Rhodium isotopes

The orf/io-amination of arenes carrying an A(-alkylbenzamide (DG by alkyl- or benzyl-azides has been reported in a reaction catalysed by cyclopentadienyl rhodium. Isotopic studies indicate that carbon-hydrogen bond cleavage to form a five-membered rhodacy-cle is rate limiting and irreversible. Coordination of the azide gives an intermediate (58) which allows insertion of an A(-alkylamido group. ... 

The rhodium catalyst (46 mg) is dissolved in acetone (10 ml) in a microhydrogenation apparatus which is then flushed three times with deuterium gas. After stirring the solution in an atmosphere of deuterium for about 1 hr the deuterium uptake ceases and constant pressure is attained. 5a-Cholest-2-ene (136, 19.5 mg) is added and the stirring continued until deuterium uptake ceases (about 3/4 hr). The solvent is evaporated to dryness and the residue is extracted with hexane and the resulting solution filtered through a small alumina column (3 g, activity 111). Evaporation of the hexane gives 2, 3 -d2-5oc-cholestane (137) 18 mg, 92% mp 78-79° isotope composition 94%d2,5%d, andl%do. ... 

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... 

Synthesis of ruthenocene from fission-product ruthenium isotopes was done by neutron irradiation ofU30g and FeCpj powder mixtures. It was shown that most of the ruthenocene found was actually produced by the decay of a precursor. Subsequent knowledge makes it apparent that the fission product recoils formed a rhodium dicyclopentadienide whose structure was preserved through the decay . The total yield of ruthenocene reached a value of 60% under some experimental conditions and was rarely less than 40%. 

C22-0037. Rhodium has only one stable isotope. Calculate the A/ Z ratio for each of the following four... 

For a comparison of experimental Mossbauer isomer shifts, the values have to be referenced to a common standard. According to (4.23), the results of a measurement depend on the type of source material, for example, Co diffused into rhodium, palladium, platinum, or other metals. For Fe Mossbauer spectroscopy, the spectrometer is usually calibrated by using the known absorption spectrum of metallic iron (a-phase). Therefore, Fe isomer shifts are commonly reported relative to the centroid of the magnetically split spectrum of a-iron (Sect. 3.1.3). Conversion factors for sodium nitroprusside dihydrate, Na2[Fe(CN)5N0]-2H20, or sodium ferrocyanide, Na4[Fe(CN)]6, which have also been used as reference materials, are found in Table 3.1. Reference materials for other isotopes are given in Table 1.3 of [18] in Chap. 1. 

Tin hold the record with 10 stable isotopes. There are 19 so-called "pure elements" of which there is only one isotope. These anisotopic elements are beryllium, fluorine, sodium, aluminum, phosphorus, scandium, manganese, cobalt, arsenic, yttrium, niobium, rhodium, iodine, cesium, praseodymium, terbium, holmium, thulium, gold, and bismuth. 

Phosphorus is an unusual element, because it has only one single isotope, phosphorus-31, and that this isotope is NMR-active with a spin of xh. The only other elements for which this is the case are fluorine, yttrium, rhodium and thulium. 

The lower trace in Figure 1 shows the results of heating the tunnel junctions (complete with a lead top electrode) in a high pressure cell with hydrogen. It is seen that the CO reacts with the hydrogen to produce hydrocarbons on the rhodium particles. Studies with isotopes and comparison of mode positions with model compounds identify the dominant hydrocarbon as an ethylidene species (12). The importance of this observation is obviously not that CO and hydrogen react on rhodium to produce hydrocarbons, but that they will do so in a tunneling junction in a way so that the reaction can be observed. The hydrocarbon is seen as it forms from the chemisorbed monolayer of CO (verified by isotopes). As... 

Whatever the route to a rhodium dihydride alkene complex, the hydrogen must be transferred sequentially to the double bond. It had always been assumed that the first C-H bond is formed / to the amido-group, so that the more stable Rh-substrate chelate is formed. This is the alkylhydride isomer observed in stoichiometric NMR studies at low temperatures, and is supported by studies under catalytic turnover conditions, assuming a normal isotope effect... 

ISOTOPES There are 52 Isotopes of rhodium, ranging from Rh-89 to Rh-122. All are produced artificially with relatively short half-lives except one stable isotope, Rh-103, which constitutes 100% of the element s existence in the Earth s crust. 

Haegele et al. (269) have used exact isotope masses and isotope abundances together in determining the detailed fragmentation patterns of square planar rhodium (I) -diketonate complexes. They found that some species postulated by other workers were in error. High resolution is needed to distinguish the 28 mass units for loss of CO (27.9949) from C2H4 (28.0313) (269) or the 69 mass units for PF2 (68.9906) from CFa (68.9952) (90). 

This mechanism clearly implicated alkane complexes as precursors to C-H activation but the IR absorptions of [Cp Rh(CO)Kr] and [Cp Rh(CO)(C6Hi2)] were not resolved and were presumed to be coincident. The temperature dependent data gave values of AH = 18 (or 22) kj mol for the unimolecular C-H (or C-D) activation step representing a normal kinetic isotope effect, kn/fco 10- However, an inverse equilibrium isotope effect (K /Kq 0.1) was found for the slightly exothermic pre-equilibrium displacement of Kr by CoHn/C Dn implying that C6Dj2 binds more strongly to the rhodium center than does C Hn-... 

In this review, we will discuss the use of in situ spectroscopic techniques, in combination with kinetic and isotopic labeling studies, to obtain a detailed mechanistic insight of the rhodium catalyzed hydroformylation. 

Allylic amide isomerization, 117 Allylic amine isomerization ab initio calculations, 110 catalytic cycle, 104 cobalt-catalyzed, 98 double-bond migration, 104 isotope-labeling experiments, 103 kinetics, 103 mechanism, 103 model system, 110 NMR study, 104 rhodium-catalyzed, 9, 98 Allylnickel halides, 170 Allylpalladium intermediates, 193 Allylsilane protodesilylation, 305 Aluminum, chiral catalysts, 216, 234, 310 Amide dimers, NMR spectra, 282, 284 Amines ... 

---