Hydroamination reactions by metal triflates: Bronsted acid vs. metal catalysis?

Catalytic hydroamination reactions involving the addition of carboxamides (X = CO), carbamates (X = CO2) and sulfonamides (X = SO2) to unactivated CC bonds are briefly reviewed. Development in this field of catalytic research is briefly charted, followed by a discussion of possible mechanisms, including arguments to support the operation of both metal and Brønsted acid catalysis in these systems. Future developments in the area are summarised. © The Royal Society of Chemistry 2010.39511711175Müller, T.E., Hultzsch, K.C., Yus, M., Foubelo, F., Tada, M., (2008) Chem. Rev., 108, p. 3795Constable, D.J.C., Dunn, P.J., Hayler, J.D., Humphrey, G.R., Leazer, J.L., Linderman, R.J., Lorenz, K., Zhang, T.Y., (2007) Green Chem., 9, p. 411Ranu, B.C., Banerjee, S., (2007) Tetrahedron Lett., 48, p. 141. , For example, seeKumar, R., Chaudhary, P., Nimesh, S., Chandra, R., (2006) Green Chem., 8, p. 356Dzhemilev, U., Tolstikov, G., Khusnutdinov, R., (2009) Russ. J. Org. Chem., 45, p. 957Quinet, C., Jourdain, P., Hermans, C., Atest, A., Lucas, I., Marko, I.E., (2008) Tetrahedron, 64, p. 1077. , See for exampleHorrillo-Martinez, P., Hultzsch, K.C., Gil, A., Branchadell, V., (2007) Eur. J. Org. Chem., p. 3311Crimmin, M.R., Arrowsmith, M., Barrett, A.G.M., Casely, I.J., Hill, M.S., Procopiou, P.A., (2009) J. Am. Chem. Soc., 131, p. 9670Hong, S., Marks, T.J., (2004) Acc. Chem. Res., 37, p. 673Walsh, P.J., Baranger, A.M., Bergman, R.G., (1992) J. Am. Chem. Soc., 114, p. 1708Müller, C., Koch, R., Doye, S., (2008) Chem.-Eur. J., 14, p. 10430Beller, M., Trauthwein, H., Eichberger, M., Breindl, C., Herwig, J., Müller, T.E., Thiel, O.R., (1999) Chem.-Eur. J., 5, p. 1306Rodriguez-Zubiri, M., Anguille, S., Brunet, J.J., (2007) J. Mol. Catal. A: Chem., 271, p. 145Bäckvall, J.E., Åkermark, B., Ljunggren, S.O., (1979) J. Am. Chem. Soc., 101, p. 2411Hahn, C., (2004) Chem.-Eur. J., 10, p. 5888. , See for exampleMotta, A., Fragala, I.L., Marks, T.J., (2006) Organometallics, 25, p. 5533Tobisch, S., (2008) Chem.-Eur. J., 14, p. 8590Aillaud, I., Collin, J., Hannedouche, J., Schulz, E., (2007) Dalton Trans., p. 5105Qian, H., Widenhoefer, R.A., (2005) Org. Lett., 7, p. 2635Karshtedt, D., Bell, A.T., Tilley, T.D., (2005) J. Am. Chem. Soc., 127, p. 12640Zhang, J., Yang, C., He, C., (2006) J. Am. Chem. Soc., 128, p. 1798Brouwer, C., He, C., (2006) Angew. Chem., Int. Ed., 45, p. 1744Giner, X., Najera, C., (2008) Org. Lett., 10, p. 2919Taylor, J.G., Whittall, N., Hii, K.K., (2005) Chem. Commun., p. 5103Taylor, J.G., Whittall, N., Hii, K.K., (2006) Org. Lett., 8, p. 3561Dias, H.V.R., Wu, J., (2008) Eur. J. Inorg. Chem., p. 509. , For a discussion of ethylene complexes ofCu(i), Ag(i) and Au(i), seeMcBee, J.L., Bell, A.T., Tilley, T.D., (2008) J. Am. Chem. Soc., 130, p. 16562Cheng, X.J., Xia, Y.Z., Wei, H., Xu, B., Zhang, C.G., Li, Y.H., Qian, G.M., Li, W., (2008) Eur. J. Org. Chem., p. 1929Rosenfeld, D.C., Shekhar, S., Takemiya, A., Utsunomiya, M., Hartwig, J.F., (2006) Org. Lett., 8, p. 4179Li, Z., Zhang, J., Brouwer, C., Yang, C.-G., Reich, N.W., He, C., (2006) Org. Lett., 8, p. 4175Wabnitz, T.C., Yu, J.Q., Spencer, J.B., (2004) Chem.-Eur. J., 10, p. 484Taylor, J.G., (2008), PhD Thesis, Imperial College LondonHuang, J.M., Wong, C.M., Xu, F.X., Loh, T.P., (2007) Tetrahedron Lett., 48, p. 3375Michaux, J., Terrasson, V., Marque, S., Wehbe, J., Prim, D., Campagne, J.M., (2007) Eur. J. Org. Chem., p. 2601Motokura, K., Nakagiri, N., Mori, K., Mizugaki, T., Ebitani, K., Jitsukawa, K., Kaneda, K., (2006) Org. Lett., 8, p. 4617Yang, L., Xu, L.W., Xia, C.G., (2008) Tetrahedron Lett., 49, p. 2882Kovacs, G., Ujaque, G., Lledos, A., (2008) J. Am. Chem. Soc., 130, p. 853Dorta, R., Egli, P., Zurcher, F., Togni, A., (1997) J. Am. Chem. Soc., 119, p. 10857Hartwig, J.F., (2004) Pure Appl. Chem., 76, p. 507. , These were shown to proceed via allylpalladium(ii) intermediates, see, and references thereinJohns, A.M., Sakai, N., Ridder, A., Hartwig, J.F., (2006) J. Am. Chem. Soc., 128, p. 9306Zhang, Z., Lee, S.D., Widenhoefer, R.A., (2009) J. Am. Chem. Soc., 131, p. 5372Anastas, P., Warner, J., (1998) Green Chemistry: Theory and Practice, , Oxford University Press, New Yor

Spatial, temporal and quantitative assessment of catalyst leaching in continuous flow

Catalyst leaching is a major impediment to the development of commercially-viable processes conducted in a liquid-phase. To date, there is no reliable technique that can accurately identify the extent and dynamics of the leaching process in a quantitative manner. In this work, a tandem flow-reactor system has been developed, which allowed us to distinguish between surface-catalyzed reactions from those occurring in solution by comparing%conversion at the exit of each reactor (S1, S2) corresponding to predominance of heterogeneous/homogeneous reactions (spatial) and two different residence times (temporal). A multiscale model is subsequently established to quantify the two types of reaction rate and simulate the catalyst leaching from a cross-coupling catalyst, PdEncat™ 30; including: (1) a multi-particle sizes model for catalyst scale; and (2) a dispersion model for reactor scale. The results show that catalyst leaching occurs via more than one process, and that the homogeneous Pd-catalyst (leached from the immobilized catalyst and dissolved in the flow) dominates the reaction and possesses a much higher activity than the heterogeneous (immobilized) Pd-catalyst. Additionally, the change of leached Pd stream inside reactors can be predicted along with the axial direction and the reaction time through the reactor-scale dispersion model

Restructuring of supported Pd by green solvents: an operando Quick EXAFS (QEXAFS) study and implications for the derivation of structure-function relationships in Pd catalysis

Transmission electron microscopy (TEM) is commonly used as an ex-situ technique to determine structural changes by comparing images of catalyst particles before and after a reaction. This requires the use of an alcoholic solvent to disperse the particles on a grid. In this work, we will show that Pd catalysts can be transformed during the procedure, by using EXAFS to determine the structure of Pd catalysts in different environments (as dry or wet samples). Supported palladium nanoparticles exposed to aqueous ethanolic solution (50% w/v) are transformed to a common, reduced, and hydrogen-contaminated state, irrespective of their initial habit or support. Catalysts comprised of nanosize PdO are reduced at ca. 350 K, whereas samples comprised of very small (ca. ≤ 10 atoms) Pd particles react with the solvent at just above room temperature and agglomerating with considerable loss of dispersion. As such any potential benefits to catalysis sought through the synthesis of very highly dispersed metallic Pd supported upon a range of inorganic dispersants will be rapidly erased through the action of such solvents

On-demand, in situ, generation of ammonium caroate (peroxymonosulfate) for the dihydroxylation of alkenes to vicinal diols

Using the dihydroxylation of alkenes as a benchmark, the reactivities of fresh and aged solutions of (NH4)2S2O8 (electrochemically generated) were compared to commercially-procured peroxydisulfate and Oxone®. The study revealed that peroxymonosulfate (Caro’s acid, PMS) is the active oxidant in such reactions. Using complementary redox colorimetry and in situ IR spectroscopy to monitor the oxidants, the competitive decomposition of peroxydisulfate in an acidic solution into PMS and H2O2 can be quantified for the first time. The new insight enabled the design and implementation of both batch and flow processes to maximise the concentration of active PMS oxidant. The utility of these oxidants for organic synthesis is demonstrated by the dihydroxylation of eight styrenes and seven alkyl alkenes, where the ammonium PMS solutions performed better than Oxone® (counterion effect). Last but not least, a non-chromatographic method for isolating and purifying the water-soluble diol product was developed

Effects of Cl on the reduction of supported PdO in ethanol/water solvent mixtures

The reduction of γ-Al2O3-supported PdO in flowing aqueous ethanol was investigated. Quick EXAFS (QEXAFS) performed at the Pd K-edge reveals that the presence of Cl can have a profound effect on the reduction process. At low loadings of Pd (1 wt-%), the size dependency of the process is inverted, compared to Cl-free samples. The extent of reduction was found to be dependent on loading/particles size. It is shown, using in situ QEXAFS at the Cl K- and Pd L3-edges, that residual Cl is not removed by the flowing solvent mixture, even at an elevated temperature of 350 K. The origins of these behaviours are discussed in terms of the differing effects that Cl may have when bonded to oxidic or reduced metal centres and the results were compared to earlier observations made on the effects of Cl on commercial polyurea encapsulated Pd ENCAT™ NP 30 catalysts

The evolution of the ventilatory ratio is a prognostic factor in mechanically ventilated COVID-19 ARDS patients

Background: Mortality due to COVID-19 is high, especially in patients requiring mechanical ventilation. The purpose of the study is to investigate associations between mortality and variables measured during the first three days of mechanical ventilation in patients with COVID-19 intubated at ICU admission. Methods: Multicenter, observational, cohort study includes consecutive patients with COVID-19 admitted to 44 Spanish ICUs between February 25 and July 31, 2020, who required intubation at ICU admission and mechanical ventilation for more than three days. We collected demographic and clinical data prior to admission; information about clinical evolution at days 1 and 3 of mechanical ventilation; and outcomes. Results: Of the 2,095 patients with COVID-19 admitted to the ICU, 1,118 (53.3%) were intubated at day 1 and remained under mechanical ventilation at day three. From days 1 to 3, PaO2/FiO2 increased from 115.6 [80.0-171.2] to 180.0 [135.4-227.9] mmHg and the ventilatory ratio from 1.73 [1.33-2.25] to 1.96 [1.61-2.40]. In-hospital mortality was 38.7%. A higher increase between ICU admission and day 3 in the ventilatory ratio (OR 1.04 [CI 1.01-1.07], p = 0.030) and creatinine levels (OR 1.05 [CI 1.01-1.09], p = 0.005) and a lower increase in platelet counts (OR 0.96 [CI 0.93-1.00], p = 0.037) were independently associated with a higher risk of death. No association between mortality and the PaO2/FiO2 variation was observed (OR 0.99 [CI 0.95 to 1.02], p = 0.47). Conclusions: Higher ventilatory ratio and its increase at day 3 is associated with mortality in patients with COVID-19 receiving mechanical ventilation at ICU admission. No association was found in the PaO2/FiO2 variation

Solvent–dependent nuclearity, geometry and catalytic activity of [(SPhos)Pd(Ph)Cl]2

The nuclearity and structures of the palladium complex [(SPhos)Pd(Ph]Cl]2 in the solid and solution states are revisited, using a combination of Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, NMR spectroscopy, mass spectrometry, DFT calculations and trapping experiments. The complex was tested for its catalytic activity in the coupling reaction between chlorobenzene and n-hexylamine, where different deactivation behaviour were observed in toluene, 1,4-dioxane and DMF