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Université de Fribourg

Palladation of diimidazolium salts at the C4 position: access to remarkably electron-rich palladium(II) centers

Heckenroth, Marion ; Kluser, Evelyne ; Neels, Antonia ; Albrecht, Martin

In: Dalton Transactions, 2008, p. 6242 - 6249

Palladation of C2-protected diimidazolium salts with Pd(OAc)₂ afforded complexes comprising C4-bound N-heterocyclic dicarbene ligands. The reactivity of these complexes towards Lewis acids (AgBF₄, AgOAc) and Brønsted acids (H₂SO₄, H₃PO₄, HOAc) revealed that abnormal C4 bonding of the carbenes markedly increases the nucleophilicity of the coordinated palladium center as compared to C2...

Université de Fribourg

Tamed tigers: stabilization of reactive carbenes

Albrecht, Martin

In: ChemPhysChem, 2008, vol. 9, no. 13, p. 1829-1831

Université de Fribourg

Rhodium(iii) complexes containing C4-bound N-heterocyclic carbenes: synthesis, coordination chemistry, and catalytic activity in transfer hydrogenation

Yang, Liangru ; Krüger, Anneke ; Neels, Antonia ; Albrecht, Martin

In: Organometallics, 2008, vol. 27, no. 13, p. 3161–3171

Direct metalation of C2-protected diimidozolium salts with RhCl₃ or [RhCl(cod)]₂ and KI afforded a series of new rhodium(III) complexes with abnormally C4-bound, cis-chelating NHC ligands. The complexes were isolated as dimetallic species containing two (μ²-I)₃-bridged rhodium(III) centers. In the presence of coordinating ligands such as CH₃CN, PPh₃, or dppe, the dimeric...

Université de Fribourg

Piano-stool iron(ii) complexes as probes for the bonding of n-heterocyclic carbenes: indications for -acceptor ability

Mercs, Laszlo ; Labat, Gaël ; Neels, Antonia ; Ehlers, Andreas ; Albrecht, Martin

In: Organometallics, 2006, vol. 25, no. 23, p. 5648 -5656

A series of new piano-stool iron(II) complexes comprising mono- and bidentate chelating N-heterocyclic carbene ligands [Fe(cp)(CO)(NHC)(L)]X have been prepared and analyzed by spectroscopic, electrochemical, crystallographic, and theoretical methods. Selectively substituting the L site with a series of ligands going from carbene to pyridine to CO suggests that CO is the strongest π...

Université de Fribourg

Palladium complexes comprising C(4)-bound diimidazolylidene carbenes

Heckenroth, Marion ; Albrecht, Martin

In: Chimia, 2008, vol. 62, no. 4, p. 253-255

Imidazolium-derived palladium dicarbene complexes have been synthesized which feature either normal C(2) carbene bonding or abnormal C(4) bonding. Comparison of the reactivity of these complexes, in particular towards Lewis acids (H⁺, Ag⁺), indicate consistently that C(4)-bound carbenes are stronger donors than their C(2)-bound analogs. As a consequence of this electronic impact, palladium...

Université de Fribourg

C4-bound imidazolylidenes: from curiosities to high-impact carbene ligands

Albrecht, Martin

In: Chemical Communications, 2008, p. 3601-3610

This feature article summarizes the progress achieved thus far in using C4-bound imidazolylidenes as a new class of ligands for transition metals. Since the discovery of this unusual carbene bonding mode in 2001, various rational routes towards complexes containing C4-bound carbenes have evolved. These advances allowed for studying the impact of this new type of ligand on the transition metal...

Université de Fribourg

Mild and rational synthesis of palladium complexes comprising C(4)-bound N-heterocyclic carbenes

Kluser, Evelyne ; Neels, Antonia ; Albrecht, Martin

In: Chemical Communications, 2006, p. 4495-4497

Oxidative addition of pyridyl-functionalised 4-iodoimidazolium salts to palladium(0) gives catalytically active complexes in which the N-heterocyclic carbene is bound to the palladium(II) centre in a non-classical bonding mode via C(4).

Université de Fribourg

Catalytically active palladium pyridylidene complexes: pyridinium ionic liquids as N-heterocyclic carbene precursors

Albrecht, Martin ; Stoeckli-Evans, Helen

Pyridinium salts similar to those used as ionic liquid solvents readily undergo palladation in the presence of a base, thus giving palladium-pyridylidene N-heterocyclic carbene complexes that are active catalysts for Suzuki-type cross-coupling reactions.