The influence of nuclearity and charge of chiral Rh diene complexes on the activity and enantioselectivity in catalytic asymmetric 1,2-additions of organoboron reagents to Ntosylimines and 1,4-additions to enones was investigated. For this purpose, cationic dimeric Rh(I) complex [(Rh(1)) 2 Cl]SbF 6 and cationic monomeric Rh(I) complex [RhOH 2 (2)]SbF 6 were synthesized from oxazolidinone-substituted 3-phenylnorbornadiene ligands 1 and 2, which differ in the substitution pattern at oxazolidinone C-5′ (CMe 2 vs CH 2 ) and compared with the corresponding neutral dimeric and monomeric Rh(I) complexes [RhCl(1)] 2 and [RhCl(2)]. Structural, electronic, and mechanistic insights were gained by X-ray crystallography, cyclic voltammetry (CV), X-ray absorption spectroscopy (XAS), and DFT calculations. CV revealed an increased stability of cationic vs neutral Rh complexes toward oxidation. Comparison of solid-state and solution XAS (extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES)) data showed that the monomeric Rh complex [RhCl(2)] maintained its electronic state and coordination sphere in solution, whereas the dimeric Rh complex [RhCl(1)] 2 exchanges bridging chloro ligands by dioxane molecules in solution. In both 1,2-and 1,4-addition reactions, monomeric Rh complexes [RhCl(2)] and [RhOH 2 (2)]SbF 6 gave better yields as compared to dimeric complexes [RhCl(1)] 2 and [(Rh(1)) 2 Cl]SbF 6 . Regarding enantioselectivities, dimeric Rh species [RhCl(1)] 2 and [(Rh(1)) 2 Cl]SbF 6 performed better than monomeric Rh species in the 1,2-addition, while the opposite was true for the 1,4-addition. Neutral Rh complexes performed better than cationic complexes. Microemulsions improved the yields of 1,2-additions due to a most probable enrichment of Rh complexes in the amphiphilic film and provided a strong influence of the complex nuclearity and charge on the stereocontrol. A strong nonlinear-like effect (NLLE) was observed in 1,2-additions, when diastereomeric mixtures of ligands 1 and epi-1 were employed. The pronounced substrate dependency of the 1,4-addition could be rationalized by DFT calculations.

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t g a r t , D 70550 S t u t t g a r t , Germany AbstractOrganic photovoltaic thin film s t r u c t u r e s made by vacuum vapor deposition have been studied. From t h e spectral response as a function of t h e absorption coefficient we conclude t h a t electron -hole generation takes place a t t h e interface between t h e organic thin film and one or b o t h of t h e semitransparent cover electrodes. The observed s h o r t circuit currents, however, are t o o large to be explained on t h e basis of a direct light-induced charge transfer at t h e organic thin film/ electrode interface. Rather, a contribution of t h e bulk-absorbed photons is necessary t o account f o r the observed quantum yield. Transfer of t h e energy t o t h e interface sites can be explained by diffusional migration of excitons. The efficiency of charge separation can be improved by combining donor a n d acceptor type partners in organic double layers. The efficiency of power conversion, however, n o t only depends on a suitable choice of t h e absorption spectra and of t h e ionic energy levels of t h e materials employed, b u t also on t h e internal cell resistance, a f a c t t h a t calls f o r high charge carrier mobilities, and hence f o r using materials with crystal structures t h a t allow s t r o n g n-electron interactions, and f o r deposition in high chemical purity and s t r u c t u r a l perfection.

Study on the interface thermal stability of metal-oxide-semiconductor structures by inelastic electron tunneling spectroscopy Appl.Hot carrier transport effects in Al 2 O 3 -based metal-oxide-semiconductor structures Hot-electron transport through Au/CaF 2 /Si (111) structure studied by ballistic electron emission spectroscopy J. Appl. Phys. 85, 941 (1999); 10.1063/1.369214 Current oscillations in thin metal-oxide-semiconductor structures observed by ballistic electron emission microscopy J.The tip of a scanning tunneling microscope ͑STM͒ was used to inject electrons into thin Pt layers of metal-oxide-semiconductor ͑MOS͒ structures. The collector currents emanating from the n-type Si͑100͒ substrates were measured as a function of the electron energy, determined by the STM tip bias V T , for different oxide biases V ox applied independently across the oxide layers. The SiO 2 layers were thermally grown in a device processing line and ranged from 27 to 62 Å in thickness. A current threshold near V T ϭ3.90 V is interpreted in terms of current transport through the SiO 2 conduction band. The current transport through the MOS structure was modeled in a single band description for zero oxide thickness, and fitted to the collector currents that had been corrected for impact ionization effects in the Si. Deviations between the two curves represent the influence of the transmission probability T ox through the SiO 2 film of finite thickness. T ox can thus be determined from the experimental data. Within an eV of threshold the magnitude of T ox was observed to be particularly sensitive to small changes in oxide bias in the range 0.3 VտV ox տϪ0.1 V. The transmission probabilities were also calculated by integrating the Boltzmann equation using Monte Carlo techniques that incorporate energy dependent effective masses and electron phonon scattering rates. Agreement between the two approaches is quite good, including the observed sensitivity on oxide bias in the threshold region, which is a direct consequence of the strong electron-optical phonon scattering in the oxide. The 27 Å thick oxide structures exhibited in the ballistic electron emission microscopy images scattered patches of high transmittance of only 1-2 nm in extent. The collector currents arising from injection at these patches indicated thresholds as low as 1.1 eV, but the observed modest currents above that threshold argue against local shorts that would arise from pinholes in the oxide.

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