Simple and Green Preparation of Tetraalkoxydiborons and Diboron Diolates from Tetrahydroxydiboron.

Tetraalkoxydiborons can be easily prepared by acid-catalyzed reactions of tetrahydroxydiboron or its anhydride with trialkyl orthoformates. Addition of diols to these reaction mixtures afforded diboron diolates in high yield. In both cases, removal of volatile byproducts is all that is required for the isolation of the diboron. These methods constitute a convenient alternative to previous preparations from tetrakis (dimethylamino) diboron and tetrahydroxydiboron.

Deciphering the Mechanism of Base-Triggered Conversion of Ammonia to Molecular Nitrogen and Methylamine to Cyanide.

We report an in-depth investigation into the ammonia oxidation mechanism by the catalyst [RuIII(tpy)(dmabpy)NH3]3+ ([Ru(NH3)]3+). Stoichiometric reactions of [Ru(NH3)]3+ were carried out with exogenous noncoordinating bases to trigger a proposed redox disproportionation reaction, which was followed using variable-temperature NMR spectroscopy. An intermediate species was identified as a dinitrogen-bridged complex using 15N NMR and Raman spectroscopy on isotopically labeled complexes. This intermediate is proposed to derive from coupling of nitridyl species formed upon sequential redox disproportion reactions. Acetonitrile displaces the dinitrogen bridge to yield free N2. DFT calculations support this lower-energy pathway versus that previously reported for ammonia oxidation by the parent [RuIII(tpy)(bpy)NH3]3+ complex. These experimental and computational results are consistent with the interpretation of redox disproportionation involving sequential hydrogen atom transfer reactions by an amide/aminyl intermediate, [Ru(NH2)-]+ ⇔ [Ru(NH2)•]+, formed upon deprotonation of the parent complex. Control experiments employing a large excess of ammonia as a base indicate this new proposed lower-energy pathway contributes to the oxidation of ammonia to dinitrogen in conditions relevant to electrocatalysis. In addition, analogous methylamine complexes, [Ru(NH2CH3)]2+/3+, were prepared to further test the proposed mechanism. Treating [Ru(NH2CH3)]3+ with a base cleanly yields two products [Ru(NH2CH3)]2+ and [Ru(CN)]+ in an ∼3:1 ratio, fully consistent with the proposed cascade of hydrogen atom transfer reactions by an intermediate.

Management of thoracic trauma.

Managing major thoracic trauma begins with identifying and anticipating injuries associated with the mechanism of injury. The key aims are to reduce early mortality and the impact of associated complications to expedite recovery and restore the patient to their pre-injury state. While imaging is imperative to identify the extent of thoracic trauma, some pathology may require immediate treatment. The majority can be managed with adequate pleural drainage, but respiratory failure and poor gas exchange may require either non-invasive or invasive ventilation. Ventilation strategies to protect from complications such as barotrauma, volutrauma and ventilator-induced lung injury are important to consider. The management of pain is vital in reducing respiratory complications. A multimodal strategy using local, regional and systemic analgesia may mitigate respiratory side effects of opioid use. With optimal pain management, physiotherapy can be fully utilised to reduce respiratory complications and enhance early recovery. Thoracic surgeons should be consulted early for consideration of surgical management of specific injuries. With a greater understanding of the mechanisms of injury and the appropriate use of available resources, favourable outcomes can be reached in this cohort of patients. Overall, a multidisciplinary and holistic approach results in the best patient outcomes.

Incidences of steroid-induced diabetes mellitus and congestive heart failure in cats given non-immunosuppressive doses of methylprednisolone acetate: 1042 cats.

Objective: Corticosteroids are indicated to treat many feline diseases. However, side effects are a limiting factor in their use. The most concerning side effects are steroid-induced diabetes mellitus (SI-DM) and steroid-induced congestive heart failure (SI-CHF). This study aims to determine the incidences of these diseases in a large population of domestic cats seen at a privately-owned, feline-only practice. Animals: Cats in the study were client-owned patients of Alamo Feline Health Center in San Antonio, Texas. Control cats (controls) were examined as part of their routine health care. Procedures: The records of 732 cats that received methylprednisolone acetate (MPA) for various clinical indications were reviewed to determine how many developed SI-DM and SI-CHF. A similar record review of 310 controls was made to determine the incidence of spontaneous diabetes mellitus (Sp-DM) and spontaneous congestive heart failure (Sp-CHF). Control cats never received any oral or injectable corticosteroids. Results: Of the cats that received MPA, 28 developed SI-DM (3.83%) and 6 developed SI-CHF (0.82%). Of the controls, 22 developed Sp-DM (7.10%) and 6 developed Sp-CHF (1.90%). Conclusion: The incidences of developing SI-DM and SI-CHF were 3.83% and 0.82%, respectively; and the risk was not increased even when repeated doses of MPA were given. Clinical relevance: The authors consider the risk-benefit ratio sufficient to justify the use of MPA when it is indicated, especially if another drug cannot be substituted with the same therapeutic results.

Incidences du diabète sucré et de l'insuffisance cardiaque congestive induits par les stéroïdes chez des chats ayant reçu des doses non immunosuppressives d'acétate de méthylprednisolone : 1042 chats. Objectif: Les corticoïdes sont indiqués pour traiter de nombreuses maladies félines. Cependant, les effets secondaires constituent un facteur limitant leur utilisation. Les effets secondaires les plus préoccupants sont le diabète sucré induit par les stéroïdes (SI-DM) et l'insuffisance cardiaque congestive induite par les stéroïdes (SI-CHF). Cette étude vise à déterminer l'incidence de ces maladies dans une large population de chats domestiques vus dans une pratique privée exclusivement féline. Animaux: Les chats de l'étude étaient des patients appartenant à des clients du Alamo Feline Health Center à San Antonio, au Texas. Les chats témoins (témoins) ont été examinés dans le cadre de leurs soins de santé de routine. Procédures: Les dossiers de 732 chats ayant reçu de l'acétate de méthylprednisolone (MPA) pour diverses indications cliniques ont été examinés afin de déterminer combien d'entre eux ont développé du SI-DM et du SI-CHF. Un examen similaire des dossiers de 310 témoins a été réalisé pour déterminer l'incidence du diabète sucré spontané (Sp-DM) et de l'insuffisance cardiaque congestive spontanée (Sp-CHF). Les chats témoins n'ont jamais reçu de corticostéroïdes oraux ou injectables. Résultats: Parmi les chats ayant reçu du MPA, 28 ont développé du SI-DM (3,83 %) et 6 ont développé du SI-CHF (0,82 %). Parmi les témoins, 22 ont développé du Sp-DM (7,10 %) et 6 ont développé du Sp-CHF (1,90 %). Conclusion: Les incidences de développement de SI-DM et de SI-CHF étaient respectivement de 3,83 % et 0,82 %; et le risque n'a pas augmenté même lorsque des doses répétées de MPA ont été administrées. Pertinence clinique: Les auteurs considèrent le rapport bénéfice/risque suffisant pour justifier l'utilisation du MPA lorsqu'il est indiqué, notamment si un autre médicament ne peut lui être substitué avec les mêmes résultats thérapeutiques.(Traduit par Dr Serge Messier).

Modulation of Oxidative Stress and Inflammation in the Aged Lacrimal Gland.

Inflammation and oxidative stress accompany aging. This study investigated the interplay between oxidative stress and inflammation in the lacrimal gland. C57BL/6 mice were used at 2 to 3, 12, and 24 months of age. Nuclear factor erythroid derived-2-related factor 2 (Nrf2)-/- and corresponding wild-type mice were used at 2 to 3 and 12 to 13 months of age. A separate group of 15.5 to 17 months of age C57BL/6 mice received a diet containing an Nrf2 inducer (Oltipraz) for 8 weeks. Aged C57BL/6 lacrimal glands showed significantly greater lymphocytic infiltration, higher levels of MHC II, IFN-γ, IL-1ß, TNF-α, and cathepsin S (Ctss) mRNA transcripts, and greater nitrotyrosine and 4-hydroxynonenal protein. Young Nrf2-/- mice showed an increase in IL-1ß, IFN-γ, MHC II, and Ctss mRNA transcripts compared with young wild-type mice and greater age-related changes at 12 to 13 months of age. Oltipraz diet significantly decreased nitrotyrosine and 4-hydroxynonenal and decreased the expression of IL-1ß and TNF-α mRNA transcripts, while decreasing the frequency of CD45+CD4+ cells in lacrimal glands and significantly increasing conjunctival goblet cell density compared with a standard diet. The findings provide novel insight into the development of chronic, low-grade inflammation and oxidative stress in age-related dry eye. New therapies targeting oxidative stress pathways will be valuable in treating age-related dry eye.

Merging Iridium-Catalyzed C-H Borylations with Palladium-Catalyzed Cross-Couplings Using Triorganoindium Reagents.

A versatile and efficient method to prepare borylated arenes furnished with alkyl, alkenyl, alkynyl, aryl, and heteroaryl functional groups is developed by merging Ir-catalyzed C-H borylations (CHB) with a chemoselective palladium-catalyzed cross-coupling of triorganoindium reagents (Sarandeses-Sestelo coupling) with aryl halides bearing a boronic ester substituent. Using triorganoindium cross-coupling reactions to introduce unsaturated moieties enables the synthesis of borylated arenes that would be difficult to access through the direct application of the CHB methodology. The sequential double catalyzed procedure can be also performed in one vessel.

Recent Advances and Challenges of Electrocatalytic N2 Reduction to Ammonia.

Global ammonia production reached 175 million metric tons in 2016, 90% of which is produced from high purity N2 and H2 gases at high temperatures and pressures via the Haber-Bosch process. Reliance on natural gas for H2 production results in large energy consumption and CO2 emissions. Concerns of human-induced climate change are spurring an international scientific effort to explore new approaches to ammonia production and reduce its carbon footprint. Electrocatalytic N2 reduction to ammonia is an attractive alternative that can potentially enable ammonia synthesis under milder conditions in small-scale, distributed, and on-site electrolysis cells powered by renewable electricity generated from solar or wind sources. This review provides a comprehensive account of theoretical and experimental studies on electrochemical nitrogen fixation with a focus on the low selectivity for reduction of N2 to ammonia versus protons to H2. A detailed introduction to ammonia detection methods and the execution of control experiments is given as they are crucial to the accurate reporting of experimental findings. The main part of this review focuses on theoretical and experimental progress that has been achieved under a range of conditions. Finally, comments on current challenges and potential opportunities in this field are provided.

Amide directed iridium C(sp3)-H borylation catalysis with high N-methyl selectivity.

A bidentate monoanionic ligand system was developed to enable iridium catalyzed C(sp3)-H activation borylation of N-methyl amides. Borylated amides were obtained in moderate to good isolated yields, and exclusive mono-borylation allowed the amide to be the limiting reagent. Selectivity for C(sp3)-H activation was demonstrated in the presence of sterically available C(sp3)-H bonds. Competitive kinetic isotope studies revealed a large primary isotope effect, implicating C-H activation as the rate limiting step.

Homogeneous electrocatalytic oxidation of ammonia to N2 under mild conditions.

We report that ruthenium polypyridyl complexes can catalyze ammonia oxidation to dinitrogen at room temperature and ambient pressure. During bulk electrolysis experiments, gas chromatography and mass spectrometry analysis of the headspace in the electrochemical cell showed that dinitrogen and dihydrogen are generated from ammonia with high faradaic efficiencies. A proposed mechanism where a hydrazine complex is the initial N-N bonded intermediate is supported by chemical and electrochemical experiments. This is a well-defined system for homogeneous electrocatalytic ammonia oxidation. It establishes a platform for answering mechanistic questions relevant to using ammonia to store and distribute renewable energy.

A qualitative focus group study concerning perceptions and experiences of Nigerian mothers on stillbirths.

OBJECTIVE: To explore the experiences and perceptions of stillbirth among mothers from a tertiary medical centre in Kano, Northern Nigeria. DESIGN: Qualitative, interpretative. SETTING: Tertiary healthcare facility, Murtala Muhammad Specialist Hospital (MMSH), Kano, Northern Nigeria. SAMPLE: Mothers who had given birth to a liveborn baby at the MMSH in the prior 6 months (n = 31). In order to capture the experiences and perception of stillbirth within this cohort we approached mothers who had in a previous pregnancy experienced a stillbirth. Of the 31 who attended 16 had a previous stillbirth. METHODS: Semi-structured Focus Group Discussions, consisting of open-ended questions about stillbirth, beliefs, experiences and influences were held in MMSH, conducted over 1 day. RESULTS: Our findings highlight that this is a resource-poor tertiary facility serving an ever-growing population, increasing strain on the hospital and healthcare workers. Many of the participants highlighted needing permission from certain family members before accessing healthcare or medical treatment. We identified that mothers generally have knowledge on self-care during pregnancy, yet certain societal factors prevented that from being their priority. Judgement and blame was a common theme, yet a complex area entwined with traditions, superstitions and the pressure to procreate with many mothers described being made to feel useless and worthless if they did not birth a live baby. CONCLUSIONS: As access to healthcare becomes easier, there are certain traditions, family and social dynamics and beliefs which conflict with scientific knowledge and act as a major barrier to uptake of healthcare services. The findings highlight the need for investment in maternity care, appropriate health education and public enlightenment; they will help inform appropriate interventions aimed at reducing stigma around stillbirth and aide in educating mothers about the importance of appropriate health seeking behaviour. Stillbirths are occurring in this area of the world unnecessarily, globally there has been extensive research conducted on stillbirth prevention. This research has highlighted some of the areas which can be tackled by modifying existing successful interventions to work towards reducing preventable stillbirths.

FULL-THICKNESS MACULAR HOLE SIZE BY HYPERTRANSMISSION SIGNAL ON SPECTRAL-DOMAIN OPTICAL COHERENCE TOMOGRAPHY.

PURPOSE: To assess the full-thickness macular hole (FTMH) size using the choroidal hypertransmission signal on spectral-domain optical coherence tomography and to compare this method to the standard aperture measurement of the minimum aperture size at the level of the neurosensory retina. DESIGN: Cross-sectional study of retrospective data. METHODS: Eyes with FTMH imaged on spectral-domain optical coherence tomography were included. Two independent masked graders used the device's built-in caliper tool to measure the FTMH minimum aperture size at the level of the neurosensory retina and the size of the corresponding hypertransmission signal below the level of the retinal pigment epithelium/Bruch membrane complex. To assess the reproducibility of the hypertransmission measurement in tilted scans, two measurements were obtained and compared; the first was traced parallel to the retinal pigment epithelium (parallel hypertransmission), and the second was horizontal to the image frame (horizontal hypertransmission), both using Image J software. RESULTS: A total of 31 eyes were enrolled. The mean FTMH minimum aperture size was smaller compared with both the choroidal parallel hypertransmission and horizontal hypertransmission measurements (mean ± SD: 335.7 ± 139.5 µm, 376.7 ± 150.6 µm, 375.1 ± 150.0 µm, respectively. P < 0.001 for both comparisons). CONCLUSION: The proposed hypertransmission measurement is a feasible and reproducible alternative to assess FTMH size and could provide the basis for an automated FTMH measurement on cross-sectional spectral-domain optical coherence tomography scans, as presented in this study, or on the spectral-domain optical coherence tomography volumetric data set by using an en face projection.

Piggyback Photochromic Contact Lens for Visual Rehabilitation and Photophobia Management in Traumatic Aniridia.

ABSTRACT: We report herein a case of fitting with a photochromic silicone hydrogel contact lens under a rigid gas-permeable lens (piggyback system) for photophobia and low vision correction after traumatic aniridia and aphakia. A 40-year-old woman was referred to our practice for contact lens fitting in her right eye, which was left aphakic after an open globe injury. She also presented traumatic aniridia in the right eye, and her left eye had been previously eviscerated. A successful fitting was obtained with a photochromic silicone hydrogel (senofilcon A) contact lens, with a Dk/t of 121 × 10-9, under an aspheric design, +13.00 D rigid gas-permeable lens. The patient displayed visual acuity and contrast sensitivity improvement and reported decreased photophobia.

Functional and Transcriptional Adaptations of Blood Monocytes Recruited to the Cystic Fibrosis Airway Microenvironment In Vitro.

Cystic fibrosis (CF) lung disease is dominated by the recruitment of myeloid cells (neutrophils and monocytes) from the blood which fail to clear the lung of colonizing microbes. In prior in vitro studies, we showed that blood neutrophils migrated through the well-differentiated lung epithelium into the CF airway fluid supernatant (ASN) mimic the dysfunction of CF airway neutrophils in vivo, including decreased bactericidal activity despite an increased metabolism. Here, we hypothesized that, in a similar manner to neutrophils, blood monocytes undergo significant adaptations upon recruitment to CFASN. To test this hypothesis, primary human blood monocytes were transmigrated in our in vitro model into the ASN from healthy control (HC) or CF subjects to mimic in vivo recruitment to normal or CF airways, respectively. Surface phenotype, metabolic and bacterial killing activities, and transcriptomic profile by RNA sequencing were quantified post-transmigration. Unlike neutrophils, monocytes were not metabolically activated, nor did they show broad differences in activation and scavenger receptor expression upon recruitment to the CFASN compared to HCASN. However, monocytes recruited to CFASN showed decreased bactericidal activity. RNASeq analysis showed strong effects of transmigration on monocyte RNA profile, with differences between CFASN and HCASN conditions, notably in immune signaling, including lower expression in the former of the antimicrobial factor ISG15, defensin-like chemokine CXCL11, and nitric oxide-producing enzyme NOS3. While monocytes undergo qualitatively different adaptations from those seen in neutrophils upon recruitment to the CF airway microenvironment, their bactericidal activity is also dysregulated, which could explain why they also fail to protect CF airways from infection.

Influence of the ACTN3 Genotype and the Exercise Intensity on the Respiratory Exchange Ratio and Excess Oxygen Consumption After Exercise.

ABSTRACT: de L. Corrêa, H, Ribeiro, HS, Maya, ÁTD, Neves, RP, de Moraes, MR, Lima, RM, Nóbrega, OT, and Ferreira, AP. Influence of the ACTN3 genotype and the exercise intensity on the respiratory exchange ratio and excess oxygen consumption after exercise. J Strength Cond Res 35(5): 1380-1388, 2021-This study aimed to assess the respiratory exchange ratio (RER) and excess postexercise oxygen consumption (EPOC) after high-intensity interval training and continuous moderate-intensity aerobic training in accordance with the ACTN3 genotype. A cross-sectional study with 30 physically active individuals who participated in 3 experimental sessions, as follows: a high-intensity interval aerobic exercise, for 3 minutes at 115% anaerobic threshold, with 90 seconds of passive recovery; a continuous moderate-intensity aerobic exercise at 85% anaerobic threshold; and a control session. Respiratory exchange ratio and V̇o2 were obtained through an indirect, calorimetry-based gas analysis method, using a breath-by-breath approach, assessed at baseline, during the trials, and at 1, 2, 3, and 4 hours after exercise. We found that lower postexercise RER values were observed only in subjects with the X allele, in both the high- and the moderate-intensity training protocols. Homozygous RR subjects showed no differences in postexercise RER compared with the scores at the control day. After both sessions of exercise, EPOC levels were higher compared with scores at the control day for 2 hours among X allele carriers, and only in the first hour among RR homozygous. Thus, the RER and EPOC presented different responses after moderate and intense exercise according to the ACTN3 genotype. Moreover, individuals with the X allele of the ACTN3 gene show a higher oxidation of fats in the postexercise period.

Distinct compartmentalization of immune cells and mediators characterizes bullous pemphigoid disease.

Bullous pemphigoid (BP) is an autoimmune blistering disease characterized by recruitment of leucocytes into skin and release of damaging enzymes, resulting in epidermal detachment and blister formation. To better understand the role of leukotriene B4 (LTB4) and other inflammatory factors in BP pathophysiology, we conducted microscopic and immunohistochemical analyses of preserved skin biopsy sections and conducted flow cytometry and ELISA analyses of matched blood and blister fluid from BP patients. Neutrophils predominated in BP blister fluid, which also contained monocytes/macrophages and T cells, but few to no eosinophils and B cells. In contrast, BP skin histology showed a different pattern, with abundant neutrophils but eosinophils being the predominant immune cell type. LTB4 pathway and neutrophil activation markers were prevalent in BP skin lesions and strongly associated with perivascular neutrophils. Blister fluid neutrophils, monocytes/macrophages and eosinophils all exhibited increased surface expression of leukotriene A4 hydrolase and neutrophil elastase (P = .002 for both). Blister fluid was also enriched in interleukins (IL)-1α, IL-1ß, IL-8, IL-10, IL-18, monocyte colony-stimulating factor (M-CSF) and vascular endothelial growth factor (VEGF). Our findings suggest differential leucocyte recruitment from blood into dermis and from dermis into blister, which correlates with disease activity, and presents potential new treatment opportunities for BP.

Elastase Exocytosis by Airway Neutrophils Is Associated with Early Lung Damage in Children with Cystic Fibrosis.

RATIONALE: Neutrophils are recruited to the airways of individuals with cystic fibrosis (CF). In adolescents and adults with CF, airway neutrophils actively exocytose the primary granule protease elastase (NE), whose extracellular activity correlates with lung damage. During childhood, free extracellular NE activity is measurable only in a subset of patients, and the exocytic function of airway neutrophils is unknown. OBJECTIVES: To measure NE exocytosis by airway neutrophils in relation to free extracellular NE activity and lung damage in children with CF. METHODS: We measured lung damage using chest computed tomography coupled with the Perth-Rotterdam Annotated Grid Morphometric Analysis for Cystic Fibrosis scoring system. Concomitantly, we phenotyped blood and BAL fluid leukocytes by flow and image cytometry, and measured free extracellular NE activity using spectrophotometric and Förster resonance energy transfer assays. Children with airway inflammation linked to aerodigestive disorder were enrolled as control subjects. MEASUREMENTS AND MAIN RESULTS: Children with CF but not disease control children harbored BAL fluid neutrophils with high exocytosis of primary granules, before the detection of bronchiectasis. This measure of NE exocytosis correlated with lung damage (R = 0.55; P = 0.0008), whereas the molecular measure of free extracellular NE activity did not. This discrepancy may be caused by the inhibition of extracellular NE by BAL fluid antiproteases and its binding to leukocytes. CONCLUSIONS: NE exocytosis by airway neutrophils occurs in all children with CF, and its cellular measure correlates with early lung damage. These findings implicate live airway neutrophils in early CF pathogenesis, which should instruct biomarker development and antiinflammatory therapy in children with CF.

Health care access, health care utilisation and sexual orientation disclosure among Black sexual minority men in the Deep South.

Background Black gay, bisexual, and other sexual minority men (BSMM) account for 39.1% of new HIV infections among men who have sex with men and 78.9% of newly diagnosed cases among Black men. Health care access, health care utilisation and disclosing sexuality to providers are important factors in HIV prevention and treatment. This study explored the associations among sexual orientation disclosure, health care access and health care utilisation among BSMM in the Deep South. METHODS: Secondary analysis of existing data of a population-based study in Jackson, Mississippi, and Atlanta, Georgia, was conducted among 386 BSMM. Poisson regression models were used to estimate prevalence ratios (PR) between sexual orientation disclosure to healthcare providers, health care access and health care utilisation. RESULTS: The mean (±s.d.) age of participants was 30.5 ± 11.2 years; 35.3% were previously diagnosed with HIV and 3.7% were newly diagnosed with HIV. Two-thirds (67.2%) self-identified as homosexual or gay; 70.6% reported being very open about their sexual orientation with their healthcare providers. After adjustment, BSMM who were not open about their sexual orientation had a lower prevalence of visiting a healthcare provider in the previous 12 months than those who were very open with their healthcare provider (PR 0.42; 95% confidence interval 0.18-0.97). CONCLUSION: Clinics, hospitals and other healthcare settings should promote affirming environments that support sexuality disclosure for BSMM.

One-Pot Iridium Catalyzed C-H Borylation/Sonogashira Cross-Coupling: Access to Borylated Aryl Alkynes.

Borylated aryl alkynes have been synthesized via one-pot iridium catalyzed C-H borylation (CHB)/Sonogashira cross-coupling of aryl bromides. Direct borylation of aryl alkynes encountered problems related to the reactivity of the alkyne under CHB conditions. However, tolerance of aryl bromides to CHB made possible a subsequent Sonogashira cross-coupling to access the desired borylated aryl alkynes.

Para-Selective, Iridium-Catalyzed C-H Borylations of Sulfated Phenols, Benzyl Alcohols, and Anilines Directed by Ion-Pair Electrostatic Interactions.

Para C-H borylations (CHB) of tetraalkylammonium sulfates and sulfamates have been achieved using bipyridine-ligated Ir boryl catalysts. Selectivities can be modulated by both the length of the alkyl groups in the tetraalkylammonium cations and the substituents on the bipyridine ligands. Ion pairing, where the alkyl groups of the cation shield the meta C-H bonds in the counteranions, is proposed to account for para selectivity. The 4,4'-dimethoxy-2,2'-bipyridine ligand gave superior selectivities.

Electronic and Structural Comparisons between Iron(II/III) and Ruthenium(II/III) Imide Analogs.

To examine structural and electronic differences between iron and ruthenium imido complexes, a series of compounds was prepared with different phosphine basal sets. The starting material for the ruthenium complexes was Ru(NAr/Ar*)(PMe3)3 (Ru1/Ru1*), where Ar = 2,6-(iPr)2C6H3 and Ar* = 2,4,6-(iPr)3C6H2, which were prepared from cis-RuCl2(PMe3)4 and 2 equiv of LiNHAr/Ar*. The starting materials for the iron complexes were the analogous Fe(NAr/Ar*)(PMe3)3 species (Fe1/Fe1*), which were not isolated but could be generated in situ from FeCl2, PMe3, and LiNHAr/Ar*. With both iron and ruthenium, the PMe3 starting materials underwent phosphine replacement with chelating ligands to give new group 8 imido complexes in the +2 oxidation state. Addition of 1,2-bis(diphenylphosphino)ethane (dppe) to M1/M1* gave Ru(NAr/Ar*)(PMe3)(dppe) and Fe(NAr/Ar*)(PMe3)(dppe). Addition of 1,2-bis(dimethylphosphino)ethane (dmpe) provided Ru(NAr/Ar*)(dmpe)2. A triphos ligand, {P(Me)2CH2}3SitBu (tP3), was also examined. Addition of tP3 to Fe1 provided Fe(NAr)(tP3) (Fe4), but a similar reaction with Ru1 only gave intractable materials. Oxidation of Fe4 with AgSbF6 gave {Fe(NAr)(tP3)}+SbF6- (Fe4a). Oxidation of Ru2 with AgSbF6 gave the unstable cation {Ru(NAr)(PMe3)(dppe)}+, which dimerized in the presence of acetonitrile via C-C bond formation at the aryl group C4 positions, affording {Ru(NAr)(PMe3)(NCMe)(dppe)}2+. This suggested that there was substantial radical character in the imide π system on oxidation and that an aromatic group substituted at the 4-position might provide greater stability. The cations {Fe(NAr*)(PMe3)(dppe)}+ (Fe2a*), {Ru(NAr*)(PMe3)(dppe)}+ (Ru2a*), and Fe4a were examined by EPR spectroscopy, which suggested differences in electronic structure depending on the metal and ligand set. CASPT2 calculations on model systems for Ru2a* and Fe2a* suggested that the large differences in electronic structure are related to the energy gap between the π-antibonding HOMO and the π-bonding HOMO-1. Both the geometry of the phosphines, which is slightly different between the iron and ruthenium analogs, and the metal center seem to contribute to this energetic difference.