RESUMEN
The direct double dehydrogenation from primary amines to nitriles without an oxidant or hydrogen acceptor is both intriguing and challenging. In this paper, we describe a non-noble metal catalyst capable of realizing such a transformation with high efficiency. A cobalt-centered N,N-bidentate complex was designed and employed as a metal-ligand cooperative dehydrogenation catalyst. Detailed kinetic studies, control experiments, and DFT calculations revealed the crucial hydride transfer, proton transfer, and hydrogen evolution processes. Finally, a tandem outer-sphere/inner-sphere mechanism was proposed for the dehydrogenation of amines to nitriles through an imine intermediate.
RESUMEN
Density functional theory calculations have been utilized to investigate the synergistic effect of palladium(0) and copper(I) catalyzed selective formation of allylated indole from (2-alkynyl)-phenylisocyanate and allyl methyl carbonate. The main competing reaction yielding the N-allyl carbamate was also considered. Calculated results indicate that using the Pd(0)-complex alone, the generation of indole is kinetically much less favored than producing the N-allyl carbamate compound. However, the co-addition of Cu(I) catalyst can considerably decrease the barrier for the intramolecular cyclization step, leading to the formation of the indole product. Analysis of the cyclization process suggests that Cu(I) complex can act as a Lewis acid to activate the linear alkyne group via a π-coordination manner prior to the formation of a 5-membered ring transition state toward indole formation. Altogether, the mechanistic insights revealed in the present study aim at a better understanding of the mechanism and the factors governing the selectivity in synergistic Pd/Cu catalysis.
RESUMEN
AIMS: To evaluate the application effect of individualized pressure setting strategy of pneumatic tourniquet in orthopaedic surgery. BACKGROUND: Some individualized setting pressures of pneumatic tourniquet are lower than the standard pressure recommended in the textbook (Nursing of Operating Room, People's Military Publishing House, 2008). DESIGN: Meta-analysis. DATA SOURCES: CL, WOS, PubMed, CNKI, CBM, VIP and Wan-fang DATA. REVIEW METHODS: We searched studies on the application effect of individualized pressure of pneumatic tourniquet from the establishment date of the databases to September 2017. Study quality was assessed using the quality evaluation method recommended in the Cochrane Handbook 5.1.0 (Higgins, 2011). The primary outcome was inflation pressure. RESULTS: We identified nine studies including 1,200 patients. The individualized pressure setting strategy can provide a lower inflation pressure (four studies), improve haemostatic effect (six studies) and reduce the incidence of related complications (eight studies). CONCLUSIONS: An individualized inflation pressure is recommended when using the tourniquet in orthopaedic surgery. And the setting pressure might be a minimum and efficiency one, by accessing the the systolic blood pressure and limb circumferences of the patient. IMPACT: This study addressed that the individualized pressure setting strategy of pneumatic tourniquet can provide a lower inflation pressure and a higher application value in orthopaedic limb surgery. However, greater attention should be focused on how to unify the individualized pressure setting strategy. Meanwhile, the instructions for use from manufacturers need to be updated. Therefore, it is recommended to conduct a large-sample multi-centre high-quality randomized controlled trial in strict accordance with the CONSORT standard.
