Rhodium complexes anionic

The anionic rhodium complexes [(PR3)2Rh(NHPh)2] Li (see above) have been shown to catalyze (TON = 21) the condensation of aniline with styrene to give the expected amine and the corresponding imine (oxidative amination) (Eq. 4.37, TOP 0-07 h- ) [161]. 

One of the only examples of a commercial process using immobilised homogeneous catalysts comprises an anionic rhodium complex [RhI2(CO)2] that is bound via ionic interactions to an ion exchange resin [3] and is used for the carbonylation of methanol. 

Anionic rhodium complexes, 32 356-364 Anionic ruthenium complexes, 32 402-406 Anions, 32 224 Anisole... 

Counterions for the anionic rhodium complexes present in catalyst solutions may also be provided by the addition of salts. A salt may be used as the sole promoter, but it appears that under many conditions a combination of salt and amine provides the best results. Table XI indicates that... 

The solvents used in these rhodium-catalyzed reactions may also act as complexing agents for counterions of the anionic rhodium complexes. For example, tetraglyme is known to coordinate alkali metal cations. Such solvation decreases the possibility of the cation interacting with the anionic rhodium catalyst and lowering its activity or solubility. The crown ethers, such as [18]-crown-6... 

Chiral solvation, in polysilane PSS induction, 3, 622 Chiral tin hydrides, applications, 9, 346 Chloranilato anionic rhodium complexes, synthesis, 7, 210 Chloride ligands... 

Another approach, developed by Chiyoda/UOP, uses a rhodium catalyst heterogenized on a polymeric cation exchange resin. This takes advantage of the fact that the rhodium catalyzed carbonylation involves anionic complexes (see Section 4.2.5 below). The Chiyoda/UOP Acetica process employs a cross-linked polyvinylpyridine which is quaternized by methyl iodide to generate cationic pyridinium sites and which hold the anionic rhodium complexes by electrostatic interactions. The polymer support is tolerant of elevated temperatures and the ionic attachment of the catalyst is quite robust, resulting in only... 

The kinetic behavior is interpreted on the basis of the well-established catalytic cycle shown in Scheme 1, comprising a sequence of reactions of anionic rhodium complexes. 

Ionic liquids such as quaternary ammonium and phosphonium salts have also attracted attention as a means of immobilizing the rhodium catalyst. Processes for carbonylation of methanol with either gas-phase [109] or liquid-phase [110] reactants using [Rh(CO)2I2] dissolved in an ionic liquid have been claimed. Ionic liquids are nonvolatile, which aids in product separation, and the anionic rhodium complex is highly soluble in them. However, the ionic liquids are relatively expensive and their high viscosities can create mass-transfer limitations associated with slow diffusion of reactants. 

As a final example of ligand reactions of carbonyls, the rhodium-catalyzed CO conversion reaction will be mentioned. Anionic rhodium complexes such as [Rh(CO)2l2] undergo nucleophilic attack by water with formation of CO2 (Eq. 2-76). 

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