摘要:
The mechanism of the platinum(II)-catalyzed intramolecular hydroamination of benzyl 4-pentenylamines has been evaluated under stoichiometric and catalytic conditions. Reaction of a benzyl 2,2-disubstituted 4-pentenylamine with [(PPh3)Pt(mu-COCl](2) forms a thermally sensitive platinum amine complex that undergoes irreversible, intramolecular ligand exchange with the pendant C=C bond to form a reactive platinum pi-alkene complex. The pi-alkene complex undergoes rapid, outer-sphere C-N bond formation, evidenced by the anti addition of Pt and N across the complexed C=C bond, to form a thermally stable zwitterionic platinamethylpyrrolidinium complex. The zwitterionic complex is rapidly and exergonically deprotonated by free amine to form a neutral, bicyclic azaplatinacyclobutane complex that likely exists as a discrete 1:1 adduct with ammonium salt in the nonpolar reaction medium and that represents the resting state of the catalytic cycle. Turnover-limiting intramolecular protodemetalation of the azaplatinacyclobutane ammonium adduct followed by ligand exchange releases the 2-methylpyrrolidine product.