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• 作者：Priya Saxena ; Natesan Thirupathi ; Munirathinam Nethaji
• 刊名：Organometallics
• 出版年：2014
• 出版时间：June 23, 2014
• 年：2014
• 卷：33
• 期：12
• 页码：3182-3197
• 全文大小：730K
• ISSN：1520-6041

文摘

Insertion reactions of six-membered cyclopalladated N,N鈥?N鈥?triarylguanidines, [魏²(C,N)Pd(渭-Br)]₂ (III鈥?b>V), with various alkynes in CH₂Cl₂ under ambient conditions afforded diinserted eight-membered palladacycles, [(魏²(C,N):畏²(C鈺?i>C)-PdBr] (1鈥?b>11), in high yield (76鈥?6%), while insertion reactions of six-membered cyclopalladated N,N鈥?N鈥?triarylguanidines, [魏²(C,N)Pd(Lewis base)Br] (VI鈥?b>XI), with various alkynes under the aforementioned conditions afforded monoinserted six-membered palladacycles, [魏²(C,N)Pd(Lewis base)Br] (12鈥?b>21), in high yield (81鈥?1%) except for 14 (23%). The insertion reaction of VI with 2 equiv of dimethyl acetylenedicarboxylate (DMAD) and the insertion reaction of 12 with 1 equiv of DMAD in CH₂Cl₂ under ambient conditions resulted in the formation of a diinserted zwitterionic five-membered palladacycle, [魏²(C,C)Pd(2,6-lutidine)Br] (22), in 76% and 70% yields, respectively. Palladacycle 22 upon reaction with AgOTf in wet MeCN afforded the ionic palladacycle [魏²(C,C)Pd(2,6-lutidine)(H₂O)][OTf] (23) in 78% yield. The ring size of the 鈥淸魏²(C,N)Pd]鈥?unit in the structurally characterized diinserted palladacycles (1路2CH₂Cl₂路H₂O, 2, 5, and 7), and monoinserted palladacycles (17, 18, and 20路C₇H₈路H₂O) is smaller than that anticipated for mono- and diinserted palladacycles, and this feature is mainly ascribed to the proclivity of III鈥?b>XI to undergo ring contraction cum amine鈥搃mine tautomerization upon alkyne insertion. Palladacycle 22 represents the first diinserted product obtained in alkyne insertion reactions of [魏²(C,N)Pd(Lewis base)X] type palladacycles. The molecular structure of 22路H₂O determined by X-ray diffraction indicates that the positive charge on the guanidinium moiety is balanced by the negative charge on the palladium atom and thus represents the first structurally characterized zwitterionic palladacycle to be reported in alkyne insertion chemistry. Plausible mechanisms of formation of 12鈥?b>21 and 22 have been outlined. The presence of more than one species in solution for some of the palladacycles in the series 1鈥?b>7 and 12鈥?b>21 was explained by invoking the C鈥揘 single-bond rotation of the CN₃ unit of the guanidine moiety, while this process in conjunction with Pd鈥揘(lutidine) bond rotation was invoked to explain the presence of four isomers of 15, as studied with the aid of variable-concentration ¹H NMR experiments carried out for 14 and 15.