Novel asymmetric michael addition of alpha-cyanopropionates to acrolein by the use of a bis(oxazolinyl)phenylstannane-derived rhodium(III) complex as a chiral Lewis acid catalyst

The rhodium complex prepared in situ by simply mixing [[RhCl(c-octene)2]2] and [(Phebox)SnMe3] (1) (Phebox = 2,6-bis(oxazolinyl)phenyl) was found to serve as an efficient catalyst for the asymmetric Michael addition of alpha-cyanopropionates (4) to acrolein under mild and neutral conditions. In the present catalytic system, both the temperature of catalyst preparation and the order of the addition of the substrates were very important for the catalytic efficiency and enantioselectivity. Detailed mechanistic studies of this catalytic system revealed that the [(Phebox)RhIII(SnMe3)Cl] complex (9), generated by oxidative addition of [[RhCl(c-octene)2]2] to 1, is an active catalyst and the turnover number (TON) of the present actual catalyst existing in a reaction mixture is greater than 10,000. The obtained (R) stereochemistry of the Michael adducts 5 can be explained by N-bonded enol intermediates C', which are formed by enolization of 4 bound to the Lewis acidic rhodium complex 9. We also found that the active catalyst 9 gradually decomposed in the presence of the remaining [[RhCl(c-octene)2]2] in the reaction mixture to form the catalytically nonactive [(Phebox)RhCl2] fragment A, whose structure was characterized by an X-ray crystallographic study after converting to the tBuNC complex 10.     

Switching of hydrogen bonds of water in ionic liquid, 1‐butyl‐3‐methylimidazolium tetrafluoroborate

We have investigated temperature‐induced Raman spectral changes of deuterated water in an ionic liquid, 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([bmim][BF₄]), between room temperature and 77 K. The comparison of the OH and OD stretching vibrational spectra at 77 K shows that the strength of the hydrogen bonds in [bmim][BF₄]–water mixtures strongly depends on the type of water, i.e. H₂O and D₂O. In the [bmim][BF₄]–D₂O system, remarkably strong hydrogen bonds form at low temperatures, but they switch to nearly free hydrogen bonds on heating. Copyright © 2013 John Wiley & Sons, Ltd.     

In situ Raman and optical microscopy of the relaxation behavior of amorphous ices under pressure

The transformation of low‐density amorphous (LDA) ice produced from high‐density amorphous (HDA) ice was studied up to 400 MPa as a function of temperature by in situ Raman spectroscopy and optical microscopy. Changes in these amorphous states of H₂O were directly tracked without using emulsions to just above the crystallization temperature T_x. The spectra show significant changes occurring above ∼125 K. The results are compared with data reported for the relaxation behavior of HDA, to form what we call relaxed HDA, or rHDA. We find a close connection with expanded HDA (eHDA), which is reported to exist as another metastable form in this P–T region. The observation of this temperature‐induced LDA transition under pressure complements the previously observed pressure‐induced reversible transition between LDA and HDA at 120–140 K. Copyright © 2009 John Wiley & Sons, Ltd.     

Self-modeling curve resolution analysis of on-line vibrational spectra of polymerisation and transesterification

This article discusses the potential of self-modeling curve resolution analysis (SMCR) for the evolution of on-line vibrational spectral data of polymerisation and transesterification. After the general introduction of the SMCR approach, representative SMCR techniques like orthogonal projection analysis (OPA) and simple-to-use interactive self-modeling mixture analysis (SIMPLISMA) are briefly outlined. As examples the SMCR analysis of the Raman spectra of the block copolymerisation of styrene and 1,3-butadiene and that of the near-infrared (NIR) spectra of the melt-extrusion transesterification of ethylene-vinylacetate copolymer will be illustrated. In the last part of this review paper, a new powerful SMCR method that we have recently proposed is demonstrated.     

Selective SERS detection of each polycyclic aromatic hydrocarbon (PAH) in a mixture of five kinds of PAHs

This paper reports the qualitative analysis and quantitative detection of polycyclic aromatic hydrocarbon (PAH) molecules with per‐6‐deoxy‐(6‐thio)‐β‐cyclodextrin (CD‐SH) modified gold nanoparticles (AuNPs) by surface‐enhanced Raman scattering (SERS) spectroscopy. For the selective sensing of PAHs, which are environmental pollutants with very low affinity to metallic surfaces, by SERS, a stable substrate with AuNPs and CD‐SH was utilized by supramolecular interaction. Quantitative detection of each PAH was carried out by SERS on inclusion complexes with different concentrations. From the SERS spectra of a mixture of five different PAHs, we could easily distinguish each PAH by its discriminant peaks. In addition, quantitative analysis of one component in a mixture of five PAHs was also investigated. This sensing platform revealed matching relationship between the host and the guest and the host–guest interaction mechanism. The proposed approach for the selective detection of PAHs holds great potential in the detection of environmental organic pollutants. Copyright © 2010 John Wiley & Sons, Ltd.     

Fourier‐Transform Raman Spectroscopic On‐Line Monitoring of the Anionic Dispersion Block Copolymerization of Styrene and 1,3‐Butadiene

The anionic dispersion block copolymerization of styrene and 1,3‐butadiene has proved a suitable technique to synthesize block copolymers of tailor‐made blocklength under technically relevant conditions. For this purpose, however, an efficient analytical on‐line technique is required to control the concentrations of individual reactants and product. The present communication shortly outlines the potential of non‐invasive light‐fiber Fourier‐transform Raman spectroscopy in combination with a self‐modeling curve‐resolution analysis to monitor the polymerization progress and to derive concentration profiles of the two monomers and polybutadiene without prior calibration of the investigated system.