A Two-Coordinate Palladium Complex with Two Dialkylphosphinyl Ligands

摘要

Transition-metal complexes with ligands having an unpaired electron have received much attention because of their unique electronic structures arid importance in bioinorganic chemistry and catalytic chemistry.1 Although phosphinyl radicals (R2P·) are one of the fascinating bifunctional ligands having an unpaired electron in addition to lone-pair electrons on the two-coordinate phosphorus center, transition-metal complexes with a phosphinyl radical ligand are still quite rare compared to the complexes with pertinent aminyl radicals (R2N·), and the structures and properties of the phosphinyl radical complexes have been discussed mainly based on EPR spectroscopy. Cowley et al. have synthesized iron and cobalt complexes of a persistent dialkylphosphinyl radical [(Me3Si)2CH]2P· with the unpaired electron localized mainly on the metal moiety. Geoffroy et al. have generated photochemically pentacarbonyl Group 6 metal complexes of diphenylphosphinyl radical in the single crystals and found that the unpaired electron is slightly delocalized onto the metal. Very recently, Streubel et al. have observed pentacarbonyl tungsten complexes of RC1P· (R = CH(SiMe3)2, C5Me5) in solution and found that the planarity of the geometry around the phosphorus atom and the distribution of unpaired electron depends on the nature of the substituents at phosphorus. Although complexes with two or more phosphinyl radical ligands are expected to show unique structure, properties, and reactivity owing to multiple interactions between phosphinyl ligands and the metal center, such complexes are still unknown.