Catalyst precursors, butane rhodium

Butyne-l,4-diol has been hydrogenated to the 2-butene-diol (97), mesityl oxide to methylisobutylketone (98), and epoxides to alcohols (98a). The rhodium complex and a related solvated complex, RhCl(solvent)(dppb), where dppb = l,4-bis(diphenylphosphino)butane, have been used to hydrogenate the ketone group in pyruvates to give lactates (99) [Eq. (15)], and in situ catalysts formed from rhodium(I) precursors with phosphines can also catalyze the hydrogenation of the imine bond in Schiff bases (100) (see also Section III,A,3). 

Rhodium compounds and complexes are also commercially important catalysts. The hydroformylation of propene to butanal (a precursor of hfr(2-ethyUiexyl) phthalate, the PVC plasticizer) is catalyzed by hydridocarbonylrhodium(I) complexes. Iodo(carbonyl)rhodium(I) species catalyze the production of acetic acid from methanol. In the flne chemical industry, rhodium complexes with chiral ligands catalyze the production of L-DOPA, used in the treatment of Parkinson s disease. Rhodium(II) carboxylates are increasingly important as catalysts in the synthesis of cyclopropyl compounds from diazo compounds. Many of the products are used as synthetic, pyrethroid insecticides. Hexacyanorhodate(III) salts are used to dope silver halides in photographic emulsions to reduce grain size and improve gradation. 

Heterofunctionalized derivatives can be prepared following the same methodology. In the case of esters and halides, rhodium(II) acetate dimer must be employed as catalyst instead of copper compounds.After transformation of the acetoxymethyl group of 7 (X = OAc) into an ester functionality, these compounds are valuable precursors of highly functionalized bi-cyclo[1.1.0]butanes since nucleophilic attack on the keto group takes place under very mild conditions. Thus, the t> /o-bicyclo[1.1.0]butane-l,2,3-tricarboxylic ester is obtained from 3-oxo-tricyclo[2.1.0.0 - ]pentane-l, 5-dicarboxylic esters upon treatment with methanol at 20 °C for three hours. 

---