KINETIC ADDITION OF NUCLEOPHILES TO ETA(3)-PROPARGYL RHENIUM COMPLEXES OCCURS AT THE CENTRAL CARBON TO PRODUCE RHENACYCLOBUTENES

Kinetic addition of nucleophiles occurs at the center carbon of eta(3) -propargyl rhenium complexes to produce rhenacyclobutenes. Reaction of P(CH3)(3) with C5Me5(CO)(2)Re[eta(3)-CH2C=CC(CH3)(3)]+BF4- (3a) gave the metallacyclobutene C5Me5(CO)(2)ReCH2C(PMe3)=CC(CH3)(3)+BF4- (4a), which was characterized by X-ray crystallography. Malonate and acetyli de nucleophiles reacted with C5Me5(CO)(2)Re[eta(3)-CH2C=CCH3]+PF6- (3b ) to give metallacyclobutene complexes. Pyridine added to the central propargyl carbon of 3b at low temperature to produce the metastable me tallacyclobutene C5Me5(CO)(2)ReCH2C(NC5H5)=CCH3+PF6- (14b) which rearr anged to the eta(2)-allene complex C5Me5(CO)(2)Re[eta(2)-H2C=C=C(NC5H5 )CH3]+PF6- (15K) at room temperature. 4-(Dimethylamino)pyridine (DMAP) added to the central carbon of the tert-butyl-substituted eta(3)-prop argyl complex 3a below -38 degrees C to give the rhenacyclobutene comp lex C5Me5(CO)(2)ReCH2C(NC5H4NMe2)=CC(CH3)(3)+BF4- (22a) which rearrang ed to the eta(2)-alkyne complex Me5(CO)(2)Re[eta(2)-(CH3)(3)CC=CCH2NC5 H4NMe2]+BF4- (23) at room temperature, Reaction of water with C5Me5(CO )(2)Re[eta(3)-CH2C=CH]+BF4- (3c) gave the hydroxyallyl complex C5Me5(C O)(2)Re[eta(3)-CH2C(OH)CH2]+BF4- (29) by a process proposed to involve nucleophilic addition of water to the central propargyl carbon of 3c followed by protonation of the metallacyclobutene intermediate.