Norbornadiene as a Building Block for the Synthesis of Linked Benzazocinones and Benzazocinium Salts through Tetranuclear Carbopalladated Intermediates

The six-membered C,N-palladacycle [Pd­(C,N-C6H4CH2CMe2NH2-2)­(μ-Cl)]2 (A) derived from phentermine reacts with norbornadiene to give a di- or tetranuclear complex arising from the double insertion of the same molecule of the strained alkene into one or two distinct Pd–aryl bonds. The tetranuclear complex has been characterized by X-ray diffraction studies and exhibits a very unusual cisoid geometry in both the disposition of the C,N-chelate ligands and the position of the palladium centers. The newly formed Pd–alkyl bonds are still reactive toward the insertion of unsaturated molecules, and the tetranuclear complex reacts with CO or isocyanides to give double benzazocinones or benzazocinium salts with a cisoid geometry, after depalladation of the corresponding organometallic intermediates which have been isolated in some cases. When the related palladacycles derived from phenethylamine or N-methylphenethylamine are used as starting materials, polymeric compounds are obtained, from which double benzazocinones or benzazocinium salts with a transoid geometry are obtained after CO or RNC insertion and subsequent depalladation. The presence of substituents on the α-carbon atom of the chelated amine influences the regiochemistry of the double carbopalladation of the norbornadiene.

由非那明（phentermine）衍生得到的六元C,N-钯环（six-membered C,N-palladacycle）[Pd(C,N-C₆H₄CH₂CMe₂NH₂-2)(μ-Cl)]₂（标记为配合物A），与降冰片二烯（norbornadiene）发生反应，该张力烯烃（strained alkene）的单分子可两次插入一条或两条独立的Pd–芳基键（Pd–aryl bonds），从而生成双核或四核配合物；其中四核配合物已通过X射线衍射研究（X-ray diffraction studies）完成表征，其C,N-螯合配体的排布与钯中心的位置均呈现极为罕见的顺式构型（cisoid geometry）。新生成的Pd–烷基键（Pd–alkyl bonds）仍可与不饱和分子发生插入反应，该四核配合物与一氧化碳（CO）或异氰化物（isocyanides）反应后，经脱钯化（depalladation）过程（部分情况下相关有机金属中间体已被分离得到），可得到具有顺式构型的双苯并氮杂环辛酮（double benzazocinones）或双苯并氮杂环辛鎓盐（benzazocinium salts）。当以苯乙胺或N-甲基苯乙胺衍生的相关钯环作为起始原料时，可得到聚合物类化合物，经一氧化碳或异氰化物（RNC）插入并后续脱钯化后，可得到具有反式构型（transoid geometry）的双苯并氮杂环辛酮或双苯并氮杂环辛鎓盐。螯合胺的α-碳原子上的取代基，会对降冰片二烯的双重碳钯化（double carbopalladation）区域选择性产生影响。