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71.
Man ML Lam KC Sit WN Ng SM Zhou Z Lin Z Lau CP 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(4):1004-1015
The heterobimetallic complexes [(eta5-C5H5)Ru(CO)(mu-dppm)Mn(CO)4] and [(eta5-C5Me5)Ru(mu-dppm)(mu-CO)2Mn(CO)3] (dppm = bis-diphenylphosphinomethane) have been prepared by reacting the hydridic complexes [(eta5-C5H5)Ru(dppm)H] and [(eta5-C5Me5)Ru(dppm)H], respectively, with the protonic [HMn(CO)5] complex. The bimetallic complexes can also be synthesized through metathetical reactions between [(eta5-C5R5)Ru(dppm)Cl] (R = H or Me) and Li+[Mn(CO)5]-. Although the complexes fail to catalyze the hydrogenation of CO2 to formic acid, they catalyze the coupling reactions of epoxides with carbon dioxide to yield cyclic carbonates. Two possible reaction pathways for the coupling reactions have been proposed. Both routes begin with heterolytic cleavage of the RuMn bond and coordination of an epoxide molecule to the Lewis acidic ruthenium center. In Route I, the Lewis basic manganese center activates the CO2 by forming the metallocarboxylate anion which then ring-opens the epoxide; subsequent ring-closure gives the cyclic carbonate. In Route II, the nucleophilic manganese center ring-opens the ruthenium-attached epoxide to afford an alkoxide intermediate; CO2 insertion into the RuO bond followed by ring-closure yields the product. Density functional calculations at the B3LYP level of theory were carried out to understand the structural and energetic aspects of the two possible reaction pathways. The results of the calculations indicate that Route II is favored over Route I. 相似文献
72.
73.
Kit Chak Chan 《Integral Equations and Operator Theory》1990,13(1):132-137
Let H(N) denote the Fréchet space of all entire functions of N variables (N1). The purpose of this paper is to prove the existence of a dense set of functions f in H(N) such that if L is any nonscalar linear differential operator with constant coefficients, then the set {p(L)fp(·) is a polynomial} is dense in H(N).Research supported in part by an NSF grant 相似文献
74.
The off-the-shelf reagent PPN+Cl- and PPN-manganese carbonylates [PPN]+[Mn(CO)4L]- (L = CO, PPh3) are good catalysts for the coupling reactions of CO2 with neat epoxides without the use of organic solvents to afford cyclic carbonates. PPN salts with weak nucleophilic anions such as PPN+BF4- and PPN+OTf- are, however, inactive for the coupling reactions. 相似文献
75.
We show theoretically that it is possible to trap light in a microresonator structure by use of four-wave mixing. The efficiency of the parametric process is substantially increased by the high group delay of light inside the structure. The energy that is trapped has a half-life of approximately 500 ps in the presence of both linear and nonlinear loss in the channel waveguides and resonators. We also demonstrate that the energy can be extracted from the cavity with a similar process. 相似文献
76.
We numerically demonstrate the feasibility of constructing an all-optical AND gate by using a microresonator structure with Kerr nonlinearity. The gate is much smaller than similar AND gates based on Bragg gratings and has lower power requirements. 相似文献
77.
Rollins AM Ung-Arunyawee R Chak A Wong RC Kobayashi K Sivak MV Izatt JA 《Optics letters》1999,24(19):1358-1360
We report on the design and initial clinical experience with a real-time endoscopic optical coherence tomography (EOCT) imaging system. The EOCT unit includes a high-speed optical coherence tomography interferometer, endoscope-compatible catheter probes, and real-time data capture and display hardware and software. Several technological innovations are introduced that improve EOCT efficiency and performance. In initial clinical studies using the EOCT system, the esophagus, stomach, duodenum, ileum, colon, and rectum of patients with normal endoscopic findings were examined. In these initial investigations, EOCT imaging clearly delineated the substructure of the mucosa and submucosa in several gastrointestinal organs; microscopic structures such as glands, blood vessels, pits, villi, and crypts were also observed. 相似文献