Rhodium high-temperature properties

High Temperature Properties. There are marked differences in the abihty of PGMs to resist high temperature oxidation. Many technological appHcations, particularly in the form of platinum-based alloys, arise from the resistance of platinum, rhodium, and iridium to oxidation at high temperatures. Osmium and mthenium are not used in oxidation-resistant appHcations owing to the formation of volatile oxides. High temperature oxidation behavior is summarized in Table 4. 

Some rhodium and platinum clusters exhibit dynamic properties, i.e., skeletal fluxionality. In the RhNMR of [Rh9P(CO)2i] , which has a capped antiprism structure, three signals possessing the intensity ratio 4 4 1 are observed at 183 K, while at 298 K there is only one signal. This experiment shows that, due to fluxionality of the skeleton, all rhodium atoms becomes equivalent. The same is indicated also by the presence of a decet in the PNMR spectrum of this compound. Similarly, [RhioS(CO)22] and [RhioE(CO)22] (E = P, As) are rigid at low temperatures but fluxional at high temperatures. 

In July, 2010, physicists at Rice University in Houston, Texas the Max Planck Instimte for Chemical Physics of Solids and the Max Planck Institute for the Physics of Complex Systems, both in Dresden, Germany and the Vienna University of Technology have reported that after seven years of research on high-temperature superconductors they have established quantum-critical scaling properties at work during the transition from one quantum phase to another. In experiments with a heavy-fermion metal containing ytterbium, rhodium, and silicon, researchers identified thermodynamic scaling properties as a result of a fermi-volume collapse. 

The two-substituted-Quinazolinap-derived rhodium complexes proved extremely efficient catalysts for the hydro-boration-oxidation of vinylarenes (Table 6). For styrene derivatives, in most cases quantitative conversions were obtained after just 2 h at the relevant temperature (entries 1-6). Higher enantioselectivities were afforded with a 4-methoxy substituent (up to 95% ee, entry 3) compared to the 4-chloro or unsubstituted styrene analogs (entries 5 and 1), a trend also observed in hydroboration with rhodium complexes of QUINAP 60. This highlights that both the electronic nature of the substrate combined with the inherent steric properties of the catalyst are important for high asymmetric induction. It is noteworthy that in most cases, optimum enantioselectivities were afforded by the... 

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