Proazaphosphatranes : a highly effective class of triaminophosphine ligands in palladium-catalyzed cross-coupling reactions /
Abstract (Summary)In recent years proazaphosphatranes of type P(RNCH?CH?)?N have proven their synthetic utility as catalysts and as stoichiometric bases in a variety of organic transformations. Herein are described their application as a supporting ligand for palladium in palladium-catalyzed cross-coupling reactions, such as Buchwald-Hartwig amination, Stille, and Suzuki reactions. Screening of various proazaphosphatranes (R = Me, Et, i-Pr, i-Bu, neo-Pent) revealed that the electron-rich, bulky, and commercially available P(i-BuNCH?CH?)?N is the most effective ligand of this series in the aforementioned reactions. Aryl halides (bromides and iodides), including notoriously unreactive aryl chlorides, have been shown to participate in these processes. It has also been discovered that for certain combinations of substrates in palladium-catalyzed Stille reactions, the proazaphosphatranes P(PhCH?NCH?CH?)?N and P(PhCH?NCH?CH?)?N(i-BuNCH?CH?) provided even more active palladium catalysts than P(i-BuNCH?CH?)?N. Additionally, the synthesis of the new bicyclic triaminophosphine ligand P(i-BuNCH?)?CMe and its efficacy in Buchwald-Hartwig amination reactions is demonstrated. This ligand provides a remarkably general, efficient, and mild palladium catalyst for aryl iodide amination. This ligand also allows a weak base, such as Cs?CO?, to function in these reactions. Finally, the first general protocol for the ligand-, copper-, and amine-free Sonogashira reaction has been developed. The success of this method hinges on the use of tetrabutylammonium acetate as the base.
School:Iowa State University
School Location:USA - Iowa
Source Type:Master's Thesis
Date of Publication: