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)(Bu-t) (4a'), MeC8H5N-P(=O)(H)(Bu-t) (4b'), and PhC8H5N-P(=O)(H)(Bu-t) (4c'). were prepared from the reactions of corresponding 1H-indoles with (PBuCl2)-Bu-t and hydrolysis followed. Further reaction of 4a', a tautomeric form of C8H6N-P(OH)(Bu-t) (4a), with Pd(COD)Cl-2 yielded a di-palladium complex, [(4a)(4a-H+)Pd(mu-Cl)](2) (6a). Crystal structures of PhC8H5N-P(Cl)(Bu-t) (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. (C) 2013 Elsevier Ltd. All rights reserved.