Mechanism of the Platinum(II)-Catalyzed Hydroamination of 4‑Pentenylamines

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(μ-Cl)­Cl]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 π-alkene complex. The π-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.