Cross-Coupling of Alkynes Catalyzed by Phebox−Rhodium Acetate Complexes

Cross-coupling between terminal alkynes and dimethyl acetylenedicarboxylate (3) in the presence of 1 mol % bis(oxazolinyl)phenyl−rhodium acetate complex, (Phebox-R)Rh(OAc)2(H2O) (1-ip, R = iPr), under 1 atm hydrogen atmosphere furnished alkynyl-substituted maleic acid dimethyl esters with high Z-selectivity. Rh−acetylide complexes (Phebox-R)Rh(OAc)(−C⋮CPh) (5-ip, R = iPr; 5-dm, R = Me2) were isolated on the reactions of 1-ip and 1-dm with phenylacetylene. Reactions of 5-ip and 5-dm with 3 provide the corresponding vinyl complexes (Phebox-R)Rh(OAc)(−C(CO2Me)C(CO2Me)C⋮CPh) (6-ip, R = iPr; 6-dm, R = Me2) with E-configuration. Further reaction of 6-ip with phenylacetylene resulted in the formation of an enyene 4a accompanied by the formation of 5-ip. The molecular structures of 5-dm and 6-dm were determined by X-ray diffraction.