Preparation and application of indolyl secondary phosphine oxides in palladium complexes catalyzed Suzuki–Miyaura cross-coupling reaction

Several new indolyl secondary phosphine oxides (SPOs), C8H6N–P(O)(H)(tBu) (4a′), MeC8H5N–P(O)(H)(tBu) (4b′), and PhC8H5N–P(O)(H)(tBu) (4c′), were prepared from the reactions of corresponding 1H-indoles with PtBuCl2 and hydrolysis followed. Further reaction of 4a′, a tautomeric form of C8H6N–P(OH)(tBu) (4a), with Pd(COD)Cl2 yielded a di-palladium complex, [(4a)(4a-H+)Pd(μ-Cl)]2 (6a). Crystal structures of PhC8H5N–P(Cl)(tBu) (3c), (4c′) and (6a) were determined by single-crystal X-ray diffraction methods. The stability of this type of SPO is presumably caused by the indolyl scaffold. In addition, SPOs are air- and moisture-stable preligands and are advantageous for the purpose of storage. In this work, these SPO ligands were employed in the Suzuki–Miyaura cross-coupling reactions as catalytic precursors. This catalytic condition has been tolerated to a variety of functional groups and the coupling reactions underwent efficiently with the arylbromides and arylchlorides, respectively.

Several new indolyl secondary phosphine oxides (SPOs) were prepared. Further reactions with Pd(COD)Cl2 yielded di-palladium complexes. These SPO ligands combined with various palladium salts were employed in the Suzuki–Miyaura reactions and exhibited satisfactory results even with less reactive arylchlorides under elevated temperature. Presumably, the indolyl scaffold provides the thermal stability of this type of SPOs. This system also showed good tolerance toward diverse functional groups.Figure optionsDownload as PowerPoint slide