Mono- and Binuclear Orthopalladated Complexes of Phosphorus Ylides Containing Nitrogen, Phosphorus or Bridging Diphosphine Ligands: Self-Assembly, Theoretical Calculations and Comparative Catalytic Activity

Abstract

Binuclear orthopalladated complexes of phosphorus ylides containing electron-withdrawing fluoro (Y1), bromo (Y2) or phenyl (Y3) substituent, [Pd{κ2(C,C)-[(C<inf>6</inf>H<inf>4</inf>-2)PPh<inf>2</inf>]CH(CO)C<inf>6</inf>H<inf>4</inf>X-4}(μ-Cl)]<inf>2</inf> (X = F (1), Br (2), Ph (3)) were obtained by two different methods from the reaction of corresponding ylides and PdCl<inf>2</inf> or Pd(OAc)<inf>2</inf>. The synthesized orthopalladated complexes 1 and 2 reacted with the monodentate ligands with various donor abilities affording the mononuclear complexes [PdCl{C,C-{CH[P(C<inf>6</inf>H<inf>4</inf>-2)Ph<inf>2</inf>]C(O)C<inf>6</inf>H<inf>4</inf>X-4]}}L] [L = triphenylphosphine (X = Cl (1a), X = Br (2a)); 3-methylpyridine (X = Cl (1b), X = Br (2b)); 4-methylpyridine (X = Br (2c)); 2,4,6-trimethylpyridine (X = Cl (1c)); pyridine (X = Cl (1d)); piperidine (X = Cl (1e)). The reaction of chloro-bridged complex 3 with bis(diphenylphosphino)ethane, dppe, and bis(diphenylphosphino)propane, dppp, in the 1:1 ratio occurred to give the symmetrical bridged complexes of general formula [Pd<inf>2</inf>Cl<inf>2</inf>{C,C-{CH[P(C<inf>6</inf>H<inf>4</inf>-2)Ph<inf>2</inf>]C(O)C<inf>6</inf>H<inf>4</inf>X-4]}<inf>2</inf>}}(μ-PP)] (PP = dppe (3a) and dppp (3b)). New complexes were fully characterized by elemental analysis, IR and NMR spectroscopies. The crystal structures of 1, 1a, 2a, 3 and 3a were determined by single-crystal X-ray diffraction analysis that revealed the self-assembly of complexes via the short contacts between donor and acceptor groups to form polymer, sheet or network supramolecular structures. Density functional theory (DFT) calculations for complexes 1, 1a and 2a indicated the good agreement with the experimental value reported in this work. The catalytic activity of 1, 1a and 2a were comparatively studied in the Suzuki cross-coupling reactions which showed the more efficiency of mononuclear complex 1a with fluoro substituent. ©2015 Elsevier B.V. All rights reserved.