Synthesis, structural and theoretical studies of Pd(II) complexes containing an orthometallated C, C-chelating phosphorus ylide

Abstract

The phosphorus ylide [Ph3PCHC(O)C6H 4-NO2-4] (1) reacted with Pd(OAc)2 to give the C, C-orthometallated complexes [Pd{K2(C, C)-C6H 4PPh2C(H)CO(C6H4-NO2-4)}(μ-X)] 2 (X = Cl (2); X = Br (3)) as a mixture of isomers, which underwent bridge cleavage reactions with monodentate ligands to afford the monomeric, neutral Pd(II) complexes [Pd{κ2(C, C)-C6H 4PPh2C(H)CO(C6H4-NO 2-4)}X(L)] (X = Cl, L=Me3Py (4), PPh3 (5); X = Br, L = Me3Py (6), 4-MePy (7), PPh3 (8). The complexes were identified and characterized by spectroscopic studies (IR and NMR). The X-ray single crystal analysis of 6 and 7 revealed the presence of an orthometallated C6H4-2-PPh2 unit and a C-linked ylide, Pd-C(H). In the crystal structure of 6, the location of the Me3Py ligand is trans to the Pd-Cylide, according to the anti-symbiotic effect, whereas in 7 the 4-MePy ligand is preferentially cis to the Pd-Cylide. Density functional theory (DFT) calculations in the reaction solvent (dichloromethane) indicated that the trans isomers of 6 and 7 are 3.03 and 0.70 kcal/mol more stable than their cis isomers, respectively. © 2013 Elsevier Ltd. All rights reserved.