Room-Temperature Isolation of Palladium(II) Organocarbonyl Intermediates in the Synthesis of Eight-Membered Lactams after Alkyne/CO Sequential Insertions

The dinuclear complexes [Pd­(C∧N)­(μ-X)]2 (C∧N = C,N-C­(Ph)C­(R′)­ArCH2CR2NH2-2; Ar = C6H4, C6H2(OMe)2-4,5; R = H, Me; R′ = Ph, CO2Me, Me; X =
Cl, Br), arising from the monoinsertion of internal alkynes into the
Pd–C bond of ortho-palladated phentermine or homoveratrylamine,
react with CO at room temperature to afford the neutral mononuclear
organocarbonyl complexes [Pd­(C∧N)­X­(CO)]. When the
reactions with CO are carried out in the presence of TlOTf, the triflato
complexes [Pd­(C∧N)­(OTf)­(CO)] are obtained. These
organo-carbonyl complexes show an unexpected stability, in spite of
containing CO and a σ-alkenyl ligand in mutually cis positions,
and represent real intermediates in the insertion reactions of CO
into the Pd–C bond. Indeed, they undergo decomposition under
the proper conditions, behaving as CO-releasing molecules or yielding
Pd(0) and the corresponding dihydro-3-benzazocinones, resulting from
a C–N coupling process. Crystal structures of each type of
compound have been determined by X-ray diffraction studies.

双核配合物[Pd(C∧N)(μ-X)]₂（其中C∧N = C,N-C(Ph)=C(R')ArCH₂CR₂NH₂-2；Ar = C₆H₄、4,5-二甲氧基亚苯基；R = H、Me；R' = Ph、CO₂Me、Me；X = Cl、Br），系内炔烃单插入至邻钯化芬特明或高藜芦胺的Pd–C键中所得到的产物。该类双核配合物在室温下与一氧化碳（CO）反应，生成中性单核有机羰基配合物[Pd(C∧N)X(CO)]。若在三氟甲磺酸铊（TlOTf）存在下开展该CO插入反应，则可得到三氟甲磺酰氧基配合物[Pd(C∧N)(OTf)(CO)]。尽管这类有机羰基配合物同时含有顺位排布的CO与σ-烯基配体，却展现出出乎意料的稳定性，且是CO插入Pd–C键反应中的真实中间体。事实上，它们在适宜条件下会发生分解：既可作为一氧化碳释放分子，也可经C–N偶联过程生成Pd(0)与对应的二氢-3-苯并氮杂卓酮。各类配合物的晶体结构均通过X射线衍射实验得以解析。