Partial Hydrogenation of Alkynes Catalyzed by [RhH2 (Ph2N3) (PPh3)2]

Noriyuki KAMEDA* and Tetsuya YONEDA

Department of Chemistry, College of Science and Technology, Nihon University;
Narashinodai, Funabashi-shi 274-8501 Japan

The homogeneous hydrogenation of different alkynes (1-hexyne, 2-hexyne, propiolic acid and dimethyl acetylenedicarboxylate) catalyzed by [RhH2 (Ph2N3) (PPh3)2] (dihydridorhodium complex) in several solvents (dimethyl sulfoxide (DMSO), N,N-dimethylformamide, tetrahydrofuran, acetone, benzene and toluene) under hydrogen at 1 atm, 303 K was studied. 1-hexyne, 2-hexyne and dimethyl acetylenedicarboxylate were reduced, although propiolic acid was left unaffected. The highest activity was observed in DMSO, and the catalytic hydrogenation activity was found to decrease in the following order, 1-hexyne>2-hexyne>dimethyl acetylenedicarboxylate. 1- and 2-hexyne could be selectively reduced to 1-hexene and cis-2-hexene respectively in essentially quantitative yields. The main hydrogenation product of the dimethyl acetylenedicarboxylate is dimethy maleate. The results are discussed in terms of the mechanism of partial hydrogenation of hexyne in DMSO.

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