A Modern Twist to a Classic Synthetic Route: Ph₃Bi-Based Redox Transmetalation Protolysis (RTP) for the Preparation of Barium Metalorganic Species

This paper reports advances in redox transmetalation/protolysis (RTP) using the readily available Ph₃Bi for the synthesis of a series of barium metal-org. species. Based on easily available starting materials, an easy one-pot procedure and workup, the authors have obtained BaL₂ compds. (L = bis(trimethylsilyl)amide, phenyl(trimethylsilyl)amide, pentamethylcyclopentadienide, fluorenide, 2,6-di-isopropylphenolate, and 3,5-diphenylpyrazolate) quant. by sonication of an excess of barium metal with triphenylbismuth and HL in perdeuterotetrahydrofuran, as established by NMR measurements. Rates of conversion are affected by both pK_a and bulk of HL. Competition occurs from direct reaction of Ba with HL thereby enhancing the overall conversion, the effect being pronounced for the less bulky and more acidic ligands. Overall the method significantly adds to the synthetic armory for barium metal-org./organometallic compds.