Catalysis
Beginning especially in the 1960s, RhCl3(H2O)3 was demonstrated to be catalytically active for a variety of reactions involving CO, H2, and alkenes. For example, RhCl3(H2O)3 was shown to dimerise ethene to a mixture of cis and trans 2-butene:
- 2 C2H4 → CH3-CH=CH-CH3
Unfortunately this reaction fails for higher alkenes.
Ethylene dimerization was shown to involve catalysis by Rh2Cl2(C2H4)4. This and many related discoveries nurtured the then young field of homogeneous catalysis, wherein the catalysts are dissolved in the medium with the substrate. Previous to this era, most metal catalysts were "heterogeneous", i.e. the catalysts were solids and the substrates were either liquid or gases. Another advance in homogeneous catalysis was the finding that PPh3-derived complexes were active catalytically as well as soluble in organic solvents. Best known of the phosphine-supported catalysts is RhCl(PPh3)3,: which catalyzes the hydrogenation and isomerization of alkenes. The hydroformylation of alkenes is catalyzed by the related RhH(CO)(PPh3)3. Catalysis by rhodium is so efficient that it has significantly displaced the previous technology based on less expensive cobalt catalysts.
Read more about this topic: Rhodium(III) Chloride