Solvent effects on piezochromism of transition metal complexes

We report solvent effects on the piezochromic behaviour of wavelengths of maximum absorption for metal-to-ligand charge-transfer (m.l.c.t.) bands of several molybdenum–diimine–carbonyl and titanium or vanadium–cyclopentadienyl or ethylmaltolate–thiocyanate complexes. These and previously published data are collated in an attempt to establish a pattern for solvent effects on piezochromism of m.l.c.t. bands. Strategies for the design of compounds and complexes for use in establishing a clear pattern for such effects are outlined.     

π(Arene) versus donor ligand complexation in the formation of the heterobimetallic lithium-potassium dianion of (S)-N-(α-methylbenzyl)allylamine

Reaction of the chiral amine (S)-N-(α-methylbenzyl)allylamine with n-BuLi in hexane and the subsequent addition of the thus formed lithium amide to n-BuK followed by thf results in the formation and crystallisation of the cyclic heterobimetallic tetramer, {[(S)-α-(PhC(H)Me)(CH₂CHCHK)N]Li · (thf)}₄ (1), containing the C-metallated and N-metallated dianion of the chiral amine. The structure reveals a degree of asymmetry derived from competitive binding of K⁺ cations to available thf molecules, π(arene) electrons, and deprotonated allylamine moieties. Solution studies indicate very strong agostic interactions with C-H bonds in the allylamine group and retention of the terminal vinylic anion rather than delocalisation.     

Bisthiourea: thermal and structural investigation

Bisthiourea derivatives 1,1′-(ethane-1,2-diyl)bis(3-phenylthiourea), 1,1′-(propane-1,3-diyl)bis(3-phenylthiourea), and 1,1′-(butane-1,4-diyl)bis(3-phenylthiourea) have been synthesized and characterized by IR, ¹H NMR, and ¹³C NMR. Suitable crystals of 1,1′-(propane-1,3-diyl)bis(3-phenylthiourea) were grown for single-crystal X-ray analysis and from the data it was observed that they organize into the P-1 space group. The thermal decomposition of these compounds has been studied by TG–DSC.     

Iridium(I)-salicylaldiminato-cyclooctadiene complexes used as catalysts for phenylborylation

Iridium(I) salicylaldiminato-cyclooctadiene complexes, Ir(-o-O-C₆H₄-CHN-R)(cod) (R = CH₂Ph (1), Ph (2); cod = 1,5-cyclooctadiene), have been prepared, characterized and used as catalysts for arylborylation via C-H activation. With 1 as a catalyst, isolated yields of up to 91% has been achieved for the borylation of benzene by bis(pinacolato)diboron in the presence of tetra-2-pyridinylpyrazine and an ionic liquid. The catalytic system could be recycled for at least three times without loss of activity.     

Iridium-catalyzed asymmetric hydrogenation of olefins using TIQ phosphine–oxazoline ligands

A novel family of tetrahydroisoquinoline (TIQ) phosphine–oxazoline ligands and four corresponding iridium complexes have been developed and applied to the asymmetric hydrogenation of unfunctionalized olefins. The results showed that the best conversion rates were observed in up to 99% with an enantiomeric excess of 91%.     

Study of the hydrostatic pressure dependence of the Raman spectrum of single-walled carbon nanotubes and nanospheres

We have investigated the behavior of single-walled carbon nanotubes and nanospheres (C(60)) under high hydrostatic pressure using Raman spectroscopy over the pressure range 0.2-10 GPa using a diamond anvil cell. Different liquid mixtures were used as pressure transmission fluids (PTF). Comparing the pressure dependence of the Raman peak positions for the nanotubes and the nanospheres in different PTF leads to the observation of a number of new phenomena. The observed shift in Raman peak position of both radial and tangential modes as a function of applied pressure and their dependence on the PTF chemical composition can be rationalized in terms of adsorption of molecular species from the of PTF on to the surface of the carbon nanotubes and/or nanospheres. The peak shifts are fully reversible and take place at a comparatively modest pressure (2-3 GPa) that is far below pressures that might be required to collapse the nanoparticles. Surface adsorption of molecular species on the nanotube or nanospheres provides a far more plausible rational for the observed phenomena than ideas based on the notion of tube collapse that have been put forward in the recent literature.     

Synthesis and NMR elucidation of novel pentacycloundecane‐based peptides

The synthesis and NMR elucidation of two novel pentacycloundecane (PCU)‐based peptides are reported. The PCU cage amino acids were synthesised as racemates and the incorporation of the cage amino acid with (S)‐natural amino acids produced diastereomeric peptides. The diastereomeric ‘cage’ peptides were separated using preparative HPLC and the NMR elucidation of these PCU containing peptides are reported for the first time. The ¹H and ¹³C NMR spectra showed series of overlapping signals of the cage skeleton and that of the peptide, making it extremely difficult to resolve the structure using one‐dimensional NMR techniques only. The use of two‐dimensional NMR techniques proved to be a highly effective tool in overcoming this problem. Copyright © 2010 John Wiley & Sons, Ltd.     

Parallel synthesis enablement of 2-pyridyl-5-cyano-pyrimidine-6-ones—a novel class of HIF-hydroxylase inhibitors

The synthesis of various substituted 2-pyridyl-5-cyano-pyrimidine-6-ones was accomplished via a three-step protocol. The key aspects of this parallel protocol was the preparation of amidines from nitriles under mild conditions followed by cyclization with ethyl (ethoxymethylene)cyanoacetate.