6533b833fe1ef96bd129c0c0

RESEARCH PRODUCT

Preparation and protonation of 2-pyrimidyl- and 2-pyrazylpalladium(II) complexes

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Abstract The oxidative addition of 2-chloropyrimidine or 2-chloropyrazine to [Pd(PPh 3 ) 4 ] yields a mixture of trans -[PdCl(C 4 H 3 N 2 - C 2 )(PPh 3 ) 2 ] (I) and [PdCl(μ-C 4 H 3 N 2 - C 2 , N 1 )(PPh 3 (II) (C 4 H 3 N 2 = 2-pyrimidyl or 2-pyrazyl group). The mononuclear complexes I are quantitatively converted into the binuclear species II upon treatment with H 2 O 2 . The reaction of II with HCl gives the N -monoprotonated derivatives cis -[PdCl 2 (C 4 H 4 N 2 - C 2 )(PPh 3 )] (III), from which the cationic complexes trans -[PdCl(C 4 H 4 N 2 - C 2 )(L) (L = PPh 3 , IV; PMe 2 Ph, V; PEt 3 , VI) can be prepared by ligand substitution reactions. Reversible proton dissociation occurs in solution for III–VI. The low-temperature 1 H NMR spectra of trans -[PdCl(C 4 H 4 N 2 - C 2 )(PMe 2 Ph) 2 ]ClO 4 show that the heterocyclic moiety undergoes restricted rotation around the PdC 2 bond and that the 2-pyrazyl group is protonated predominantly at the N 1 atom. These results and the 13 C NMR data for the PEt 3 derivatives are interpreted on the basis of a significant d π → π ★ back-bonding contribution to the palladium—carbon bond of the protonated ligands.