Hybrid ligands: synthesis, characterization and co-ordinative properties of a mixed phosphine–β-ketophosphorus ylide

Abstract

Direct C-phosphination at the methyl carbon of the keto-stabilized ylide MeC(O)CHPPh ₃ was achieved using 2 equivalents of LiBu and 1 equivalent of PPh ₂ Cl. The structure of the resultant phosphine–phosphorus ylide, Ph ₂ PCH ₂ C(O)CHPPh ₃ , was shown by an X-ray diffraction study to comprise a 1:1 mixture of two rotamers built around the CH ₂ –C(O) axis, the C(O)CHPPh ₃ moiety of both conformers adopting a cisoid form. A rotational barrier of 10 kJ mol ^-1 between the two isomers was found using molecular-mechanics simulation. Oxidation of the ylide with sulfur resulted in quantitative formation of the corresponding phosphine sulfide Ph ₂ P(S)CH ₂ C(O)CHPPh ₃ . By treating 2 equivalents of Ph ₃ PCHC(O)CH ₂ PPh ₂ (L) with [{Pd(η ³ -C ₃ H ₄ Me-2)Cl} ₂ ], the P-monodentate complex [PdCl(η ³ -C ₃ H ₄ Me-2)L] 1 was formed quantitatively. Reaction of 2 equivalents of L with [{PdCl(C ₆ H ₄ CH ₂ NMe ₂ - o)} ₂ ] in tetrahydrofuran afforded, in quantitative yield, the stable cationic complex [Pd(C ₆ H ₄ CH ₂ NMe ₂ -o) L]Cl 2 where the hybrid ligand is P,O-bonded to the palladium, thus illustrating the nucleophilic character of the oxygen atom of the ylide. The BF ₄ ^- analogue of the latter complex, 3, prepared in order to exclude counter-anion effects, was obtained by treating 1 with AgBF ₄ . The nickel complexes [Ni(η ⁵ -C ₅ Ph ₅ )L]X (X = I 4 or Br 5), in which the ligand is bound as in 1 and 2, were obtained by treating the corresponding [Ni(η ⁵ -C ₅ Ph ₅ )X(CO)] complexes with the ylide L.