the complex containing the strongly π-accepting pTol-Bian ligand. Under argon, the cathodic paths of [Mo(η3-2-R-allyl)(6,6′-dmbipy)(CO)2Cl] terminate at ambient temperature with 5-coordinate [Mo(6,6′-dmbipy)(CO)3]2– instead of [Mo(η3-2-R-allyl)(6,6′-dmbipy)(CO)2]−, which is stabilized in chilled electrolyte. [Mo(η3-allyl)(6,6′-dmbipy)(CO)2]− catalyzes CO2 reduction only when it is generated at the second cathodic wave of the parent complex, while [Mo(η3-2-methallyl)(6,6′-dmbipy)(CO)2]− is already moderately active at the first cathodic wave. This behavior is fully consistent with absent dimerization under argon on the cyclic voltammetric time scale. The electrocatalytic generation of CO and formate is hampered by the irreversible formation of anionic tricarbonyl complexes replacing reactive [Mo(η3-2-methallyl)(6,6′-dmbipy)(CO)2]2 along the cathodic route.