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Metal-organic framework-808 has been functionalized with 11 amino acids (AA) to produce a series of MOF-808-AA structures. The adsorption of CO2 under flue gas conditions revealed that glycine- and DL-lysine-functionalized MOF-808 (MOF-808-Gly and -DL-Lys) have the highest uptake capacities. Enhanced CO2 capture performance in the presence of water was observed and studied using single-component sorption isotherms, CO2/H2O binary isotherm, and dynamic breakthrough measurements. The key to the favorable performance was uncovered by deciphering the mechanism of CO2 capture in the pores and attributed to the formation of bicarbonate as evidenced by 13C and 15N solid-state nuclear magnetic resonance spectroscopy studies. Based on these results, we examined the performance of MOF-808-Gly in simulated coal flue gas conditions and found that it is possible to capture and release CO2 by vacuum swing adsorption. MOF-808-Gly was cycled at least 80 times with full retention of performance. This study significantly advances our understanding of CO2 chemistry in MOFs by revealing how strongly bound amine moieties to the MOF backbone create the chemistry and environment within the pores, leading to the binding and release of CO2 under mild conditions without application of heat.

Bubble point and cloud point pressures for mixtures of CO2 and 1–4 wt% polydimethyl siloxane (PDMS, Mw 237, 410, 1250, 2000, 3780, 5970, 9430) terminated with CO2-philic trimethylsilyl groups are presented. The two-phase pressure loci at 23 °C and 40 °C are relatively flat and the cloud point pressures increase with PDMS molecular weight to a value of approximately 23 MPa for PDMS 9430. If PDMS is end-functionalized with CO2-phobic groups, however, the resultant molecules will exhibit higher cloud point pressures. Further, there is an optimal PDMS molecular weight for enhancing CO2 solubility of the end-functionalized compound. For example, when PDMS is terminated at each end with ethyl-naphthalene, the lowest cloud point pressures at 40 °C for mixtures of 1–4 wt% of the compound in CO2 are attained for a PDMS molecular weight of 2357. If the PDMS has a molecular weight of 1207 or less, the compound becomes less CO2-soluble because the unfavorable enthalpic interactions of CO2 and the ethyl-naphthalene groups become dominant. For PDMS of molecular weight 5664 or more, the entropic effects associated with higher molecular weight PDMS mixing with CO2, coupled with the unfavorable enthalpic effects between the end groups and CO2, result in the compound being CO2-insoluble. Finally, these design principles were used to generate 10 other end-functionalized PDMS-based compounds capable of dissolving at 1 wt% in CO2 at 23 °C and a pressure below 5000 psi based on PDMS segments containing 10–40 repeat units.

The major thermal degradation pathway seen with 1,5-bis(3-aminopropyl)-1,1,3,3,5,5-hexamethyltrisiloxane/triethylene glycol (GAP-1/TEG) is the formation of a urea-containing compound. Degradation is increased at higher temperatures, longer reaction times, higher CO2 concentrations (in the form of carbamate loading), and low water levels. A judicious choice of operating conditions can significantly decrease urea byproduct formation. Reducing the desorption temperature from 140 to 100 °C and adding 5 wt % water to the 60:40 mixture of GAP-1/TEG resulted in a 500-fold reduction in amine loss after 4 days in a CO2-rich environment. After 56 days of continuous heating under the same conditions, ∼87% original GAP-1 was retained at 100 °C compared to only ∼20% at 140 °C. The urea byproduct appears to be the only major degradation pathway under these conditions, with 100% of the mass balance accounted for by the urea and amine components.

A series of cyclic amide and urea materials were prepared and screened as small molecule thickeners for organic solvents, dense CO2, and mixtures thereof. In addition to a cyclohexane or benzene core, both of which are mildly CO2-phobic, these molecules contained either ester, amide, or urea groups responsible for establishing intermolecular interactions necessary for increasing solution viscosity. These groups also function to connect siloxane or heavily acetylated CO2-philic segments to the cyclic core of the thickener molecule. Many of these compounds were shown to thicken conventional organic liquids (e.g., toluene, hexane), usually after heating and cooling the mixture. A propyltris(trimethylsiloxy)silane-functionalized benzene trisurea material was also shown to thicken compressed liquid propane and butane. Attaining solubility and self-assembly in CO2 proved more challenging, however. Several ester, amide, and urea containing compounds were discovered that are soluble in dense CO2 at low loadings (...

A series of aromatic amide-functionalized, low-molecular-weight polydimethylsiloxanes were synthesized, and their solubility and thickening ability in supercritical carbon dioxide (scCO2) were evaluated. Amide-terminated polydimethylsiloxane (PDMS) oligomers with simple or electron-rich aromatic groups were found to be moderate viscosity oils, indicating that the end groups do not interact strongly enough to be thickeners. Attachment of electron-deficient aromatic groups, such as 4-nitrophenyl, biphenyl, or anthraquinone, onto these amides produced solid polysiloxanes, even at relatively higher degrees of polymerization on the PDMS core (x = 40–50). PDMS derivatives with anthraquinone-2-carboxamide (AQCA) end groups were clear, somewhat rubbery solids. These compounds were found to act as thickeners and gelators of hexanes. In addition, they were able to thicken and/or gel mixtures of hexane and scCO2. The best results were obtained with an AQCA-terminated branched PDMS. Branched fluorenone-2-carboxamide ...

Significance Catalytic hydrogenation and dehydrogenation reactions are extremely important in organic chemistry and recently for energy storage in the form of chemical bonds. Although catalysts are known which catalyze both reactions, the rates and conditions required for the two are frequently very different due to the differences associated with the bonds to be activated (C–H/O–H/N–H and C = O/C = N/H–H). The use of a bifunctional catalyst would substantially simplify the design of processes related to energy storage. In this work, organometallic complexes of iron and iridium are shown to act as catalysts for reversible dehydrogenation of alcohols to carbonyl compounds. This finding opens a pathway to the development of catalysts for direct reversible electrochemical dehydrogenation of organic fuels in energy generation and storage reactions.

The electrochemical properties of the (PCP)RhI(H2) (1-H2, PCP = κ3-C6H3–2,6-(CH2P(tBu2)) complex was examined by cyclic voltammetry in acetonitrile (MeCN), dimethylsulfoxide (DMSO) and 1,2-difluorobenzene (1,2-DFB). Upon oxidation in weakly or non-coordinating media such as 0.05 M NaBArF24 in 1,2-difluorobenzene, simple one electron oxidation to [(PCP)RhII(H2)]+ is observed. Conversely, in coordinating solvents (e.g. acetonitrile and dimethylsulfoxide) the reactivity is dominated by solvent coordinated species with a slight variation in the RhIII/II oxidation potentials as a function of the supporting electrolyte conductivity. A computational analysis of these reactions in support of the proposed mechanism is presented.

The kinetics and thermodynamics of the binding of several small molecules, L (L = N2, H2, D2, and C2H4), to the coordinatively unsaturated pincer-PCP rhodium(I) complexes Rh[(t)Bu2PCH2(C6H3)CH2P(t)Bu2] (1) and Rh[(t)Bu2P(CH2)2(CH)(CH2)2P(t)Bu2] (2) in organic solvents (n-heptane, toluene, THF, and cyclohexane-d12) have been investigated by a combination of kinetic flash photolysis methods, NMR equilibrium studies, and density functional theory (DFT) calculations. Using various gas mixtures and monitoring by NMR until equilibrium was established, the relative free energies of binding of N2, H2, and C2H4 in cyclohexane-d12 were found to increase in the order C2H4N2H2. Time-resolved infrared (TRIR) and UV-vis transient absorption spectroscopy revealed that 355 nm excitation of 1-L and 2-L results in the photoejection of ligand L. The subsequent mechanism of binding of L to 1 and 2 to regenerate 1-L and 2-L is determined by the structure of the PCP ligand framework and the nature of the solvent. In both cases, the primary transient is a long-lived, unsolvated species (τ = 50-800 ns, depending on L and its concentration in solution). For 2, this so-called less-reactive form (LRF) is in equilibrium with a more-reactive form (MRF), which reacts with L at diffusion-controlled rates to regenerate 2-L. These two intermediates are proposed to be different conformers of the three-coordinate (PCP)Rh fragment. For 1, a similar mechanism is proposed to occur, but the LRF to MRF step is irreversible. In addition, a parallel reaction pathway was observed that involves the direct reaction of the LRF of 1 with L, with second-order rate constants that vary by almost 3 orders of magnitude, depending on the nature of L (in n-heptane, k = 6.7 × 10(5) M(-1) s(-1) for L = C2H4; 4.0 × 10(6) M(-1) s(-1) for L = N2; 5.5 × 10(8) M(-1) s(-1) for L = H2). Experiments in the more coordinating solvent, THF, revealed the binding of THF to 1 to generate 1-THF, and its subsequent reaction with L, as a competing pathway.

To retrospectively analyse surgical outcome and complications in patients with ocular myopathy undergoing ptosis correction and to introduce preoperative prophylactic lower lid elevation in this group.The medical records of all ocular myopathy patients who had undergone oculoplastic surgery between June 1995 and May 2006 were obtained. Patients' demographics, surgical details and measurements, and complications were recorded.29 patients were identified; 21 with chronic progressive external ophthalmoplegia (CPEO), 7 with myotonic dystrophy (MD) and 1 with oculopharyngeal muscular dystrophy (OPMD). Then, 61 procedures to adjust eyelid height were performed, comprising levator resection, brow suspension, anterior lamellar repositioning, lower lid elevation and upper lid lowering. Palpebral aperture was significantly increased in all patient groups, by procedure and diagnosis, more significantly following brow suspension compared with levator resection. The patients' feedback was very positive. Post-operative complications were few, included corneal exposure and ulceration, ptosis recurrence, arched brow, and sling infection, all of which were successfully treated.Our results demonstrate subjective and objective benefit following surgery in these patients, with a low complication rate. The use of pre-operative prophylactic lower lid elevation procedures is a promising modality.

PURPOSE To date, there have only been 5 reported cases of orbital cellulitis following implantation of an aqueous tube shunt for glaucoma. Previously reported cases have involved eyes with significant comorbidities and successful management has often required the removal of the device alongside systemic antibiotic therapy. PATIENTS AND METHODS We present a 53-year-old man with severe orbital cellulitis, 3 months after routine implantation of a Baerveldt tube shunt for primary open angle glaucoma. The patient was managed medically, with topical and systemic antibiotic therapy. The patient went on to make a full recovery with the tube in situ. RESULTS AND CONCLUSIONS We report that a more conservative approach (without tube removal) to be successful in a case where there is no evidence of tube exposure. It is important to appreciate that in some cases of orbital cellulitis without clear signs of intraocular involvement, a tube can be left in situ.

CO2 miscible and immiscible displacements and hydrocarbon miscible floods are commonly plagued by low volumetric sweep efficiency, early gas breakthrough, high gas utilization ratios, and significant gas re-compression and recycle. Rather than addressing these problems via the water-alternating-gas (WAG) injection sequence that reduces gas relative permeability or the generation of gas-in-brine foams for reduced mobility, we propose increasing the viscosity of high pressure CO2 or NGL via the dissolution of dilute concentrations of thickening agents. There are two strategies for increasing the viscosity of high pressure fluids; the dissolution of ultrahigh molecular weight polymers or associating polymers, or the dissolution of small molecules that self-assemble in solution to form viscosity-enhancing linear or helical supramolecular structures. Ideally a very small amount of the thickener will be required (roughly 0.1wt%) to elevate the CO2 or NGL viscosity to the same value as the oil being displaced (typically a 10-100 fold increase). Further, the thickened CO2 or thickened NGL should be a stable, transparent solution that does not require a heating/cooling cycle for viscosity enhancement to occur. Thickener solubility and viscosity were determined over a 25-100oC range. Each of the three major NGL constituents (ethane, propane and butane) was thickened with an ultrahigh molecular polymer (commercial drag reducing agent), resulting in a 2-30 fold increase in viscosity at polymer concentrations of 0.5wt% or less. The polymer dissolved at the lowest pressure in butane and was most effective as a thickener in butane. Three small molecule thickeners were identified for the NGL constituents; tri-alkyl-tin fluoride, hydroxyaluminum disoap, and a phosphate ester-crosslinker mixture. Remarkable viscosity enhancements were attained for propane and butane with the tri-alkyl-tin fluoride and aluminum soap; the crosslinked phosphate ester solutions exhibited modest viscosity increases. Only tri-alkyl-tin fluoride thickened ethane. CO2 thickeners were assessed with a falling ball viscometer and pressure drop associated with flow through Berea sandstone. 4-5 fold increases in viscosity were attained with 1wt% of a high molecular weight polyfluoroacrylate. 3-4 fold increases in viscosity were attained with 1wt% high molecular weight polydimethyl siloxane, but a very large amount of toluene co-solvent was required. Although a remarkably effective small molecule thickener was designed for CO2 (100-fold increase at 1.3wt%), it required a heating/cooling cycle and a very large amount of hexane co-solvent. We have identified the first polymeric and small molecule thickeners ever reported for ethane. Further, this study presents the largest viscosity increases ever reported for propane and butane with polymers and small molecule thickeners. We have presented the most effective polymeric thickeners for CO2 reported to date. This paper also summarizes numerous molecular architectures that are not viable for CO2 and highlights the most promising compounds that continue to be refined.

Reliable calculations of redox potentials could provide valuable insight into catalytic mechanisms of electrochemically active transition-metal complexes as well as guidelines for the design of new electrocatalysts. However, the correlation between theoretical and experimental data is often uncertain, since redox properties depend strongly on experimental conditions of electrochemical measurements, including the nature of the solvent, electrolyte, and working electrode. Here, we show that the use of internal references allows for quantitative theoretical predictions of redox potentials with standard deviations σ comparable to typical experimental errors of cyclic voltammetry measurements. Agreement for first-, second-, and third-row transition-metal complexes is demonstrated even at a rather modest level of density functional theory (σ = 64 mV for the UB3LYP/6-311G* level). This is shown for a series of benchmark redox couples, including ([MCp2]0/+ (Cp = η5-cyclopentadienyl), [MCp*2]0/+ (Cp* = η5-1,2,3,4,...

Background: To assess agreement between the Diaton, a new transpalpebral tonometer, and Goldmann applanation tonometry, the accepted gold standard. Design: Comparative study of two devices in a hospital setting. Participants: Two hundred and fifty-one patients attending the eye casualty and general ophthalmology clinics at St James' University Hospital, Leeds between February and December 2009. Methods: Intraocular pressure was measured using Goldmann applanation tonometry and Diaton tonometry by one examining ophthalmologist. Patient preference for either technique was also recorded. Main Outcome Measures: Intraocular pressure measured by Diaton was compared with intraocular pressure measured by Goldmann applanation tonometry. Limits of agreement were determined using the Bland-Altman method. Results: Two hundred and fifty right eyes underwent both Goldmann applanation tonometry and Diaton tonometry. Mean intraocular pressure was 13.8 ± 3.6 mmHg using Goldmann applanation tonometry and 13.2 ± 4.3 mmHg using Diaton tonometry. Upper and lower limits of agreement were +8.4 mmHg and −9.6 mmHg, respectively. Order of intraocular pressure measurement and positioning did not influence limits of agreement in a clinically significant manner. Overall, more patients expressed preference for Diaton tonometry (40.2%) than Goldmann applanation tonometry (30.3%). Those aged 50 or less were more likely to prefer Diaton tonometry. Conclusions: The Diaton tonometer is portable, lightweight, user-friendly and well tolerated by patients. However, it shows poor agreement with Goldmann applanation tonometry, thereby precluding it from being regarded as a substitute in routine clinical practice.

Co(III) agostic alkyl complexes [Cp*Co(L)(CH2CH2-μ-H)][B(ArF)4] (Cp* = C5(CH3)5, L = P(OCH3)3, 1a, or P(CH3)3, 1b; ArF = 3,5-(CF3)2C6H3) react with H2 to yield ethane and trihydride complexes characterized as η2-dihydrogen hydride species [Cp*Co(L)(H)(η2-H2)][B(ArF)], 2a and 2b, in which there is rapid scrambling between the η2-H2 ligand and the terminal Co−H. Complexes 2a and 2b react with a variety of neutral donor ligands (L‘ = RCN, PMe3, P(OMe)3, H2O, CH3OH) to yield [Cp*Co(L)(L‘)(H)][B(ArF)4] complexes. Reaction of silanes with either 1a,b in the presence of traces of water or 2a,b yields η2-silane hydrides, [Cp*Co(L)(H)(η2-HSiR3)][B(ArF)4]. Analysis of the dynamics of these species by NMR spectroscopy provides evidence for an extremely rapid process involving silyl migration between hydrogens and a slower process in which a cobalt-silyl η2-H2 complex is formed as an intermediate and results in hydrogen scrambling between the two diastereomers of [Cp*Co(L)(H)(η2-H-SiHMePh)][B(ArF)4]. The structures a...

Palladium(II)-catalyzed ethylene oligomerization reactions using a new [(P∧N)Pd(CH3)(NCArF)][SbF6] complex, 2b (P∧N = phosphine−oxazoline, ArF = 3,5-(CF3)2C6H3), are described. Analysis of the X-ray crystal structure of the (P∧N)Pd(CH3)Cl precatalyst, 2a, reveals a unique axial Pd···H interaction (2.33 A) with a ligand Csp3−H bond. Exposure of this complex to ethylene in methylene chloride produces a Schulz−Flory distribution of α-olefins ranging from C4 to C24. Effects of varying ethylene pressure and reaction temperature on oligomerizations are reported. The turnover frequency exhibits saturation behavior as ethylene pressure is increased; carrying out a Lineweaver−Burk analysis provides a barrier of 17.5 kcal/mol for migratory insertion of the palladium alkyl ethylene species. The invariance of the Schulz−Flory constant with added quantities of nitrile suggests that chain transfer occurs through a process best described as chain transfer to monomer. The catalyst resting state is shown to vary as a func...

The ideal carbon dioxide (CO2) thickener would be an affordable, safe, water-insoluble additive that could dissolve in CO2 at typical wellhead and reservoir conditions during CO2 enhanced oil recovery (EOR) and elevate the viscosity of CO2 to the same value as the oil. Further, the additive would not require heating or an organic co-solvent to achieve dissolution. A CO2 thickener could be a transformative technology in that it would eliminate unfavorable mobility ratios during CO2 EOR and reduce or eliminate the need for WAG. A detailed history of prior attempts to thicken CO2 with either high molecular weight polymers or small associating compounds is presented. Our strategy for designing a novel small molecule CO2 thickener is then detailed. Each thickener candidate contains a strongly CO2-philic segment (e.g. a very short polymer or oligomer of silicone oil or polyprolylene glycol), and one or more somewhat CO2-phobic functional groups that induces intermolecular interactions that can lead to the formation of viscosity-enhancing supramolecular structures in solution.

A homogeneous organometallic Ir complex was shown to catalyze the electro-oxidation of 4-methoxybenzyl alcohol to p-anisaldehyde at a very low applied potential with remarkably high selectivity and Faradaic efficiency. In the chemical catalysis, when stoichiometric oxidant and anionic base were used to separately accept electrons and protons, aldehyde selectivity was in agreement with electrolysis results.

Two new CO(2)-soluble rhenium(I) bipyridine complexes bearing the fluorinated alkyl ligands 4,4'-(C(6)F(13)CH(2)CH(2)CH(2))(2)-2,2'-bipyridine (1a), and 4,4'-(C(8)F(17)CH(2)CH(2)CH(2))(2)-2,2'-bipyridine (1b) have been prepared and their photophysical properties investigated in CH(3)CN and supercritical CO(2). Electrochemical and spectroscopic characterization of these complexes in CH(3)CN suggests that the three methylene units effectively insulate the bipyridyl rings and the rhenium center from the electron-withdrawing effect of the fluorinated alkyl chains. Reductive quenching of the metal-to-ligand charge-transfer excited states with triethylamine reveals quenching rate constants in supercritical CO(2) that are only 6 times slower than those in CH(3)CN.

Despite the fundamental importance of the hydricity of a transition metal hydride (ΔG(H–)°(MH) for the reaction M–H → M+ + H–) in a range of reactions important in catalysis and solar energy storage, ours (J. Am. Chem. Soc.2009, 131, 2794) are the only values reported for water solvent, and there has been no basis for comparison of these with the wider range already determined for acetonitrile solvent, in particular. Accordingly, we have used a variety of approaches to determine hydricity values in acetonitrile of Ru(II) hydride complexes previously studied in water. For [Ru(η(6)-C6Me6)(bpy)H]+ (bpy = 2,2′-bipyridine), we used a thermodynamic cycle based on evaluation of the acidity of [Ru(η(6)-C6Me6)(bpy)H]+ pKa = 22.5 ± 0.1 and the [Ru(η(6)-C6Me6)(bpy)(NCCH3)(1/0)](2+/0) electrochemical potential (−1.22 V vs Fc+/Fc). For [Ru(tpy)(bpy)H]+ (tpy = 2,2′:6′,2″-terpyridine) we utilized organic hydride ion acceptors (A+) of characterized hydricity derived from imidazolium cations and pyridinium cations, and determined K for the hydride transfer reaction, S + MH+ + A+ → M(S)2+ + AH (S = CD3CN, MH+ = [Ru(tpy)(bpy)H]+), by 1H NMR measurements. Equilibration of initially 7 mM solutions was slow--on the time scale of a day or more. When E°(H+/H–) is taken as 79.6 kcal/mol vs Fc+/Fc as a reference, the hydricities of [Ru(η(6)-C6Me6)(bpy)H]+ and [Ru(tpy)(bpy)H]+ were estimated as 54 ± 2 and 39 ± 3 kcal/mol, respectively, in acetonitrile to be compared with the values 31 and 22 kcal/mol, respectively, found for aqueous media. The pKa estimated for [Ru(tpy)(bpy)H]+ in acetonitrile is 32 ± 3. UV–vis spectroscopic studies of [Ru(η(6)-C6Me6)(bpy)]0 and [Ru(tpy)(bpy)]0 indicate that they contain reduced bpy and tpy ligands, respectively. These conclusions are supported by DFT electronic structure results. Comparison of the hydricity values for acetonitrile and water reveals a flattening or compression of the hydricity range upon transferring the hydride complexes to water.

To assess agreement between the Diaton, a new transpalpebral tonometer, and Goldmann applanation tonometry, the accepted gold standard.Comparative study of two devices in a hospital setting.Two hundred and fifty-one patients attending the eye casualty and general ophthalmology clinics at St James' University Hospital, Leeds between February and December 2009.Intraocular pressure was measured using Goldmann applanation tonometry and Diaton tonometry by one examining ophthalmologist. Patient preference for either technique was also recorded.Intraocular pressure measured by Diaton was compared with intraocular pressure measured by Goldmann applanation tonometry. Limits of agreement were determined using the Bland-Altman method.Two hundred and fifty right eyes underwent both Goldmann applanation tonometry and Diaton tonometry. Mean intraocular pressure was 13.8 ± 3.6 mmHg using Goldmann applanation tonometry and 13.2 ± 4.3 mmHg using Diaton tonometry. Upper and lower limits of agreement were +8.4 mmHg and -9.6 mmHg, respectively. Order of intraocular pressure measurement and positioning did not influence limits of agreement in a clinically significant manner. Overall, more patients expressed preference for Diaton tonometry (40.2%) than Goldmann applanation tonometry (30.3%). Those aged 50 or less were more likely to prefer Diaton tonometry.The Diaton tonometer is portable, lightweight, user-friendly and well tolerated by patients. However, it shows poor agreement with Goldmann applanation tonometry, thereby precluding it from being regarded as a substitute in routine clinical practice.

A homogeneous organometallic Ir complex was shown to catalyze the electro-oxidation of 4-methoxybenzyl alcohol to p-anisaldehyde at a very low applied potential with remarkably high selectivity and Faradaic efficiency. In the chemical catalysis, when stoichiometric oxidant and anionic base were used to separately accept electrons and protons, aldehyde selectivity was in agreement with electrolysis results.

The structure and electrochemical properties of a series of bis(imino)pyridine Co(II) complexes (NNN)CoX(2) and [(NNN)(2)Co][PF(6)](2) (NNN = 2,6-bis[1-(4-R-phenylimino)ethyl]pyridine, with R = CN, CF(3), H, CH(3), OCH(3), N(CH(3))(2); NNN = 2,6-bis[1-(2,6-(iPr)(2)-phenylimino)ethyl]pyridine and X = Cl, Br) were studied using a combination of electrochemical and theoretical methods. Cyclic voltammetry measurements and DFT/B3LYP calculations suggest that in solution (NNN)CoCl(2) complexes exist in equilibrium with disproportionation products [(NNN)(2)Co](2+) [CoCl(4)](2-) with the position of the equilibrium heavily influenced by both the solvent polarity and the steric and electronic properties of the bis(imino)pyridine ligands. In strong polar solvents (e.g., CH(3)CN or H(2)O) or with electron donating substituents (R = OCH(3) or N(CH(3))(2)) the equilibrium is shifted and only oxidation of the charged products [(NNN)(2)Co](2+) and [CoCl(4)](2-) is observed. Conversely, in nonpolar organic solvents such as CH(2)Cl(2) or with electron withdrawing substituents (R = CN or CF(3)), disproportionation is suppressed and oxidation of the (NNN)CoCl(2) complexes leads to 18e(-) Co(III) complexes stabilized by coordination of a solvent moiety. In addition, the [(NNN)(2)Co][PF(6)](2) complexes exhibit reversible Co(II/III) oxidation potentials that are strongly dependent on the electron withdrawing/donating nature of the N-aryl substituents, spanning nearly 750 mV in acetonitrile. The resulting insight on the regulation of redox properties of a series of bis(imino)pyridine cobalt(II) complexes should be particularly valuable to tune suitable conditions for reactivity.

Rhenium(I) and ruthenium(II) complexes have been successfully used for photochemical CO2 reduction to CO or formate. However, a typical turnover frequency for such reactions is