Palladium catalyzed cross-coupling reactions are a versatile tool in organic chemistry for the production of small molecules. Current research interests involve the development of new catalyst systems for various palladium catalyzed reactions. Previous work has suggested the active species for most palladium-catalyzed cross-coupling reactions to be a mono-ligated palladium(0). Therefore, the design of precatalysts with an established 1:1 L:Pd ratio are of interest. Specifically, we are focused on the synthesis of mono-ligated palladium(II) precatalysts of general formula [(R3P)PdCl2]2, using di-(tert-butyl) neopentyl phosphine (DTBNpP) and trineopentyl phosphine (TNpP) as ligands. The [(DTBNpP)PdCl2]2 precatalyst was used to optimize reaction conditions for the Suzuki cross coupling of aryl bromides with aryl boronic acids. Under optimized conditions, both [(DTBNpP)PdCl2]2 and [(TNpP)PdCl2]2 were effective precatalysts for the coupling of a wide range of substrates. In addition to precatalyst activity, we investigated the possible reduction routes of the precatalysts under optimized conditions and monitored reactions by 31P NMR spectroscopy. Spectra obtained from 31P NMR experiments revealed a side reaction resulting in a catalytically inactive palladacycle species. Efforts were made to better understand the cause of this side reaction. It was found that palladacycle formation is solvent dependent with less polar solvent greatly inhibiting generation of the inactive palladium species. The results obtained from the mechanistic investigations led to further optimization of reaction conditions to decrease the amounts of catalytically inactive side products formed. Under new reaction conditions the amount of precatalyst required to achieve complete conversion was significantly decreased.

Mechanistic investigations of palladium(II) precatalysts: Effects of reaction conditions on precatalyst activity in the Suzuki cross-coupling of aryl bromides

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.