This work details the synthesis, characterization, and catalytic activity of reactive low‐coordinate organozinc complexes. The complexes activate hydrogen and they appear to be more active in hydrogenation of ketones and imines than their tridentate pincer analogs. This is thought, in part, to be due to the lack of trailing third phosphorus arm present in previous work. DFT computations reveal a sigma‐bond metathesis mechanism is comparable to an alternative aromatization/dearomatization metal‐ligand cooperative mechanism.
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Abstract Dinuclear manganese hydride complexes of the form [Mn2(CO)8(
μ ‐H)(μ ‐PR2)] (R=Ph,1 ; R=i Pr,2 ) were used inE ‐selective alkyne semi‐hydrogenation (E ‐SASH) catalysis. Catalyst speciation studies revealed rich coordination chemistry and the complexes thus formed were isolated and in turn tested as catalysts; the results underscore the importance of dinuclearity in engendering the observedE ‐selectivity and provide insights into the nature of the active catalyst. The insertion product obtained from treating2 with (cyclopropylethynyl)benzene contains acis ‐alkenyl bridging ligand with the cyclopropyl ring being intact. Treatment of this complex with H2affords exclusivelytrans ‐(2‐cyclopropylvinyl)benzene. These results, in addition to other control experiments, indicate a non‐radical mechanism forE ‐SASH, which is highly unusual for Mn−H catalysts. The catalytically active species are virtually inactive towardscis totrans alkene isomerization indicating that theE ‐selective process is intrinsic and dinuclear complexes play a critical role. A reaction mechanism is proposed accounting for the observed reactivity which is fully consistent with a kinetic analysis of the rate limiting step and is further supported by DFT computations. -
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Rationale Silicone wristbands have emerged as valuable passive samplers for monitoring of personal exposure to environmental contaminants in the rapidly developing field of
exposomics . Once deployed, silicone wristbands collect and hold a wealth of chemical information that can be interrogated using high‐resolution mass spectrometry (HRMS) to provide a broad coverage of chemical mixtures.Methods Gas chromatography coupled to Orbitrap™ mass spectrometry (GC/Orbitrap™ MS) was used to simultaneously perform suspect screening (using in‐house database) and unknown screening (using vendor databases) of extracts from wristbands worn by volunteers. The goal of this study was to optimize a workflow that allows detection of low levels of priority pollutants, with high reliability. In this regard, a data processing workflow for GC/Orbitrap™ MS was developed using a mixture of 123 environmentally relevant standards consisting of pesticides, flame retardants, organophosphate esters, and polycyclic aromatic hydrocarbons as test compounds.
Results The optimized unknown screening workflow using a search index threshold of 750 resulted in positive identification of 70 analytes in validation samples, and a reduction in the number of false positives by over 50%. An average of 26 compounds with high confidence identification, 7 level 1 compounds and 19 level 2 compounds, were observed in worn wristbands. The data were further analyzed via suspect screening and retrospective suspect screening to identify an additional 36 compounds.
Conclusions This study provides three important findings: (1) a clear evidence of the importance of sample cleanup in addressing complex sample matrices for unknown analysis, (2) a valuable workflow for the identification of unknown contaminants in silicone wristband samplers using electron ionization HRMS data, and (3) a novel application of GC/Orbitrap™ MS for the unknown analysis of organic contaminants that can be used in exposomics studies.
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