Solvent exchange rhodium complexes

The mechanism of the Rh-BINAP complex-promoted isomerization of N,N-di-ethylgeranylamine is briefly summarized, which is a digested abstract of literature [2,9,27,45,46]. The reaction starts from the simple nitrogen-coordinated cationic rhodium complex 73 generated by ligand exchange between the complex 17 and the substrate 45 (L denotes solvent molecules, THF, MeOH, CH2CI2, or BINAP), Eq. 15. 

Notice that none of the flow sheets uses solvent extraction exclusively. Because the aqueous chemistry of osmium and ruthenium is very complex, most operators remove these elements by distillation of the tetraoxides, MO4. Also, it has been advantageous to use ion exchange to separate and concentrate rhodium. The various extraction routes for individual elements are discussed in the following sections. 

The dimeric tetraacetato bridged Rh2(OCOCH3)4 has been obtained by the interaction of ammonium chlororhodate(III) or rhodium (III) hydroxide with acetic acid.1-3 Other (car-boxylato)rhodium(II) compounds were prepared directly in a similar way or from the acetate by exchange.2,3 Halo car-boxylates (RCOO, R = CC13, CF3, CH2C1, etc.) were prepared also by interaction of rhodium trichloride with the appropriate sodium salt in ethanol.4 The carboxylatcs are normally first isolated as a solvent adduct, e.g., [Rh(OCOR)2-C2H5OH]2 but are easily converted to the unsolvated complex. The acetate is readily prepared in a modification of this last procedure. A similar method is satisfactory for the preparation of other lower carboxylates as well as halo carboxylates. 

A more detailed understanding of the conjugate-base mechanism for the hydrolysis of kinetically inert amine complexes of cobalt(III) and rhodium(III) is possible if liquid ammonia is used as a solvent. Such techniques allow the separation of parameters for the pre-equilibrium step ( Tcb) and the rate-determining step. A polyamine complex generally contains more than one potentially acidic proton and each proton is characterized by its own acidity constant (Kcb)- exchange rates for... 

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