Polysiloxane microspheres functionalized with imidazole groups as a palladium catalyst support

Polysiloxane microspheres containing a large number of silanol groups were obtained by an emulsion process of modified polyhydromethylsiloxane. N‐substituted imidazole groups were grafted on these microspheres by the silylation of their silanol groups with N‐[γ‐(dimethylchlorosilyl)propyl]imidazole hydrochloride. The progress of the reaction was monitored using ²⁹Si and ¹³C magic angle spinning (MAS) NMR and its impact on microsphere morphology was studied using scanning electron microscopy (SEM). The usefulness of the imidazole‐functionalized microspheres as a support for a metal catalyst was demonstrated by their reaction with PdCl₂(PhCN)₂. In this way a new heterogenized catalyst, Pd(II) complex with imidazole ligands supported on polysiloxane microspheres, was generated. This catalyst, MPd , was characterized using ¹³C and ²⁹Si MAS NMR, X‐ray photoelectron, Fourier transform infrared and far‐infrared spectroscopies, X‐ray diffraction, SEM–energy‐dispersive X‐ray spectroscopy and wide‐angle X‐ray scattering. The catalyst appears in two structures, as Pd(II) complex and Pd(0) nanoclusters. Its catalytic activity was tested using a model reaction, the hydrogenation of cinnamaldehyde, and compared with that of an analogous complex operating in a homogeneous system. MPd showed a high activity in the promotion of hydrogenation of cinnamaldehyde. The activity in the substrate conversion was stable at least in five cycles of this reaction. The main product was hydrocinnamaldehyde which could be obtained with a yield above 70%. A mechanism of the reaction is proposed. Copyright © 2016 John Wiley & Sons, Ltd.     

Antiferroelectric phase in liquid crystalline compounds containing an azo group in their molecular core

Novel lactic acid derivatives containing an azo group in their molecular core have been synthesised and their mesomorphic properties established. Compounds with a short aliphatic non-chiral chain exhibited the SmA* phase and ferroelectric (FE) SmC* phase. The monotropic antiferroelectric (AF) phase was found in the homologues with a longer terminal chain. Spontaneous polarisation and tilt angle were measured for the FE and AF phases. Dielectric spectroscopy in the frequency range 1 Hz–10 MHz was carried out and dielectric properties established within the temperature range of the smectic phases. Two high frequency modes were detected in the AF phase. Small-angle X-ray measurements were conducted, and the temperature dependence of layer spacing values is established and discussed.     

Anomalous phase sequence in new chiral liquid crystalline materials

We have prepared and studied a series of rod-like liquid crystalline compounds with the molecular core laterally substituted by bromine atom and with the lactate unit in the chiral terminal chain. Microscopic observation under the polarising microscope, x-ray and dielectric spectroscopy results enable us to establish the TGBA–SmA–TGBA_RE–TGBC phase sequence. The presence of the re-entrant TGBA phase below the regular SmA phase, found for three homologues, is quite uncommon. Results are discussed and compared with the previously studied compounds with regular phase sequences.