Preparation and protonation of 2-pyrimidyl- and 2-pyrazylpalladium(II) complexes |
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Authors: | Bruno Crociani Francesca Dibianca Amalia Giovenco Alberto Scrivanti |
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Institution: | Istituto di Chimica Generale, University of Palermo Italy;Centra Chimica Tecnologia Composti Metatlorganici Elementi Transizione, C.N.R., Padova Italy |
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Abstract: | The oxidative addition of 2-chloropyrimidine or 2-chloropyrazine to Pd(PPh3)4] yields a mixture of trans-PdCl(C4H3N2-C2)(PPh3)2] (I) and PdCl(μ-C4H3N2-C2,N1)(PPh3 (II) (C4H3N2 = 2-pyrimidyl or 2-pyrazyl group). The mononuclear complexes I are quantitatively converted into the binuclear species II upon treatment with H2O2. The reaction of II with HCl gives the N-monoprotonated derivatives cis-PdCl2(C4H4N2-C2)(PPh3)] (III), from which the cationic complexes trans-PdCl(C4H4N2-C2)(L) (L = PPh3, IV; PMe2Ph, V; PEt3, VI) can be prepared by ligand substitution reactions. Reversible proton dissociation occurs in solution for III–VI. The low-temperature 1H NMR spectra of trans-PdCl(C4H4N2-C2)(PMe2Ph)2]ClO4 show that the heterocyclic moiety undergoes restricted rotation around the PdC2 bond and that the 2-pyrazyl group is protonated predominantly at the N1 atom. These results and the 13C NMR data for the PEt3 derivatives are interpreted on the basis of a significant dπ → π★ back-bonding contribution to the palladium—carbon bond of the protonated ligands. |
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