Preparation,<i>via</i>Double Oxidative Addition, and Characterization of Bimetallic Platinum and Palladium Complexes: Unique Building Blocks for Supramolecular Macrocycles.¹³C NMR Analysis of the Nature of the Palladium−Carbon Bond

Abstract

The high-yield preparation, by double oxidative addition, of nine novel platinum and palladium bis(trans-M(PR3)2X)aryl (M = Pt or Pd; R = PPh3 or PEt3; X = Br or I; aryl = 1,4-benzene, 4,4‘-biphenyl, 4,4‘‘-ter-p-phenyl, 4,4‘-tolane, or 4,4‘-benzophenone) complexes from the reaction of Pt(PPh3)4, Pt(PEt3)4, or Pd(PPh3)4 with the respective dihalo aromatic in toluene is described. These complexes were fully characterized by elemental analysis, mass spectrometry, and NMR (1H, 13C{1H}, and 31P{1H}) and vibrational (IR or Raman) spectroscopies. The single-crystal molecular structure of 4,4‘-bis(trans-Pt(PEt3)2I)biphenyl (2a) was determined by X-ray crystallography. The key structural feature of this complex is the dihedral angle of 18.9° between the two planes defined by the phenyl groups of the biphenyl linkage. The nature of the palladium−carbon bond is investigated by 13C{1H} NMR spectroscopy; Taft's σR parameter is found to correlate in a linear fashion with [δ(Cipso) − δ(Co)] for these palladium complexes...