Palladium carbene complexes for selective alkene di- and oligomerization

A series of palladium complexes were synthesized that comprise three sterically different C,N-bidentate coordinating NHC-pyridine ligands (NHC = N-heterocyclic carbene). In one set, the pyridine and the carbene are linked by a flexible CH2 group (a), in the other two sets, the two ligand units are directly linked and feature a shielding mesityl substituent on the carbene and either an unsubstituted pyridine (b) or a xylyl-substituted pyridine unit (c). Investigation of the reactivity of cationic complexes [Pd(C^N)Me(NCMe)]+, 6, analogues to Brookhart’s α-diimine system, towards alkenes showed a strong correlation between the catalytic activity and selectivity and the ligand setting. While 6a was inactive in ethylene conversion, 6b afforded low-molecular weight olefins (oligomerization), and 6c produced exclusively butene (dimerization). With styrene as substrate, exclusive dimerization occurred with all three complexes. Steric and electronic factors were identified that govern the disparate activity and selectivity, and that allow for efficient tailoring of the catalytic performance.Other funderSwiss National Science FoundationMIUR (Italy)University College DublinNB embargo date January 12, 2013 -- JG; au, ti, sp, ke, li -TS 08.05.1

Late Transition Metal Complexes with Pincer Ligands that Comprise N-Heterocyclic Carbene Donor Sites

The incorporation of N-heterocyclic carbenes into the well-established pincer ligand platform entails a number of attractive benefits. For example, NHCs are strong donors, and the metal–carbene bond is often remarkably robust towards oxidative and hydrolytic conditions and thus sustains in air, moisture, and even highly acidic environments. Moreover, NHCs can be readily functionalized and modulated and thus provide excellent opportunities for fine-tuning the properties of a coordinated metal center. As a consequence, the combination of the concepts of pincer ligands and of NHCs has much appeal and continues to attract considerable interest. This chapter summarizes accomplishments over the last 5 years in the domain of pincer carbene complexes containing Group 8–10 metals, including synthetic aspects as well as application of these complexes, which has included in particular catalysis and to a lesser extent materials science and medicinal areas