Neutral Metal Atoms Acting as a Leaving Group in Gas-Phase SN2 Reactions: M(CH3)+ + NH3 鈫?CH3NH3+ + M (M = Zn, Cd, Hg)

详细信息    查看全文

• 作者：Robert Kretschmer ; Maria Schlangen ; Martin Kaupp ; Helmut Schwarz
• 刊名：Organometallics
• 出版年：2012
• 出版时间：May 28, 2012
• 年：2012
• 卷：31
• 期：10
• 页码：3816-3824
• 全文大小：363K
• 年卷期：v.31,no.10(May 28, 2012)
• ISSN：1520-6041

文摘

Under ambient conditions, mass-selected 鈥渂are鈥?M(CH₃)⁺ ions (M = Zn, Cd, Hg) react with ammonia with cleavage of the metal鈥揷arbon bond and concomitant C鈥揘 coupling, yielding N-protonated methylamine, CH₃NH₃⁺; the neutral atomic metals M serve as a novel type of leaving group. In contrast, all three cationic metal amides, M(NH₂)⁺, do not afford C鈥揘 bond formation in quasi-thermal ion/molecule reactions with methane. With regard to the mechanism, computational studies reveal that CH₃NH₃⁺ is generated in a clean gas-phase S_N2 reaction with inversion of configuration at the carbon center; nucleophilic substitution with configurational retention is prohibited by a kinetic barrier. Further, N鈥揌 bond activation in the couples M(CH₃)⁺/NH₃ and C鈥揌 bond activation in M(NH₂)⁺/CH₄ are kinetically inhibited by transition structures which are higher in energy in comparison to the entrance channels.