Fine Tuning of the Substituents on the N-Geminal Phosphorus/Silicon-Based Lewis Pairs for the Synthesis of Z-Type Silyliminophosphoranylalkenes

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• 作者：Jiancheng Li ; Yan Li ; Indu Purushothaman ; Susmita De ; Bin Li ; Hongping Zhu ; Pattiyil Parameswaran ; Qingsong Ye ; Weiping Liu
• 刊名：Organometallics
• 出版年：2015
• 出版时间：September 14, 2015
• 年：2015
• 卷：34
• 期：17
• 页码：4209-4217
• 全文大小：419K
• ISSN：1520-6041

文摘

Reactions of the N-aryl(diphenylphosphanyl)aminosilane Ph₂PN(Ar)SiCl_3鈥?i>nMe_n (Ar = 2,4,6-Me₃C₆H₂, n = 0 (1a), 1 (2a), 2 (3a), 3 (4a); Ar = 2,6-iPr₂C₆H₃, n = 0 (1b), 1 (2b), 2 (3b), 3 (4b)) with methyl propiolate and dimethyl acetylenedicarboxylate (DMAD) give two types of products, the zwitterionic heterocycles [Ph₂PN(2,4,6-Me₃C₆H₂)SiCl₃](HC鈺怌CO₂Me) (5c) and [Ph₂PN(Ar)SiCl_3鈥?i>nMe_n](MeO₂CC鈺怌CO₂Me) (Ar = 2,4,6-Me₃C₆H₂, n = 0 (5a), 1 (6a), 2 (7a); Ar = 2,6-iPr₂C₆H₃, n = 0 (5b), 1 (6b), 2 (7b)) and (Z)-silyliminophosphoranylalkene ArN鈺怭(Ph₂)C(CO₂Me)鈺怌(CO₂Me)SiMe₃ (Ar = 2,4,6-Me₃C₆H₂ (8a), 2,6-iPr₂C₆H₃ (8b)). The reaction of Ph₂PN(SiMe₃)₂ with DMAD gives only the acyclic alkene Me₃SiN鈺怭(Ph₂)(MeO₂C)C鈺怌(CO₂Me)SiMe₃ (9), which is similar to 8a,b. In these reactions, compounds 1a鈥?b>4a and 1b鈥?b>4b behave as N-geminal P/Si-based Lewis pairs, which undergo a dipolar cycloaddition reaction with the alkyne. The theoretical calculations indicate that the reactions proceed through a concerted cycloaddition reaction mechanism. The stability of these heterocycles decreases as the number of the Me substituent on the pentacoordinated Si atom increases. When the Si center is substituted with three Me groups (4a,b), the heterocyclic intermediates undergo ring opening by Si鈥揘 bond cleavage and concomitant N鈺怭 bond formation resulting in 8a,b. The formation of the acyclic (Z)-alkene (8a,b and 9) can be considered as a stepwise S_N2 reaction at the silicon center.