Kinetic addition of nucleophiles to η3-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 acetylide 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 metallacyclobutene C5Me5(CO)(2)ReCH2C(NC5H5)=CCH3+PF6- (14b) which rearranged 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)-propargyl complex 3a below -38 degrees C to give the rhenacyclobutene complex C5Me5(CO)(2)ReCH2C(NC5H4NMe2)=CC(CH3)(3)+BF4- (22a) which rearranged to the eta(2)-alkyne complex C5Me5(CO)(2)Re[eta(2)-(CH3)(3)CC=CCH2NC5H4NMe2]+BF4- (23) at room temperature, Reaction of water with C5Me5(CO)(2)Re[eta(3)-CH2C=CH]+BF4- (3c) gave the hydroxyallyl complex C5Me5(CO)(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.