The rapid growth of the biodiesel industry has led to a large surplus of its major byproduct, i.e. glycerol, for which new applications need to be found. Research efforts in this area have focused mainly on the development of processes for converting glycerol into value-added chemicals and its reforming for hydrogen production, but recently, in line with the increasing interest in the use of alternative greener solvents, an innovative way to revalorize glycerol and some of its derivatives has seen the light, i.e. their use as environmentally friendly reaction media for synthetic organic chemistry. The aim of the present Feature Article is to provide a comprehensive overview on the developments reached in this field.

Amides are versatile building blocks in synthetic organic chemistry, presenting a wide range of pharmacological applications, and are used as raw materials in industry for the large-scale production of engineering plastics, detergents and lubricants. The development of green procedures for the synthesis of this relevant class of compounds from various starting materials, which replace antiquated methods using carboxylic acid derivatives and amines, is therefore of prime interest in modern chemistry. In this review article, a survey of metal-catalyzed synthetic approaches of amides conducted in an environmentally friendly aqueous medium is given.

The catalytic isomerization of propargylic alcohols promoted by transition-metals represents a straightforward and appealing route to synthetically useful alpha,beta-unsaturated carbonyl compounds. Three different reaction pathways are known for these atom-economical transformations: (i) the so-called Meyer-Schuster and Rupe rearrangements, in which a formal 1,3- or 1,2-shift of the hydroxyl group takes place, and (ii) the redox-type isomerization, which involves a simultaneous oxidation of the alcohol unit and reduction of the C[triple bond]C bond. In this Perspective article an overview of the different metal catalysts presently available to promote these isomerization reactions, their mechanisms of action as well as relevant synthetic applications, is provided.

The complexes Os(η 5-C5H5)Cl{η 2-HC⋮CC(OH)R2}(PiPr3) (R = Ph (1a), Me (1b)) react with TlPF6 to give [Os(η 5-C5H5){η 2-HC⋮CC(OH)R2}(PiPr3)]PF6 (R = Ph (2a), Me (2b)). The structures of 1a and 2a have been determined by X-ray diffraction. The comparative study of the data reveals a shortening of the Os−C(alkyne) distances on going from 1a to 2a, whereas the acetylenic bond lengths remain almost identical. Comparison of their 1H and 13C{1H} NMR spectra shows that the HC⋮ proton resonances and the chemical shifts of the acetylenic carbon atoms of 2a and 2b are substantially shifted toward lower field than are those of 1a and 1b. DFT calculations were carried out on Os(η 5-C5H5)Cl(η 2-HC⋮CR)(PH3) (R = H (A), R = CH3 (A CH3 )) and [Os(η 5-C5H5)(η 2-HC⋮CR)(PH3)]+ (R = H (B), R = CH3 (B CH3 )) model systems in order to study the differences in bonding nature of the two parent alkyne complexes, 1 and 2. Calculations give geometries very close to the X-ray-determined ones, and by using the GIAO method we succeed in qualitatively reproducing the experimental 1H and 13C chemical shifts. Both structural and spectroscopic changes can be explained by the participation of the acetylenic second π orbital (π⊥) in the metal−alkyne bonding. As we go from 1 to 2 or from A to B, the extraction of the chloride ligand transforms the 2-electron-donor alkyne ligand to a 4-electron-donor ligand, with both the π|| and the π⊥ orbitals donating to the metal and stabilizing the otherwise 16-electron unsaturated complex 2. Calculations also predict an increase of dissociation energies of the alkyne, and an enhancement in the energy of rotation of the alkyne, for complex B. Finally, Bader's atoms in molecules (AIM) analysis shows that differences in coordination nature are also reflected in the topological properties of electron density.