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

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.