Mononuclear and binuclear o-xylylene derivatives of Pd(II)

Article abstract of DOI:10.1016/S0020-1693(97)05792-7

The synthesis of binuclear complexes of composition C₆H₄-o-(CH₂PdX(PMe₃) ₂)₂ (X=Cl, 4a; Br, 4b) that contain bridging o-xylylene units, can be accomplished by reaction of the corresponding α,α′-dihaloxylenes with the Pd(0) species [Pd(η²-CH₂=CHCO₂Me)(PMe₃) ₂] (1). For X=Cl, partial oxidative addition takes place when the reaction is conducted at room temperature, leading to the mononuclear compound Pd(CH₂C₆H₄-o-CH₂Cl)Cl(PMe ₃)₂ (3a) which undergoes a slow decomposition process in solution that involves oxidative addition of the chloromethyl group to palladium. The binuclear derivative 4a can also be obtained by reaction of the metallacycle Pd(CH₂C₆H₄-o-CH₂)(PMe ₃)₂ (9) with PdCl₂(PMe₃)₂. Complexes 4a, 4b and 3a react with carbon monoxide and t-butyl isocyanide, giving rise to the corresponding acyl and imidoyl products. However, in the case of the imidoyl complex derived from 3a, (i.e., compound 13), the reactive chloromethyl group experiences a nucleophilic attack either by the metal or by the nitrogen atom of the imidoyl functionality to give respectively either unstable Pd(IV) species or the cationic amidocarbene complex 15. The structure of the cation of the 15·BPh₄^- salt has been determined by X-ray diffraction methods. Crystal data for 15·BPh₄^-: orthorhombic, Pna2₁, a=19.826(5), b=11.076(4), c=19.131(5) A, Z=4, R1=0.0544 and wR2=0.4141.