Mixed P-N and As-N Bis-Ylide palladium complexes: Cooperative intramolecular interactions, conformational preferences, and C-H bond activations

Elena Serrano, Cristina Vallés, Jorge J. Carbó, Agustí Lledós, Tatiana Soler, Rafael Navarro, Esteban P. Urriolabeitia

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Abstract

The mixed ylide-pyridinium salts [Ph3P=C(H)C(O)CH 2NC5H5]Cl (2a) and [Ph3As=C(H)C(O) CH2-NC5H5]Br (15) have been prepared by reaction of the P and As ylides [Ph3P=C(H)C(O)CH2Cl] and [Ph3As=C(H)C(O)CH2Br] (14), respectively, with pyridine. These ylides react with Pd(II) salts in the presence of bases, affording the four-membered C,C-chelated complexes cis-[PdCl2{η2- Ph3EC(H)C(O)C-(H)NC5H5} (E = P (3), As (16)) as single diastereoisomers (meso form, RS/SR). Density functional theory (DFT) calculations revealed that the same conformational preferences are present in free mixed bis-ylides. We have established the presence of two cooperative intramolecular interactions of moderate strength by means of Bader analysis of the electron density on model free bis-ylides: the 1,4-E⋯O interactions (E = P, As) and the 1,6-CH⋯O hydrogen bonds. The intramolecular 1,4-As⋯O interactions have been fully characterized for the first time. These interactions play a key role in determining the preferred conformations, which then are transferred to the complexes. Complex 3 reacts with AgClO 4 to give the dinuclear species [Pd(μ-Cl){η2- Ph3PC(H)C(O)C(H)NC5H5}]2(ClO 4)2 (4), which further reacts with L ligands to give [PdCl{η2-Ph3PC(H)C(O)C(H)NC5H 5}L](ClO4) (L = PPh3 (6), PPhMe2 (7)) as single geometric isomers. The molecular structure of 6 has been determined by X-ray diffraction methods. Complex 6 evolves in refluxing NCMe to give the ortho-metalated derivative [PdCl(C6H4-2-PPh 2C(H)C(O)CH2NC5H5)(PPh 3)]ClO4 (18). In addition, ylide 2a reacts with PtCl 2 in refluxing 2-methoxyethanol to give the ortho-platinated complex [Pt(μ-Cl)(C6H4-2-PPh2C(H)C(O)CH 2NC5H5)](Cl)2 (20). The role of the electronic and steric factors in the cleavage of the halide bridging system in 4 and in the ortho-metalation reactions affording 18 and 20 is also discussed. © 2006 American Chemical Society.
Original languageEnglish
Pages (from-to)4653-4664
JournalOrganometallics
Volume25
Issue number19
DOIs
Publication statusPublished - 11 Sep 2006

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