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

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.