Molecular Magnesium Hydrides Mukherjee, Debabrata; Okuda, Jun
Angewandte Chemie International Edition,
February 5, 2018, Volume:
57, Issue:
6
Journal Article
Peer reviewed
Solid magnesium hydride MgH2∞ has been pursued as a potential hydrogen‐storage material. Organic chemists were rather interested in soluble magnesium hydride reagents from mid‐20th century. It was ...only in the last two decades that molecular magnesium hydride chemistry received a major boost from organometallic chemists with a series of structurally well‐characterized examples that continues to build a whole new class of compounds. More than 40 such species have been isolated, ranging from mononuclear terminal hydrides to large hydride clusters with more than 10 magnesium atoms. They provide not only insights into the structure and bonding of Mg−H motifs, but also serve as models for hydrogen‐storage materials. Some of them are also recognized to participate in catalytic transformations, such as hydroelementation. Herein, an overview of these molecular magnesium hydrides is given, focusing on their synthesis and structural characterization.
Searching for the right size: Molecular magnesium hydrides, including larger clusters have been studied as potential hydrogen‐storage materials. An overview of structurally well‐defined molecular magnesium hydrides including larger clusters is compiled with emphasis on their synthesis, characterization, and properties.
Several comorbidities have been shown to be associated with coronavirus disease 2019 (COVID-19) related severity and mortality. However, considerable variation in the prevalence estimates of ...comorbidities and their effects on COVID-19 morbidity and mortality have been observed in prior studies. This systematic review and meta-analysis aimed to determine geographical, age, and gender related differences in the prevalence of comorbidities and associated severity and mortality rates among COVID-19 patients. We conducted a search using PubMed, Scopus, and EMBASE to include all COVID-19 studies published between January 1st, 2020 to July 24th, 2020 reporting comorbidities with severity or mortality. We included studies reporting the confirmed diagnosis of COVID-19 on human patients that also provided information on comorbidities or disease outcomes. We used DerSimonian and Laird random effects method for calculating estimates. Of 120 studies with 125,446 patients, the most prevalent comorbidity was hypertension (32%), obesity (25%), diabetes (18%), and cardiovascular disease (16%) while chronic kidney or other renal diseases (51%, 44%), cerebrovascular accident (43%, 44%), and cardiovascular disease (44%, 40%) patients had more COVID-19 severity and mortality respectively. Considerable variation in the prevalence of comorbidities and associated disease severity and mortality in different geographic regions was observed. The highest mortality was observed in studies with Latin American and European patients with any medical condition, mostly older adults (≥ 65 years), and predominantly male patients. Although the US studies observed the highest prevalence of comorbidities in COVID-19 patients, the severity of COVID-19 among each comorbid condition was highest in Asian studies whereas the mortality was highest in the European and Latin American countries. Risk stratification and effective control strategies for the COVID-19 should be done according to comorbidities, age, and gender differences specific to geographical location.
The application of solid calcium hydride CaH2 has been mostly confined to its use as a desiccant, although its catalytic activity has long been known. Since the first isolation of a well‐defined ...molecular calcium hydride in 2006, the past decade has witnessed a gradual emergence of this new family of compounds. Although the detrimental Schlenk equilibrium has kept the number of examples low, the novelty of their reactivity, especially in small‐molecule activation, holds great promise. This Minireview gives an overview of the molecular calcium hydrides reported to date, highlighting their synthesis, structure, and reactivity.
More than just a drying agent: Structurally well‐defined molecular calcium hydrides are summarized in this Minireview, with a focus on their synthesis, structure, and reactivity, including catalysis.
Triphenylborane (BPh3) was found to catalyze the reduction of tertiary amides with hydrosilanes to give amines under mild condition with high chemoselectivity in the presence of ketones, esters, and ...imines. N,N‐Dimethylacrylamide was reduced to provide the α‐silyl amide. Preliminary studies indicate that the hydrosilylation catalyzed by BPh3 may be mechanistically different from that catalyzed by the more electrophilic B(C6F5)3.
The simple borane triphenylborane (BPh3) catalyzes the chemoselective reduction of tertiary amides by hydrosilanes to give amines in the presence of halogen, ester, nitro, cyano, ketone, and imine groups. Conjugated amides are reduced to α‐silyl amides.
This clinical practice guideline for the evaluation and diagnosis of chest pain provides recommendations and algorithms for clinicians to assess and diagnose chest pain in adult patients.
A ...comprehensive literature search was conducted from November 11, 2017, to May 1, 2020, encompassing randomized and nonrandomized trials, observational studies, registries, reviews, and other evidence conducted on human subjects that were published in English from PubMed, EMBASE, the Cochrane Collaboration, Agency for Healthcare Research and Quality reports, and other relevant databases. Additional relevant studies, published through April 2021, were also considered. Structure: Chest pain is a frequent cause for emergency department visits in the United States. The "2021 AHA/ACC/ASE/CHEST/SAEM/SCCT/SCMR Guideline for the Evaluation and Diagnosis of Chest Pain" provides recommendations based on contemporary evidence on the assessment and evaluation of chest pain. This guideline presents an evidence-based approach to risk stratification and the diagnostic workup for the evaluation of chest pain. Cost-value considerations in diagnostic testing have been incorporated, and shared decision-making with patients is recommended.
A magnesium-catalyzed ester hydroboration reaction rapidly and efficiently (<0.5 mol% catalyst) provides alkoxy borane products viaester cleavage. Oxidized functional groups, such as cyano-, nitro-, ...cyclopropyl- and conjugated olefins, are unaffected by the ester reduction. Moreover, metal-catalyzed hydroboration reactions have been previously suggested to involve second-order interactions of hydroborane reagents and M-X (X = R and OR) for B-X bond formation. Catalytic kinetic studies rule out this traditional sigma -bond metathesis mechanism for B-O bond formation, and instead a pathway involving a zwitterionic alkoxyborate is proposed.
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