Rhodium, chlorotris hydrogenation alkenes

Halpern J, Okamoto T and Zakhariev A 1976 Mechanism of the chlorotris(triphenylphosphine)rhodium(l)-catalyzed hydrogenation of alkenes J. Mol. Catal. 2 65-9... 

Acyl chlorides containing an a hydrogen are smoothly converted to alkenes, with loss of HCI and CO, on heating with chlorotris(triphenylphosphine)rhodium, with metallic platinum, or with certain other catalysts. The mechanism probably involves conversion of RCH2CH2COCI to RCH2CH2—RhCO(Ph3P)2Cl2 followed by a concerted syn elimination of Rh and H. See also 14-39 and 19-12. 

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. 

Scheme 6.14. A representation of the reduction of an alkene with hydrogen (H2) and chlorotris(triphenylphosphine)rhodium (ClRh[(C6H5)3P]3).

Chlorotris(triphenylphosphine)rhodium(i) can also catalyse hydrogen transfer from dioxan to an alkene. The rate-determining step in this reaction is considered to be oxidative addition of C—bonds of dioxan to the catalyst ... 

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