Synthesis and characterization of Co and Ni complexes stabilized by keto- and acetamide-derived P,O-type phosphine ligands.

The coordination properties of the beta-keto phosphine ligands R(2)PCH(2)C(O)Ph (, R = i-Pr; , R = Ph), of the new acetamide-derived phosphine ligand (i-Pr)(2)PNHC(O)Me () and of Ph(2)PNHC(O)Me () have been examined towards Ni(ii) complexes. Comparisons are made between systems in which the PCH(2) function of the ketophosphine has been replaced with an isoelectronic PNH group in amide-derived ligands, or the PCH functionality of phosphinoenolates with a PN group in phosphinoiminolate complexes. Furthermore, ligands and reacted with [(eta(5)-C(5)H(5))CoI(2)(CO)] to afford the phosphine mono-adducts [(eta(5)-C(5)H(5))CoI(2){Ph(2)PCH(2)C(O)Ph}] () and [(eta(5)-C(5)H(5))CoI(2){Ph(2)PNHC(O)Me}] (), respectively, which upon reaction with excess NEt(3) yielded the phosphinoenolate complex [(eta(5)-C(5)H(5))[upper bond 1 start]CoI{Ph(2)PCH[horiz bar, triple dot above]C([horiz bar, triple dot above]O[upper bond 1 end])Ph}] () and the phosphinoiminolate complex [(eta(5)-C(5)H(5))[upper bond 1 start]CoI{Ph(2)PN[horiz bar, triple dot above]C([horiz bar, triple dot above]O[upper bond 1 end])Me}] (), respectively. The complexes cis-[[upper bond 1 start]Ni{(i-Pr)(2)PN[horiz bar, triple dot above]C([horiz bar, triple dot above]O[upper bond 1 end])Me}(2)] () and cis-[[upper bond 1 start]Ni{Ph(2)PN[horiz bar, triple dot above]C([horiz bar, triple dot above]O[upper bond 1 end])Me}(2)] () were obtained similarly from NiCl(2) and (3) and (4), respectively, in the presence of a base. The phosphinoenolate complex [[upper bond 1 start]Ni{(i-Pr)(2)PCH[horiz bar, triple dot above]C([horiz bar, triple dot above]O[upper bond 1 end])Ph}(2)] () exists in ethanol as a mixture of the cis and trans isomers, in contrast to cis-[[upper bond 1 start]Ni{(Ph(2)PCH[horiz bar, triple dot above]C([horiz bar, triple dot above]O[upper bond 1 end])Ph}(2)], and the solid-state structure of the trans isomer of was established by X-ray diffraction. The structures of the ligand (3) and of the complexes , in .3/2CH(2)Cl(2), , and have also been determined by X-ray diffraction and are compared with those of related complexes. Complexes , and contain a five-membered heteroatomic metallocyclic moiety, which is constituted by five different chemical elements. The structural consequences of the steric bulk of the P substituents and of the electronic characteristics of the P,O chelates are discussed.