Synthesis and catalytic activity of histidine-based NHC ruthenium complexes

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

Electron-induced chemistry of alcohols

We studied dissociative electron attachment to a series of compounds with one or two hydroxyl groups. For the monoalcohols we found, apart from the known fragmentations in the 6–12 eV range proceeding via Feshbach resonances, also new weaker processes at lower energies, around 3 eV. They have a steep onset at the dissociation threshold and show a dramatic D/H isotope effect. We assigned them as proceeding via shape resonances with temporary occupation of σ*O–H orbitals. These low energy fragmentations become much stronger in the larger molecules and the strongest DEA process in the compounds with two hydroxyl groups, which thus represent an intermediate case between the behavior of small alcohols and the sugar ribose which was discovered to have strong DEA fragmentations near zero electron energy [S. Ptasińska, S. Denifl, P. Scheier and T. D. Märk, J. Chem. Phys., 2004, 120, 8505]. Above 6 eV, in the Feshbach resonance regime, the dominant process is a fast loss of a hydrogen atom from the hydroxyl group. In some cases the resulting (M– 1)⁻ anion (loss of hydrogen atom) is sufficiently energy-rich to further dissociate by loss of stable, closed shell molecules like H₂ or ethene. The fast primary process is state- and site selective in several cases, the negative ion states with a hole in the nO orbital losing the OH hydrogen, those with a hole in the σC–H orbitals the alkyl hydrogen

A chelating tetrapeptide rhodium complex comprised of a histidylidene residue: biochemical tailoring of a NHC-Rh hydrosilylation catalyst

Coupling of a histidinium salt with a MetAlaAla amino acid sequence followed by metallation with [RhCl(cod)]2 yields a rhodium(I) NHC complex with a pending peptide residue. Methionine chelation, induced by chloride abstraction from the metal coordination sphere, affords an efficient hydrosilylation catalyst precursor comprised of a peptidic macrocyclic chelate backbone.European Research CouncilSwiss National Science Foundatio

Transition metal bioconjugates with an organometallic link between the metal and the biomolecular scaffold

This overview compiles recent advances in the synthesis and application of organometallic bioconjugates that comprise a metal–carbon linkage between the metal and the biomolecular scaffold. This specific area of bioorganometallic chemistry has been spurred by the discovery of naturally occurring bioorganometallic compounds and afforded organometallic bioconjugates from transition metals binding to amino acids, nucleic acids and other biomolecules. These artificial bioorganometallic compounds have found application in various domains, including catalysis, medicinal chemistry, bioanalysis, and materials science.European Research CouncilScience Foundation IrelandSwiss National Science Foundatio

Peptide-tethered monodentate and chelating histidylidene metal complexes: synthesis and application in catalytic hydrosilylation

The N-delta,N-epsilon-dimethylated histidinium salt (His*) was tethered to oligopeptides and metallated to form Ir(III) and Rh(I) NHC complexes. Peptide-based histidylidene complexes containing only alanine, Ala-Ala-His*-[M] and Ala-Ala-Ala-His*-[M] were synthesised ([M] = Rh(cod) Cl, Ir(Cp*)Cl-2), as well as oligopeptide complexes featuring a potentially chelating methionine and tyrosine residue, Met-Ala-Ala-His*-Rh(cod)Cl and Tyr-Ala-Ala-His*-Rh(cod)Cl. Chelation of the methionine-containing histidylidene ligand was induced by halide abstraction from the rhodium centre, while tyrosine remained non-coordinating under identical conditions. High catalytic activities in hydrosilylation were achieved with all peptide-based rhodium complexes. The cationic S-Met,C-His*-bidentate peptide rhodium catalyst outperformed the monodentate neutral peptide complexes and constitutes one of the most efficient rhodium carbene catalysts for hydrosilylation, providing new opportunities for the use of peptides as N-heterocyclic carbene ligands in catalysis.European Research CouncilCOST ActionSwiss National Science Foundatio

Synthesis and catalytic activity of histidine-based NHC ruthenium complexes

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 comsxsxsplexes show appreciable activity in the catalytic transfer hydrogenation of ketones.European Research CouncilSwiss National Science FoundationAlfred Werner Foundatio

Benign Synthesis of Indoles from Anilines and Epoxides: New Application for Ruthenium Pincer Catalysts

For the first time, ruthenium pincer complexes such as Ru-MACHO-BH were successfully used as catalysts in the domino-synthesis of indoles from anilines and epoxides. Following previously optimised procedures, a variety of indoles were produced in an atom-efficient manner with water and hydrogen as the only stoichiometric side-products. The ?-amino alcohol, resulting from the ring-opening of the epoxide with the aniline derivative, undergoes dehydrogenation, followed by condensation with excess aniline and the final intramolecular cyclisation affords the desired indole. Ru-MACHO-BH showed similar catalytic activity than our previously reported in situ prepared catalyst (Ru3(CO)12/dppf) without further optimisation of the reaction conditions