1739-81-7Relevant articles and documents
On the electronic impact of abnormal C4-bonding in n-heterocyclic carbene complexes
Heckenroth, Marion,Neels, Antonia,Garnier, Michael G.,Aebi, Philipp,Ehlers, Andreas W.,Albrecht, Martin
, p. 9375 - 9386 (2009)
Sterically similar palladium dicarbene complexes have been synthesized that comprise permethylated dicarbene ligands which bind the metal center either in a normal coordination mode via C2 or abnormally via C4. Due to the strong structural analogy of the complexes, differences in reactivity patterns may be attributed to the distinct electronic impact of normal versus abnormal carbene bonding, while stereoelectronic effects are negligible. Unique reactivity patterns have been identified for the abnormal carbene complexes, specifically upon reaction with Lewis acids and in oxidative addition-reductive elimination sequences. These reactivities as well as analytical investigations using X-ray diffraction and X-ray photoelectron spectros-copy indicate that the C4 bonding mode increases the electron density at the metal center substantially, classifying such C4-bound carbene ligands amongst the most basic neutral donors known thus far. A direct application of this enhanced electron density at the metal center is demonstrated by the catalytic H2 activation with abnormal carbene complexes under mild conditions, leading to a catalytic process for the hydrogenation of olefins.
Synthesis, Stability, and (De)hydrogenation Catalysis by Normal and Abnormal Alkene- And Picolyl-Tethered NHC Ruthenium Complexes
Malan, Frederick P.,Singleton, Eric,Van Rooyen, Petrus H.,Albrecht, Martin,Landman, Marilé
, p. 2624 - 2635 (2019/07/03)
A series of p-cymene and cyclopentadienyl Ru(II)-aNHC complexes were synthesized from 2-methylimidazolium salts with either an N-bound alkenyl (1, 3) or picolyl tether (6, 7). The C(5)-Me substituted alkenyl-tethered analogues (2, 4) were also synthesized. Ag-mediated C(2)-dealkylation was a prominent side reaction that led to the formation of normally bound NHC Ru(II) complexes, which in selected cases were isolated (5, 8). A C(4)- over C(2)-selectivity for ruthenium binding was established by protecting the C(2)-position with an iPr group on the imidazolium precursor, for which unique p-cymene (9) and cyclopentadienyl (10) Ru(II)-aNHC derivatives were synthesized. All complexes were applied in the transfer hydrogenation of ketones and in secondary alcohol oxidation, with higher catalytic activity for the p-cymene over the cyclopentadienyl systems, as well as the alkenyl- over the picolyl-containing aNHC complexes.