Dicoordinate phosphorus-centered radical (phosphinyl radical) is a fascinating reactive intermediate in phosphorus chemistry because it has a bifunctional phosphorus center owing to an unpaired electron and a lone pair. I report herein synthesis, structure, properties, and various reactions of the first stable dialkylphosphinyl radical, 2,2,5,5-tetrakis(trimethylsilyl)-1-phosphacyclopentane-1-yl (
8), which is monomeric both in solution and in the solid state. Palladium complex bearing two phosphinyl radicals as ligands (
24) is also synthesized by the ligand exchange reaction of tetrakis(trimethylphosphine)palladium with two equivalents of radical
8. Complex
24 shows unique phosphorus-palladium double bond character. Antimony and bismuth analogues of phosphinyl radicals are elusive species but are thought to be important intermediates. We have succeeded in the observation of antimony- and bismuth-centered radicals (
30 and
31) as persistent species in solution by the dissociation of the corresponding dimer.
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