Rhodium couplings

Hz again gave higher values for P0 aoyi rhodium couplings compared to... 

Calvet, high-temperature version 16) Platinum to platinum-rhodium couples 30-800 (500°C)... 

A variety of examples of 2D-NMR experiments is provided in reference [21]. The structure elucidation of the di-rhodium compound shown in Figure 11.3 was mostly carried out in this way. For example, 2D 11 l-31P heteronuclear multiple quantum correlation (HMQC) experiments were used to show that two rhodium-coupled hydride resonances are connected to a single type of 31P nucleus. 

Identical results have been obtained with platinum and rhodium couples for preparation of model exhaust gas catalysts. 

A couple consisting of gold wire and a ware containing 60 per cent, of gold, the remainder being palladium, has approximately six times the thermo-electromotive force of a platinum-rhodium couple. Its utility, however, is curtailed by the liability to undergo disintegration which characterises palladium alloys.4... 

Temperature is maintained in a very small cylindrical furnace, the jacket of which is water-cooled. Temperatures are measured by a platinum-rhodium couple supported on the torsion arm and inserted very close to the sample. Temperatures are recorded on the second point of the Speedomax and this point is provided with controls for maintaining the temperature as desired. The apparatus is also provided with auto-... 

For the platinum/rhodium couple though, the amplitude of the response is extremely low. 

Analysis of A found C, 13.8% H, 2.1% P, 21.3% F, 39.2% and Rh, 23.6%. The mass spectrum of A showed a highest mass peak at m/z = 436. When compound A was heated to 60°C it was converted initially into an isomeric derivative B which subsequently formed a third isomer C. The H n.m.r. spectra of compounds A, B and C, measured at room temperature, are listed in the table. These spectra can be assigned by taking into account proton-proton and proton-rhodium couplings [l( " Rh) natural abundance of Rh isotope is 100%], proton-phosphorus couplings are not observed under these conditions. Interpret these data as fully as you can. Deduce the molecular structures of the complexes A, B and C and suggest a mechanism for the isomerization. 

Anilines have been reduced successfully over a variety of supported and unsupported metals, including palladium, platinum, rhodium, ruthenium, iridium, (54), cobalt, and nickel. Base metals require high temperatures and pressures (7d), whereas noble metals can be used under much milder conditions. Currently, preferred catalysts in both laboratory or industrial practice are rhodium at lower pressures and ruthenium at higher pressures, for both display high activity and relatively little tendency toward either coupling or hydrogenolysis,... 

The amount of coupled product was found to depend importantly on the catalytic metal a sequence for increased coupling to dicyclohexylamine was found to be Ru < Rh Pd Pt (59), a sequence that reflects one reason for the industrial preference for rhodium and ruthenium in hydrogenation of anilines. 

Laister and Benham have shown that under more arduous conditions (immersion for 6 months in sea-water) a minimum thickness of 0-025 mm of silver is required to protect steel, even when the silver is itself further protected by a thin rhodium coating. In similar circumstances brass was completely protected by 0 012 5 mm of silver. The use of an undercoating deposit of intermediate electrode potential is generally desirable when precious metal coatings are applied to more reactive base metals, e.g. steel, zinc alloys and aluminium, since otherwise corrosion at discontinuities in the coating will be accelerated by the high e.m.f. of the couple formed between the coating and the basis metal. The thickness of undercoat may have to be increased substantially above the values indicated if the basis metal is affected by special defects such as porosity. 

The complex ion (Figure 2.32) contains Rh2 bound cis to two phosphorus atoms (2.216 A) and more distantly to four oxygens (2.201—2.398 A), exhibiting a distortion ascribed to the Jahn-Teller effect it is paramagnetic (fi = 1.80 fiB) and exhibits an ESR spectrum (Figure 2.33) showing rhodium hyperfine coupling as the doublet for g. ... 

The 31P NMR spectrum of RhH2Cl(PBu2)2 is shown in Figure 2.69 the triplets show coupling with two equivalent hydrogens, split further by coupling with rhodium (/(Rh-P) 110.3 Hz /(P-H) 14.9 Hz). 

The interaction of small, well defined, rhodium clusters, Rh and Rhs, with O2 has been investigated (220) by matrix infrared, and UV-visible, spectroscopy, coupled with metal/02 concentration studies, warm-up experiments, and isotopic oxygen studies. A number of binuclear O2 complexes were identified, with stoichiometries Rh2(02)n, n = 1-4. In addition, a trinuclear species Rhs(02)m, m = 2 or 6, was identified. The infrared data for these complexes, as well as for the mononuclear complexes Rh(02)x, = 1-2 (229), are summarized in Table XI. Metal-concentration plots that led to the determination of... 

The ability of enzymes to achieve the selective esterification of one enantiomer of an alcohol over the other has been exploited by coupling this process with the in situ metal-catalysed racemisation of the unreactive enantiomer. Marr and co-workers have used the rhodium and iridium NHC complexes 44 and 45 to racemise the unreacted enantiomer of substrate 7 [17]. In combination with a lipase enzyme (Novozyme 435), excellent enantioselectivities were obtained in the acetylation of alcohol 7 to give the ester product 43 (Scheme 11.11). A related dynamic kinetic resolution has been reported by Corberdn and Peris [18]. hi their chemistry, the aldehyde 46 is readily racemised and the iridium NHC catalyst 35 catalyses the reversible reduction of aldehyde 46 to give an alcohol which is acylated by an enzyme to give the ester 47 in reasonable enantiomeric excess. 

Rhodium-catalyzed Heck-type coupling of boronic acids with activated alkenes was carried out in an aqueous emulsion.82 The couplings between arylboronic acids and activated alkenes catalyzed by a water-soluble tm-butyl amphosrhodium complex were found to progress at room temperature to generate Heck-type products with high yields and excellent selectivity. It was necessary to add two equivalents of the... 

---