An Alternative Approach to PEPPSI Catalysts: From Palladium Isonitriles to Highly Active Unsymmetrically Substituted PEPPSI Catalysts

Abstract

A series of new pyridine‐enhanced precatalyst preparation, stabilization, and initiation (PEPPSI)‐type complexes bearing different types of carbene ligands was prepared by the modular and convergent template synthesis strategy. Nitrogen acyclic carbenes, saturated and unsaturated five‐membered NHC, saturated six‐membered NHCs, and five‐membered N‐heterocyclic oxo‐carbene (NHOC) ligands on palladium were prepared this way. These new organometallic compounds then were tested in Suzuki and Negishi cross‐coupling reactions by using substrates with one or two substituents in ortho‐position of the new CC bond being formed. Both aryl chlorides and bromides were tested as coupling partners. In some cases, the new ligands gave results similar to Organ’s successful IPr‐based and IPent‐based PEPPSI derivatives, with aryl bromides 0.05 mol % catalyst load still gave satisfactory results, with aryl chlorides 0.5 mol % were needed.

One-Pot Tandem Hiyama Alkynylation/Cyclizations by Palladium(II) Acyclic Diaminocarbene (ADC) Complexes Yielding Biologically Relevant Benzofuran Scaffolds

“…With the success of the transition-metal N-heterocyclic carbene (NHC) complexes in homogeneous catalysis being well-recognized now, − their application in more challenging domains of catalysis such as bifunctional catalysis, , asymmetric catalysis, and the tandem reactions are of contemporary interest. Alongside, the quest for exploring new variants of the carbene ligands is being simultaneously pursued for meeting the demands of these intriguing catalyses. − ,,, In this context, a special class of heteroatom-stabilized singlet carbene ligands in the form of the acyclic diaminocarbene (ADC) is worth mentioning. − Owing to their remarkably simple preparative procedures, as opposed to the long and protracted preparation methods of the contemporary phosphine and the NHC ligands, the ADC ligands have attracted attention lately. − Furthermore, the absence of any geometric constraints that allow free orientation of the ligand substituents make these ADC ligands different from their cyclic ones, for example, the NHC ligands, thereby imparting different catalytic properties to these ligands.…”

Suzuki–Miyaura and Hiyama coupling catalyzed by PEPPSI-type complexes with non-bulky NHC ligand

“…In addition, PEPPSI complexes can be easily obtained and are easy to handle in contrast to other Pd-NHC precursors [8][9][10][11][12][13][14][15]. Recently the new preparations of PEPPSI complexes have been reported [16,17].…”

Polystyrene-Supported Acyclic Diaminocarbene Palladium Complexes in Sonogashira Cross-Coupling: Stability vs. Catalytic Activity

“…The presence of only one C≡N peak indicates on the presence in the structure of one unreacted isocyanide ligand. The longwave shift of the C≡N peak on the transition PdCl 2 (CNR) 2 → PdCl 2 (ADC)(CNR) accords with higher σ-donating ability of the ADC ligand compared to isocyanide [53][54][55][56][57].…”