A new set of nickelacyclic carboxylates (“nickelalactones”) containing pyridine as supporting ligand: synthesis, structures and application in C–C– and C–S– linkage reactions

Nickelacycles of the type [(py)2Ni(CH2CH2COO)] (1a), [(py)2Ni(C(Et)double bond; length as m-dashC(Et)–COO)] (2a), and [(py)Ni(CH2C(CH3)C(CH3)–CH2–COO)] (3a) were synthesized and structurally investigated by NMR, IR spectroscopy and in case of 1a and 2a by X-ray diffraction analysis. In 1a and 2a the Ni(II) ion has square-planar geometry, in contrast to the η3allyl compound [(bipy)Ni(CH2C(CH3)C(CH3)–CH2–COO)] (3b), in which nickel center adopts square-pyramidal geometry. 1a reacts with di(2-pyridyl)dimethylsilane (Me2(2-py)2Si) under exchange of the pyridine ligands to give 1c. 1a–3a and their bipy derivatives react with di-p-tolyldisulfide to form β-thioesters upon workup. Furthermore, reaction of 2-bromopropiophenone with nickelacycles of the type 2 results in the formation of 3,4-diethyl-6-hydroxy-5-methyl-6-phenyl-5,6-dihydro-2H-pyrane-2-one in good yields (64–75%). These reactions offer attractive new preparative routes for functionalized organic compounds.