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 s * 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. Ptasin´ska, S. Denifl, P. Scheier and T. D. Ma¨rk, 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 À 1) À anion (loss of hydrogen atom) is sufficiently energyrich to further dissociate by loss of stable, closed shell molecules like H 2 or ethene. The fast primary process is state-and site selective in several cases, the negative ion states with a hole in the n O orbital losing the OH hydrogen, those with a hole in the s C-H orbitals the alkyl hydrogen.

A bi-catalytic system, in which Ru-MACHO-BH and Ru(H)2(dppe)2 interact in a synergistic manner, was developed for the base-free dehydrogenation of methanol. A total TON > 4200 was obtained with only trace amounts of CO contamination (<8 ppm) in the produced gas.

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.

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. Scheme 1 Synthesis of the rhodium tetrapeptides. Reagents: (i) HCl, dioxane; then Boc-Met-Ala-Ala-OH, HATU, NEtiPr 2 , THF; (ii) [NEt 3 Me]I, Ag 2 O, CH 2 Cl 2 , then [RhCl(cod)] 2 ; (iii) KPF 6 , CH 2 Cl 2 -H 2 O.

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.The use of naturally abundant products as versatile starting materials for ligand development is an appealing concept in homogeneous catalysis and is an increasingly popular strand of bioinorganic and bioorganometallic chemistry. 1 A variety of biologically relevant classes of compounds have been functionalised for transition metal coordination, including DNA, 2 carbohydrates, 3 steroids, 4 alkaloids 5 and vitamins such as biotin. 6 Proteins constitute a particularly attractive platform for ligand synthesis, partly because of the diversity of the functional groups in the amino acid side chains. 7 Both covalent and supramolecular anchoring of complexes onto peptidic scaffolds has successfully been demonstrated. 8 Covalent linkers may be established, for example, via side chain functionalisation of the amino acids. 9 Histidine is remarkable in this respect, since imidazole has been widely employed as a precursor for N-heterocyclic carbenes, 10 which are probably the most popular class of ligands during the last decade. 11Alkylation of the histidine side chain and the subsequent metallation of the histidinium salt hence constitutes an attractive approach to bioorganometallic chemistry. 12 This provides potential catalyst precursors with activity and selectivity properties that may be tailored by biochemical principles inherent to enzymes, such as second coordination sphere modification or side-chaindirected substrate recognition. Towards this end, we report here a straightforward synthesis of catalytically active ruthenium centres anchored covalently to a histidine side chain through a histidinederived NHC spectator ligand. The synthesis of the histidine-derived carbene ligand precursors started with the protection of the amine and the acid group of native histidine (Scheme 1). An acetyl unit was chosen as the amine protecting group because of its facile introduction and high chemical stability. Acetyl histidine 2 was obtained according to known procedures 13 and subsequently esterified at the C-terminus. 14 The corresponding methyl ester 3a was only soluble in highly polar solvents, which hampered the subsequent transformations considerably. Therefore, the corresponding butyl ester 3b, comprising a longer alkyl chain, was prepared by esterification in n-BuOH. While the yields were high, racemisation at the a-carbon occurred during the work-up, as demonstrated by the loss of any optical rotation of 3 at the sodium D-line. Attempts to avoid the racemisation, by using milder bases or a phosphate buffer (pH = 7.2) for the neutralisation, have not been successful thus far. Optical instability of the N-acetyl protected amino acids is well-established 15 and of...

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A divacant Keggin polyanion has been decorated with a N-heterocyclic carbene (NHC) iridium(I) organometallic complex to provide a molecular model of an Ir-based supported catalyst. The characterization of the hybrid compound has been performed by multinuclear NMR spectroscopy, infrared spectroscopy, cyclic voltammetry, and mass spectroscopy, and the results are in agreement with a bisfunctionalization of the polyoxometalate scaffold. The resulting supported homogeneous complex has been successfully used to catalyze the transfer hydrogenation from iPrOH to benzophenone [with a turnover number (TON) of 680 and a turnover frequency (TOF) of up to 540 h–1]

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