In spite of its large availability in natural or shale gas deposits, the use of methane in the chemical industry as feedstock from a synthetic point of view yet constitutes a challenge in modern chemistry. Only the production of the so-called syngas, a mixture of CO and H2 derived from the complete cleavage of the methane molecule, operates at the industrial level. The relevance of methane in the current industry, mainly toward methanol production, is described in this Tutorial. The methanol economy has been already proposed as an alternative to current fuel sources. Methanol synthesis directly from methane would imply the activation of the latter. Toward this end, the different methodologies reported to activate methane with transition metal complexes as well as the few examples of the catalytic functionalization of methane are presented.

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

DedicatedtoProf. GregorioA sensio on the occasion of his 70th birthdayAbstract: Organoboron compounds have become one of the most versatile buildingb locks in organic synthesis owing to their accessible and efficient conversion into many different functional groups.I np articular,a lkenyl boronates have received ag reat deal of attentiona sv ery reactive substrates in Suzuki-Miyaura cross-coupling reactions. Accord-ingly,e fforts towards the development of efficient methods to prepare this type of compound are ongoing. In this contribution, the progress in the search for synthetic routes for alkenylb oronates and their use in av ariety of organic transformationsisa ccounted.

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.

The complex Tp(Br3)Cu(NCMe) (1) is an excellent catalyst for the regioselective carbene transfer reaction to tertiary C-H bonds of hydrocarbons, at room temperature, using the readily available ethyl diazoacetate (EDA) as the carbene source.

The control of the cis/trans diastereoselectivity by catalyst design in the olefin cyclopropanation reaction with ethyl diazoacetate is reviewed. Catalysts based on ruthenium, copper, rhodium, iron, osmium and cobalt are discussed. The degree of stereocontrol achieved for styrene and related aryl‐containing olefins is higher than that for terminal alkenes with no aryl substituents.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

DFT Becke3LYP calculations are applied to the computational study of the activation of alkane C−H bonds by metallocarbene homoscorpionate complexes. A total of 16 different combinations of metallocarbene complex and alkane are explored, defined by the use of TpAgC(H)(CO2CH3), TpBr3AgC(H)(CO2CH3), TpCuC(H)(CO2CH3), and TpBr3CuC(H)(CO2CH3) species as metallocarbene and methane, ethane, propane, and butane as alkane. The reaction is found to be under kinetic control, and the selectivity is decided in a step with a low-barrier transition state where the key bond-breaking and bond-forming processes take place in a concerted way. This transition state has several possible conformations, which are systematically explored to find the one with lowest energy for each reaction. Variations of the energy barrier as a function of the nature of metal, ligand, and alkane are analyzed and discussed.

In situ prepared copper catalysts Tp(X)Cu (Tp(X) = homoscorpionate) catalyze the olefin cyclopropanation reaction using ethyl diazoacetate as the carbene source. Very high values of both activity and diastereoselectivity toward the cis isomer have been obtained for styrene, alpha-methylstyrene, 1-hexene, 1-octene, vinyl acetate, n-butyl vinyl ether, 2,5-dimethyl-2,4-hexadiene, and 3,3-dimethyl-1-butene. The effect of the temperature in the diastereoselectivity was almost negligible within the range -10 to +30 degrees C. Kinetic studies have allowed us to propose that the homoscorpionate ligand might act in a dihapto form during the catalytic process. This transformation seems to operate under kinetic control, where the formation of the cis isomer would govern the reaction rate.