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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

A magnetic iron(III) switch with controlled and adjustable thermal response for solution processing

Gandolfi, Claudio ; Morgan, Grace G. ; Albrecht, Martin

In: Dalton Transactions, 2012, vol. 41, no. 13, p. 3726-3730

Spin crossover requires cooperative behavior of the metal centers in order to become useful for devices. While cooperativity is barely predictable in solids, we show here that solution processing and the covalent introduction of molecular recognition sites allows the spin crossover of iron(III) sal₂trien complexes to be rationally tuned. A simple correlation between the number of molecular...

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

Chelating C4-bound imidazolylidene complexes through oxidative addition of imidazolium salts to palladium(0)

Krüger, Anneke ; Kluser, Evelyne ; Müller-Bunz, Helge ; Neels, Antonia ; Albrecht, Martin

In: European Journal of Inorganic Chemistry, 2012, p. -

Oxidative addition of donor-functionalised 4-iodoimidazolium salts to palladium(0) provides a selective route for the preparation of abnormal chelating N-heterocyclic carbene complexes and enables the introduction of a variety of donor groups. The activation of the C4 position does not necessitate protection of the imidazolium C2 position, thereby leaving this site available for further...

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

Normal and abnormal carbene complexes derived from thiazole: Preparation and a preliminary investigation of their relative catalytic performance

Stander-Grobler, Elzet ; Schuster, Oliver ; Strasser, Christoph E. ; Albrecht, Martin ; Cronje, Stephanie ; Raubenheimer, Helgard G.

In: Polyhedron, 2011, vol. 30, no. 17, p. 2776-2782

Readily prepared 2-, 4- and 5-bromo-3-methyl thiazolium triflates react by oxidative substitution with M(PPh₃)₄ (M = Ni or Pd) to furnish five of the expected normal and abnormal cationic thiazolylidene complexes (1a, 1b, 2a, 2b, and 3b). Carbene complex formation is accompanied by a ca. 40 ppm downfield shift of the α-N carbene carbons in Pd...

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

Pyridine-derived N-heterocyclic carbenes: an experimental and theoretical evaluation of the bonding in and reactivity of selected normal and abnormal complexes of nickel(II) and palladium(II)

Stander-Grobler, Elzet ; Schuster, Oliver ; Heydenrych, Greta ; Cronje, Stephanie ; Tosh, Evangeline ; Albrecht, Martin ; Frenking, Gernot ; Raubenheimer, Helgard G.

In: Organometallics, 2011, vol. 29, no. 22, p. 5821–5833

We report a thorough investigation of a series of isomeric complexes with the general formula trans-(pyridylidene)M(PPh₃)₂Cl (M = Pd, Ni). For the first time, a systematic comparison of normal, abnormal, and remote bonding modes is presented. X-ray structural and ¹³C NMR data indicate the importance of carbenoid mesomeric contributions in their compound class....

Université de Fribourg

Synthesis and tunability of abnormal 1,2,3-triazolylidene palladium and rhodium complexes

Poulain, Aurélie ; Canseco-Gonzalez, Daniel ; Hynes-Roche, Rachel ; Müller-Bunz, Helge ; Schuster, Oliver ; Stoeckli-Evans, Helen ; Neels, Antonia ; Albrecht, Martin

In: Organometallics, 2011, vol. 30, no. 5, p. 1021–1029

Palladation of N3-alkylated 1,2,3-triazolium salts with Pd(OAc)₂ afforded a μ²−I₂ bridged bimetallic complex [Pd(trz)I₂]₂ and monometallic bis(carbene) complexes Pd(trz)₂I₂ as a mixture of trans and cis isomers (trz = 1,2,3-triazol-5- ylidene). Addition of excess halide or modification of the palladation procedure from direct functionalization to a transmetalation...

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.