De problematiek van de kasgrondteelten: Mogelijke oplossingen aangedragen door ondernemers met substraatbedden in het bijzonder

De kasgrond glastuinbouw ziet zich geconfronteerd met stijgende kosten en een afname van de hoeveelheid toegelaten gewasbeschermingsmiddelen. Het middelenpakket tegen schadelijke bodemschimmels en aaltjes wordt mogelijk verkleind (Spruit e.a. 2008). Op dit moment is grondstomen nog een optie, maar door de sterk toenemende energie- en arbeidskosten wordt grondstomen steeds duurder. In voorgaande gesprekken met ondernemers en betrokkenen blijkt dat een teeltsysteem dat relatief goedkoop, en gemakkelijk in de praktijk is in te passen, de voorkeur heeft. Doelstelling van dit project is daarom het in kaart brengen van problemen met mogelijke oplossingen ten aanzien van bodemproblematiek in kasgrondteelten

Ru-Zn heteropolynuclear complexes containing a dinucleating bridging ligand: Synthesis, structure, and isomerism

10.1021/ic5017559Mononuclear complexes in- and out-[Ru(Cl)(trpy)(Hbpp)]+ (in-0, out-0; Hbpp is 2,2'-(1H-pyrazole-3,5-diyl)dipyridine and trpy is 2,2':6',2?-terpyridine) are used as starting materials for preparation of Ru¿Zn heterodinuclear out-{[Ru(Cl)(trpy)][ZnCl2](µ-bpp)} (out-2) and heterotrinuclear in,in- and out,out-{[Ru(Cl)(trpy)]2(µ-[Zn(bpp)2])}2+ (in-3, out-3) constitutional isomers. Further substitution of the Cl ligand from the former complexes leads to Ru¿aqua out,out-{[Ru(trpy)(H2O)]2(µ-[Zn(bpp)2])}4+ (out-4) and the oxo-bridged Ru¿O¿Ru complex in,in-{[RuIII(trpy)]2(µ-[Zn(bpp)2(H2O)]µ-(O)}4+ (in-5). All complexes are thoroughly characterized by the usual analytical techniques as well as by spectroscopy by means of UV¿vis, MS, and when diamagnetic NMR. CV and DPV are used to extract electrochemical information and monocrystal X-ray diffraction to characterize complexes out-2, in-3, out-3, and in-5 in the solid state. Complex out-3 photochemically isomerizes toward in-3, as can be observed by NMR spectroscopy and rationalized by density functional theory based calculations

Experimental and theoretical investigations of new dinuclear palladium complexes as precatalysts for the amination of aryl chlorides

A series of new palladium dinuclear species with general formula [Pd2X(mu-X)[mu-P(t)Bu2(Bph-R)]] (X = Cl, Br; Bph = biphenyl; R = H, Me, NMe2) have been prepared. The two palladium centers in these species are bridged by one of the aromatic rings of the biphenyl group present in the corresponding phosphine. The X-ray crystal structure of one of these complexes has been obtained, providing a clear picture of the bonding pattern. The stability of these dimers in solution is shown to be highly dependent on the nature of the phosphine R group and also on the bridging halide. When R = NMe2, the dimers dissociate, yielding the palladium(II) compounds PdX2[P(t)Bu2(BPh-NMe2)] (X = Cl, Br), and the X-ray crystal structure of one of them (X = Br) has shown that the biphenyl group from the phosphine interacts directly with the metal center. This interaction seems to play an important role in stabilizing the otherwise coordinatively unsaturated palladium(II) complex. In contrast, when R = H or Me, the analogous monomeric palladium(II) complexes are unstable and undergo cyclometalation to generate a palladium(II) dinuclear species in which each of the two phosphines cyclometalates with the palladium centers forming a strained four-membered ring. In addition to their unusual structures, these aryl-bridged dimers have also proven to be excellent precatalysts for the amination of aryl chlorides. To rationalize some of the experimental results, a detailed DFT computational study has been carried out and is presented herein

Small Bite-Angle P–OP Ligands for Asymmetric Hydroformylation and Hydrogenation

A series of small bite-angle phosphine-phosphite (P–OP) ligands have been synthesized by a two-step method. The key intermediate was prepared by an unprecedented asymmetric carbonyl reduction of a phosphamide using the CBS (Corey–Bakshi–Shibata) catalyst. The topology of these ligands (a configurationally stable stereogenic carbon with two heteroatom substituents) and their small bite-angle (created by the close proximity of the two ligating groups to the metal center) together provide a rigid asymmetric environment around this center, enabling high stereoselectivity in hydroformylations and hydrogenations of standard substrates

Small Bite-Angle P–OP Ligands for Asymmetric Hydroformylation and Hydrogenation

A series of small bite-angle phosphine-phosphite (P–OP) ligands have been synthesized by a two-step method. The key intermediate was prepared by an unprecedented asymmetric carbonyl reduction of a phosphamide using the CBS (Corey–Bakshi–Shibata) catalyst. The topology of these ligands (a configurationally stable stereogenic carbon with two heteroatom substituents) and their small bite-angle (created by the close proximity of the two ligating groups to the metal center) together provide a rigid asymmetric environment around this center, enabling high stereoselectivity in hydroformylations and hydrogenations of standard substrates

1,1-P–OP Ligands with P‑Stereogenic Phosphino Groups in Asymmetric Hydrogenations and Hydroformylations

A new series of narrow-bite-angle phosphine–phosphite (1,1-P–OP) ligands (<b>3a</b>–<b>d</b>) has been efficiently prepared from the enantiopure (<i>S</i>_P)-<i>tert</i>-butyl­(hydroxymethyl)­methylphosphino borane complex <b>1</b>, a crucial intermediate. The catalytic performance of the ligands in Rh-mediated asymmetric hydrogenations and hydroformylations is described. The corresponding rhodium complexes provided excellent efficiencies (full conversion in all cases) and high enantioselectivities (up to 98% ee) for the asymmetric hydrogenation of structurally diverse functionalized alkenes. Furthermore, rhodium catalysts derived from these 1,1-P–OP ligands were highly active and gave excellent regioselectivities (branched/linear product ratios of up to 97/3) and moderate enantioselectivities in the hydroformylation of different terminal olefins

Efficient self-sorting of a racemic tetra-urea calix4pyrrole into a single heterodimeric capsule

A racemic calix4pyrrole self-sorts into a single achiral heterodimeric capsule. This process is induced either by encapsulation of one ditopic or two monotopic N-oxide guests. The influence of the guest structure in the dynamics of the disproportionation process of the two homochiral capsules is reported. The unidirectional sense of rotation of the urea groups assigned to the heterodimeric capsule is explained as the outcome of an induction of chirality from the stereogenic centers. © 2010 American Chemical Society