Preparation of stable alkyl complexes of Ni(I) and their one-electron oxidation to Ni(II) complex cations

The three-coordinate nickel(I) alkyl complexes (dtbpe)Ni(CH2CMe3) (2), (dtbpe)Ni(CH2SiMe3) (3), and (dtbpe)Ni(CH2CMe2Ph) (4) have been prepared by treatment of (dtbpe)NiCl]2 with alkyllithium reagents. While thermally robust, they each undergo mild one-electron oxidation to give the corresponding Ni(II) complex cations (dtbpe)Ni(CH2CMe3)+] (5), (dtbpe)Ni(CH2SiMe3)+] (6), and (dtbpe)Ni(CH2CMe2Ph)+] (7) as red-brown PF6-] or BArF4-] salts. In contrast to cationic amido and phosphido analogues that undergo alpha-deprotonation to afford imido and phosphinidene derivatives, deprotonation of 5-7 occurs at a gamma-CH3 group to give metallacyclobutane products (dtbpe)Ni(CH2CMe2CH2) (8), (dtbpe)Ni(CH2SiMe2CH2) (9), and (dtbpe)Ni(CH2CPhMeCH2) (10), not (dtbpe)Ni=CHR.