Cationic (fluoromesityl)palladium(II) complexes |
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Authors: | Camino Bartolomé Jose Miguel Martín-Alvarez Fernando Villafañe |
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Institution: | Química Inorgánica, Facultad de Ciencias, Universidad de Valladolid, 47005 Valladolid, Spain |
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Abstract: | Halide abstraction from Pd(μ-Cl)(Fmes)(NCMe)]2 (Fmes = 2,4,6-tris(trifluoromethyl)phenyl or nonafluoromesityl) with TlBF4 in CH2Cl2/MeCN gives Pd(Fmes)(NCMe)3]BF4, which reacts with monodentate ligands to give the monosubstituted products trans-Pd(Fmes)L(NCMe)2]BF4 (L = PPh3, P(o-Tol)3, 3,5-lut, 2,4-lut, 2,6-lut; lut = dimethylpyridine), the disubstituted products trans-Pd(Fmes)(NCMe)(PPh3)2]BF4, cis-Pd(Fmes)(3,5-lut)2(NCMe)]BF4, or the trisubstituted products Pd(Fmes)L3]BF4 (L = CNtBu, PHPh2, 3,5-lut, 2,4-lut). Similar reactions using bidentate chelating ligands give Pd(Fmes)(L-L)(NCMe)]BF4 (L-L = bipy, tmeda, dppe, OPPhPy2-N,N′, (OH)(CH3)CPy2-N,N′). The complexes trans-Pd(Fmes)L2(NCMe)]BF4 (L = PPh3, tht) (tht = tetrahydrothiophene) and Pd(Fmes)(L-L)(NCMe)]BF4 (L-L = bipy, tmeda) were obtained by halide extraction with TlBF4 in CH2Cl2/MeCN from the corresponding neutral halogeno complexes trans-Pd(Fmes)ClL2] or Pd(Fmes)Cl(L-L)]. The aqua complex trans-Pd(Fmes)(OH2)(tht)2]BF4 was isolated from the corresponding acetonitrile complex. Overall, the experimental results on these substitution reactions involving bulky ligands suggest that thermodynamic and kinetic steric effects can prevail affording products or intermediates different from those expected on purely electronic considerations. Thus,water, whether added on purpose or adventitious in the solvent, frequently replaces in part other better donor ligands, suggesting that the smaller congestion with water compensates for the smaller M-OH2 bond energy. |
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Keywords: | Palladium Fluoromesityl Steric effects Kinetic Aqua Cationic |
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