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(double bond; length as m-dashO)(H)(tBu) (4a′), MeC8H5N–P(double bond; length as m-dashO)(H)(tBu) (4b′), and PhC8H5N–P(double bond; length as m-dashO)(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.