Remarkable CO-catalyst effect of gold nanoclusters on olefin oxidation catalyzed by a manganese-porphyrin complex

The effect of dodecanethiolate-protected metallic nanoclusters of gold (Au:SC12, 1), silver (Ag:SC12), palladium (Pd:SC12), and platinum (Pt:SC12) on the catalytic activity of Mn(TPP)Cl (TPP = tetraphenylporphinato) was investigated in styrene oxidation with iodosylbenzene. Among the four metal clusters, only Au:SC12 led to appreciable acceleration of the catalytic reaction. The major role of the Au cluster was to regenerate the active catalytic path involving Mn(III) and Mn(V) from the deactivated Mn(IV) species. The binary 1/Mn(TPP)Cl catalyst system showed an absorption spectrum characteristic of Mn(III)-porphyrin after reaction, whereas a catalytically ineffective Mn(IV) species was observed as the sole porphyrin species in the absence of the Au cluster or in the presence of Pd, Ag, and Pt clusters. Accordingly, the slow oxidation reaction with Mn(TPP)Cl was accelerated by the addition of Au:SC12, and complete conversion of Mn(IV) into Mn(III) was observed in the absorption spectrum. 1H NMR inspection of the reaction of Au:SC12 and iodosylbenzene revealed that the surface dodecyl groups were partially oxidized into dodecanal and eliminated from the cluster surface, thereby producing unprotected gold sites on the surface. A reactivation mechanism involving the reaction of the Mn-porphyrin and the oxidant activated on the gold surface is proposed.     

Anisole-diphenoxide ligands and their zirconium dichloride and dialkyl complexes

Linear triphenol H3[RO3] (2,6-bis(3-tert-butyl-5-methyl-2-hydroxybenzyl)-4-R-phenol; R = Me, tBu) was found to undergo selective mono-deprotonation and mono-O-methylation. Deprotonation of H3[RO3] with 1 equiv of nBuLi resulted in the formation of Li{H2[RO3]}(Et2O)2 (R = Me (1a), tBu (1b)), in which the central phenol unit was lithiated. Treatment of H3[RO3] with methyl p-toluenesulfonate in the presence of K2CO3 in CH3CN gave the corresponding anisol-diphenol H2[RO2O] (2,6-bis(3-tert-butyl-5-methyl-2-hydroxybenzyl)-4-R-anisole; R = Me (2a), tBu (2b)). Reaction of H2[RO2O] with 2 equiv of nBuLi gave the dilithiated derivatives Li2[RO2O]. The lithium salts were reacted with ZrCl4 in toluene/THF to obtain the dichloride complex [RO2O]ZrCl2(thf) (R = Me (3a), tBu (3b)). 3b underwent dimerization along with a loss of THF to generate {[tBuO2O]ZrCl2}2 (4), whereas 4 was dissolved in THF to regenerate the monomer 3b. Alkylation of 3 with MeMgBr, PhCH2MgCl, and Me3SiCH2MgCl gave [MeO2O]ZrMe2(thf) (5), [RO2O]Zr(CH2Ph)2 (R = Me (6a), tBu (6b)), and [tBuO2O]Zr(CH2SiMe3)2 (7), respectively. Reaction of 3b with LiBHEt3 produced the hydride-bridged dimer [Li2(thf)4Cl]{[tBuO3]Zr}2(micro-H)3} (8), in which demethylation of the dianionic [tBuO2O] ligand took place to give the trianionic [tBuO3] ligand. The X-ray crystal structures of 1b, 2a, 3a, 4, 6a, and 7 were reported.     

Decentralized delayed-feedback control of an optimal velocity traffic model

The jam phenomenon in traffic flow wastes not only considerable traffic-transportation time but also great amounts of fuel due to many accelerate-decelerate actions. From traffic-economic and traffic-pollution viewpoints, the suppression of traffic jam is an important issue we have to solve. The present paper shows that -norm, which has been used in the field of control theory, can reveal the traffic jam phenomenon in an optimal velocity traffic model under an open boundary condition. Furthermore, we suppress the traffic jam in the model by the decentralized delayed-feedback control method. Some numerical simulations are shown to verify our theoretical results. Received 27 October 1999     

Optical Spectrogram Scope Using Time-to-Two-Dimensional Space Conversion and Interferometric Time-of-Flight Cross Correlation

We demonstrate a new tool called optical spectrogram scope for visualization of a spectrogram or a scalogram of optical ultrafast phenomena. The optical spectrogram scope is constructed on the basis of the time-to-two-dimensional-space conversion technique capable of converting a set of time-varying frequency distributions into two-dimensional spatial ones.     

Separation of carrier free95mTc from niobium targets irradiated with alpha-particles

A^95mTc tracer with an excellent quality was prepared by a simple sublimation method after α-bombardment of niobium metal. Technetium-95m produced by the⁹³Nb(α,2n)^95mTc reaction was separated from the niobium targets in a quartz tube by heating at 1100°C in an oxygen gas flow. Technetium-95m sublimed as an oxide was deposited on the inner wall of the quartz tube outside an electric furnace, and then collected as a pertechnetate solution by washing with water. The ICP-MS analysis of the^95mTc solution revealed its excellent quality, compared to a^95mTc solution prepared from the same targets through a wet chemical separation method and a commercial^95mTc solution. With this tracer, the precision of ICP-MS analysis of⁹⁹Tc in environmental samples are highly improved.     

Multiple cluster model (MCM) for surface reaction systems

Multiple cluster model (MCM) for investigating surface reactions is formulated. In this model the reaction center, where electron correlation effects often play a key role, is described by an accurate high‐level approximation, and bulk effects such as the lattice distortion energy are evaluated using a simple low‐level approximation. Therefore, the MCM can properly simulate the potential energy hypersurface of the surface reaction system with a feasible computational cost. Since there exists no fixed atom in the MCM, we can rigorously characterize the stationary point (the minimum energy point or the transition state) on the potential energy hypersurface by vibrational frequency analysis. The MCM can be applied not only to surface systems, but also to various large systems. A detailed comparison of the MCM with the integrated molecular orbital+molecular mechanics (IMOMM), the integrated molecular orbital+molecular orbital (IMOMO), and ONIOM developed by Morokuma and co‐workers is also presented. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 71: 403–413, 1999