Pd(acac)(PR3)(PhCN)][BF4] and [Pd(acac)(S)2][BF4] (R = phenyl, 2-methoxyphenyl; S = benzonitrile, pyridine): Synthesis, characterization, reactivity and catalytic behavior. Crystal structure of Pd(κ2-O,O′-acac)(κ1-C-acac)(P(2-MeOC6H4)3)

Abstract

The Pd(II)complexes [Pd(acac)(PR3)(PhCN)][BF4] and [Pd(acac)(S)2][BF4] (acac = acetylacetonate; R = phenyl, 2-methoxyphenyl; S = benzonitrile, pyridine, CD3CN) were synthesized by the reaction of Pd(acac)2 or Pd(acac)2·PR3 with 2 equiv. of BF3·OEt2 in the presence of appropriate ligands (S). The structural features of the complexes were analyzed by NMR and FTIR spectroscopies. Computed FTIR spectra was in agreement with the corresponding experimental data, the correlation between ν(CN) of the κ1-nitrile ligands and DFT-calculated geometrical features of the complexes was proposed. Complex Pd (κ2-O,O′-acac)(κ1-C-acac)(TOMPP) (TOMPP = tris(ortho-methoxyphenyl)phosphine) was characterized by X-ray diffractometry. XRD, 1H and 31P NMR analyses were consistent with formation of three unequally populated rotamers of Pd(κ2-O,O′-acac)(κ1-C-acac)(TOMPP) in CDCl3 which differ in the orientation of the endo-(2-methoxy)phenyl ring in exo2 conformation of coordinated TOMPP. Reaction of [Pd(acac)(PR3)(PhCN)]BF4 with L (L = pyridine, morpholine, TOMPP) in the majority of cases gave mixtures of [Pd(acac)(PR3)(L)]BF4, [Pd(acac)(L)2]BF4, and [Pd(acac)(PR3)2]BF4 as result of sequence of ligand substitution reactions. The cationic palladium catalyst precursors were found to be active catalysts for phenylacetylene polymerization and oligomerization. Only cationic pre-catalysts with bulky TOMPP ligand gave high-molecular weight polyphenylacetylene. Catalysts with less bulky substituents mostly formed phenylacetylene oligomers. When activated with BF3⋅OEt2, these palladium complexes can also be used as catalysts for the vinyl addition polymerization of norbornene with activities 104–107 gpolymer molPd h−1.