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 η 3 -propargyl rhenium complexes to produce rhenacyclobutenes. Reaction of P(CH 3 ) 3 with C 5 Me 5 (CO) 2 Re[η 3 -CH 2 C⋮CC(CH 3 ) 3 ] + BF 4 - ( 3a ) gave the metallacyclobutene C 5 Me 5 (CO) 2 ReCH 2 C(PMe 3 ) CC(CH 3 ) 3 + BF 4 - ( 4a ), which was characterized by X-ray crystallography. Malonate and acetylide nucleophiles reacted with C 5 Me 5 (CO) 2 Re[η 3 -CH 2 C⋮CCH 3 ] + PF 6 - ( 3b ) to give metallacyclobutene complexes. Pyridine added to the central propargyl carbon of 3b at low temperature to produce the metastable metallacyclobutene C 5 Me 5 (CO) 2 ReCH 2 C(NC 5 H 5 ) CCH 3 + PF 6 - ( 14b ) which rearranged to the η 2 -allene complex C 5 Me 5 (CO) 2 Re[η 2 -H 2 C C C(NC 5 H 5 )CH 3 ] + PF 6 - ( 15K ) at room temperature. 4-(Dimethylamino)pyridine (DMAP) added to the central carbon of the tert -butyl-substituted η 3 -propargyl complex 3a below −38 °C to give the rhenacyclobutene complex C 5 Me 5 (CO) 2 ReCH 2 C(NC 5 H 4 NMe 2 ) CC(CH 3 ) 3 + BF 4 - ( 22a ) which rearranged to the η 2 -alkyne complex C 5 Me 5 (CO) 2 Re[η 2 -(CH 3 ) 3 CC⋮CCH 2 NC 5 H 4 NMe 2 ] + BF 4 - ( 23 ) at room temperature. Reaction of water with C 5 Me 5 (CO) 2 Re[η 3 -CH 2 C⋮CH] + BF 4 - ( 3c ) gave the hydroxyallyl complex C 5 Me 5 (CO) 2 Re[η 3 -CH 2 C(OH)CH 2 ] + BF 4 - ( 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.