Halide vapor complexation reactions

In most cases RXi Is a more volatile halide and Is present only as a vapor whereas GXy may be In a condensed or vapor phase depending on the temperature and total pressure of the system. Stoichiometric coefficients and thermodynamic quantities for reaction 1 have been measured using a variety of experimental techniques. Including mass-spectrometry, chemical transport and spectrophotometry. A large number of halide vapor complexes have been reported, and extensive reviews on their systematlcs and thermodynamics of formation are already available (4-9). 

It has been established that the apparent volatilities of transition and rare-earth metal halides are increased by several orders of magnitude through reactions of type (1) and (2) giving rise to vapor complex formation. The enhancement of the vapor densities of transition metal and/or rare-earth metal ions has commonly (see for example Papatheodorou 1982) been reported in the form of the uolatility enhancement factor. That is, when a reaction occurs between a solid rare-earth halide with low vapor pressure Ps (e.g. NdCb) and a more volatile salt (carrier gas) with partial pressure P (e.g. AlCl3,NaCl), and the partial pressure of the vapor complex is Pq, then the volatility enhancement factor is determined at unit pressure of the carrier gas as ... 

A summary of the vapor complexes formed in rare-earth halide/alkali halide binary systems according to the general reaction scheme (1) (sect. 1.1) is given in the present section. Studied systems involving divalent metal halides include only the ScCl3-MgCl2... 

Codeposition of silver vapor with perfluoroalkyl iodides at -196 °C provides an alternative route to nonsolvated primary perfluoroalkylsilvers [272] Phosphine complexes of trifluaromethylsilver are formed from the reaction of trimethyl-phosphme, silver acetate, and bis(trifluoromethyl)cadmium glyme [755] The per-fluoroalkylsilver compounds react with halogens [270], carbon dioxide [274], allyl halides [270, 274], mineral acids and water [275], and nitrosyl chloride [276] to give the expected products Oxidation with dioxygen gives ketones [270] or acyl halides [270] Sulfur reacts via insertion of sulfur into the carbon-silver bond [270] (equation 188)... 

Perfluoroalkyl or -aryl halides undergo oxidative addition with metal vapors to form nonsolvated fluonnated organometallic halides and this topic has been die subject of a review [289] Pentafluorophenyl halides react with Rieke nickel, cobalt, and iron to give bispentafluorophenylmetal compounds, which can be isolated in good yields as liquid complexes [290] Rieke nickel can also be used to promote the reaction of pentafluorophenyl halides with acid halides [297] (equation 193)... 

Dihydro-l,2-azaborolyl sandwich complexes, available by metal-vapor synthesis ( 6.5.3.3), can be prepared in a greater variety by reaction of metal halides with azaborolyl anions, e.g. " ° ... 

Protonation of a carbonyl oxygen rather than the metal may be encouraged in this case by the high coordination number of vanadium. This would then promote halide attack on the carbonyl carbon to yield an intermediate hydroxyhalocarbene, which reacts further to yield the indicated products. This system represents a potential photoassisted water-gas shift catalyst system since H3V(CO)3(diars) upon photolysis with a mercury vapor lamp yields H2, and in the presence of CO regenerates the starting complex HV(CO)4(diars). The feasibility of coupling these two reactions in the same reaction solution remains to be demonstrated. 

The matrix isolation technique has been applied, in conjunction with the salt/molecule reaction technique, to model the high temperature gas phase reactions of alkali halide salt molecules. The reactions with Lewis acids such as SiFi, HF and CO2 yielded ion pair products which were quenched into inert matrices for spectroscopic study. Difficulties arising from lattice energy considerations in alkali halide salt reactions are minimized by the initial vaporization of the salt reactant. The reaction of such salt molecules with Lewis bases, including H2O and NH3, yielded complexes similar in nature to transition metal coordination complexes, with binding through the alkali metal cation to the base lone pair. 

Arene complexes are usually prepared by the following methods (i) metal vapor synthesis (see Metal Vapor Synthesis of Transition Metal Compounds).(ii) AEAIX3 reduction of a metal halide in the presence of the arene and (hi) alkyne cyclotrimerization (see Cyclodimerization -tri-merization Reactions). Synthetic procedmes to obtain r] -arene derivatives have been reviewed by Pampaloni and Calderazzo. Over the past ten years, studies in this... 

The Rochow Process. Rochow found that alkyl and aryl halides react directly with silicon when their vapors contacted silicon at elevated temperatures to produce complex mixtures of organosilicon halides. The reaction is promoted by a wide variety of metals from both the main group and the transition series, but the most efficient catalyst is copper. The most studied reaction of this type is the reaction between methyl chloride and silicon to give dimethyldichlorosilane and methyltrichlorosilane. Dimethyldichloro-silane is major feedstock silane for methylsilicon polymers. 

---