Rhodium halides

Rhodium halides occur mainly in the -t-3 state. In some cases where a soluble and insoluble form have been reported, the former may be a hydrate. 

It has the VF3 structure (Rh-F 1.961 A) having a hep array of fluorines with rhodium occupying 1/3 of the octahedral holes. Various hydrates have been reported 

Insoluble red RhCl3 is made by direct combination, with similar routes for the other trihalides 

All of these probably have the AICI3 structure (unconfirmed for RM3) with bond lengths (EXAFS) of 2.337 A (Rh-Cl) [13] and 2.48 A (Rh-Br) [14]. Soluble chlorides and bromides are made by dissolving the oxide in the appropriate acid. 

Rhodium trihalides (and complexes like K3RhBr6) are frequently added to photographic emulsions in trace quantities to improve the gradation of the emulsion (the rhodium effect ) [15]. 

RhF3 [12] can be conveniently made by fluorination RhCl3 -F — RhF3 

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The 17-ethylene ketal of androsta-l,4-diene-3,17-dione is reduced to the 17-ethylene ketal of androst-4-en-3,17-dione in about 75% yield (66% if the product is recrystallized) under the conditions of Procedure 8a (section V). However, metal-ammonia reduction probably is no longer the method of choice for converting 1,4-dien-3-ones to 4-en-3-ones or for preparing 5-en-3-ones (from 4,6-dien-3-ones). The reduction of 1,4-dien-3-ones to 4-en-3-ones appears to be effected most conveniently by hydrogenation in the presence of triphenylphosphine rhodium halide catalysts. Steroidal 5-en-3-ones are best prepared by base catalyzed deconjugation of 4-en-3-ones. ... 

CVD Reactions. The rhodium halides, like those of the other platinum group metal s, are volatile with a decomposition pointtoo close to the vaporization point to make them usable for CVD transport. The metal is commonly produced by the decomposition of metallo-organic precur-... 

The preparation of carbonylmetals by treating a transition metal halide either with carbon monoxide and zinc, or with iron pentacarbonyl is well-known and smooth. However, a violent eruptive reaction occurs if a methanolic solution of a cobalt halide, a rhodium halide or a ruthenium halide is treated with both zinc and iron pentacarbonyl. 

A very dangerous fire and moderate explosion hazard when exposed to heat or flame can react vigorously with oxidizing materials. Warning pyrophoric in air. Mixtures with nitrogen oxide explode above 50°C. Violent reaction with zinc + transition metal halides (e.g., cobalt halides, rhodium halides, ruthenium halides). Mixtures with acetic acid + water produce a pyrophoric powder. To fight fire, use water, foam, CO2, dr " chemical. See also CARBONYLS and IRON COMPOUNDS. 

The iridium- (and rhodium-) halide complexes may be extracted as ion-pairs with DAM, diphenylguanidine or tribenzylamine [76]. The process has been used as a basis for extraction-spectrophotometric methods of Ir determination. 

James, Rempel and Rosenberg [201-203] as weU as Stanko, Petrov and Thomas [204] have studied the carbonylation of rhodium halides in aqueous acid solutions under mild conditions. Reactions appear to proceed via a rhodium(III) carbonyl complex which is believed to react with water to form an insertion product prior to CO2 formation, equation (156). 

The multiple desilyation of silyated cydopentadienes is promoted by ionic ruthenium and rhodium halides. For example the reaction of ruthenium trichloride with... 

When formaldehyde reacts with rhodium halides, carbonylation proceeds (hydrocarbonylation between formaldehyde and a ruthenium halide as described in Chapter 16 proceeds). A Vaska type rhodium complex is obtained by the reaction with phosphine as shown in eq. (18.7) [17]. 

The rhodiumphosphinecarbonyl complex affords RhH(CO)(PPh3)3 by reduction with NaBH4 in the presence of phosphine as shown in eq. (18.8) [ 18]. The phos-phinecarbonylhydride is also prepared by the reduction of rhodium halides with NaBH4 [18] or with KOH in the presence of formaldehyde as shown in eqs. (18.9) and (18.10). 

Grignard reagents also react with inorganic halides to give coupled products. Examples of such halides are cupric chloride, lead chloride, silver bromide, silver cyanide, nickel chloride, palladium chloride, chromic chloride, iron halide, ruthenium halide, and rhodium halide. 

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