Pyridine Arms Research Articles

Tetraphenylethylene tethered 1-(pyridine-2-yl)imidazo[1,5-a]pyridine: Synthesis, aggregation induced emission, copper(II) ion detection and imaging of latent fingerprint

The development of aggregation induced emissive probe with high sensitivity and selectivity for Cu2+ ions is a fascinating research in biomedical sciences. In this context, we have successfully synthesized an aggregation induced emissive probe for the selective detection of Cu2+ ions by incorporating a 1-(pyridine-2-yl)imidazo[1,5-a]pyridine arm in the tetraphenylethylene framework. The aggregates have been characterized using pivotal microscopic and photophysical measurements. The results exhibits that the aggregates have a spherical shape with an average size of 90 nm and a fluorescence quantum yield of ∼23 %. The aggregated fluorescent probe exhibited an excellent selectivity towards Cu2+ ions with a detection limit of 83 nM and presented a good efficacy over diverse environmental water samples. Furthermore, the quenching type is delineated as static due to complexation followed by deaggregation which was supported by dynamic light scattering and Tyndall effect experiments. In addition, the high solid state emissive property of the probe makes it a potential candidate for latent fingerprint analysis to gather level 2 and 3 information thereby playing a substantial role in forensic investigations.

Synthesis and structural characterization of diorganotin(IV) complexes with a tridentate N‐heterocyclic podand ligand and investigation of their catalytic activity in Baeyer–Villiger oxidation of cyclic ketones to lactones

Diorganotin(IV) complexes of composition [Me2SnL] (1), [n‐Bu2SnL] (2), and [Bz2SnL] (3) were synthesized by reacting the N2,N6‐di(pyridin‐2‐yl)pyridine‐2,6‐dicarboxamide pro‐ligand (H2L, where H2 denotes the two acidic protons) with Me2SnO, n‐Bu2SnO, and Bz2SnO, respectively, in refluxing toluene. The amide ligand leads to highly stable diorganotin(IV) complexes via the dianionic tridentate donor set (Npy, N−, N−) with pendent pyridine arms, and the coordination domain is completed by the respective two alkyl ligands. Solution‐state structures of the compounds 1–3 were studied by 1H, 13C, and 119Sn nuclear magnetic resonance (NMR) spectroscopy, revealing that the complexes adopt a five‐coordinate structure in non‐coordinating solvent. Additionally, homogenity and purity of the bulk materials of 1–3 were judged using the high‐resolution mass spectrometry in acetonitrile solution. The molecular and crystal structures of 1·0.5C6H6, 2, and 3 in the solid phase were established by single‐crystal X‐ray diffraction analysis. For all three compounds, the core defined by the rigid tridentate pyridine dicarboxamide ligand and the Sn‐coordinating C atoms adopts nearly C2v symmetry and thus matches none of the most popular geometries for five‐coordinated species, namely square‐pyramidal or trigonal‐bipyramidal coordination. Thermogravimetric analysis (TGA) was performed to probe the thermal stabilities of 1–3. The results serve as a basis for designing highly efficient diorganotin(IV) mimics for catalytic applications. Catalytic studies of ε‐caprolactone formation via Baeyer–Villiger oxidation of cyclohexanone with aqueous H2O2 were performed under microwave (MW) irradiation. The consequences of several reaction parameters like catalyst quantity, time, temperature, and solvent were studied.

Synthesis, Structure, and Photophysical Properties of Platinum(II) (N,C,N') Pincer Complexes Derived from Purine Nucleobases†.

The synthesis of a series of Pt{κ3-N,C,N'-[L]}X (X = Cl, RC≡C) pincer complexes derived from purine and purine nucleosides is reported. In these complexes, the 6-phenylpurine skeleton provides the N,C-cyclometalated fragment, whereas an amine, imine, or pyridine substituent of the phenyl ring supplies the additional N'-coordination point to the pincer complex. The purine N,C-fragment has two coordination positions with the metal (N1 and N7), but the formation of the platinum complexes is totally regioselective. Coordination through the N7 position leads to the thermodynamically favored [6.5]-Pt{κ3-N7,C,N'-[L]}X complexes. However, the coordination through the N1 position is preferred by the amino derivatives, leading to the isomeric kinetic [5.5]-Pt{κ3-N1,C,N'-[L]}X complexes. Extension of the reported methodology to complexes having both pincer and acetylide ligands derived from nucleosides allows the preparation of novel heteroleptic bis-nucleoside compounds that could be regarded as organometallic models of Pt-induced interstrand cross-link. Complexes having amine or pyridine arms are green phosphorescence emitters upon photoexcitation at low concentrations in CH2Cl2 solution and in poly(methyl methacrylate) (PMMA) films. They undergo self-quenching at high concentrations due to molecular aggregation. The presence of intermolecular π-π stacking and weak Pt···Pt interactions was also observed in the solid state by X-ray diffraction analysis.

Imidazo[1,5-a]pyridine-3-ylidenes and dipyridoimidazolinylidenes as ancillary ligands in Palladium allyl complexes with potent in vitro anticancer activity

The synthesis and characterization of silver and palladium allyl complexes bearing imidazo[1,5-a]pyridine-3-ylidene and dipyridoimidazolinylidene ligands is reported.NMR analysis of the starting azolium salts revealed the weaker σ-donor character of these NHC ligands compared to the most common imidazol-2-ylidenes and imidazolin-2-ylidenes.All cationic palladium allyl complexes showed remarkable antitumoral activity toward a panel of cisplatin-sensitive and cisplatin-resistant cell lines, with IC50 in the micro- and nano-molar range.Among the tested derivatives, those with a pyridine arm combine good anticancer activity with a poor cytotoxicity against normal cells. Finally, all palladium complexes, especially the bisNHC species, showed good photoluminescence properties, with emission in the blue/green region.

Cationic PCP and PCN NHC Core Pincer-Type Mn(I) Complexes: From Synthesis to Catalysis

The coordination chemistry of NHC core pincer-type PCP and PCN ligands with Mn(I) center was systematically investigated. The reaction of [Mn(CO)5Br] with free carbenes, conveniently prepared from the corresponding imidazolium salts and a strong base, lead to the initial formation of bidentate fac-[MnBr(CO)3(κ 2 P,C,L)] complexes bearing a pending phosphine or pyridine donor extremity (L), which upon bromide abstraction, afford cationic [Mn(CO)3(κ 3 P,C,L)](OTf) derivatives exhibiting a meridional or a facial coordinating geometry of tridentate NHC core ligand depending on its relative flexibility. All bi-and tridentate Mn(I) complexes were characterized by X-ray diffraction analysis. The impact of the tridentate ligand structure on catalytic performance was illustrated in the Mn-catalyzed hydrogenation of acetophenone revealing fac-[Mn(CO)3(κ 3 P,C,N)](OTf) based on a 5,6-membered metallacyclic architecture to be the most active, thus evidencing the role of the pyridine arm lability in the catalytic cycle.

CO2 Capture by 2-(Methylamino)pyridine Ligated Aluminum Alkyl Complexes.

A set of novel, easily synthesized aluminum complexes, Al[κ2-N,N-2-(methylamino)pyridine]2R (R = Et, iBu) are reported. When subjected to 1 atm of CO2 pressure, each hemilabile pyridine arm dissociates and facilitates cooperative activation of the CO2 substrate reminiscent of a Frustrated Lewis Pair. This reaction has limited precedent for Al/N based Lewis Pair systems, and this is the first system readily shown to sequester multiple equivalents of CO2 per aluminum center. The ethyl variant then reacts further, inserting a third equivalent of CO2 into the aluminum alkyl to generate an aluminum carboxylate. Examples of this type of reactivity are rare under thermal conditions. A joint experimental/computational study supports the proposed reaction mechanism.

Rigidifying Ag(I) Complexes for Selective Nitrene Transfer

AbstractOne of the challenges in achieving tunable and predictable C−H bond amidation via silver‐catalyzed nitrene transfer (NT) is the conformational flexibility and dynamic nature of many Ag(I) complexes. This fluxional behavior can make it difficult to obtain a clear understanding of the factors responsible for influencing the site‐selectivity of the amidation event. Mechanistic studies on related systems suggest that π⋅⋅⋅π and Ag⋅⋅⋅π interactions play important roles in altering the preference for nitrene transfer at sites adjacent to π systems, including benzylic, allylic, and propargylic C−H bonds. In this paper, we report a Ag(I) catalyst designed to improve the preference for reaction at benzylic, allylic, and propargylic C−H bonds over more electron‐rich tertiary alkyl C(sp3)−H bonds by enhancing non‐covalent interactions. Rigidifying a flexible tris(2‐pyridylmethyl)amine ligand scaffold by tying back the sp3 nitrogen into a piperidine ring strengthened non‐covalent interactions between the π‐containing substituents on the substrate and the pyridine arm of the catalyst and improved the site‐selectivity of the nitrene transfer event.

Homogeneous Electrochemical Reduction of CO2 to CO by a Cobalt Pyridine Thiolate Complex.

The chemical and electrochemical reduction of CO2 to value added chemicals entails the development of efficient and selective catalysts. Synthesis, characterization and electrochemical CO2 reduction activity of a air-stable cobalt(III) diphenylphosphenethano-bis(2-pyridinethiolate)chloride [{Co(dppe)(2-PyS)2}Cl, 1-Cl] complex is divulged. The complex reduces CO2 under homogeneous electrocatalytic conditions to produce CO with high Faradaic efficiency (FE > 92%) and selectivity in the presence of water. Through detailed electrochemical investigations, product analysis, and mechanistic investigations supported by theoretical calculations, it is established that complex 1-Cl reduces CO2 in its Co(I) state. A reductive cleavage leads to a dangling protonated pyridine arm which enables facile CO2 binding through a H-bond donation and facilitates the C-O bond cleavage via a directed protonation. A systematic benchmarking of this catalyst indicates that it has a modest overpotential (∼180 mV) and a TOF of ∼20 s-1 for selective reduction of CO2 to CO with H2O as a proton source.

Cis Donor Influence on O-O Bond Lability in Iron(III) Hydroperoxo Complexes: Oxidation Catalysis and Ligand Transformation.

The FeIII/FeII redox potentials for [Fe(tpen)]2+/3+, [Fe(tpena)]+/2+, and [Fe(tpenO)]+/2+ (N-R-N,N',N'-tris(2-pyridylmethyl)ethane-1,2-diamine, where R = CH2C6H4N, CH2COO-, CH2CH2O-, respectively) span 470 mV with the oxidation potentials following the order [FeII(tpenO)]+ (MeOH) < [FeII(tpena)]+ (MeCN) < [FeII(tpen)]2+ (MeCN). In their +3 oxidation states the complexes react with 1 equiv of H2O2 to give the purple [FeIII(OOH)(HL)]n+ (n = 2 for L = tpena, tpenO; n = 3 for L = tpen). A pyridine arm is decoordinated in these complexes, furnishing a second coordination sphere base which is protonated at ambient pH. The lifetimes of these transient species depend on how readily the substrate (sometimes the solvent) is oxidized and reflect the trend in both the O-O bond lability and oxidizing potency of the putative iron-based oxidant derived from the iron(III) peroxides. In methanol solution, [FeIII(tpenO)]2+ and [FeIII(tpena)]2+ exist in their Fe(III) states and hence the formation of [FeIII(OOH)(Htpena)]2+ and [FeIII(OOH)(HtpenO)]2+ is instantaneous. This is in contrast to the short lag time that occurs before adduct formation between [FeII(tpen)]2+ and H2O2 due to the requisite prior oxidation of the solution-state iron(II) complex to its iron(III) state. Stabilization of the +3 iron oxidation state in the resting state catalysts affords complexes that activate H2O2 more readily with the consequence of higher yields in the oxidation of the C-H bonds using H2O2 as terminal oxidant. The presence of a cis monodentate carboxylato donor increases the rate of oxidation by hydrogen atom transfer in comparison to the systems with an alkoxo or pyridine in this position. Competing with substrate oxidation is the oxidative modification of the alkoxido group in [FeIII(tpenO)]2+, converting it to a carboxylato group in the presence of H2O2: in effect, transforming tpenO to tpena.

Synthesis, coordination properties and DFT studies of novel trans-disubstituted hexaaza-macrocycles containing pyridine and/or ethyldioxolane arms

Novel trans-disubstituted hexaaza-macrocyclic ligands L1 and L2 were successfully prepared by the alkylation of the trans secondary amines presented in L with pyridine and ethyldioxolane groups, respectively. The coordination properties of compounds L1 and L2 towards different transition, post-transition and lanthanoid metal ions were explored. Colorless crystals of [NaL1]I and L2´Br2, suitable for X-ray diffraction, were obtained by slow evaporation of an acetonitrile solution of compounds L1 or L2, showing an anti conformation between the methyl groups and the pendant arms in trans positions. The [ML1]n+ (M = Ni2+, Cu2+, Zn2+) systems were investigated by DFT calculations (B3LYP model).

{Ru(CO)x}-core terpyridine complexes: Lysozyme binding affinity, DNA and photoinduced carbon monoxide releasing properties

Reaction of 4′-(2-pyridyl)-2,2′:6′,2″-terpyridine (LPY) and 4′-(4-phenylmorpholine)-2,2′:6′,2″-terpyridine (Lmorph) with {[RuCl2(CO)3]}2 in methanol affords [RuCl2(LPY-κ2N1N2)(CO)2] (1) and a mixture of [RuCl2(Lmoph-κ2N1N2)(CO)2]/[RuCl2(Lmorph-κ3N1N2N3)(CO)] (2), respectively. Their photoactivatable CO releasing properties are investigated upon the exposure to light source at 365 nm. One CO molecule is released from 1 at the excitation wavelength 365 nm, while the ligand changes its bidentate mode into the meridional tridentate one. The illumination profile and the influence of the uncoordinated pyridine arm on CO release are examined by solution 1H and 13C NMR spectroscopy. The electronic transitions are studied by TDDFT. The DNA and hen white egg lysozyme binding affinity of the complexes are studied by UV/Vis. and electrospray ionization mass spectrometry. Stable lysozyme complexes, capable of photo induce CO, are formed via the loss of the labile chloride ligands or terpyridine moiety.

Synthesis of Pd(II) large dinuclear macrocyclic complex tethered through two dipyridine-bridged aza-crowns as an efficient copper- and phosphine-free Sonogashira catalytic reaction

For the first time the new 32-membered macrocyclic dinuclear palladium complex of two aza-crown macrocycles, bearing two pyridine arms, Pd2L2Cl4 was synthesized and characterized by elemental analysis, IR, NMR spectroscopy and single crystal X-ray diffraction methods. Pd2L2Cl4 was investigated as a moisture/air-stable catalyst for Sonogashira cross-coupling reaction in the absence of copper and phosphine ligand in DMSO. Thermal stability, possible occurrence of tandem reactions, promoted catalytic performance as well as synergistic effects are of advantageous features of Pd2L2Cl4. By employing Taguchi method, optimum conditions (110 °C, 6 h, KOAc, 2 mol% cat.) were determined. Moreover, the homogenous catalyst represented good reusability up to four cycles. Comparing the catalytic activity of several other previously reported Pd(II) dinuclear complexes, Pd2L2Cl4 enjoys the advantages of short time of reaction and thermal stability.

Synthesis, Crystal Structure and DFT Studies of a New Dinuclear Ag(I)-Malonamide Complex.

The synthesis and structural aspects of a new dinuclear silver (I) complex with malonamide type ligand (L) is reported. Each Ag ion in the [Ag2L2(NO3)2]·H2O complex is coordinated to two ligands, L, each acting as a bridged ligand via its two pyridine arms; Ag(I) acts as a connector between them. Two types of Ag-ligands close contacts were detected: Ag–N1, Ag–N4 from the two L units, and Ag–O5, Ag—O6 from the two nitrate anions, wherein both the nitrate ions are inside the cage formed by the [Ag2L2] unit. The coordination geometry around each Ag(I) is a distorted tetrahedron. The [Ag2L2(NO3)2] complex units are connected by weak intermolecular C—H…O interactions. The different intermolecular interactions were quantified using Hirshfeld surface analysis. Using two DFT methods (B3LYP and WB97XD), the nature and strength of the Ag–N and Ag–O interactions were described using atoms in molecules (AIM) and natural bond orbital (NBO) analyses. Topological parameters indicated that the strength of the two Ag–N bonds was similar, while that of the two Ag–O interactions were significantly different. Moreover, the Ag–N interactions have a predominant covalent character, while the Ag–O interactions are mainly ionic. The NBO analysis indicated that the most important anti-bonding Ag-orbital in these interactions has an s-orbital character.

Synthesis and Properties of Salicylaldehydes Fine-Tuned by Modular Assembly using "Plug-and-Socket"-Type Extendibility.

A salicylaldehyde derivative bearing four pyridine arms, 3,5-bis(N,N-bis(2-pyridylmethyl)aminomethyl)-2,4-dihydroxybenzaldehyde (Hbpsal) as a "socket", was prepared and used to derive a series of zinc complexes with various extra anions "plugged" into their vacant site. The crystal structure and 1 H NMR spectra were noticeably influenced by the extra anions, allowing fine-tuning of the properties by "plug-and-socket"-type modification. Similar to unsubstituted salicylaldehyde, the zinc complexes reacted with primary amines to afford Schiff-base compounds. Because of the potential chirality around the coordination sphere, reaction with a chiral amine resulted in an equilibrium system between diastereomers, the potential of which as chiral sources tunable by the extra anions is discussed. Some of the complexes were further converted into zinc- or nickel-salphen (=N,N-bis(salicylidene)-1,2-phenylenediamine) complexes. The electrochemical properties of the nickel complex were slightly modified by the extra anions, whereas the photophysical properties of the zinc complex appeared unchanged.

Copper(II)‐Bioinspired Models for Copper Amine Oxidases: Oxidative Half‐Reaction in Water

AbstractThe quinone cofactor is generated at the oxidative half‐reaction of copper amine oxidases (CAO) activity, which is key biogenesis step in biology. The copper(II) complexes [Cu(L1)SO3CF3]SO3CF3, 1; [Cu(L1)ClO4]ClO4, 2 [L1=1,4‐bis[(pyridin‐2‐yl‐methyl)]‐1,4‐diazepane]; [Cu(L2)SO3CF3]SO3CF3, 3 and [Cu(L2)ClO4]ClO4, 4 [L2=1, 4‐bis[2‐(pyridin‐2‐yl)ethyl]‐1,4‐diazepane] were synthesized as models for copper amine oxidases. The molecular structure of complexes was determined by single crystal X‐ray studies and shows distorted square pyramidal geometry (τ, 0.064 ‐ 0.285). The average Cu‐N(2.0 Å) bond distances of model complexes are similar to the Cu‐NHis bond distances in native CAOs enzyme (Cu‐NHis‐456, 2.0‐2.1 Å, Cu‐NHis‐458, 1.9‐2.2 Å and Cu‐NHis‐624,1.9 −2.1 Å).Only one Cu(II)/Cu(I) redox couple (‐0.296 to −0.343 V) was noted in acetonitrile for 1–4 but a well‐defined redox couple around −0.349 to −0.404 V with an additional anodic peak around −0.056 to −0.128 V appeared in the water. The electronic spectra of 1–4 at pH ∼ 6.0 in water, shows ligand‐based absorption band around 260 −264 nm with a shoulder around 290 nm and the d‐d transition appeared around 593–640 nm. Also, an unusual low‐energy transition is centered at 965 nm due to axial field splitting of the eg orbital sets. Interestingly, on raising of the pH solution to ∼7 ‐ 10 instigates a transition of square pyramidal coordination geometry into trigonal bipyramidal for 1–4. This geometrical interconversion is further supported by appearance of two Cu(II)/Cu(I) redox couples around −0.313 to −0.390 V and −0.056 to −0.309 V at pH ranges of ∼7 ‐ 10. All the complexes exhibits almost similar solution EPR parameter (g||, 2.21 ‐ 2.45; A||, 174 ‐ 193 × 10−4 cm−1) to CAO (g||, 2.32; A||, 153×10−4cm−1)5 at 70 K. The model complexes convert substrate 2‐aminophenol into o‐quinone simultaneously using molecular oxygen via oxidative deamination pathway and this formation accomplished by new absorption band at 430 nm with rate of 0.53 ‐ 11.2 ×10−3 s−1 in water. The asymmetric Cu‐Npy bonds and higher distortion in the square pyramidal geometry of 1 and 2 presumed to facilitate geometrical change via decoordination of one the pyridine arms and leads faster dioxygenation reaction than 3 and 4. This decoordinated pyridine arm act as like an acid‐base catalyst to accept and donate protons as in CAO catalysis by amino acid residues at secondary coordination sphere.

C(sp3)–H Alkenylation Catalyzed by Cationic Alkylhafnium Complexes: Stereoselective Synthesis of Trisubstituted Alkenes from 2,6-Dimethylpyridines and Internal Alkynes

Dibenzylhafnium complexes 3a–d, supported by dianionic bidentate or tridentate ligands, upon activation via abstraction by either [Ph3C][B(C6F5)4] or B(C6F5)3 served as catalysts for the C(sp3)–H alkenylation of 2,6-dimethylpyridines with dialkylalkynes to give corresponding C(sp3)–H alkenylated products 6. Complex 3c, containing a pyridine arm in the ligand skeleton, exhibited the highest catalytic activity among 3a–d; initial addition of 2,6-dimethylpyridine (4a) to the C6D5Br solution of 3c followed by [Ph3C][B(C6F5)4] and 3-hexyne (5a) produced trisubstituted alkene 6aa in stereoselective manner in up to 50% yield without any byproducts, while the addition of 5a prior to 4a and [Ph3C][B(C6F5)4] to the C6D5Br solution of 3c generated 6aa, together with the formation of byproduct (E)-(2-ethylpent-2-en-1-yl)benzene (7). When an asymmetrical pyridine, 3-bromo-2,6-dimethylpyridine, was used as the coupling partner, the corresponding trisubstituted alkene was obtained selectively. Catalytically active catio...

Indenyl Compounds with Constrained Hapticity: The Effect of Strong Intramolecular Coordination

A series of cyclopentadienyl and indenyl molybdenum(II) compounds with intramolecularly coordinated pyridine arms, including scorpionate‐like species bearing two irreversibly coordinated arms on the indenyl core, were synthesized and characterized. All presented structural types were confirmed by X‐ray diffraction analysis. Owing to the strong nucleophilicity of pyridine, the intramolecular interaction was found to be considerably stronger than that in analogous species bearing tertiary amines in the side chain. Although the starting compounds for the syntheses were isostructural, the reaction outcomes differed considerably. The cyclopentadienyl precursor gave a pentacoordinate η5:κN‐compound, whereas the indenyl analogue produced a hexacoordinate species with the unprecedented η3:κN‐coordination mode of the indenyl ligand and thus represents an unusual example of the so‐called indenyl effect. The unusually high stability of the η3:κN‐coordination compounds toward η3 to η5 haptotropic rearrangement was clarified by theoretical calculations. As the strong intramolecular interaction prevented rotation of the indenyl moiety, it could not reach the conformation suitable for the η3 to η5 rearrangement. As a result, the low hapticity was effectively locked.

Properties and ATRP activity of copper complexes with substituted tris(2-pyridylmethyl)amine-based ligands.

Synthesis, characterization, electrochemical studies, and ATRP activity of a series of novel copper(I and II) complexes with TPMA-based ligands containing 4-methoxy-3,5-dimethyl-substituted pyridine arms were reported. In the solid state, Cu(I)(TPMA*(1))Br, Cu(I)(TPMA*(2))Br, and Cu(I)(TPMA*(3))Br complexes were found to be distorted tetrahedral in geometry and contained coordinated bromide anions. Pseudo-coordination of the aliphatic nitrogen atom to the copper(I) center was observed in Cu(I)(TPMA*(2))Br and Cu(I)(TPMA*(3))Br complexes, whereas pyridine arm dissociation occurred in Cu(I)(TPMA*(1))Br. All copper(I) complexes with substituted TPMA ligands exhibited a high degree of fluxionality in solution. At low temperature, Cu(I)(TPMA*(1))Br was found to be symmetrical and monomeric, while dissociation of either unsubstituted pyridine and/or 4-methoxy-3,5-dimethyl-substituted pyridine arms was observed in Cu(I)(TPMA*(2))Br and Cu(I)(TPMA*(3))Br. On the other hand, the geometry of the copper(II) complexes in the solid state deviated from ideal trigonal bipyramidal, as confirmed by a decrease in τ values ([Cu(II)(TPMA*(1))Br][Br] (τ = 0.92) > [Cu(II)(TPMA*(3))Br][Br] (τ = 0.77) > [Cu(II)(TPMA*(2))Br][Br] (τ = 0.72)). Furthermore, cyclic voltammetry studies indicated a nearly stepwise decrease (ΔE ≈ 60 mV) of E1/2 values relative to SCE (TPMA (-240 mV) > TPMA*(1) (-310 mV) > TPMA*(2) (-360 mV) > TPMA*(3) (-420 mV)) on going from [Cu(II)(TPMA)Br][Br] to [Cu(II)(TPMA*(3))Br][Br], confirming that the presence of electron-donating groups in the 4 (-OMe) and 3,5 (-Me) positions of the pyridine rings in TPMA increases the reducing ability of the corresponding copper(I) complexes. This increase was mostly the result of a stronger influence of substituted TPMA ligands toward stabilization of the copper(II) oxidation state (log β(I) = 13.4 ± 0.2, log β(II) = 19.3 (TPMA*(1)), 20.5 (TPMA*(2)), and 21.5 (TPMA*(3))). Lastly, ARGET ATRP kinetic studies show that with more reducing catalysts an induction period is observed. This was attributed to slow regeneration of Cu(I) species from the corresponding Cu(II).

Coordination controlled atropoisomerism in phenanthroline-strapped porphyrins: A swinging affair

A phenanthroline-strapped porphyrin bearing two pyridine side arms attached to opposite meso positions was designed as a potential cytochrome c oxidase model and its zinc and copper(I)-zinc complexes were prepared. In the zinc porphyrin complex, the pyridine arms underwent a rapid exchange of their coordination to the zinc atom on the open face of the strapped-porphyrin, as demonstrated by variable temperature NMR studies. Only the β2 atropoisomer was observed for the zinc complex because of the rapid exchange. This swinging motion no longer occurred when Cu I was bound within the phenanthroline strap. In this Cu I / Zn II complex, the αβ atropoisomer predominated and one pyridine was coordinated to the zinc atom on the proximal side and the other pyridine was bound to the copper on the distal face. This work shows that allostery can be effective to control atropoisomery in phenanthroline strapped porphyrin as heme protein models.

Ru(II) thioether complexes with dangling pyridine ligands

Through two different methods, new Ru(II) polypyridyl complexes were prepared in an attempt to replicate previously reported heptacoordinate Ru(II) syntheses. The tetradentate thioethers, 1,8-bis(2′-pyridyl)-3,7-dithianonane (Pdto), 1,9-bis(2′-pyridyl)-3,7-dithianonane (Pdtn), and 1,10-bis(2′-pyridyl)-3,8-dithiadecane (Pdtd), were used to form dinuclear ruthenium(II) complexes of the type [{Ru(L1)}2(μ-Cl)2]2+via reaction with RuCl3·xH2O. Upon reaction of the dinuclear complexes with the triimine ligand 2,6-bis(N′-methyl-benzimidazolyl)pyridine (Me2Bzimpy), facile symmetrical bridge cleavage occurs, producing mononuclear complexes of the form [Ru(L1)(L2)]2+, where L1 is one of the three tetradentate thioether ligands and L2 is the tridentate triimine. A second method of producing the mononuclear [Ru(L1)(L2)]2+ complexes involves the reaction of Ru(L2)Cl3 with L1 under ethanolic conditions. In such mononuclear complexes, one of the pyridine arms of the tetradentate thioether is forced to be uncoordinated, due to the firmly hexacoordinate nature of Ru(II). A similar experiment was conducted using the pentadentate thioether 1,11-bis(2′-pyridyl)-3,6-9-dithianonane (Pttu) and the diimine Phen, forming the stable hexacoordinate [Ru(Pttu)(Phen)]2+ complex. The mononuclear complexes exhibit single-electron Ru(II)→Ru(III) oxidative response, in the range of +825 to +845mV versus APE, involving the removal from an electron from the t2g orbital set.