Rhodium hydrated chlorides, reaction with

Complexes of this type can be prepared in three principal ways. The most obvious is by allowing hydrated rhodium trichloride to react with the bidentate ligand (equation 231).229 Unfortunately this method gives rise to both cis and trans products. However, the reactions between rhodium(III) halides and l,2-bis(diphenylphosphino)benzene (90) yield the trans product in the case of the chloride, whilst both the bromide and iodide form the cis product.1037... 

Dichlorotetracarbonyldirhodium has been obtained by the action of carbon monoxide at high temperature and pressure on a mixture of anhydrous rhodium(III) chloride and finely divided copper powder and by reaction of rhodium(III) chloride 3-hydrate with carbon monoxide saturated with methanol at moderate temperatures and atmospheric pressure. The preparation described here is a modification of the latter method, without use of methanol. This procedure is considerably simpler than the recently described preparation which involves adsorption of rhodium chloride on silica gel, chlorination, and subsequent carbonylation. ... 

Double insertion of ethylene into aniline with the aid of rhodium(III) chloride hydrate gives the cyclization product, 2-methylquinoline (Eq. 3) [10]. Forcing reaction conditions and the use of an excess amount of aniline were required for this catalytic reaction. 

The cis and trans forms of dichlorobis(ethylenediamine)-rhodium(III) nitrate are obtained from solutions of the corresponding chlorides by reaction with concentrated nitric acid. Solutions of the chlorides are prepared from hydrated rhodium(III) chloride by treatment with ethylenediamine dihydrochloride, the hydrochloric acid set free being neutralized with potassium hydroxide in such a manner that no excess base is ever present. ... 

The reduction of metal ions in higher oxidation states by CO and H20 has been known for many years. Work on the reduction of Hg2+, Ag+, Ni2+, Cu2 +, and Pd2+ has been summarized recently (4). The reduction of these metal ions does not proceed via a stable intermediate carbonyl. Since a metal carbonyl must be an intermediate in this reaction, however, the coordinated carbonyl must be very susceptible to attack by water, reacting as soon as it is formed. The ability of a metal in a higher oxidation state to activate a coordinated carbonyl to attack by as weak a nucleophile as water was noted previously in the description of the work by James et al., on the reduction of rhodium(III) by carbon monoxide and water (62). Here a stable rhodium(III) carbonyl, Rh(CO)Cl2-, can be observed as the initial product of reaction of RhCl3 3HzO with CO. The Rh(III) is then efficiently reduced to the rhodium(I) anion [RhCl2(CO)2], even in nonaqueous solvents such as dimethylacetamide, where the only water available for reaction is the water of hydration of the starting rhodium chloride. 

Platinum in a finely divided form is obtained by the in situ reduction of hydrated platinum dioxide (Adams catalyst) finely divided platinum may also be used supported on an inert carrier such as decolourising carbon. Finely divided palladium prepared by reduction of the chloride is usually referred to as palladium black. More active catalysts are obtained however when the palladium is deposited on decolourising carbon, barium or calcium carbonate, or barium sulphate. Finely divided ruthenium and rhodium, usually supported on decolourising carbon or alumina, may with advantage be used in place of platinum or palladium for some hydrogenation reactions. 

Potassium hexachlororhodate(III) 1-hydrate may be obtained by chlorination of a mixture of powdered rhodium and potassium chloride, followed by crystallization from the reaction mixture solution in the presence of excess potassium chloride. It may also be prepared by reaction of sodium hexachlororhodate(III) solution with concentrated potassium chloride solution, followed by evaporation to incipient crystallization. Both of these methods are reported to yield potassium pentachloroaquorhodate(III) if potassium chloride is not present in excess. - Anhydrous potassium hexachlororhodate(III) is obtained by heating potassium hexachlororhodate(III) 1-hydrate at 100 to 120°. ... 

Little information is available on microemulsion-mediated synthesis of rhodium particles. Considering the importance of Rh nanoparticles in catalytic reactions, Kishida et al [426] developed a method using microemulsions. The reverse micelle was prepared with the surfactant NP-5 and cyclohexane as the continuous phase. An aqueous solution of rhodium chloride was solubilized in the micelle and hydrazine directly added to it at 25°C. The average particle size of rhodium thus obtained was about 3 nm. Kishida et al. [427] later extended the method to the use of a variety of non-ionic and ionic surfactants (C-15, i.e. polyoxyethylene(15)cetyl ether, L-23, i.e. polyoxyethylene(23)lauryl ether, NP-5 and NaAOT), as also cyclohexane or 1-hexanol (according to necessity) as the continuous phase. The reactants remained the same, i.e. rhodium chloride and hydrazine hydrate. In addition, the rhodium particles thus synthesized were coated with silica via hydrolysis-polycondensation of tetraethyl orthosilicate. The size of Rh varied in the range 1.5-4.0 nm in a typical case, a 4 nm particle was covered with a 14 nm thick layer of silica. 

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