HYBRID LIGANDS - SYNTHESIS, CHARACTERIZATION AND COORDINATIVE PROPERTIES OF A MIXED PHOSPHINE-BETA-KETOPHOSPHORUS YLIDE

Direct C-phosphination at the methyl carbon of the keto-stabilized yli de MeC(O)CH=PPh3 was achieved using 2 equivalents of LiBu and 1 equiva lent of PPh2Cl. The structure of the resultant phosphine-phosphorus yl ide, Ph2PCH2C(O)CH=PPh3, was shown by an X-ray diffraction study to co mprise a 1:1 mixture of two rotamers built around the CH2-C(O) axis, t he C(=O)CH=PPh3 moiety of both conformers adopting a cisoid form. A ro tational barrier of 10 kJ mol(-1) between the two isomers was found us ing molecular-mechanics simulation. Oxidation of the ylide with sulfur resulted in quantitative formation of the corresponding phosphine sul fide Ph2P(S)CH2-C(O)CH=PPh3. By treating 2 equivalents of Ph3P=CHC(O)C H2PPh2 (L) with [{Pd(eta(3)-C3H4Me-2)Cl}(2)], the P-monodentate comple x [PdCl(eta(3)-C3H4Me-2)L] 1 was formed quantitatively. Reaction of 2 equivalents of L with [{PdCl(C6H4CH2NMe2-o)}(2)] in tetrahydrofuran af forded, in quantitative yield, the stable cationic complex [Pd(C6H4CH2 NMe2-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 BF4- 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(eta(5)-C5Ph5)L]X (X = I 4 or Br 5), in whi ch the ligand is bound as in 1 and 2, were obtained by treating the co rresponding [Ni(eta(5)-C5Ph5)X(CO)] complexes with the ylide L.