Now showing 1 - 10 of 66
  • Publication
    Non-classical N-Heterocyclic carbene complexes
    (RSC Publishing, 2010) ;
    The expansion of the concept of N-heterocyclic carbenes as ligands for transition metals to mesoionic ligand systems has led to the discovery of a wide range of non-classical carbene-type ligands. These non-classical carbene-type ligands are characterised by a significantly lower heteroatom stabilisation of the (putative) free carbene, a situation that also affects the ligand donor properties and hence the reactivity of the coordinated metal centre. Based on the unique impact of non-classical carbene-type ligands, a number of attractive transition metal-catalysed processes have been disclosed in recent years, predominantly in the area of cross-coupling reactions, hydrogenations, and olefin metathesis
  • Publication
    Beyond catalysis: N-heterocyclic carbene complexes as components for medicinal, luminescent, and functional materials applications
    (RSC Publishing, 2010) ;
    This tutorial review compiles the advances that have been achieved in using transition metal complexes containing N-heterocyclic carbene ligands as components for materials. Applications of metal carbene complexes in fields different from catalysis are remarkably scarce. During the last few years, promising results have been accomplished in particular by utilizing such complexes as antimicrobial and cytotoxic agents, as photoactive sites in luminescent materials, for self-assembly into liquid crystalline materials and metallasupramolecular structures, and as synthons for molecular switches and conducting polymeric materials. These initial achievements clearly underline the great potential of N-heterocyclic carbene complexes in various fields of materials science.
      2195Scopus© Citations 617
  • Publication
    Rhodium-mediated activation of an alkane-type C–H bond
    (RSC Publishing, 2010-01-14) ; ;
    Abnormal C4-bonding of N-heterocyclic carbenes effectively modulates the electron density at rhodium and allows for the selective cleavage of an unactivated C(sp3)–H bond, whereas no such intramolecular C–H bond breaking is observed when the carbene binds normally through the C2 carbon.
      343Scopus© Citations 29
  • Publication
    Solvent-dependent switch of ligand donor ability and catalytic activity of ruthenium(II) complexes containing pyridinylidene amide (PYA) n-heterocyclic carbene hybrid ligands
    Chelating ligands incorporating both N-[1-alkylpyridin-4(1H)-ylidene]amide (PYA) and N-heterocyclic carbene (NHC) donor sites were prepared and used for the synthesis of ruthenium(II) complexes. Cyclic voltammetry, NMR, and UV–vis spectroscopy of the complexes indicate a solvent-dependent contribution of the limiting resonance structures associated with the ligand in solution. The neutral pyridylidene imine structure is more pronounced in apolar solvents (CH2Cl2), while the mesoionic pyridinium amide form is predominant in polar solvents (MeOH, DMSO). The distinct electronic properties of these hybrid PYA-NHC ligands in different solvents have a direct influence on the catalytic activity of the ruthenium center, e.g., in the dehydrogenation of benzyl alcohol to benzaldehyde. The activity in different solvents qualitatively correlates with the solvent permittivity.
      526Scopus© Citations 39
  • Publication
    Dinuclear ruthenium complexes containing a new ditopic phthalazin- bis(triazole) ligand that promotes metal-metal interactions
    Much attention has been paid to heterocyclic N-containing ligands due to their applicability as bridging ligands in the synthesis of redox active dinuclear metal complexes. With this aim, we report the synthesis and full characterization of a novel phthalazine-triazole ligand (1,4-bis(1-methyl-1H-1, 2,3-triazol-4-yl)phthalazine). Moreover, we show that the phthalazine nitrogen atoms of this N-heterocyclic ligand are more reactive towards alkylating agents than the triazole groups. New ruthenium (ii) complexes containing this ligand have been obtained and characterized both structurally and electrochemically. The geometry imposed by the ligand allows the placement of two ruthenium centers in very close proximity so that efficient through-space interactions take place, a concept of crucial importance for electron transfer processes.
      355Scopus© Citations 21
  • Publication
    Iridium, ruthenium, and palladium complexes containing a mesoionic fused imidazolylidene ligand
    Imidazo[1,2-a]pyridine consisting of a pyridine fused to an imidazolium salt at the imidazolium N1–C2 bond and hence protected from forming normal imidazole-2-ylidene complexes undergoes selective activation of the C5–H bond with Ag2O, i.e. at the imidazolium carbon that is proximal to the pyridine nitrogen. While the silver carbene complex is unstable, transmetallation with [IrCp*Cl2]2, [RuCl2(cym)]2, and [PdCl(allyl)]2 afforded stable mesoionic carbene complexes. Two iridium(III) complexes containing one fused carbene ligand and one palladium(II) complex containing two carbene ligands at the metal centre were structurally characterized. The absence of substituents adjacent to the carbene carbon prevents wingtip group activation, and it imparts a reduced stability of the complexes in particular under (mildly) acidic conditions.
      369Scopus© Citations 12
  • Publication
    A chelating tetrapeptide rhodium complex comprised of a histidylidene residue: biochemical tailoring of a NHC-Rh hydrosilylation catalyst
    (Royal Society of Chemistry, 2012-10-15) ;
    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.
      347Scopus© Citations 39
  • Publication
    Synthesis of pincer-type N-heterocyclic carbene palladium complexes with a hemilabile ligand and their application in cross-coupling catalysis
    Benzimidazolium salts containing both a neutral imine and a masked carboxylate functional group for potential metal chelation were prepared. Palladation of the ester-protected ligand afforded a N,C-bidentate carbene complex 4. Subsequent ester hydrolysis preserved the bidentate coordination mode and yielded complex 5 with a pending COOH group exclusively. However, when ester deprotection was carried out prior to metalation, the N,C,O-tridentate pincer-type coordinated palladium complex 7 was obtained. Proton-abstraction of the dangling COOH group in the bidentate ligand of complex 5 by treatment with a base led to the formation of the N,C,O-tridentate coordinated Pd system 7, and inversely, exposure of the tridentate bound Pd complex 7 with acid afforded the N,C-bidentate ligand coordination mode in complex 5, demonstrating hemilability of the oxygen donor site in the pincer ligand. All three palladium(II) complexes 4, 5, and 7 were evaluated in cross-coupling catalysis and revealed distinct activity differences that are dependent on the type of coupling (Suzuki vs. Heck) and the substrate (Ar-Br vs. Ar-Cl). These differences suggest that judicious choice of donor groups in pincer-type complexes is a viable strategy for catalyst optimization.
      313Scopus© Citations 26
  • Publication
    Catalytic and Organometallic Chemistry of Earth-Abundant Metals
    (American Chemical Society, 2014-10-27) ; ;
    Why Earth - abundant metals? Their low cost, ready availability, comparatively low toxicity and greater sustainability are all factors leading to a major renaissance in the study of the organometallic chemistry of Earth - abund ant metals over the last few years.
      297Scopus© Citations 52