Université de Fribourg

Efficient electronic communication of two ruthenium centers through a rigid ditopic N-heterocyclic carbene linker

Nussbaum, Michael ; Schuster, Oliver ; Albrecht, Martin

In: Chemistry – A European Journal, 2013, vol. 19, no. 51, p. 17517–17527

A ditopic benzobis(carbene) ligand precursor was prepared that contained a chelating pyridyl moiety to ensure co-planarity of the carbene ligand and the coordination plane of a bound octahedral metal center. Bimetallic ruthenium complexes comprising this ditopic ligand [L₄Ru-C,N-bbi-C,N-RuL₄] were obtained by a transmetalation methodology...

Université de Fribourg

Probing intermetallic coupling in dinuclear N-heterocyclic carbene ruthenium(II) complexes

Mercs, Laszlo ; Neels, Antonia ; Stoeckli-Evans, Helen ; Albrecht, Martin

In: Inorganic Chemistry, 2011, vol. 50, no. 17, p. 8188–8196

A series of bimetallic N-heterocyclic carbene (NHC) ruthenium(II) complexes were synthesized, which comprise two [RuCl₂(cymene)(NHC)] units that are interlinked via the NHC nitrogens by alkyl chains of different length. Electrochemical characterization revealed two mutually dependent oxidation processes for the complex with a methylene linker, indicating moderate intramolecular electronic...

Université de Fribourg

Modulating the steric, electronic, and catalytic properties of cp* ruthenium half-Sandwich complexes with β-diketiminato ligands

Phillips, Andrew D. ; Thommes, Katrin ; Scopelliti, Rosario ; Gandolfi, Claudio ; Albrecht, Martin ; Severin, Kay ; Schreiber, Dominique F. ; Dyson, Paul J.

In: Organometallics, 2011, vol. 30, no. 22, p. 6119–6132

Five different types of β-diketiminate ligands, bearing electron-donating to strongly electron-withdrawing substituents, were synthesized and used in the synthesis of Cp* ruthenium complexes (Cp* = η⁵-C₅Me₅). One series consists of complexes with a covalent RuIII–Cl bond, and the other series features a reduced RuII center, where the chloride is abstracted by...

Université de Fribourg

Transfer hydrogenation of ketones and activated olefins using chelating NHC ruthenium complexes

Horn, Sabine ; Gandolfi, Claudio ; Albrecht, Martin

In: European Journal of Inorganic Chemistry, 2011, vol. 2011, no. 18, p. 2863–2868

N-Heterocyclic carbene (NHC) ruthenium complexes consisting of different donor substituents attached to the NHC ligand efficiently catalyse the transfer hydrogenation of ketones and of activated olefins in α,β-unsaturated ketones to give saturated alcohols. The most active catalyst precursor contains a tethered olefin as a hemilabile donor site. This complex also converts nitriles and,...

Université de Fribourg

Synthesis and catalytic activity of histidine-based NHC ruthenium complexes

Monney, Angèle ; Venkatachalam, Galmari ; Albrecht, Martin

In: Dalton Transactions, 2011, vol. 40, no. 12, p. 2716-2719

Main-chain C,N-protected histidine has been successfully alkylated at both side-chain nitrogens. The corresponding histidinium salt was metallated with ruthenium(II) by a transmetalation procedure, thus providing histidine-derived NHC ruthenium complexes. These bio-inspired complexes show appreciable activity in the catalytic transfer hydrogenation of ketones.

Université de Fribourg

Main-chain organometallic polymers comprising redox-active iron(II) centers connected by ditopic N-heterocyclic carbenes

Mercs, Laszlo ; Neels, Antonia ; Stoeckli-Evans, Helen ; Albrecht, Martin

In: Dalton Transactions, 2009, vol. 35, p. 7168-7178

Main-chain organometallic polymers were synthesized from bimetallic iron(II) complexes containing a ditopic N-heterocyclic carbene (NHC) ligand [(cp)(CO)LFe(NHC∼NHC)Fe(cp)(CO)L]X₂ (where NHC∼NHC represents a bridging dicarbene ligand, L = I⁻ or CO). Addition of a diimine ligand such as pyrazine or 4,4′-bipyridine, interconnected these bimetallic complexes and gave the...

Université de Fribourg

Chelating NHC ruthenium(II) complexes as robust homogeneous hydrogenation catalysts

Gandolfi, Claudio ; Heckenroth, Marion ; Neels, Antonia ; Laurenczy, Gbor ; Albrecht, Martin

In: Organometallics, 2009, vol. 28, no. 17, p. 5112–5121

A series of ruthenium(II) complexes have been prepared by using bidentate chelating N-heterocyclic carbene (NHC) ligands that feature different donor groups E (E = olefin, thioether, carboxylate, and NHC). Rigid coordination of all donor sites was concluded from NMR spectroscopy, and the electronic impact of the donor group was evaluated by electrochemical analyses. The chelating donor group had...

Université de Fribourg

Probing the potential of N-heterocyclic carbenes in molecular electronics: redox-active metal centers interlinked by a rigid ditopic carbene ligand

Mercs, Laszlo ; Neels, Antonia ; Albrecht, Martin

In: Dalton Transactions, 2008, vol. 41, p. 5570-5576

Bimetallic homonuclear iron(II) and ruthenium(II) N-heterocyclic carbene complexes have been synthesized and crystallographically analyzed. As a spacer ligand for interconnecting the two redox-active metal centers, a ditopic carbene ligand has been used that comprises two carbene sites annelated to benzene. Detailed electrochemical and spectroelectrochemical analyses of the bimetallic...

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...