Rhodium fluoride

The departure from the 1 1 reaction stoichiometry in the xenon-rhodium hexafluoride system is less than for the platinum system. This is surprising in view of the greater instability and chemical reactivity of the rhodium fluoride. Ruthenium hexafluoride, which is less reactive than rhodium hexafluoride, has been reported [7] to react non-stoichiometrically with xenon. Perhaps the use of small quantities of rhodium fluoride favored the 1 1 addition. There is as yet no evidence for the oxidation state of rhodium in the adduct, although the formulation Xe -1- [RhFe] would, as in the corresponding platinum case, appear to be energetically more favorable than Xe +[RhF6] . 

Rhodium is a relatively inactive metal. It is not attacked by strong acids. When heated in air, it combines slowly with oxygen. It also reacts with fluorine, chlorine and bromine when very hot. It forms compounds such as rhodium fluoride (RhF3) and rhodium chloride (RhCl3)... 

The eliminaUon of carbon monoxide from nonfluonnated acyl fluorides, however, does not result in a fluonne compound Although it was claimed earlier that benzoyl fluoride can be converted into fluorobenzene by using tris(triphenyl-phosphme)rhodium chloride, recent studies proved that the product is benzene and not fluorobenzene [91]... 

There is also clear evidence of a change from predominantly class-a to class-b metal charactristics (p. 909) in passing down this group. Whereas cobalt(III) forms few complexes with the heavier donor atoms of Groups 15 and 16, rhodium(III), and more especially iridium (III), coordinate readily with P-, As- and S-donor ligands. Compounds with Se- and even Te- are also known. Thus infrared. X-ray and nmr studies show that, in complexes such as [Co(NH3)4(NCS)2]" ", the NCS acts as an A -donor ligand, whereas in [M(SCN)6] (M = Rh, Ir) it is an 5-donor. Likewise in the hexahalogeno complex anions, [MX ] ", cobalt forms only that with fluoride, whereas rhodium forms them with all the halides except iodide, and iridium forms them with all except fluoride. 

Ionic liquids have already been demonstrated to be effective membrane materials for gas separation when supported within a porous polymer support. However, supported ionic liquid membranes offer another versatile approach by which to perform two-phase catalysis. This technology combines some of the advantages of the ionic liquid as a catalyst solvent with the ruggedness of the ionic liquid-polymer gels. Transition metal complexes based on palladium or rhodium have been incorporated into gas-permeable polymer gels composed of [BMIM][PFg] and poly(vinyli-dene fluoride)-hexafluoropropylene copolymer and have been used to investigate the hydrogenation of propene [21]. 

The pattern of iridium halides resembles rhodium, with the higher oxidation states only represented by fluorides. The instability of iridium(IV) halides, compared with stable complexes IrCl4L2 and the ions IrX (X = Cl, Br, I), though unexpected, finds parallels with other metals, such as plutonium. Preparations of the halides include [19]... 

The analogous rhodium complexes exhibit very low activity, even in the presence of fluoride ions [143]. In contrast, (PRjljRhCl (R = Ph, Et) and the corresponding... 

Antimony, arsenic, selenium, tellurium, iridium, iron, molybdenum, osmium, potassium, rhodium, tungsten (and when primed with charcoal,) aluminium, copper, lead, magnesium, silver, tin, zinc. Interaction of lithium or calcium with chlorine tri- or penta-fluorides is hypergolic and particularly energetic. 

Miura reported a 1,4-shift of rhodium in the reaction of norbornene with arylboronic acids (Scheme 3) where rhodium moves from an alkyl sp2-carbon to an aryl sp2-carbon, and the arylrhodium species further reacts with another molecule of norbornene.30 Polyalkylated phenyls are obtained in good yields. Cesium fluoride facilitates the transmetallation, generating the phenylrhodium complex which then coordinates to the -face of norbornene. 

Organotrialkoxysilanes (ArSi(OR)3) were used as organometallic reagents without fluoride additives (Scheme 56).144,144a ArSi(OR)3 was easy to use because of its higher air and moisture stability. Oi and co-workers believed that hydrolysis of the trialkoxysilanes to generate silanetriols was likely occurring prior to transmetallation of the cationic rhodium complex. 

Besides rhodium catalysts, palladium complex also can catalyze the addition of aryltrialkoxysilanes to a,(3-unsaturated carbonyl compounds (ketones, aldehydes) and nitroalkenes (Scheme 60).146 The addition of equimolar amounts of SbCl3 and tetrabutylammonium fluoride (TBAF) was necessary for this reaction to proceed smoothly. The arylpalladium complex, generated by the transmetallation from a putative hypercoordinate silicon compound, was considered to be the catalytically active species. 

Fluorosilylsubstituted aryl derivatives were found to be useful reagents for carbon-carbon bond formation via palladium-catalyzed cross-coupling with aryl halides in the presence of fluoride anions as Si—C bond activator in dimethylformamide (DMF), as well as rhodium-catalyzed 1,4-addition to a, 3-unsaturated ketones in the presence of a fluoride anion source (Equation 14.11) [66, 69, 70],... 

In research al the Institute or Radiochemistry. Karlsruhe, West Germany during Ihe early 1970s. investigators prepared alloys of Curium with iridium, palladium, plalinum. and rhodium. These alloys were prepared by hydrogen reduction of the curium oxide or fluoride in the presence of finely divided noble metals. The reaction is called a coupled reaction because the reduction of the metal oxide can be done in the presence of noble metals. The hydrogen must be extremely pure, w ith an oxygen content of less than 10 -s Inrr. 

Fig. 5. Idealized, close-packed structures for (a) niobium and (b) rhodium penta-fluorides. Atoms in the first, second, third, and fourth layers are shown as single, double, crossed, and hatched circles, respectively. The symbols for overlapped atoms are shown dashed. The bridge bonds are shaded.

The volume of space occupied, per fluorine atom, has often been quoted as about 18 A3. For the transition metal fluorides this is approximately so, although there is considerable variation, and the values are more often lower. For a particular metal, the variation in volume occupied with change in oxidation state is not simple. Thus for vanadium the volumes are VF2, 19.5 VF j, 17.2 VF4, 16.1 VF5, 16.1 A3, whereas for rhodium the values are RhF j, 15.5 RhF4, 15.5 RhF5, 16.9 RhFfi, 16.7 A3. 

The addition of alkoxycarbonylcarbene derived by catalysed decomposition of methyl diazoacetate to several simple, and in particular terminal, alkynes leads to low yields S7), but the reaction with 1 -trimethylsilylalkynes proceeds reasonably efficiently subsequent removal of the silyl-group either by base or fluoride ion provides a route to l-alkyl-3-cyclopropenecarboxylic acids. In the same way 1,2-bis-trimethylsilyl-ethyne can be converted to cyclopropene-3-carboxylic acid itself58 . The use of rhodium carboxylates instead of copper catalysts also generally leads to reasonable yields of cyclopropenes, even from terminal alkynes 59). 

For cobalt, rhodium, nickel, palladium, silver, and gold no oxide fluorides have been reported. 

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