Copper(II) coordination to ligands immobilized on photoluminescent porous silicon

Increased preorganization can be achieved by immobilizing ligands on solid supports. Photoluminescent porous silicon, which can undergo facile hydrosilylation, was used as a support for open chain neutral N- and O-donor ligands. The abilities of these ligands to bind the divalent metal ions Ni(2+), Cu(2+), Zn(2+), and Pb(2+) are examined. Immobilized ligands selectively complexed Cu(II) over the other metal ions studied. Ligands immobilized on photoluminescent porous silicon also removed a significant amount, up to 98%, of Cu(II) from copper(II)-spiked, organic-rich, seawater samples.     

The determination of anionic detergents with the bis (ethylenediamine)copper(II) ion

A method is described for the determination of anionic detergents. The detergent anions are extracted into chloroform as an ion-association compound with the bis(ethylenediamine)copper(II) cation. Determinations are completed by colorimetry or atomic absorption spectrometry. With a 150-ml water sample, the limit or detection is 0.03 μg ml^-1 (as LAS) for colorimetry or 0.06 μg ml^-1 for a.a.s. The method requires only one phase separation step and is highly selective. It is directly applicable to brine and sea-water samples.     

Palladium-Catalyzed Coupling of L-Proline Acid Chloride with Vinylstannanes

Vinylstannanes were found to undergo a palladium-catalyzed coupling with L-N-protected proline acid chloride to produce the corresponding N-protected α'-amino-α,β-unsaturated ketones in moderate to good yield.     

Proto‐Urea‐RNA (Wöhler RNA) Containing Unusually Stable Urea Nucleosides

The RNA world hypothesis assumes that life on Earth began with nucleotides that formed information‐carrying RNA oligomers able to self‐replicate. Prebiotic reactions leading to the contemporary nucleosides are now known, but their execution often requires specific starting materials and lengthy reaction sequences. It was therefore proposed that the RNA world was likely proceeded by a proto‐RNA world constructed from molecules that were likely present on the early Earth in greater abundance. Herein, we show that the prebiotic starting molecules bis‐urea (biuret) and tris‐urea (triuret) are able to directly react with ribose. The urea‐ribosides are remarkably stable because they are held together by a network of intramolecular, bifurcated hydrogen bonds. This even allowed the synthesis of phosphoramidite building blocks and incorporation of the units into RNA. Investigations of the nucleotides’ base‐pairing potential showed that triuret:G RNA base pairs closely resemble U:G wobble base pairs. Based on the probable abundance of urea on the early Earth, we postulate that urea‐containing RNA bases are good candidates for a proto‐RNA world.     

Palladium-Catalysed Couplings of Halofurans with Activated Alkenes and Terminal Alkynes. A Short Synthesis of Dihydrowyerone

The palladium-catalysed coupling of bromofurans with activated alkenes and of furanoyl chlorides with either terminal alkynes or alkynyl stannanes gave good yields of the corresponding vinyl furans and alkynyl ketones. These studies culminated in a short synthesis of the antifungal agent dihydrowyerone.     

Reactivity Studies of Iridium Pyridylidenes [TpMe2Ir(C6H5)2(C(CH)3C(R)NH] (R=H,Me, Ph)

The reactivity of a series of iridium? pyridylidene complexes with the formula [Tp^Me2Ir(C₆H₅)₂(C(CH)₃C(R)N H] ( 1 a – 1 c ) towards a variety of substrates, from small molecules, such as H₂, O₂, carbon oxides, and formaldehyde, to alkenes and alkynes, is described. Most of the observed reactivity is best explained by invoking 16 e^? unsaturated [Tp^Me2Ir(phenyl)(pyridyl)] intermediates, which behave as internal frustrated Lewis pairs (FLPs). H₂ is heterolytically split to give hydride? pyridylidene complexes, whilst CO, CO₂, and H₂C?O provide carbonyl, carbonate, and alkoxide species, respectively. Ethylene and propene form five‐membered metallacycles with an IrCH₂CH(R)N (R=H, Me) motif, whereas, in contrast, acetylene affords four‐membered iridacycles with the IrC(?CH₂)N moiety. C₆H₅(C?O)H and C₆H₅C?CH react with formation of Ir? C₆H₅ and Ir? C?CPh bonds and the concomitant elimination of a molecule of pyridine and benzene, respectively. Finally the reactivity of compounds 1 a – 1 c against O₂ is described. Density functional theory calculations that provide theoretical support for these experimental observations are also reported.