Search

bibliog

A series of square planar metalloporphyrins (M(TPP), TPP is 5,10,15,20-tetraphenylporphyrin and M(TPFPP), TPFPP is 5,10,15,20-tetrapentafluorophenylporphyrin; M is Zn2+, Ni2+, Pd2+, or Pt2+) with distinct meso-substituents were prepared, and their magneto-optical activity (MOA) was characterized by magnetic circular dichroism (MCD) and magneto-optical rotary dispersion spectroscopy (MORD; also known as Faraday rotation spectroscopy). MOA is crucial in the development of next-generation magneto-optical devices and quantum computing. The data show that the presence of meso-pentafluorophenyl substituents results in significant increase in MOA in comparison to the homologous phenyl group. Differences in the MOA of these metalloporphyrins are rationalized using the Gouterman four-orbital model and pave the way for rational design of improved and tailorable magneto-optical materials.

The Internationalists: How a Radical Plan to Outlaw War Remade the World By Oona A. Hathaway and Scott 3. Shapiro Simon & Schuster, 608 pp., $30.00 Almost since the day [...]

The electrochemical oxidation of sensitive propargylic benzylic alcohols having varying substituents is reported. We describe the preparation and characterization of N-hydroxytetrafluorophthalimide (TFNHPI) and pseudo-high-throughput development of a green electrochemical oxidation protocol for sensitive propargylic benzylic alcohols that employs TFNHPI as a stable electrochemical mediator. The electrochemical oxidation of propargylic benzylic alcohols was leveraged to develop short synthetic pathways for preparing gram quantities of resveratrol natural products such as pauciflorols.

Two brominated 10,10-dimethylisocorrole (10-DMIC) derivatives containing Pd(II) centers have been prepared and characterized. These compounds were prepared via bromination of 10,10-dimethylbiladiene-based oligotetrapyrroles. Bromination of free base 10,10-dimethylbiladiene (DMBil1) followed by metalation with Pd(OAc)2, as well as bromination of the corresponding Pd(II) dimethylbiladiene complex (Pd[DMBil1]) provide routes to Pd(II) hexabromo-10,10-dimethyl-5,15-bis(pentafluorophenyl)-isocorrole (Pd[10-DMIC-Br6]) and Pd(II) octabromo-10,10-dimethyl-5,15-bis(pentafluorophenyl)-isocorrole (Pd[10-DMIC-Br8]). The solid-state structures of the two brominated isocorrole complexes are presented, as is that for a new decabrominated dimethylbiladiene derivative (DMBil-Br10). The electronic and spectroscopic properties of the brominated biladiene and isocorrole derivatives were probed using a combination of voltammetric methods and steady-state UV–vis absorption and emission experiments. Data obtained from these experiments allow the properties of the brominated biladiene and isocorrole derivatives to be compared to previously studied biladiene derivatives (i.e., DMBil1and Pd[DMBil1]). CV and DPV experiments demonstrate that Pd[10-DMIC-Br6]and Pd[10-DMIC-Br8]support well-behaved multielectron redox chemistry, similar to that which has been observed for other nonaromatic tetrapyrroles containing sp3-hybridized meso-carbons. Spectroscopic experiments reveal that bromination of the dimethylbiladiene core shifts this system’s UV–vis absorption profile to lower energy and that the dimethylisocorrole complexes support panchromatic absorption profiles that extend across the UV–vis and into the near-IR region. Photosensitization experiments demonstrate that unlike previously studied Pd(II) biladiene constructs, DMBil-Br10, Pd[10-DMIC-Br6], and Pd[10-DMIC-Br8]support limited triplet excited state chemistry with O2, indicating that the novel nonaromatic tetrapyrrole derivatives described in this work may be best suited for applications other than singlet oxygen sensitization.

Excited states of tris(2,2′-bipyridine)ruthenium(II), [Ru(bpy)3]2+, can be deactivated by a wide range of ferrocene derivatives. The pathway by which deactivation takes place, either energy transfer (EnT) or electron transfer (ET), depends on several factors inherent to each specific donor–acceptor (D···A) system. In this work, we provide mechanistic insight into bimolecular quenching between [Ru(bpy)3]2+*and several ferrocene (Fc) derivatives in a variety of solvents. By introducing various functional groups onto the cyclopentadienyl ring of ferrocene, the chemical properties of the organometallic complexes were altered by tuning the oxidation potentials and charge of the iron complexes, and the manner in which the [Ru(bpy)3]2+excited state is quenched by each ferrocene complex in solvents of various dielectric constants, including anhydrous acetonitrile (ACN), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and water (pH 10), was assessed. Through the use of transient absorption (TA) spectroscopy, the mechanism of [Ru(bpy)3]2+*quenching by each of five ferrocene derivatives (i.e., either EnT or ET) in the aforementioned solvents was evaluated. On the basis of these studies, electrostatic factors relating to the charge on the ferrocene moiety were found to influence the quenching pathway(s) for the [Ru(bpy)3]2+···Fc systems under interrogation. When the ferrocene moiety is positively charged, the [Ru(bpy)3]2+excited state is quenched by EnT to Fc, while when the ferrocene moiety is neutral or negatively charged, the [Ru(bpy)3]2+excited state is quenched via reductive ET.

A homologous set of 5,5-dimethylphlorin macrocycles in which the identity of one aryl ring is systematically varied has been prepared. These derivatives contain ancillary pentafluorophenyl (3H(PhlF)), mesityl (3H(PhlMes)), 2,6-bismethoxyphenyl (3H(PhlOMe)), 4-nitrophenyl (3H(PhlNO2)), or 4-tert-butylcarboxyphenyl (3H(PhlCO2tBu)) groups at the 15-meso-position. These porphyrinoids were prepared in good yields (35–50%) and display unusual multielectron redox and photochemical properties. Each phlorin can be oxidized up to three times at modest potentials and can be reduced twice. The electron-donating and electron-releasing properties of the ancillary aryl substituent attenuate the potentials of these redox events; phlorins containing electron-donating aryl groups are easier to oxidize and harder to reduce, while the opposite trend is observed for phlorins containing electron-withdrawing functionalities. Phlorin substitution also has a pronounced effect on the observed photophysics, as introduction of electron-releasing aryl groups on the periphery of the macrocycle is manifest in larger emission quantum yields and longer fluorescence lifetimes. Each phlorin displays an intriguing supramolecular chemistry and can bind 2 equiv of fluoride. This binding is allosteric in nature, and the strength of halide binding correlates with the ability of the phlorin to stabilize the buildup of charge. Moreover, fluoride binding to generate complexes of the form 3H(PhlR)·2F–modulates the redox potentials of the parent phlorin. As such, titration of phlorin with a source of fluoride represents a facile method to tune the ability of this class of porphyrinoid to absorb light and engage in redox chemistry.

The synthesis, electrochemistry, and photophysical characterization of a 10,10-dimethyl-5,15-bis(pentafluorophenyl)biladiene (DMBil1) linear tetrapyrrole supporting PdIIor PtIIcenters is presented. Both of these nonmacrocyclic tetrapyrrole platforms are robust and easily prepared via modular routes. X-ray diffraction experiments reveal that the Pd[DMBil1]and Pt[DMBil1]complexes adopt similar structures and incorporate a single PdIIand PtIIcenter, respectively. Additionally, electrochemical experiments revealed that both Pd[DMBil1]and Pt[DMBil1]can undergo two discrete oxidation and reduction processes. Spectroscopic experiments carried out for Pd[DMBil1]and Pt[DMBil1]provide further understanding of the electronic structure of these systems. Both complexes strongly absorb light in the UV–visible region, especially in the 350–600 nm range. Both Pd[DMBil1]and Pt[DMBil1]are luminescent under a nitrogen atmosphere. Upon photoexcitation of Pd[DMBil1], two emission bands are observed; fluorescence is detected from ∼500–700 nm and phosphorescence from ∼700–875 nm. Photoexcitation of Pt[DMBil1]leads only to phosphorescence, presumably due to enhanced intersystem crossing imparted by the heavier PtIIcenter. Phosphorescence from both complexes is quenched under air due to energy transfer from the excited triplet state to ground state oxygen. Accordingly, irradiation with light of λ ≥ 500 nm prompts Pd[DMBil1]and Pt[DMBil1]to photosensitize the generation of 1O2(singlet oxygen) with impressive quantum yields of 80% and 78%, respectively. The synthetic accessibility of these complexes coupled with their ability to efficiently photosensitize 1O2may make them attractive platforms for development of new agents for photodynamic therapy.

Two homologous complexes of the type [(NHC)AuI–Ar], in which the aryl substituent was either phenyl or pentafluorophenyl, were prepared. Treatment of [(IPr)AuIC6F5] with PhICl2leads directly to the expected AuIIIoxidation addition product [(IPr)AuIII(Cl)2C6F5]. This complex is thermally stable but undergoes photochemical reductive elimination to deliver [(IPr)AuICl] and C6F5Cl. In contrast, the reaction of [(IPr)AuIPh] with PhICl2does not deliver an isolable AuIIIoxidation addition product but rather leads directly to the formation of [(IPr)AuICl] and PhCl, presumably via a [(IPr)AuIII(Cl)2Ph] intermediate. These related reactivity pathways are rationalized on the basis of the electronic structures of the two [(NHC)AuI–Ar] complexes.

Although metal–organic frameworks featuring coordinatively unsaturated transition metal sites are relatively common, examples with redox-active cations are rare. In this report, we describe the electrochemically mediated synthesis of TiIII-MIL-101 from the inexpensive Ti4+precursor TiCl4. The framework obtained via electrosynthesis is identical to that prepared from the significantly more expensive and air-sensitive starting material TiCl3. The above electrosynthetic strategy was also extended to prepare TiIII-MIL-100 and two high-quality extended TiIII-MIL structures, for the first time. These materials represent examples of titanium-based MOFs with extended pore structures. Several physical methods demonstrate that these materials are superior in quality to samples of the analogous MOFs prepared via conventional routes from starting exogenous TiCl3. Given the ease with which the electrosyntheses may be carried out and their compatibility with a broad range of bridging ligands, we expect that this new methodology will find utility for the synthesis of a number of novel materials containing coordinatively unsaturated, redox-active metal cations.

Two new Re(I)bipyridyltricarbonyl chloride complexes, Re(BB3)(CO)3Cl and Re(BB4)(CO)3Cl, featuring BODIPY groups appended to the 5,5′- or 6,6′-positions of the bipyridine ligand, respectively, were synthesized as structurally isomeric compliments to a previously reported 4,4′-substituted homologue, Re(BB2)(CO)3Cl. X-ray crystal structures of the compounds show that the 4,4′-, 5,5′-, and 6,6′-substitution patterns place the BODIPY groups at progressively shorter distances of 9.43, 8.39, and 5.56 Å, respectively, from the complexes’ Re centers. The photophysical properties of the isomeric complexes were investigated to ascertain the manner in which the heavy rhenium atom might induce intersystem crossing of the pendant BODIPY moieties positioned at progressively shorter through-space distances. Electronic absorption spectroscopy revealed that the three metal complexes retain the strong visible absorption features characteristic of the bpyBODIPY (BB2–BB4) ligands; however, the fluorescence of the parent borondipyrromethane appended ligands is attenuated by more than an order of magnitude in Re(BB2)(CO)3Cl and Re(BB3)(CO)3Cl and by more than two orders of magnitude in Re(BB4)(CO)3Cl. Furthermore, phosphorescence from Re(BB4)(CO)3Cl is observed under a nitrogen atmosphere, consistent with highly efficient ISC to the triplet-excited state. Singlet oxygen sensitization studies confirm that all three complexes produce singlet oxygen with quantum yields that increase as the distance of the BODIPY groups to the heavy rhenium center is decreased. The trends observed across the series of rhenium complexes with respect to emission and 1O2sensitization properties can be rationalized in terms of the varied distal separation between the metal center and BODIPY groups in each system.

The electrochemical conversion of CO2to CO is a process important for generation of carbon-based fuels using energy produced from intermittent, renewable energy sources. Electrodeposited thin films of bismuth-based materials are promising platforms for this transformation when used for CO2electrolysis in the presence of imidazolium-based ionic liquids including [BMIM]OTf and [EMIM]OTF. In this study, the composition and function of a bismuth-based carbon monoxide evolving catalyst (Bi-CMEC) has been probed. In particular, the composition of both the electrodeposited bismuth material and the catholyte has been scrutinized in an effort to understand the factors that drive efficient catalyst operation. A combination of XPS depth profiling, XANES, and EXAFS experiments were employed to identify the bulk composition of the bismuth catalyst, which is shown to be composed of both metallic and oxidized phases. The identity of the catholyte solvent has been shown to influence the nature and efficacy of CO2reduction by the Bi-based catalyst system, as mass transport of both CO2- and imidazolium-based ionic liquid to the electrode surface dramatically impacts the kinetics and selectivity for CO production at the cathode/electrolyte interface.

Photodynamic therapy (PDT) represents a minimally invasive and highly localized treatment strategy to ablate tumors with few side effects. In PDT, photosensitizers embedded within tumors are activated by light and undergo intersystem crossing, followed by energy transfer to molecular oxygen, resulting in the production of toxic singlet oxygen (1O2). Previously, we reported a robust, linear tetrapyrrole palladium(II) complex, Pd[DMBil1], characterized by its facile and modular synthesis, broad absorption profile, and efficient 1O2quantum yield of ΦΔ= 0.8 in organic media. However, the insolubility of this porphyrinoid derivative in aqueous solution prevents its use under biologically relevant conditions. In this work, we report the synthesis of Pd[DMBil1]-PEG750, a water-soluble dimethylbiladiene derivative that is appended with a poly(ethylene) glycol (PEG) functionality. Characterization of this complex shows that this PEGylated biladiene architecture maintains the attractive photophysical properties of the parent complex under biologically relevant conditions. More specifically, the absorption profile of Pd[DMBil1]-PEG750closely matches that of Pd[DMBil1]and obeys the Beer–Lambert Law, suggesting that the complex does not aggregate under biologically relevant conditions. Additionally, the emission spectrum of Pd[DMBil1]-PEG750retains the fluorescence and phosphorescence features characteristic of Pd[DMBil1]. Importantly, the PEGylated photosensitizer generates 1O2with ΦΔ= 0.57, which is well within the range to warrant interrogation as a potential PDT agent for treatment of cancer cells. The Pd[DMBil1]-PEG750is biologically compatible, as it is taken up by MDA-MB-231 triple negative breast cancer (TNBC) cells and has an effective dose (ED50) of only 0.354 μM when exposed to λex> 500 nm light for 30 min. Impressively, the lethal dose (LD50) of Pd[DMBil1]-PEG750without light exposure was measured to be 1.87 mM, leading to a remarkably high phototoxicity index of ∼5300, which is vastly superior to existing photosensitizers that form the basis for clinical PDT treatments. Finally, through flow cytometry experiments, we show that PDT with Pd[DMBil1]-PEG750induces primarily apoptotic cell death in MDA-MB-231 cells. Overall these results demonstrate that Pd[DMBil1]-PEG750is an easily prepared, biologically compatible, and well-tolerated photochemotherapeutic agent that can efficiently drive the photoinduced apoptotic death of TNBC cells.

The metal-to-ligand charge transfer excited states of [Ru(bpy)3]2+(bpy = 2,2′-bipyridine) may be deactivated via energy transfer or electron transfer with ferrocene derivatives in aqueous conditions. Stern–Volmer quenching analysis revealed that the rate constant for [Ru(bpy)3]2+excited-state quenching depends on solution pH when a ferrocenyl-amidinium derivative (Fc–am) containing a proton-responsive functionality tethered to the ferrocene center was present. By contrast, the rate constant with which the [Ru(bpy)3]2+excited state is quenched by an analogous ferrocene derivative (ferrocenyl-trimethylammonium, Fc–mam) that lacks a protonic group does not depend on pH. These results show that the presence (or absence) of a readily transferrable proton modulates quenching rate constants in bimolecular events involving [Ru(bpy)3]2+and ferrocene. More surprisingly, transient absorption spectroscopy reveals that the mechanismby which the [Ru(bpy)3]2+excited state is quenched by Fc–amappears to be modulated by solution proton availability, switching from energy transfer at low pH when Fc–amis protonated, to electron transfer at high pH when Fc–amis deprotonated. The mechanistic switching that is observed for this system cannot be aptly explained using a simple driving force dependence argument, suggesting that more subtle factors dictate the pathway by which the [Ru(bpy)3]2+excited state is deactivated by ferrocene in aqueous solutions.

The iron(II) semiquinonate character within the iron(III) catecholate species has been proposed by numerous studies to account for the O2reactivity of intradiol catechol dioxygenases, but a well-characterized iron(II) semiquinonate species that exhibits intradiol cleaving reactivity has not yet been reported. In this study, a detailed electronic structure description of the first iron(II) o-semiquinonate complex, [PhTttBu]Fe(phenSQ) [PhTttBu= phenyltris(tert-butylthiomethyl)borate; phenSQ = 9,10-phenanthrenesemiquinonate; Wang et al. Chem. Commun.2014, 50, 5871–5873], was generated through a combination of electronic and Mössbauer spectroscopies, SQUID magnetometry, and density functional theory (DFT) calculations. [PhTttBu]Fe(phenSQ) reacts with O2to generate an intradiol cleavage product, diphenic anhydride, in 16% yield. To assess the dependence of the intradiol reactivity on the identity of the metal ion, the nickel analogue, [PhTttBu]Ni(phenSQ), and its derivative, [PhTttBu]Ni(3,5-DBSQ) (3,5-DBSQ = 3,5-di-tert-butyl-1,2-semiquinonate), were prepared and characterized by X-ray crystallography, mass spectrometry, 1H NMR and electronic spectroscopies, and SQUID magnetometry. DFT calculations, evaluated on the basis of the experimental data, support the electronic structure descriptions of [PhTttBu]Ni(phenSQ) and [PhTttBu]Ni(3,5-DBSQ) as high-spin nickel(II) complexes with antiferromagnetically coupled semiquinonate ligands. Unlike its iron counterpart, [PhTttBu]Ni(phenSQ) decomposes slowly in an O2atmosphere to generate 14% phenanthrenequinone with a negligible amount of diphenic anhydride. [PhTttBu]Ni(3,5-DBSQ) does not react with O2. This dramatic effect of the metal-ion identity supports the hypothesis that a metal(III) alkylperoxo species serves as an intermediate in the intradiol cleaving reactions. The redox properties of all three complexes were probed using cyclic voltammetry and differential pulse voltammetry, which indicate an inner-sphere electron-transfer mechanism for the formation of phenanthrenequinone. The lack of O2reactivity of [PhTttBu]Ni(3,5-DBSQ) can be rationalized by the high redox potential of the metal-ligated 3,5-DBSQ/3,5-DBQ couple.

Although the number of Veterans Treatment Courts (VTCs) has been growing at a rapid rate, thus far, VTC components have not been standardized, due in part to a lack of empirical evidence on the extent to which components vary across VTCs nationwide and change over time. This study analyzed data collected by the Department of Veterans Affairs’ Veterans Justice Program, on VTCs in 2012 (n= 173 Courts), 2013 (n= 266), and 2014 (n= 351), to describe Court characteristics, participant eligibility criteria, and Courts’ mentoring component. Despite growth in VTC numbers, the survey found consistency over time in these aspects of VTCs. Regarding characteristics, the majority of Courts had jurisdiction at the county level. Across survey years, the range of means was 22–24 for veteran participant census, 10–14 for number of months spent in the Court for misdemeanors, and 18–19 for number of months spent in the Court for felonies. Eligibility requirements suggested openness to veterans of different backgrounds and status. Less than two thirds of Courts had the mentoring component; Courts with the mentoring component had a higher participant census and a longer duration of participants’ time under Court supervision than Courts without this component. Existing mentoring programs were organized mainly by volunteers. VTCs’ adherence to policies supportive of veterans may benefit from having paid mentor coordinators in order to further ensure this hallmark of VTCs.

The preparation of tertiary nitroalkanes via the nickel-catalyzed alkylation of secondary nitroalkanes using aliphatic iodides is reported. Previously, catalytic access to this important class of nitroalkanes via alkylation has not been possible due to the inability of catalysts to overcome the steric demands of the products. However, we have now found that the use of a nickel catalyst in combination with a photoredox catalyst and light leads to much more active alkylation catalysts. These can now access tertiary nitroalkanes. The conditions are scalable as well as air and moisture tolerant. Importantly, reduction of the tertiary nitroalkane products allows rapid access to α-tertiary amines.

Over half of veterans in the criminal justice system have mental health or substance use disorders. However, there is a critical lack of information about female veterans in the criminal justice system and how diagnosis prevalence and treatment entry differ by sex.

A new 5,5-dimethylphlorin derivative (3H(PhlCF3)) was prepared and studied through a combination of redox, photophysical, and computational experiments. The phlorin macrocycle is significantly distorted from planarity compared to more traditional tetrapyrrole architectures and displays solvatochroism in the soret region of the UV–vis spectrum (∼370–420 nm). DFT calculations indicate that this solvatochromic behavior stems from the polarized nature of the frontier orbital (LUMO+1) that is most heavily involved in these transitions. Compound 3H(PhlCF3)also displays an intriguing supramolecular chemistry with certain anions; this phlorin can cooperatively hydrogen-bond two equivalents of fluoride to form 3H(PhlCF3)·2F–but does not bind larger halides such as Cl–or Br–. Analogous studies revealed that the phlorin can hydrogen-bond with carboxylate anions such as acetate to form 1:1 complexes such as 3H(PhlCF3)·OAc–. These supramolecular assemblies are robust and form even in relatively polar solvents such as MeCN. Hydrogen-bonding of fluoride and acetate anions to the phlorin N–H residues significantly attenuates the redox and photophysical properties of the phlorin. Moreover, The ability to independently vary the size and pKaof a series of carboxylate hydrogen-bond acceptors has allowed us to probe how phlorin–anion association is controlled by the anion’s size and/or basicity. These studies elucidate the physical properties and the electronic effects that shape the supramolecular chemistry displayed by the phlorin platform.

A set polyethylene glycol (PEG)-appended BODIPY architectures (BOPEG1–BOPEG3) have been prepared and studied in CH2Cl2, H2O:CH3CN (1:1) and aqueous solutions. BOPEG1and BOPEG2both contain a short PEG chain and differ in substitution about the BODIPY framework. BOPEG3is comprised of a fully substituted BODIPY moiety linked to a PEG polymer that is roughly 13 units in length. The photophysics and electrochemical properties of these compounds have been thoroughly characterized in CH2Cl2and aqueous CH3CN solutions. The behavior of BOPEG1–BOPEG3correlates with established rules of BODIPY stability based on substitution about the BODIPY moiety. Electrogenerated chemiluminescence (ECL) for each of these compounds was also monitored. BOPEG1, which is unsubstituted at the 2- and 6-positions dimerized upon electrochemical oxidation while BOPEG2, which contains ethyl groups at the 2- and 6-positions, was much more robust and served as an excellent ECL luminophore. BOPEG3is highly soluble in water due to the long PEG tether and demonstrated modest ECL activity in aqueous solutions using tri-n-propylamine (TPrA) as a coreactant. As such, BOPEG3represents the first BODIPY derivative that has been shown to display ECL in water without the need for an organic cosolvent, and marks an important step in the development of BODIPY based ECL probes for various biosensing applications.

Porphyrins are attractive chromophores for incorporation into light harvesting devices. Some of the most efficient porphyrin derivatives in this regard are synthetically complex platforms with specially tailored electronic properties. This work details the unique geometric and electronic structure of the phlorin framework. X-ray crystallography and NMR spectroscopy demonstrate that unlike typical tetrapyrrole macrocycles, the phlorin is not aromatic. These unusual electronics are manifest in distinct photophysical and redox properties, as the phlorin displays a rich multielectron redox chemistry. The phlorin also displays an intriguing supramolecular chemistry and can reversibly bind up to 2 equiv of fluoride in cooperative fashion. Accordingly, this synthetically accessible sensitizer displays a rich multielectron redox chemistry, excellent spectral coverage, and an intriguing anion binding chemistry that distinguishes this system from more commonly studied porphyrinoids.

Two new 2,2′-bipyridine (bpy)-based ligands with ancillary BODIPY chromophores attached at the 4- and 4′-positions were prepared and characterized, which vary in the substitution pattern about the BODIPY periphery by either excluding (BB1) or including (BB2) a β-alkyl substituent. Both absorb strongly throughout the visible region and are strongly emissive. The basic photophysics and electrochemical properties of BB1and BB2are comparable to those of the BODIPY monomers on which they are based. The solid-state structures and electronic structure calculations both indicate that there is negligible electronic communication between the BODIPY moieties and the intervening bpy spacers. Electrogenerated chemiluminescence spectra of the two bpy-BODIPY derivatives are similar to their recorded fluorescence profiles and are strongly influenced by substituents on the BODIPY chromophores. These 2,2′-bipyridine derivatives represent a new set of ligands that should find utility in applications, including light-harvesting, photocatalysis, and molecular electronics.

The selective 4e–/4H+reduction of dioxygen to water is an important reaction that takes place at the cathode of fuel cells. Monomeric aromatic tetrapyrroles (such as porphyrins, phthalocyanines, and corroles) coordinated to Co(II) or Co(III) have been considered as oxygen reduction catalysts due to their low cost and relative ease of synthesis. However, these systems have been repeatedly shown to be selective for O2reduction by the less desired 2e–/2H+pathway to yield hydrogen peroxide. Herein, we report the initial synthesis and study of a Co(II) tetrapyrrole complex based on a nonaromaticisocorrole scaffold that is competent for 4e–/4H+oxygen reduction reaction (ORR). This Co(II) 10,10-dimethyl isocorrole (Co[10-DMIC]) is obtained in just four simple steps and has excellent yield from a known dipyrromethane synthon. Evaluation of the steady state spectroscopic and redox properties of Co[10-DMIC]against those of Co porphyrin (cobalt 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin, [Co(TPFPP)]) and corrole (cobalt 5,10,15-tris(pentafluorophenyl)corrole triphenylphosphine, Co[TPFPC](PPh3)) homologues demonstrated that the spectroscopic and electrochemical properties of the isocorrole are distinct from those displayed by more traditional aromatic tetrapyrroles. Further, the investigation of the ORR activity of Co[10-DMIC]using a combination of electrochemical and chemical reduction studies revealed that this simple, unadorned monomeric Co(II) tetrapyrrole is ∼85% selective for the 4e–/4H+reduction of O2to H2O over the more kinetically facile 2e–/2H+process that delivers H2O2. In contrast, the same ORR evaluations conducted for the Co porphyrin and corrole homologues demonstrated that these traditional aromatic systems catalyze the 2e–/2H+conversion of O2to H2O2with near complete selectivity. Despite being a simple, easily prepared, monomeric tetrapyrrole platform, Co[10-DMIC]supports an ORR catalysis that has historically only been achieved using elaborate porphyrinoid-based architectures that incorporate pendant proton-transfer groups or ditopic molecular clefts or that impose cofacially oriented O2binding sites. Accordingly, Co[10-DMIC]represents the first simple, unadorned, monomeric metalloisocorrole complex that can be easily prepared and shows a privileged performance for the 4e–/4H+peractivation of O2to water as compared to other simple cobalt containing tetrapyrroles.

Presents a report prepared by an American Association of University Professors (AAUP) Committee C on College and University Teaching, Research and Publication regarding external regulation of academic activities and workloads in public higher education. Historical dimensions of intervention and support; Styles of intervention and supervision.