Synthesis, structure and spectroscopic investigations of luminescent heterobimetallic gold(I)-Rhodium(I) species

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2005.Some images on CDROM are in colour.Includes bibliographical references (leaves 33-34, first group).A novel, three-coordinate gold(I) dimer, Au2(tfepm)3Cl2 (la, lb), was synthesized and structurally characterized. Four gold(I)-rhodium(I) heterobimetallic complexes, AuIRh'(tBuNC)2(-dppm)2C12 (2), Au'Rh'(tBuNC)2(u-dmpm)2Cl2 (3), Au'Rh'(tBuNC)2(,u-tfepm)2C12 (4), and AuIRh(tBuNC)2(u-tfepma)2Cl2 (5) were synthesized and 2, 3, and 5 were crystallographically characterized. Absorption spectra at room temperature, excitation spectra, emission spectra, and phosphorescence lifetimes of glass-solution and solid state samples at 77 K are reported for 2-5 and interpreted in context of crystallographic structure, electronic structure, and time-dependent density functional theory (TD-DFT) calculations. 2-5 are intensely luminescent at 77 K, with 4 and 5 exhibiting "dual emission."by Jillian Lee Dempsey.S.B

When Electrochemistry Met Methane: Rapid Catalyst Oxidation Fuels Hydrocarbon Functionalization

An electrochemical strategy for rapid generation of the highly reactive species necessary for C−H bond functionalization may enable improved technology for methane conversion

Hydrogen Evolution Catalyzed by Cobaloximes

Cobaloximes are among a promising class of small molecules which catalytically evolve hydrogen at modest overpotentials. Motivated by the imminent need to develop efficient solar energy conversion processes, a number of research groups have recently revisited the catalytic activity of cobaloximes, which was initially reported by Espenson almost three decades ago. Both Espenson’s seminal work and the studies reported during this recent resurgence are chronicled in the introductory Chapter 1. The next three chapters introduce photochemical methods for detecting catalytic intermediates and determining kinetics associated with the elementary steps of hydrogen evolution. Four catalytic pathways are considered; each beginning with the reduction of a CoII-diglyoxime to generate CoI, which reacts with a proton donor to produce a CoIII-hydride. In a homolytic pathway, two CoIII-hydrides react in a bimolecular step to eliminate H₂. Alternatively, in a heterolytic pathway, protonation of CoIII-hydride produces H₂ and CoIII. The CoIII-hydride may also be reduced further to a CoII-hydride, which can react via analogous heterolytic or homolytic pathways. In Chapter 2, kinetics of electron transfer reactions of a Co-diglyoxime complex are presented. These experimental results, along with a detailed thermodynamic analysis of proposed hydrogen evolution pathways, shed new light on the barriers and driving forces of the elementary reaction steps involved in proton reduction. A strong thermodynamic preference for a CoIII-hydride homolytic pathway over a CoIII-hydride heterolytic route is identified as the key finding from this work. In Chapter 3, phototriggered hydride generation utilized in conjunction with time-resolved spectroscopy is introduced as a novel method for mechanistic investigations. Here, excited-state proton transfer from an organic photoacid to a CoI-diglyoxime triggers the formation of the reactive CoIII-hydride. This and the subsequent reactivity of CoIII-hydride are monitored spectroscopically. The reaction kinetics are consistent with a heterolytic route for hydrogen evolution that proceeds via a CoII-hydride intermediate. Chapter 4 extends these mechanistic investigations to aqueous media by employing photoionization and pulse radiolysis methods to trigger CoII-diglyoxime reduction. Chapters 5 and 6 focus on the design and construction of second generation cobaloximes. In Chapter 5, the thermodynamic preference for bimolecular reactivity of two CoIII-hydrides is probed with a binuclear cobaloxime. A covalent alkyl tether is used to decrease the volume required for diffusional collisions. Electrocatalytic activity is consistent with a rate-limiting step associated with the formation of the hydride, as seen in mononuclear catalysts, and thus no enhancement of catalytic activity is observed. However, as an efficient water splitting device may require the tethering of catalysts to an electrode surface, this ligand should allow binuclear association of immobilized catalysts. A strategy for covalently grafting cobaloxime derivatives to silicon electrodes is introduced in Chapter 6. A terminal olefin is incorporated into a glyoxime backbone, a functionality amenable to surface-based coupling reactions. The bifunctional cobaloxime is an active catalyst, and initial efforts to prepare the chemically modified electrode are discussed. Three appendices are provided, including work on the photochemical generation of powerful OsII reductant, electron transfer reactions of N,N’,3,3’-tetramethyl-4,4’-bipyridinium, and annotated MATLAB scripts utilized for kinetics analysis.</p

When Electrochemistry Met Methane: Rapid Catalyst Oxidation Fuels Hydrocarbon Functionalization

An electrochemical strategy for rapid generation of the highly reactive species necessary for C−H bond functionalization may enable improved technology for methane conversion

Electrochemical and spectroscopic methods for evaluating molecular electrocatalysts

© 2017 Macmillan Publishers Limited. Modern energy challenges have amplified interest in transition metal-based molecular electrocatalysts for fuel-forming reactions. The activity of these homogeneous electrocatalysts, and the mechanisms by which they operate, can be uncovered using state-of-the-art electrochemical methods. Catalyst performance can be benchmarked according to metrics obtainable from cyclic voltammograms by analysis of catalytic plateau currents and peak potentials, as well as by foot-of-the-wave analysis. The application of complementary spectroscopic techniques, including spectroelectrochemistry, stopped-flow rapid mixing and transient absorption, are also discussed. In this Review, we present case studies highlighting the utility of these analytical methods in the context of renewable energy. Alongside these examples is a discussion of the theoretical underpinnings of each method, outlining the conditions necessary for the analysis to be rigorous and the type of information that can then be extracted

Identification of an Electrode-Adsorbed Intermediate in the Catalytic Hydrogen Evolution Mechanism of a Cobalt Dithiolene Complex

Analysis of a cobalt bis­(dithiolate) complex reported to mediate hydrogen evolution under electrocatalytic conditions in acetonitrile revealed that the cobalt complex transforms into an electrode-adsorbed film upon addition of acid prior to application of a potential. Subsequent application of a reducing potential to the film results in desorption of the film and regeneration of the molecular cobalt complex in solution, suggesting that the adsorbed species is an intermediate in catalytic H₂ evolution. The electroanalytical techniques used to examine the pathway by which H₂ is generated, as well as the methods used to probe the electrode-adsorbed species, are discussed. Tentative mechanisms for catalytic H₂ evolution via an electrode-adsorbed intermediate are proposed

Efficacy of interferon beta-1a plus remdesivir compared with remdesivir alone in hospitalised adults with COVID-19: a double-bind, randomised, placebo-controlled, phase 3 trial

Functional impairment of interferon, a natural antiviral component of the immune system, is associated with the pathogenesis and severity of COVID-19. We aimed to compare the efficacy of interferon beta-1a in combination with remdesivir compared with remdesivir alone in hospitalised patients with COVID-19. We did a double-blind, randomised, placebo-controlled trial at 63 hospitals across five countries (Japan, Mexico, Singapore, South Korea, and the USA). Eligible patients were hospitalised adults (aged ≥18 years) with SARS-CoV-2 infection, as confirmed by a positive RT-PCR test, and who met one of the following criteria suggestive of lower respiratory tract infection: the presence of radiographic infiltrates on imaging, a peripheral oxygen saturation on room air of 94% or less, or requiring supplemental oxygen. Patients were excluded if they had either an alanine aminotransferase or an aspartate aminotransferase concentration more than five times the upper limit of normal; had impaired renal function; were allergic to the study product; were pregnant or breast feeding; were already on mechanical ventilation; or were anticipating discharge from the hospital or transfer to another hospital within 72 h of enrolment. Patients were randomly assigned (1:1) to receive intravenous remdesivir as a 200 mg loading dose on day 1 followed by a 100 mg maintenance dose administered daily for up to 9 days and up to four doses of either 44 μg interferon beta-1a (interferon beta-1a group plus remdesivir group) or placebo (placebo plus remdesivir group) administered subcutaneously every other day. Randomisation was stratified by study site and disease severity at enrolment. Patients, investigators, and site staff were masked to interferon beta-1a and placebo treatment; remdesivir treatment was given to all patients without masking. The primary outcome was time to recovery, defined as the first day that a patient attained a category 1, 2, or 3 score on the eight-category ordinal scale within 28 days, assessed in the modified intention-to-treat population, defined as all randomised patients who were classified according to actual clinical severity. Safety was assessed in the as-treated population, defined as all patients who received at least one dose of the assigned treatment. This trial is registered with ClinicalTrials.gov, NCT04492475. Between Aug 5, 2020, and Nov 11, 2020, 969 patients were enrolled and randomly assigned to the interferon beta-1a plus remdesivir group (n=487) or to the placebo plus remdesivir group (n=482). The mean duration of symptoms before enrolment was 8·7 days (SD 4·4) in the interferon beta-1a plus remdesivir group and 8·5 days (SD 4·3) days in the placebo plus remdesivir group. Patients in both groups had a time to recovery of 5 days (95% CI not estimable) (rate ratio of interferon beta-1a plus remdesivir group vs placebo plus remdesivir 0·99 [95% CI 0·87–1·13]; p=0·88). The Kaplan-Meier estimate of mortality at 28 days was 5% (95% CI 3–7%) in the interferon beta-1a plus remdesivir group and 3% (2–6%) in the placebo plus remdesivir group (hazard ratio 1·33 [95% CI 0·69–2·55]; p=0·39). Patients who did not require high-flow oxygen at baseline were more likely to have at least one related adverse event in the interferon beta-1a plus remdesivir group (33 [7%] of 442 patients) than in the placebo plus remdesivir group (15 [3%] of 435). In patients who required high-flow oxygen at baseline, 24 (69%) of 35 had an adverse event and 21 (60%) had a serious adverse event in the interferon beta-1a plus remdesivir group compared with 13 (39%) of 33 who had an adverse event and eight (24%) who had a serious adverse event in the placebo plus remdesivir group. Interferon beta-1a plus remdesivir was not superior to remdesivir alone in hospitalised patients with COVID-19 pneumonia. Patients who required high-flow oxygen at baseline had worse outcomes after treatment with interferon beta-1a compared with those given placebo. The National Institute of Allergy and Infectious Diseases (USA)