Rhodium, chlorotris hydrogenation catalyst reduction

Reduction of the heterocyclic ring of the benzo[h]quinoline occurs selectively using chlorotris(triphenylphosphine)rhodium(I) as the hydrogenation catalyst (R.H. Fish. J.L. Tan and A. D. Thormodsen, J. org. Chem., 1984, 4500). 

Similarly, reduction of the unsaturated lactone 4 by hydrogenation over palladium on carbon yielded only the tetrasubstituted monohydrogenated product. In this case Wilkinson s catalyst [chlorotris(triphenylphosphane)rhodium] is the catalyst of choice for the regio- and diastereose-lective reduction of the exocyclic double bond7. 

Some catalysts suffer a different type of alkyne poisoning. Chlorotris(triphenylphosphine)rhodium(I) is an effective terminal alkyne polymerization catalyst. When this complex is used in the reduction of these alkynes, it gradually loses its activity because of the competing polymerization reaction. Even initially the rate of alkyne hydrogenation is much slower than that of the corresponding alkene because of the greater binding constant of the former substrate. 

Selective reduction of both double bonds in a,jS-unsaturated carbonyl compounds that also contain an isolated olefin is possible with appropriate catalyst and reaction conditions . Chlorotris(biphenylphosphine)rhodium hydrogenates the isolated double bond. Thus, carvone, 13, is reduced to dihydrocarvone, 14, with careful measure of the uptake of Hj ... 

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