Synthesis and characterization of palladium(II) complexes with the α-stabilized phosphoylide ligand Ph3PC(H)CONMe2

Abstract

The reactivity of the ylide Ph₃PC(H)CONMe₂ towards different palladium(II) complexes has been explored. Reaction with the cationic solvated complexes [Pd(dmba)(NCMe)₂]A, [Pd(R-dmphea)(NCMe)₂]A and [Pd(dmba)(py)(thf)]A (dmba = C₆H₄CH₂NMe₂-2; R-dmphea = R-C₆H₄CHMeNMe₂-2; py = pyridine; A = ClO₄^–) resulted in the formation of [Pd(dmba)(OH₂){CH(CONMe₂)(PPh₃)}]A 1, [Pd(R-dmphea)(OH₂){CH(CONMe₂)(PPh₃)}]A 2, and [Pd(dmba)(py){CH(CONMe₂)(PPh₃)}]A 3 respectively, in which the ylide is co-ordinated through its carbon atom, and trans to the NMe₂ group. The nucleophilic character of the ylidic carbon atom promotes cleavage of the halide bridging systems of the dinuclear precursors [{Pd(µ-Br)(η³-C₃H₅)}₂], [{Pd(µ-Cl)(C–P)}₂], [{Pd(µ-Cl)(C₆F₅)(tht)}₂], [{Pd(µ-Cl)(dmba)}₂], [{Pd(µ-Cl)(R-dmphea)}₂], [{Pd(µ-Cl)[C₆H₂(OMe)₂-4,5-CHNCH₂Ph-2]}₂] and [{Pd(µ-Cl)Cl(PPh₃)}₂] (C–P = o-(di-o-tolylphosphino)benzyl; tht = tetrahydrothiophene), giving neutral mononuclear derivatives in which the ylide is selectively C-co-ordinated [PdBr(η³-C₃H₅){CH(CONMe₂)(PPh₃)}] 4, [PdCl(C–P){CH(CONMe₂)(PPh₃)}] 5, [PdCl(C₆F₅)(tht){CH(CONMe₂)(PPh₃)}] 6, [PdCl(dmba){CH(CONMe₂)(PPh₃)}] 7, [PdCl(R-dmphea){CH(CONMe₂)(PPh₃)}] 8, [PdCl{C₆H₂(OMe)₂-4,5-CHNCH₂Ph-2}{CH(CONMe₂)(PPh₃)}] 9 and [PdCl₂(PPh₃){CH(CONMe₂)(PPh₃)}] 10. Complexes with the ylide co-ordinated through the heteroatom (oxygen or nitrogen) were not found. This selective C-co-ordination is discussed in terms of electronic and steric factors.