Exploiting the Mor-DalPhos – ancillary ligand in challenging Pd-catalysed monoarylation reactions
This minreview highlights the successful recent development of the heterobidentate DalPhos P,N ligand family for use in palladium catalysis. This ligand type can be viewed as offering an intermediate electron donating capacity relative to monodentate phosphines or carbenes and chelating bis(phosphine) ligands that are commonly employed in palladium catalysis. Notably, Pd/Mor-DalPhos mixtures have enabled the first examples of room temperature monoarylation of ammonia, as well enabling for the first time the monoarylation of hydrazine as well as acetone.
The application of homogeneous transition metal catalysis has revolutionized modern chemical synthesis (1), as recognized by the awarding of the Nobel Prizes for Chemistry in 2001, 2005, and 2010.(2-10) In the context of palladium-catalysed cross-coupling reactions, the arylation of amines (i.e. Buchwald-Hartwig amination) and the ?-arylation of carbonyl compounds have evolved into highly useful C-N and C-C bond-forming protocols that are complementary to other established cross-coupling methodologies (e.g. Suzuki, Negishi, Heck, etc.) (11-16). In the quest to expand the scope and utility of Buchwald-Hartwig amination and ?-arylation protocols, considerable focus has been directed toward the development of ancillary co-ligands that enable more challenging substrate pairings to be accommodated with suitable functional group tolerance and under milder conditions. As a result, a number of effective ligation strategies have emerged, including sterically demanding monodentate ligands such as biaryl monophosphines (L1) (13, 16) and N-heterocyclic carbenes (L2) (17) as well as rigid bisphosphine ligand motifs (e.g. ...