Search

We have prepared and characterized two diradicaloid systems 5a and 5b that originated from the oxidation of a 1,7-(4-(2,6-di- tert -butyl)phenol)-substituted aza-BODIPY core. The aza-BODIPY diradicaloids were characterized by a large array of experimental and computational methods. The diamagnetic closed-shell state was postulated as the ground state in solution and a solid-state with the substantial thermal population originating from both open-shell diradical and open-shell triplet states observed at room temperature. Transient absorption spectroscopy indicates fast (<10 ps) excited state deactivation pathways associated with the target compounds' diradical character in solution at room temperature. Variable-temperature 1 H NMR spectra indicate the solvent dependency of the diradical character in 5a and 5b . The diradicaloids could be stepwise reduced to the mixed-valence radical-anion and dianion states upon consequent single-electron reductions. Similarly, deprotonated 1,7-(4-(2,6-di- tert -butyl)phenol)-substituted aza-BODIPYs can be oxidized to the diradicaloid form. Both mixed-valence and dianionic forms exhibit an intense absorption in the NIR region. Density functional theory (DFT) and time-dependent DFT calculations were used to explain the transformations in the UV-Vis-NIR spectra of all target compounds.

Palladium(II) hexafluoroacetylacetonate (Pd(Hfacac) 2 ) is known to form adducts of bases, such as lutidine (2,6-dimethylpyridine). When treated with approximately 3 equiv of lutidine, Pd(Hfacac) 2 yields a 1:1 complex as reported in the literature, Pd( O , O -Hfacac)( C -Hfacac)(lutidine), 1 . However, when the amount of excess lutidine is increased, a new complex, 2 , is formed. A single-crystal X-ray structure of 2 proves it is a rare example of a dimeric palladium complex containing two Pd(Hfacac)(lutidine) fragments bridged by a dianionic trifluoroacetonate ligand, μ-CHC(O)CF 3 . The formation of 2 is accompanied by a white precipitate determined to be a mixture of trans -Pd(O 2 CCF 3 ) 2 (lutidine) 2 ( 3 ), confirming the fate of the missing trifluoroacetate fragment from the cleavage of the Hfacac ligand, and [lutidinium][Hfacac] ( 4 ). Subsequent experiments revealed the determinative role that water played in this reaction. The mechanism of cleavage of the Hfacac ligand was explored by DFT methods., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Desalination is considered a promising solution to alleviate water shortages, yet current methods are often restricted, due to challenges like high energy consumption, significant cost, or limited desalination capacity. In this study, we present a novel approach of redox flow desalination (RFD) utilizing the highly aqueous-soluble and reversible redox-active compound, potassium 1,1'-bis(sulfonate) ferrocene (1,1'-FcDS). This water-soluble organic compound yielded stable and rapid desalination, sustaining extended operation without notable decay and achieving an impressive desalination rate of up to 457.5 mmol·h -1 ·m -2 and energy consumption as low as 40.2 kJ·mol NaCl -1 . Specifically, the RFD device effectively desalinated a 50 mM NaCl solution to potable standards within 6000 s using 1,1'-FcDS. It maintained an average energy consumption of 178.16 kJ·mol NaCl -1 and exhibited negligible deterioration in desalination rate, energy efficiency, and charge efficiency throughout a rigorous 12,000 s cycling test. Furthermore, the versatility of this method was demonstrated by effectively treating saline water with varying initial concentrations from 10 mM to 50 mM, showcasing its potential across a broad spectrum of applications.

Iron phthalocyanines play crucial fundamental and applied roles ranging from bulk colorants to components of advanced materials. In this Frontier article, we discuss four aspects concerning the influence of the axial ligands on spectroscopic and redox properties of iron(II) phthalocyanines: (i) iron versus macrocycle oxidation cite as a function of Lever's E L parameter; (ii) energy of the metal-to-ligand charge-transfer transitions as a function of Lever's E L parameter; (iii) iron versus macrocycle reduction in iron(II) phthalocyanines; (iv) Mössbauer quadrupole splitting as a function of axial ligand binding through the prism of d z 2 orbital population.

A comprehensive field- and temperature-dependent examination of nuclear magnetic resonance paramagnetic relaxation enhancements (PREs) for the constitutive protons of [Co(Tpm) 2 ][BF 4 ] 2 is presented. Data for an apically substituted derivative clearly establish that bis-Tpm complexes of Co(II) undergo Jahn-Teller dynamics about the molecular threefold axis. PREs from the parent Tpm complex were used to numerically extract the electron relaxation times ( T 1e ). The Tpm complex showed field-dependent behavior, with an approximately 40% higher activation barrier than the related trispyrazolylborate (Tp) complex, based on fits to the T 1e vs T , B 0 data. Analysis of the field-dependent line widths revealed a surprisingly large contribution from susceptibility (Curie) relaxation (20-35% at the highest field), and a molecular radius (9.5 Å) that is consistent with a tightly associated counterion slowing rotation in solution. Density functional theory showed a shared vibration that is consistent with the Jahn-Teller and appears proportionately higher in energy in [Co(Tpm) 2 ] 2+ . Complete active-space self-consistent field calculations support ascribing electron relaxation to enhanced mixing of the two E g orbital sets that accompanies the tetragonal distortion and the differences in electron correlation times to the higher Jahn-Teller activation barrier in [Co(Tpm) 2 ] 2+ .

We report a systematic investigation of a series of Ag(II) and Ag(III) complexes of porphyrins and their analogues using UV-vis magnetic circular dichroism (MCD) spectroscopies and theoretical calculations. Ag(II) and Ag(III) octaethyl- and tetraarylporphyrins show the usual sign sequence in the Q-band region (i.e., negative to positive intensities with increasing energy) of their MCD spectra, indicative of the ΔHOMO > ΔLUMO relationship (ΔHOMO is the energy difference between Michl's a and s orbitals, and ΔLUMO is the energy difference between Michl's -a and - s pair of MOs). In contrast, Ag(II) complexes of β,β'-pyrrole-modified porphyrins (with an effective chlorin-type π-system) and Ag(III) corroles have sign reverse features in the MCD spectra of their Q-band region (ΔHOMO < ΔLUMO relationships). The Ag(III) complex of N-confused porphyrin shows the ΔHOMO > ΔLUMO relationship in the neutral state and the ΔHOMO < ΔLUMO relationship in the protonated form.

Polymers with low ceiling temperatures (T c ) are highly desirable as they can depolymerize under mild conditions, but they typically suffer from demanding synthetic conditions and poor stability. We envision that this challenge can be addressed by developing high-T c polymers that can be converted into low-T c polymers on demand. Here, we demonstrate the mechanochemical generation of a low-T c polymer, poly(2,5-dihydrofuran) (PDHF), from an unsaturated polyether that contains cyclobutane-fused THF in each repeat unit. Upon mechanically induced cycloreversion of cyclobutane, each repeat unit generates three repeat units of PDHF. The resulting PDHF completely depolymerizes into 2,5-dihydrofuran in the presence of a ruthenium catalyst. The mechanochemical generation of the otherwise difficult-to-synthesize PDHF highlights the power of polymer mechanochemistry in accessing elusive structures. The concept of mechanochemically regulating the T c of polymers can be applied to develop next-generation sustainable plastics., (© 2023. The Author(s).)

The reduction of iron(II) phthalocyanine (Pc(2-)Fe II ) or its bisaxially coordinated complexes results in the formation of the purple/red [PcFe] - , [PcFeL] - , and [PcFeX] 2- (L is neutral and X is anionic ligand) species. The X-ray structure of the [K(DME) 4 ][PcFe] complex exhibits a square-planar [PcFe] - anion. 1 H NMR spectra of the reduced species have one or two phthalocyanine broad peaks between 15 and 17 ppm. Solution magnetic moments are consistent with the presence of a single unpaired electron. A solid-state Mössbauer spectrum of [K(DME) 4 ][PcFe] is consistent with an early report [Taube, R. Pure Appl. Chem. 1974, 38, 427-438]. The solid-state EPR spectrum of the [PcFe] - anion is close to that recorded by Konarev et al. [ Dalton Trans. 2012, 41, 13841-13847]. Solution EPR spectra of reduced species have axial symmetry ( g ⊥ ∼ 2.08-2.17 and g || ∼ 1.95-1.96) and correlate well with spectra reported by Lever and Wilshire in 1978 [ Inorg. Chem. 1978, 17, 1145-1151]. The UV-vis spectra of pentacoordinated [PcFeL] - and [PcFeX] 2- anions consist of the characteristic bands around 810, 690, and 515 nm. These bands correlate well with the set of MCD pseudo A -terms and resemble transitions in the [Pc(3-)M] - and [Pc(3-)ML] - compounds. The UV-vis and MCD spectra of [PcFeL] - and [PcFeX] 2- complexes are in stark contrast to the crystallographically characterized reference [Pc(2-)Co I ] - anion, which is EPR silent, has a regular diamagnetic 1 H NMR spectrum, and has an intense Q-band at 699 nm, which correlates well with the strong MCD A -term. The DFT and TDDFT calculations are suggestive of the iron(II) center in a (d xy ) 2 (d xz , yz ) 3 (d z 2 ) 1 ( s = 1) electronic configuration that is antiferromagnetically coupled with the one-electron-reduced Pc(3-) ligand (i.e., [Pc(3-)Fe II ] - , [Pc(3-)Fe II L] - , and [Pc(3-)Fe II X] 2- ). The calculated EPR, Mössbauer, and UV-vis spectra of [PcFe] - , [PcFeL] - , and [PcFeX] 2- complexes are in excellent agreement with the experimental data, thus resolving the controversy between axial s = 1/2 like EPR and Pc(3-)-like UV-vis spectra of these compounds.

We have prepared a series of complexes of the type [Ir III (ppy) 2 (L] n + complexes ( 1-4 ), where ppy is a substituted 2-phenylpyridine and L is a chelating phosphine thioether ligand. The parent complex ( 1 ) comprises an unsubstituted phenylpyridine ligand, whereas complex 2 contains a nitro substituent on the pyridine ring, complex 3 features a diphenylamine group on the phenyl ring, and 4 has both nitro and diphenylamine groups. Crystallographic, 1 H NMR, and elemental analysis data are consistent with each of the chemical formulae. DFT (density functional theory) computational results show a complicated electronic structure with contributions from Ir, ppy, and the PS ligand. Ultrafast pump-probe data show strong contributions from the phenylpyridine moieties as well as strong panchromatic excited state absorption transitions. The data show that nitro and/or diphenylamine substituents dominate the spectroscopy of this series of compounds.

A group of bidentate nitrogen and sulfur donor pyrazole derivative ligands abbreviated as Na[RNCS(Pz)], Na[RNCS(Pz Me2 )], Na[RNCS(Pz Me3 )], Na[RNCS(Pz PhMe )], Na[RNCS(Pz Ph2 )], where (R = Et, Ph), and their Cu (II) complexes were synthesized and characterized by spectroscopic and physicochemical methods. The crystal structure of [Cu(PhNCSPz Me3 ) 2 ] was determined by X-ray crystallography analysis and the results described a distorted square planar coordination geometry for this complex. Also, the cyclic voltammetry investigations indicated that the synthesized copper complex is an electrochemically active species. Moreover, the cytotoxic activity of all of the twenty synthesized compounds was evaluated using MTT assay against the MCF-7 (human breast carcinoma) cell lines, in vitro. Cu (II) complexes indicate significant cytotoxicity against the MCF-7 cell lines as compared with the free ligands. The docking studies showed that the copper complexes have better interactions with EGFR and CDK2 proteins, compared to the free ligands, and most of the studied compounds have a higher value of binding energy relative to the studied controls. The results of QSAR analysis suggest that dipole moment is in direct correlation with the obtained IC 50 values, and it strongly impact the anticancer effects generated by the compounds. Our findings suggest that the developed copper complexes can be good candidates for further evaluations as chemotherapeutic agents in the treatment of cancer., (© 2022. The Author(s), under exclusive licence to Springer Nature B.V.)

A sterically strained 32π-electron antiaromatic bis-BODIPY macrocycle in which two BODIPY fragments are linked by p-divinylbenzene groups was prepared and characterized. Unlike regular BODIPYs, the fluorescence in this macrocycle is quenched. The broad signals in the NMR spectra of the macrocycle were explained by the vibronic freedom of the p-divinylbenzene fragments. The possible diradicaloid nature of the macrocycle was excluded on the basis of variable-temperature EPR spectra in solution and in solid state, which is indicative of its closed-shell quinoidal structure. The meso-C-H bond in the macrocycle and its precursor BODIPY dialdehyde 3 forms a weak hydrogen bond with THF and is susceptible for the nucleophilic attack by organic amines and cyanide anion. The reaction products of such a nucleophilic attack have meso-sp 3 carbon atoms and were characterized by NMR, mass spectrometry and, in one case, X-ray crystallography. Unlike the initial bis-BODIPY macrocycle, the adducts have strong fluorescence in the 400 nm region. The electronic structure and spectroscopic properties of new chromophores were probed by density functional theory (DFT) and time-dependent DFT (TDDFT) calculations and correlate well with the experimental data., (© 2022 Wiley-VCH GmbH.)

Herein we present two new ferrocene compounds Fc3 and Fc4 with, respectively, propyl and butyl zwitterionic side chains. These compounds are highly soluble in water (0.66 M for Fc3 and 2.01 M for Fc4 ). When paired with anthraquinone-2,7-disulfonate as the anolyte, these zwitterionic ferrocenes exhibit excellent performance under neutral aqueous conditions. Voltage and energy efficiencies were ca. 88%, and the Coulombic efficiency was over 99% for both high-concentration redox flow batteries. We observed a difference in stability between the lengths of the zwitterionic chains, with Fc4 showing higher stability than Fc3 , and the capacity decreased by ∼5% at the end of 20 cycles (∼1% per day). Density functional theory calculations revealed striking differences in the conformational properties between Fc3 and Fc4 , with Fc4 retaining a linear structure of the side chain in solution, while Fc3 favored both linear and curved geometries.

1 H NMR spectroscopy is a powerful tool for the conformational analysis of ortho -phenylene foldamers in solution. However, as o -phenylenes are integrated into ever more complex systems, we are reaching the limits of what can be analyzed by 1 H- and 13 C-based NMR techniques. Here, we explore fluorine labeling of o -phenylene oligomers for analysis by 19 F NMR spectroscopy. Two series of fluorinated oligomers have been synthesized. Optimization of monomers for Suzuki coupling enables an efficient stepwise oligomer synthesis. The oligomers all adopt well-folded geometries in solution, as determined by 1 H NMR spectroscopy and X-ray crystallography. 19 F NMR experiments complement these methods well. The resolved singlets of one-dimensional 19 F{ 1 H} spectra are very useful for determining relative conformer populations. The additional information from two-dimensional 19 F NMR spectra is also clearly valuable when making 1 H assignments. The comparison of 19 F isotropic shielding predictions to experimental chemical shifts is not, however, currently sufficient by itself to establish o -phenylene geometries.

A series of photochromic complexes with general formulas of [Ru(bpy) 2 (NHC-SR)] 2+ and [Ru(bpy) 2 (NHC-S(O)R)] 2+ were prepared and investigated by X-ray crystallography, electrochemistry, and ultrafast transient absorption spectroscopy {where bpy is 2,2'-bipyridine and NHC-SR and NHC-S(O)R are chelating thioether (-SR) and chelating sulfoxide [-S(O)R] N-heterocyclic carbene (NHC) ligands}. The only differences between these complexes are the nature of the R group on the sulfur (Me vs Ph), the identity of the carbene (imidazole vs benzimidazole), and the number of linker atoms in the chelate (CH 2 vs C 2 H 4 ). A total of 13 structures are presented {four [Ru(bpy) 2 (NHC-SR)] 2+ complexes, four [Ru(bpy) 2 (NHC-S(O)R)] 2+ complexes, and five uncomplexed ligands}, and these reveal the expected coordination geometry as predicted from other spectroscopy data. The data do not provide insight into the photochemical reactivity of these compounds. These carbene ligands do impart stability with respect to ground state and excited state ligand substitution reactions. Bulk photolysis reveals that these complexes undergo efficient S → O isomerization, with quantum yields ranging from 0.24 to 0.87. The excited state reaction occurs with a time constant ranging from 570 ps to 1.9 ns. Electrochemical studies reveal an electron transfer-triggered isomerization, and voltammograms are consistent with an ECEC (electrochemical-chemical electrochemical-chemical) reaction mechanism. The carbene facilitates an unusually slow S → O isomerization and an unusally fast O → S isomerization. Temperature studies reveal a small and negative entropy of activation for the O → S isomerization, suggesting an associative transition state in which the sulfoxide simply slides along the S-O bond during isomerization. Ultrafast studies provide evidence of an active role of the carbene in the excited state dynamics of these complexes.

In this report, we present a study into the structure and electronic properties of difluoroboronsalicylaldoxime (DFBS), a boron-based structural analog of coumarin. The modification of the heterocyclic ring of coumarin with boron results in a compound with similar structural parameters and molecular orbitals to coumarin. DFT and TDDFT calculations reveal a significant stabilization of the LUMO in DFBS; this is supported by a ∼40 nm red shift of the lowest electronic transition in the absorption spectrum. Interestingly, DFBS is emissive, while unmodified coumarin is effectively non-radiative. Comparisons between DFBS, emissive coumarin variants, and unmodified coumarin suggest that the charge transfer character of the transition contributes to the fluorescence.

A promising solution to address the challenges in plastics sustainability is to replace current polymers with chemically recyclable ones that can depolymerize into their constituent monomers to enable the circular use of materials. Despite some progress, few depolymerizable polymers exhibit the desirable thermal stability and strong mechanical properties of traditional polymers. Here we report a series of chemically recyclable polymers that show excellent thermal stability (decomposition temperature >370 °C) and tunable mechanical properties. The polymers are formed through ring-opening metathesis polymerization of cyclooctene with a trans-cyclobutane installed at the 5 and 6 positions. The additional ring converts the non-depolymerizable polycyclooctene into a depolymerizable polymer by reducing the ring strain energy in the monomer (from 8.2 kcal mol -1 in unsubstituted cyclooctene to 4.9 kcal mol -1 in the fused ring). The fused-ring monomer enables a broad scope of functionalities to be incorporated, providing access to chemically recyclable elastomers and plastics that show promise as next-generation sustainable materials., (© 2021. The Author(s), under exclusive licence to Springer Nature Limited.)

An organometallic complex that mimics an amino acid, also known as an amino acid isostere, can be synthesized from a functionalized bipyridine ligand and a fac -[Re(CO) 3 ] + center. The reaction of an achiral ligand and metal results in a racemic mixture of chiral-at-metal complexes. These metal species have amine and carboxy termini, a side chain type unit that can be varied, as well as the chiral metal that is analogous to the α carbon of an amino acid. The racemic mixtures can be separated into enantiomers by chiral chromatography, and the metal complexes can be incorporated into peptides by using solid-phase peptide synthesis.

Redox flow batteries (RFBs) are scalable devices that employ solution-based redox active components for scalable energy storage. To maximize energy density, new highly soluble catholytes and anolytes need to be synthesized and evaluated for their electrochemical performance. To that end, we synthesized a series of imidazolium ferrocene bis(sulfonate) salts as highly soluble catholytes for RFB applications. Six salts with differing alkyl chain lengths on the imidazolium cation were synthesized, characterized, and electrochemically analyzed. While aqueous solubility was significantly improved, the reactivity of the imidazolium cation and the increased viscosities of the salt solutions in water (which increase with increasing imidazolium chain length) limit the applicability of these materials to RFB design.

The bis(pyridylimino)isoindoline (BPI) ligand is a tridentate chelate that binds to metals via a meridional coordination mode. However, when this ligand forms a complex with Re(CO) 3 , an almost exclusively facial moiety, the BPI ligand deforms to coordinate in a facial mode. We have in-vestigated this deformation via structural and theoretical means, and the non-planar binding mode of the ligand bathochromically shifts the metal to ligand charge transfer (MLCT) transition., Competing Interests: Conflicts of interest There are no conflicts to declare.

The reaction of diiminoisoindoline and iminoxoisoindoline with aminoazoles results in the formation of bidentate chelates that can be considered a semihemiporphyrazine. These chelates react with BF 3 to produce fluorescent compounds that are structurally analogous to the BODIPY dyes. These difluoroboron semihemiporphyrazines (BOSHPYs) aggregate, and the type of aggregation (H or J) is determined by a single atom at the periphery of the ligand (O or N). Notably, the imine terminated compounds remain fluorescent upon aggregation.

Transient absorption data of [FeII(tpy)(CN)3]- reveals spectroscopic signatures indicative of 3MLCT with a ∼10 ps kinetic component. These data are supported by DFT and TD-DFT calculations, which show that excited state ordering is responsive to the number of cyanide ligands on the complex.

The direct borylation of two bis(pyrazolylimino)isoindoline chelates with BF 3 and base under dry conditions results in the formation of two boron adducts. These are ring-contracted analogs of biliazine and can be considered as subbiliazines, as they have bowl-shaped structures similar to subphthalocyanine. Additionally, a new iminooxoisoindoline BF 2 complex was made from hydrolysis of the free base in the presence ofBF 3 . The electronic structures of the free bases and subbiliazines were probed by density functional theory (DFT) and time-dependent DFT (TDDFT) methods.

Several Re(i)pyca conjugates incorporating long aliphatic amines have been synthesized through a one-pot methodology. The compounds have been fully characterized, and seven compounds have been structurally elucidated by single crystal X-ray diffraction. The C14 variant was probed as a potential organometallic IR dye. Large unilamellar vesicles were generated with DOPC and the C14 compound and we observed incorporation of the rhenium complex as observed by FTIR microscopy.

A bridging carbon analog of the well-studied bis(pyridyl)iminoisoindoline (BPI) can be produced via a one step reaction between diiminoisoindoline and pyridine-2-acetonitrile. The resultant bis(pyridineylidene)isoindoline (BPYI) is structurally analogous to BPI and can readily form metal complexes. However, it exhibits a markedly different electronic structure with intense absorption bands in the visible region of the spectrum.

Synthesis and characterisation of a dithiadiaza chelator NSNS2A, as well as copper complexes thereof are reported in this paper. Solution structures of copper(i/ii) complexes were calculated using density functional theory (DFT) and validated by both NMR and EPR spectroscopy. DFT calculations revealed a switch in the orientation of tetragonal distortion upon protonation, which might be responsible for poor stability of the Cu(II)NSNS2A complex in aqueous media, whilst the same switch in tetragonal distortion was experimentally observed by changing the solvent. The chelator was radiolabeled with 64Cu and evaluated using PET/MRI in rats. Despite a favorable redox potential to stabilize the cuprous state in vivo, the 64Cu(II)NSNS2A complex showed suboptimal stability compared to its tetraazamacrocyclic analogue, 64Cu(TE2A), with a significant 64Cu uptake in the liver.

In this report, we present a study on the synthesis, structure, and electronics of a series of (8-amino)quinoline and (4-amino)phenanthridine complexes of Re(CO) 3 X, where X = Cl and Br. In all cases, the (amino)heterocycles bind as bidentate ligands, with surprisingly symmetric modes of binding based on Re-N bond lengths. Between the complexes of (8-amino)quinolines and (4-amino)phenanthridines studied in this report, we do not observe much structural variation, and remarkably similar UV-visible absorption spectra. Expansion of the π-system in the (4-amino)phenanthridine complexes does result in an increase in the intensity of the lowest energy transitions (λ max ), which computational modeling suggests are more purely MLCT in character compared with the mixed π-π*/MLCT character of these transitions in the smaller (8-amino)quinoline-supported complexes. DFT and TDDFT modeling further showed that consideration of spin-orbit coupling (SOC) is essential; omitting SOC misses the π-π* contributions to λ max and is unable to accurately model the observed electronic absorption spectra., Competing Interests: Conflicts of interest There are no conflicts to declare. Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

The hemiporphyrazine type chelate and phthalocyaninine analog biliazine (H2BlzH) and its metal complexes can be synthesized in one-step from a monosubstituted diiminisoindoline (DII). This singly substituted precursor is produced from the reaction of unsubstituted DII and 2-aminopyrazole. The biliazine macrocycle is a tetradentate chelate where the ring is closed via a strong hydrogen bond at the meso position. Although the hydrogen bond closes the ring, there is little evidence for 18-electron type annulene aromaticity across the macrocycle, as seen in the UV-visible and MCD spectra and supported by DFT calculations.

The synthesis of a heteromacrocyclic bifunctional chelator with phosphonic acid pendent arms is presented along copper(ii) complexation. Ligand N 2 S 2 -POH featuring N,N'-bis-substituted phosphonate pendent arms was isolated in respectable yields, characterized, and chelated to copper(ii). Implementation of both Moedritzer-Irani and Kabachnik-Fields conditions using aza-thia macrocycle 1,8-dithia-4,11-diazacyclotetradecane afforded 1,8-dithia-4,11-diazacyclotetradecane-4,11-diyl-bis-(methylene)-bis-(phosphonic acid) (N 2 S 2 -POH). Kinetic NMR studies provided four acid dissociation constants with respect to hydronium ion concentration. Benesi-Hildebrand binding experiment provided a conditional formation constant of 2.8 × 10 4 M -1 . Heteromacrocycle N 2 S 2 -POH readily formed an encapsulated copper(ii) chelate at room temperature, which was examined through EPR analysis.

Though numerous applications require degradable polymers, there are surprisingly few polymer systems that combine superior stability and controllable degradability. Particularly, the degradability of a conventional degradable polymer is typically enabled by cleavable groups on the backbone, which can be attacked by stimuli in ambient conditions, causing undesirable material deterioration. Here we report a general strategy to overcome this issue: "locking" the degradability during handling and use of the polymers and "unlocking" it when degradation is needed. This strategy is demonstrated with a cyclobutane-fused lactone (CBL) polymer. The cyclobutane keeps polymer backbone intact under conditions that hydrolyze the lactone and allows the ester group to be recovered when undesirable hydrolysis occurs. When backbone degradation is needed, the degradability can be unlocked by mechanochemical activation that converts the polyCBL into a linear polyester. The rare combination of two intrinsically conflicting properties, i.e., backbone stability and accessible degradability, can make this polymer a potential option for new sustainable materials.

Synthesis of 1,11-dithia-4,8-diazacyclotetradecane ( L1 ), a constitutional isomer of the macrocyclic [14]aneN 2 S 2 series, is accompanied with reaction and method optimization. Chelation of L1 with copper(II) provided assessment of lattice packing, ring contortion, and evidence of conformational fluxionality in solution through two unique crystal structures: L1Cu(ClO4) 2 and [(L1Cu) 2 μ-Cl](ClO 4 ) 3 . Multiple synthetic approaches are presented, supplemented with reaction methodology and reagent screening to access [14]aneN 2 S 2 L1 . Reductive alkylation of bis-tosyl-cystamine was integrated into the synthetic route, eliminating the use and isolation of volatile thiols and streamlining the synthetic scale-up. Late-stage cleavage of protecting sulfonamides was addressed using reductive N-S cleavage to furnish macrocyclic freebase L1 .

The TeF 5 group is significantly underexplored as a highly fluorinated substituent on an organic framework, despite it being a larger congener of the acclaimed SF 5 group. In fact, only one aryl-TeF 5 compound (phenyl-TeF 5 ) has been reported to date, synthesized using XeF 2 . Our recently developed mild TCICA/KF approach to oxidative fluorination provides an affordable and scalable alternative to XeF 2 . Using this method, we report a scope of extensively characterized aryl-TeF 5 compounds, along with the first SC-XRD data on this compound class. The methodology was also extended to the synthesis and structural study of heretofore unknown aryl-TeF 4 CF 3 compounds. Additionally, preliminary reactivity studies unveiled some inconsistencies with previous literature regarding phenyl-TeF 5 . Although our studies conclude that the arene-based TeF 5 (and TeF 4 CF 3 ) group is not quite as robust as the SF 5 group, we find that the TeF 5 group is more stable than previously thought, thus opening a door to explore new applications of this motif., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Diiminoisoindoline (DII) is a crucial reagent for the synthesis of phthalocyanine as well as related macrocycles and chelates such as hemiporphyrazine and bis(iminopyridyl)isoindoline. In this report, we present the synthesis and characterization of four 1,3-diylideneisoindolines prepared via the reaction of several organic CH acids and DII. These orange or red compounds exhibit intense π → π* transitions in the UV-visible region. The redox properties and electronic structures of all new compounds were investigated using cyclic voltammetry and density functional theory (DFT). The observed electrochemistry and UV-visible transitions are in good agreement with the DFT and time-dependent DFT calculations, which indicate that the HOMO is largely centered at the O═C-C-C═O fragments, and the lowest unoccupied molecular orbital is more extended onto the isoindoline unit.

Zwitterionic structure is necessary for Ni II complexes to catalyze carbonylative polymerization (COP) of cyclic ethers. The cationic charge at the Ni II center imparts sufficient electrophilicity to the Ni-acyl bond for it to react with cyclic ethers to give an acyl-cyclic ether oxonium intermediate, while the ligand-centered anionic charge ensures that the resultant oxonium cation is ion-paired with the Ni 0 nucleophile. The current catalysts give non-alternating copolymers of carbon monoxide and cyclic ethers and are the most effective when both ethylene oxide and tetrahydrofuran are present as the cyclic ether monomers., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The synthesis of a rigid macrobicyclic N,S lactam L1 and a topologically favored in/in N,S cryptand L2 are reported with X-ray structure analysis, dynamic correlation NMR spectroscopy, and computational analysis. Lactam L1 exhibits two distinct rotameric conformations (plus their enantiomeric counterparts) at 25 °C, as confirmed via NMR spectroscopy and computational analysis. Coalescence of the resonances of L1 was observed at 115 °C, allowing for complete nuclei to frequency correlation. Combining computational investigations with experimental data, topological equilibria and relative energies/strain relating to the perturbation of the pore were determined. Due to the increased conformational strain of the N 2 S 2 template, the nitrogen lone pairs in L2 elicit a unique transannular interaction, resulting in a thermodynamically favored in/in nephroidal racemate. The combination of preferred topology, steric relief, and electronic localization of L2 induces a chiral environment imparted through the amine with a computed inversion barrier of 10.3 kcal mol -1 .

This report presents the synthesis and characterization of mono- and bis(amino acid ester) ferrocene complexes generated using a sulfonamide linking strategy as an alternative to the more heavily explored amide linking strategy. These compounds were investigated to test their ability to form hydrogen bonding interactions both in the solid state and in solution, and were compared to the previously observed intramolecular interstrand crosslinking seen in amide-linked ferrocene constructs. Synthesized compounds also included controls that do not exhibit sulfonamide N-H bonds and thus cannot engage in hydrogen bonding. In the solid state, we observe both S=O⋯H-N and C=O⋯H-N intermolecular interactions, but we do not observe any intramolecular interstrand hydrogen bonding. In the solution phase, we also do not see any intramolecular hydrogen bonding interactions in these compounds as measured by titration of d 6 -DMSO as a competitive hydrogen bonding reagent. We also collected CD spectra on these compounds, which revealed that the chiral peptides can induce dichroism in the dd transition of the ferrocene units. Our results indicate that the peptide-ferrocene linking group governs whether intermolecular hydrogen bonding interactions can occur between the amino acids adjacent to the cyclopentadienyl groups., Competing Interests: Declarations of interest None.

We report the crystallography, emission spectra, femtosecond pump-probe spectroscopy, and density functional theory computations for a series of ruthenium complexes that comprise a new class of chelating triphenylphosphine based ligands with an appended sulfoxide moiety. These ligands differ only in the presence of the para-substitutent (e.g., H, OCH 3 , CF 3 ). The results show a dramatic range in photoisomerization reactivity that is ascribed to differences in the electron density of the phosphine ligand donated to the ruthenium and the nature of the excited state.

The synthesis of two new heteroleptic Cu(I) photosensitizers (PS), [Cu(Xantphos)(NN)]PF 6 (NN = biq = 2,2'-biquinoline, dmebiq = 2,2'-biquinoline-4,4'-dimethyl ester; Xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene), along with the associated structural, photophysical, and electrochemical properties, are described. The biquinoline diimine ligand extends the PS light absorbing properties into the visible with a maximum absorption at 455 and 505 nm for NN = biq and dmebiq, respectively, in CH 2 Cl 2 solvent. Following photoexcitation, both Cu(I) PS are emissive at low energy, albeit displaying stark differences in their excited state lifetimes (τ MLCT = 410 ± 5 (biq) and 44 ± 4 ns (dmebiq)). Cyclic voltammetry indicates a Cu-based HOMO and NN-based LUMO for both complexes, whereby the methyl ester substituents stabilize the LUMO within [Cu(Xantphos)(dmebiq)] + by ∼0.37 V compared to the unsubstituted analogue. When combined with H 2 O, N,N-dimethylaniline (DMA) electron donor, and cis-[Rh(NN) 2 Cl 2 ]PF 6 (NN = Me 2 bpy = 4,4'-dimethyl-2,2'-bipyridine, bpy = 2,2'-bipyridine, dmebpy = 2,2'-bipyridine-4,4'-dimethyl ester) water reduction catalysts (WRC), photocatalytic H 2 evolution is only observed using the [Cu(Xantphos)(biq)] + PS. Furthermore, the choice of cis-[Rh(NN) 2 Cl 2 ] + WRC strongly affects the catalytic activity with turnover numbers (TON Rh = mol H 2 per mol Rh catalyst) of 25 ± 3, 22 ± 1, and 43 ± 3 for NN = Me 2 bpy, bpy, and dmebpy, respectively. This work illustrates how ligand modification to carefully tune the PS light absorbing, excited state, and redox-active properties, along with the WRC redox potentials, can have a profound impact on the photoinduced intermolecular electron transfer between components and the subsequent catalytic activity.

α-Amidinoazadi(benzopyrro)methenes were synthesized using the Re(CO) 3 unit as a templating agent. The products of these template reactions are six-coordinate rhenium complexes, with a facial arrangement of carbonyls, a noncoordinating anion, and a tridentate α-amidinoazadi(benzopyrro)methene ligand. The tridentate ligand shows the conversion of one diiminoisoindoline sp 2 carbon to a sp 3 carbon, which has been seen in the "helmet" and bicyclic phthalocyanines. The bidentate diiminoisoindoline fragment tilts out of the plane of coordination. Five examples of α-amidinoazadi(benzopyrro)methenes produced from these reactions using different nitrile solvents, including the nitrile activation of acetonitrile, propionitrile, butyronitrile, cyclohexanecarbonitrile, and benzonitrile.

Several BOPHY derivatives with and without ferrocene fragments, and with electron-withdrawing ester groups appended to the β-pyrrolic positions have been prepared and characterized by NMR, UV/Vis near-infrared (NIR), high-resolution mass spectrometry, and fluorescence spectroscopy, as well as X-ray crystallography. The redox properties of new BOPHYs were probed by electrochemical (cyclic and differential pulse voltammetry) and spectroelectrochemical methods. In an attempt to prepare BOPHY derivatives with a cyano group at the bridging position using a similar approach for BODIPY cyanation, adducts from the nucleophilic attack of the cyanide anion on the bridging position in BOPHY have been isolated and characterized by spectroscopic methods. Oxidation of such adducts, however, resulted in formation of either the starting BOPHYs, or partial extrusion of the BF 2 fragment from the BOPHY core, which was confirmed by spectroscopy and X-ray crystallography. DFT and TDDFT calculations on all target materials correlate well with the experimental data, and suggest the dramatic reduction of the nitrogen atom basicity at the hydrazine bridge of the BOPHY upon introduction of the cyano group at the bridging-carbon atom., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Neutral and deprotonated anionic Ni(II), Pd(II), Cu(II), and Cu(III) complexes of tetrakis(perfluorophenyl)-N-confused porphyrin (PF-NCP) were prepared and investigated by UV-visible and magnetic circular dichroism (MCD) spectroscopies. As in the previously reported Ni(II) adduct of tetraphenyl N-confused porphyrin, we observe sign reverse (positive to negative intensities with increasing energy) features in the MCD spectra of the neutral Ni(II), Pd(II), and Cu(II) complexes of PF-NCP, which is indicative of rare ΔHOMO < ΔLUMO relationships. Upon deprotonation of Ni(II), Pd(II), and Cu(II) complexes, these features revert to those of more typical porphyrin MCD spectra consistent with a ΔHOMO > ΔLUMO condition. The Cu(III) PF-NCP complex shows features similar to those of the deprotonated divalent metal systems. Spectroscopic features in all target complexes as well as previously published metal-free and Ni(II) NCP systems were correlated with the density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. Calculation data are consistent with the tautomeric rearrangement of the electronic structures of NCP cores playing dominant roles, with smaller contribution from the central metal ions in the observed optical and magneto-optical properties. This is true for all described NCP systems to date, as they affect the stabilization/destabilization of the N-confused porphyrin-centered Gouterman orbitals.

Although boron-based fluorophores incorporating nitrogenous chelating ligands have received much attention, there has been little work on examples of boron-salphen and azine derivatives. In this report, we present several π expanded boron salphen type complexes, incorporating both bis(2-hydroxynaphthaldehyde)azine as well as ortho, meta and para variants of the analogous 2-hydroxynaphthaldehyde salphen compounds. For the azine, we observed only the formation of a single BF 2 adduct, while for the naphth-phen compounds dimeric BF 2 binding was observed. All new compounds were fully characterized via X-ray diffraction, and both DFT and TDDFT studies were carried out to probe the electronic structures of these fluorophores.

The 1,3,7,9-tetraferrocenylazadipyrromethene (3) and the corresponding 1,3,5,7-tetraferrocene aza-BODIPY (4) were prepared via three and four synthetic steps, respectively, starting from ferrocenecarbaldehyde using the chalcone-type synthetic methodology. The novel tetra-iron compounds have ferrocene groups directly attached to both the α- and the β-pyrrolic positions, and the shortest Fe-Fe distance determined by X-ray crystallography for 3 was found to be ∼6.98 Å. These new compounds were characterized by UV-vis, nuclear magnetic resonance, and high-resolution electrospray ionization mass spectrometry methods, while metal-metal couplings in these systems were probed by electro- and spectroelectrochemistry, chemical oxidations, and Mössbauer spectroscopy. Electrochemical data are suggestive of the well-separated stepwise oxidations of all four ferrocene groups in 3 and 4, while spectroelectrochemical and chemical oxidation experiments allowed for characterization of the mixed-valence forms in the target compounds. Intervalence charge-transfer band analyses indicate that the mixed-valence [3] + and [4] + complexes belong to the weakly coupled class II systems in the Robin-Day classification. This interpretation was further supported by Mössbauer spectroscopy in which two individual doublets for Fe(II) and Fe(III) centers were observed in room-temperature experiments for the mixed-valence [3] n+ and [4] n+ species (n = 1-3). The electronic structure, redox properties, and UV-vis spectra of new systems were correlated with Density Functional Theory (DFT) and time-dependent DFT calculations (TDDFT), which are suggestive of a ferrocene-centered highest occupied molecular orbital and chromophore-centered lowest unoccupied molecular orbital in 3 and 4 as well as predominant spin localization at the ferrocene fragment attached to the α-pyrrolic positions in [3] + and [4] + .

Paramagnetic resonance studies (EPR, ESEEM, ENDOR, and NMR) of a series of cobalt(II) bis-trispyrazolylmethane tetrafluoroborates are presented. The complexes studied include the parent, unsubstituted ligand (Tpm), two pyrazole-substituted derivatives (4Me and 3,5-diMe), and tris(1-pyrazolyl)ethane (Tpe), which includes a methyl group on the apical carbon atom. NMR and ENDOR establish the magnitude of 1 H hyperfine couplings, while ESEEM provides information on the coordinated 14 N. The data show that the pyrazole 3-position is more electron rich in the Tpm analogues, that the geometry about the apical atom influences the magnetic resonance, and that apical atom geometry appears more fixed in Tpm than in Tp. NMR and ENDOR establish that the BF 4 - counterion remains associated in fluid solution. In the case of the Tpm 3,5Me complex, it appears to associate in solution, in the same position it occupies in the X-ray structure.

Half-hemiporphyrazine macrocycles, which can be called "semihemiporphyrazines", were synthesized using the Re(CO) 3 unit as a templating agent. The products of these template reactions are six-coordinate rhenium complexes, with a facial arrangement of carbonyls, a halide, and a bidentate semihemiporphyrazine chelate that tilts out of the plane of coordination. Three types of semihemiporphyrazines can be produced from these reactions, depending on the alternate heterocycle to the isoindoline unit; structures including pyridine, thiazole, and benzimidazole were formed. The electronic structures of these compounds were probed using spectroscopy as well as density functional theory methods.

Several new 1,1'-bis(sulfonyl)ferrocenes designed for the synthesis of sulfonamide linked biological conjugates have been prepared. 1,1'-Bis(sulfonylbromide)ferrocene can be produced from the corresponding sulfonylchloride via a bis(sulfonylhydrazide) intermediate. Bis(sulfonyl- N -hydroxybenzotriazole)ferrocene can also be synthesized from the sulfonyl chloride, and reaction of glycine methyl ester with the sulfonyl chloride affords a [3]ferrocenophane complex. All new compounds have been structurally characterized by X-ray crystallography.

A series of 1,1'-bis(sulfonyl)ferrocene compounds were produced via the 1,1'-bis(sulfonate)ferrocene ammonium salt. This compound can be readily converted to 1,1' bis(sulfonylchloride)ferrocene. By varying stoichiometry and reaction times, both mono- and bis-sulfonamide derivatives can be synthesized. All new compounds presented in this report have been structurally characterized. The structures of the bis-sulfonamide systems are similar to the well-studied bis(amide) ferrocene compounds. Intermolecular hydrogen bonding is observed, typically between NH and SO groups of neighboring sulfonamides. However in the bis(GABA) derivative, intermolecular NH to CO hydrogen bonding interactions are present.

Acetyl ferrocene and diacetyl ferrocene both readily react with an excess of hydrazine to afford the corresponding hydrazone compounds. These compounds can then be linked to Re(CO) 3 via a metal-mediated Schiff base reaction, resulting in a series of ferrocene-Re(CO) 3 conjugates with different stoichiometries. Conjugates with 1:1, 1:2, and 2:1 ferrocene: Re(CO) 3 ratios can be produced via this "modular" type synthesis approach. Several examples of these conjugates were structurally characterized, and their spectroscopic, electrochemical, and spectroelectrochemical behaviors were investigated. The electronic structures of these compounds were also probed using DFT and TDDFT calculations.

A large set of free-base and transition-metal 5,10,15,20-tetraphenyl-substituted chlorins, bacteriochlorins, and isobacteriochlorins and their pyrrole-modified analogues were investigated by combined UV-visible spectroscopy, magnetic circular dichroism (MCD), density functional theory (DFT), and time-dependent DFT (TDDFT) approaches and their spectral characteristics were compared to those of the parent compounds, free-base tetraphenylporphyrin 1H2 and chlorin 2H2. It was shown that the nature of the pyrroline substituents in the chlorin derivatives dictates their specific UV-vis and MCD spectroscopic signatures. In all hydroporphyrin-like cases, MCD spectroscopy suggests that the ΔHOMO is smaller than the ΔLUMO for the macrocycle-centered frontier molecular orbitals. DFT and TDDFT calculations were able to explain the large broadening of the UV-vis and MCD spectra of the chlorin diones and their derivatives compared to the other hydroporphyrins and hydroporphyrin analogues. This study contributes to the further understanding of the electronic effects of replacing a pyrrole in porphyrins by pyrrolines or other five-membered heterocycles (oxazoles and imidazoles).

The Re(CO)3 unit was used to template the formation of aza(dibenzopyrro)methene (ADBM) in the presence of pyridine or N-methylimidazole. The products of these template reactions are six-coordinate complexes, with a facial arrangement of the carbonyls, a bidentate ADBM, and a sixth ligand (pyridine or N-methylimiadozle). Three types of ADBM ligands are produced from these reactions, depending on the degree of hydrolysis; bis(imine)-terminated, bis(oxo)-terminated, and mixed-imine/oxo chelates were formed.

We have synthesized two Re(CO)3-modified lysine complexes (1 and 2), where the metal is attached to the amino acid at the Nε position, via a one-pot Schiff base formation reaction. These compounds can be used in the solid phase synthesis of peptides, and to date we have produced four conjugate systems incorporating neurotensin, bombesin, leutenizing hormone releasing hormone, and a nuclear localization sequence. We observed uptake into human umbilical vascular endothelial cells as well as differential uptake depending on peptide sequence identity, as characterized by fluorescence and rhenium elemental analysis.