Iron nanoparticles (Fe-NP) supported on chemically-derived graphene (CDG) were prepared and identified as an effective catalyst for the hydrogenation of alkenes and alkynes. The catalyst can easily be separated by magnetic decantation.
Tailor-made ligands are essential for efficient selectivity control in homogeneous metal-complex catalysis. Since the theoretical prediction of an optimal ligand for a given reaction, substrate, and desired selectivity is impossible, combinatorial approaches have emerged to accelerate catalyst discovery.[1] However, these approaches still suffer from limited access to structurally diverse and meaningful ligand libraries. The problem is particularly acute for the important class of bidentate ligands, for which the synthesis, in many cases, involves nontrivial operations that are unsuited for automation. Even more difficult is the synthesis of nonsymmetric bidentate ligands with two different donor sites.As a solution to this problem, we recently introduced an alternative to the classical bidentate-ligand synthesis, the selfassembly of monodentate to bidentate ligands through complementary hydrogen bonding.[2-4] Thus, on the basis of a platform analogous to the A-T base pair, the aminopyridine-isoquinolone system, libraries of achiral and chiral phosphine and phosphonite ligands were evaluated (Scheme 1 a). From these studies, excellent catalysts for regioselective hydroformylation, [5] anti-Markovnikov hydration of alkynes, [6] as well as asymmetric hydrogenation [7] have emerged. In all cases, combinatorial ligand variations were achieved by changing the donor site (Do a/b in Scheme 1 a) on the aminopyridine-isoquinolone platform. It was unclear whether this approach would be restricted to the aminopyridine-isoquinolone self-assembly system, or whether, indeed, a variation of the A-T base-pair analogous platform would also be possible (Scheme 1 b). It was reasonable to expect that any change of the platform geometry or the hydrogen-bonding system would have an immediate impact on the ligand bite angle (q) and the coordination geometry at the metal center, and thus, an important influence on the catalyst performance.[8]Herein, we report on the development of the first library of self-assembled ligands based on new heterocyclic platforms analogous to the A-T base pair. From a first evaluation of this new library of self-assembled phosphine ligands, an extremely regioselective hydroformylation catalyst emerged, in which the ligands behavior was bidentate, even in protic solvents such as methanol.As A-analogous donor-acceptor ligands (L DA in Scheme 1 b), the heterocycle-functionalized phosphines 1-5 were chosen. As T-analogous acceptor-donor ligands (L AD in Scheme 1 b), we selected the known isoquinolone 6 and the new 7-azaindole 7. The preparation of the ligands is described in the Supporting Information.The coordination properties of all 10 possible ligand combinations were studied through the NMR spectroscopic investigation of the corresponding platinum complexes [Cl 2 Pt(L DA )(L AD )] (Table 1). 31 P NMR spectroscopy showed, in all cases, the selective formation of a defined complex with a heterodimeric ligand. In the 31 P NMR spectra, an AB spin system with a 2 J(P,P) coupling constant of 14.8-17.2 Hz was det...
Tailor-made ligands are essential for efficient selectivity control in homogeneous metal-complex catalysis. Since the theoretical prediction of an optimal ligand for a given reaction, substrate, and desired selectivity is impossible, combinatorial approaches have emerged to accelerate catalyst discovery.[1] However, these approaches still suffer from limited access to structurally diverse and meaningful ligand libraries. The problem is particularly acute for the important class of bidentate ligands, for which the synthesis, in many cases, involves nontrivial operations that are unsuited for automation. Even more difficult is the synthesis of nonsymmetric bidentate ligands with two different donor sites.As a solution to this problem, we recently introduced an alternative to the classical bidentate-ligand synthesis, the selfassembly of monodentate to bidentate ligands through complementary hydrogen bonding.[2-4] Thus, on the basis of a platform analogous to the A-T base pair, the aminopyridine-isoquinolone system, libraries of achiral and chiral phosphine and phosphonite ligands were evaluated (Scheme 1 a). From these studies, excellent catalysts for regioselective hydroformylation, [5] anti-Markovnikov hydration of alkynes, [6] as well as asymmetric hydrogenation [7] have emerged. In all cases, combinatorial ligand variations were achieved by changing the donor site (Do a/b in Scheme 1 a) on the aminopyridine-isoquinolone platform. It was unclear whether this approach would be restricted to the aminopyridine-isoquinolone self-assembly system, or whether, indeed, a variation of the A-T base-pair analogous platform would also be possible (Scheme 1 b). It was reasonable to expect that any change of the platform geometry or the hydrogen-bonding system would have an immediate impact on the ligand bite angle (q) and the coordination geometry at the metal center, and thus, an important influence on the catalyst performance.[8]Herein, we report on the development of the first library of self-assembled ligands based on new heterocyclic platforms analogous to the A-T base pair. From a first evaluation of this new library of self-assembled phosphine ligands, an extremely regioselective hydroformylation catalyst emerged, in which the ligands behavior was bidentate, even in protic solvents such as methanol.As A-analogous donor-acceptor ligands (L DA in Scheme 1 b), the heterocycle-functionalized phosphines 1-5 were chosen. As T-analogous acceptor-donor ligands (L AD in Scheme 1 b), we selected the known isoquinolone 6 and the new 7-azaindole 7. The preparation of the ligands is described in the Supporting Information.The coordination properties of all 10 possible ligand combinations were studied through the NMR spectroscopic investigation of the corresponding platinum complexes [Cl 2 Pt(L DA )(L AD )] (Table 1). 31 P NMR spectroscopy showed, in all cases, the selective formation of a defined complex with a heterodimeric ligand. In the 31 P NMR spectra, an AB spin system with a 2 J(P,P) coupling constant of 14.8-17.2 Hz was det...
Infolge des extremen Hochwasserereignisses an der Elbe im August 2002 kam es zu Beschädigungen und zur Überlastung der Hochwasserentlastungsanlage der Talsperre (TS) Malter sowie im Unterlauf zu massiven Überschwemmungen der Roten Weißeritz. Nach diesem katastrophalen Hochwasser wurden die Bemessungsabflüsse für die TS Malter überprüft und mussten deutlich erhöht werden. Die Leistungsfähigkeit der Hochwasserentlastungsanlage war für diese neuen Bemessungsabflüsse nicht mehr ausreichend. Die Landestalsperrenverwaltung des Freistaats Sachsen (LTV) hat dementsprechend die Erweiterung der Hochwasserentlastungsanlage geplant. Um die Überflutungssicherheit nach DIN 19700‐10 wiederherzustellen, wurde, auch aufgrund der Auflage des Denkmalschutzes, die alte Schussrinne zu erhalten, ein Konzept entwickelt, welches auch den Bau einer neuen, zweiten Schussrinne mit zusätzlichem neuem Tosbecken beinhaltet [1]. Die beiden Schussrinnen sollen über ein neuartiges Teilungsbauwerk mit einer vertikalen Strömungstrennung beaufschlagt werden. Um die Leistungsfähigkeit zu gewährleisten, wurde der Vorentwurf am Forschungsinstitut Wasser und Umwelt der Universität Siegen in einem physikalischen Modellversuch im Maßstab 1:25 überprüft und optimiert. Mit dem Modellversuch konnte u. a. die Geometrie des vertikalen Teilungsbauwerks so optimiert werden, dass mit der Umsetzung der Erweiterung der Hochwasserentlastungsanlage die Überflutungssicherheit der TS Malter wiederhergestellt werden kann. Development of a novel vertical diversion structure for spillways – Water engineering model tests for the Malter Dam Due to the extreme flood event on the Elbe river in August 2002, there was damage and overloading of the spillway of the Malter Dam and massive flooding of the Rote Weißeritz. After this catastrophic Elbe flood event, the design discharges for the Malter Dam were significantly increased. The performance of the spillway was not sufficient for the new design discharges. The State Reservoir Administration of Saxony (LTV) has planned accordingly expanding the spillway. To restore the flood safety after DIN 19700‐10, a concept was developed, which also includes the construction of a new, second spillway chute with additional new stilling basin, also due to the restrictions of the Monument protection to obtain the old spillway chute [1]. Both spillways are to be applied by a new division structure with a vertical flow separation. To ensure the performance the preliminary draft of the expansion of the spillway was reviewed and optimized in a physical model test in 1:25 scale at the Research Institute Water and Environment of the University of Siegen. With the hydraulic model test could the geometry of the vertical diversion structure be optimized so that with the implementation of the expansion of the spillway the flooding safety of Malter Dam can be restored.
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