The use of methane, the lightest hydrocarbon and primary component of natural gas, as a source for fine chemicals production remains an appealing goal on scientific, economic and environmental grounds (1-4). Transition metal catalyzed C-H bond activation is a promising approach to achieve functionalization of the strong and relatively inert C-H bonds of alkanes more generally. In one possible scenario, these reactions proceed by metal-promoted C-H bond oxidative cleavage followed by insertion of a suitable X group into the M-C bond and release of the functionalized product by means of reductive elimination of the C-X-H unit (5). Individual reaction steps for this and related catalytic cycles have been widely reported (6), but a major challenge has been that removal of the functionalized fragments from the metal coordination sphere is often unfavorable, due to the robustness of the M-C bonds. Only FINAL VERSION ACCEPTED

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plitudes [I> 2cr(I)] together with Friedel reflections; R =0.066. N-La-N angles ofthe diagonals 175.0--17X.5": La-N 2.734-2.831 A (mean value 2.770 A): intra-2 N-N 2.772-2.976 A (mean value 2.917 A); inter-2-

The specific interaction of a variety of modified hevein domains to chitooligosaccharides has been studied by NMR spectroscopy in order to assess the importance of aromatic-carbohydrate interactions for the molecular recognition of neutral sugars. These mutant AcAMP2-like peptides, which have 4-fluoro-phenylalanine, tryptophan, or 2-naphthylalanine at the key interacting positions, have been prepared by solid-phase synthesis. Their three-dimensional structures, when bound to the chitin-derived trisaccharide, have been deduced by NMR spectroscopy. By using DYANA and restrained molecular dynamics simulations with the AMBER 5.0 force field, the three-dimensional structures of the protein-sugar complexes have been obtained. The thermodynamic analysis of the interactions that occur upon complex formation have also been carried out. Regarding binding affinity, the obtained data have permitted the deduction that the larger the aromatic group, the higher the association constant and the binding enthalpy. In all cases, entropy opposes binding. In contrast, deactivation of the aromatic rings by attaching fluorine atoms decreases the binding affinity, with a concomitant decrease in enthalpy. The role of the chemical nature of the aromatic ring for establishing sugar contacts has been thus evaluated.

The reaction between acetylenes and sulfoxides, studied as a test case for gold-catalyzed intermolecular addition, provides the oxyarylation compounds 3 in good yields. Unpredictably, in all cases a single regioisomer arising from the electrophilic aromatic alkylation at the position adjacent to the sulfur atom is obtained instead of the expected Friedel-Crafts regioisomer. A new concerted mechanism based on DFT calculations is proposed to account for the products in this intermolecular gold(I)-catalyzed reaction.

The copper complex Tp (CF3)2,Br Cu(NCMe) (1, Tp (CF3)2,Br = hydrotris((3,5-bis(trifluoromethyl)-4-bromo)-pyrazol-1-yl)borate) catalyzes the insertion of the CHCO 2 Et group (from ethyl diazoacetate N 2 CHCO 2 Et, EDA) into the C-H bonds of methane, in a homogeneous process that uses supercritical carbon dioxide (scCO 2 ) as the reaction medium.Other light alkanes such as ethane, propane and butane have been also functionalized with this copper-based catalyst, in the first example of the derivatization of the series of C 1 -C 4 alkanes with this metal with a soluble catalyst.

Phosphine ligands have been demonstrated to have an effect on reactivity and selectivity in the competitive intramolecular palladium-catalysed Suzuki-Miyaura coupling of dibromo sulfoxide 1a possessing two different hybridised electrophilic carbons. It was found that the bromine bond to the sp(3)-hybridised carbon is selectively replaced in the presence of unhindered phosphines such as PPh(3) or xantphos. The use of hindered phosphine ligands such as P(o-tol)(3) and P(1-naphthyl)(3) reversed the selectivity, conducting the cross-coupling at the Csp(2)-Br. Identical trends were observed in external competition experiments carried out with bromomethyl sulfoxide and different substituted bromoarenes. DFT and DFT/MM calculations showed that the selectivity observed is mainly due to the different facility of the ligands to dissociate. Bisphosphine catalysts favour coupling at the sp(3) carbon, whereas monophosphine catalysts prefer the sp(2) carbon.

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