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 R2PCH2C(O)Ph (HL1, R = i-Pr; HL2, R = Ph), of the new acetamide-derived phosphine ligand (i-Pr)(2)PNHC(O) Me (HL3) and of Ph2PNHC(O) Me (HL4) have been examined towards Ni(II) complexes. Comparisons are made between systems in which the PCH2 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 HL2 and HL4 reacted with [(eta(5)-C5H5)CoI2(CO)] to afford the phosphine mono-adducts [(eta(5)-C5H5)CoI2{Ph2PCH2C(O)Ph}] (1) and [(eta(5)-C5H5)CoI2{Ph2PNHC(O)Me}] (3), respectively, which upon reaction with excess NEt3 yielded the phosphinoenolate complex [(eta(5)-C5H5)CoI{Ph2PCH (center dot center dot center dot) under barC((center dot center dot center dot) under barO)Ph}] (2) and the phosphinoiminolate complex [(eta(5)-C5H5)CoI{Ph2PN (center dot center dot center dot) under barC((center dot center dot center dot) under barO)Me}] (4), respectively. The complexes cis-[Ni{(i-Pr)(2)PN (center dot center dot center dot) under barC((center dot center dot center dot) under barO)Me}(2)] (6) and cis-[Ni{Ph2PN (center dot center dot center dot) under barC((center dot center dot center dot) under barO)Me}(2)] (7) were obtained similarly from NiCl2 and HL3 and HL4, respectively, in the presence of a base. The phosphinoenolate complex [Ni{(i-Pr)(2)PCH (center dot center dot center dot) under barC((center dot center dot center dot) under barO) Ph}(2)] (5) exists in ethanol as a mixture of the cis and trans isomers, in contrast to cis-[Ni{(Ph2PCH (center dot center dot center dot) under barC((center dot center dot center dot) under barO)Ph}(2)], and the solid-state structure of the trans isomer of 5 was established by X-ray diffraction. The structures of the ligand HL3 and of the complexes 1, 3 in 3 center dot 3/2CH(2)Cl(2), 4, 6 and 7 have also been determined by X-ray diffraction and are compared with those of related complexes. Complexes 4, 6 and 7 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.