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 (H 2 O) ( 1-ip, R = i Pr), 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 = i Pr; 5-dm, R = Me 2 ) 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(CO 2 Me) C(CO 2 Me)C⋮CPh) ( 6-ip, R = i Pr; 6-dm, R = Me 2 ) 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.