Mixed P−N and as−N bis-ylide palladium complexes: Cooperative intramolecular interactions, conformational preferences, and C−H bond activations

12 pages, 4 schemes, 4 tables, 7 figures.-- Supporting Information Available: http://pubs.acs.org.The mixed ylide−pyridinium salts [Ph3PC(H)C(O)CH2NC5H5]Cl (2a) and [Ph3AsC(H)C(O)CH2NC5H5]Br (15) have been prepared by reaction of the P and As ylides [Ph3PC(H)C(O)CH2Cl] and [Ph3AsC(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 AgClO4 to give the dinuclear species [Pd(μ-Cl){η2-Ph3PC(H)C(O)C(H)NC5H5}]2(ClO4)2 (4), which further reacts with L ligands to give [PdCl{η2-Ph3PC(H)C(O)C(H)NC5H5}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-PPh2C(H)C(O)CH2NC5H5)(PPh3)]ClO4 (18). In addition, ylide 2a reacts with PtCl2 in refluxing 2-methoxyethanol to give the ortho-platinated complex [Pt(μ-Cl)(C6H4-2-PPh2C(H)C(O)CH2NC5H5)](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.Funding by the Dirección General de Investigación Científica y Técnica (DGICYT) (Spain, Projects CTQ2005-01037, CTQ2005-09000-C02-01, CTQ2005-03141, and CTQ2005-06909-C02-01) is gratefully acknowledged.Peer reviewe