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 η3-propargyl rhenium complexes to produce rhenacyclobutenes. Reaction of P(CH3)3 with C5Me5(CO)2Re[η3-CH2C⋮CC(CH3)3]+BF4 - (3a) gave the metallacyclobutene C5Me5(CO)2ReCH2C(PMe3)CC(CH3)3 +BF4 - (4a), which was characterized by X-ray crystallography. Malonate and acetylide nucleophiles reacted with C5Me5(CO)2Re[η3-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)2ReCH2C(NC5H5)CCH3 +PF6 - (14b) which rearranged to the η2-allene complex C5Me5(CO)2Re[η2-H2CCC(NC5H5)CH3]+PF6 - (15K) at room temperature. 4-(Dimethylamino)pyridine (DMAP) added to the central carbon of the tert-butyl-substituted η3-propargyl complex 3a below −38 °C to give the rhenacyclobutene complex C5Me5(CO)2ReCH2C(NC5H4NMe2)CC(CH3)3 +BF4 - (22a) which rearranged to the η2-alkyne complex C5Me5(CO)2Re[η2-(CH3)3CC⋮CCH2NC5H4NMe2]+BF4 - (23) at room temperature. Reaction of water with C5Me5(CO)2Re[η3-CH2C⋮CH]+BF4 - (3c) gave the hydroxyallyl complex C5Me5(CO)2Re[η3-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.