Low-valent cobalt complexes can promote intramolecular (3 + 2) cycloadditions of alkyne-tethered cyclopropenes to provide bicyclic systems containing highly substituted cyclopentadienyl moieties with electronically diverse functional groups. The adducts can be easily transformed into new types of CpRh(III) and CpIr(III) complexes, which show catalytic activity in several relevant transformations. Preliminary computational (DFT) and experimental studies provide relevant information on the mechanistic peculiarities of the cobalt-catalyzed process and allow us to rationalize its advantages over the homologous rhodium-promoted reaction.
View Article and Find Full Text PDFCobalt(I) catalysts equipped with bisphosphine ligands can be used to promote formal (3 + 2 + 2) intramolecular cycloadditions of enynylidenecyclopropanes of type . The method provides synthetically appealing 5,7,5-fused tricyclic systems in good yields and with complete diastereo- and chemoselectivity. Interestingly, its scope differs from that of previously reported annulations based on precious metal catalysts, specifically rhodium and palladium.
View Article and Find Full Text PDFCommun Earth Environ
September 2022
European green agricultural policies have been relaxed to allow cultivation of fallow land to produce animal feed and meet shortfalls in exports from Ukraine and Russia. However, conversion of semi-natural habitats will disproportionately impact long term biodiversity and food security.
View Article and Find Full Text PDFImportance: The Delta variant is now the predominant circulating SARS-CoV-2 strain worldwide. Severity of illness in persons infected with the SARS-CoV-2 Delta variant compared with the Beta variant is not known.
Objective: To directly compare clinical outcomes in persons infected with the SARS-CoV-2 Delta variant vs those infected with the Beta variant in Qatar.
Aim And Objective: Coronally advanced flap (CAF) with connective tissue graft (CTG) has been considered the gold standard for obtaining complete root coverage. However, some limitations have been reported with the use of CTG, especially because it increases morbidity and leads to postoperative pain and bleeding. Recently, platelet-rich fibrin (PRF) has been used in periodontal plastic surgery for the treatment of gingival recessions (GRs).
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