The catalytic activation of small molecules by transition metals is a promising area of research that has been developed for decades to achieve the production of fine chemicals. This present work focuses on the activation of the small molecules CO (carbon monoxide) and 2,6-dimethylphenyl isocyanide by a rhenium(III) complex. The insertion of CO into the rhenium-benzyl bond afforded an acyl species which was observed in situ and characterized by NMR spectroscopy. DFT (B3PW91-D3) studies showed that the mechanism for the insertion of the CO molecule starts with the formation of a CO adduct followed by migration of the anionic ligand benzyl, to the carbon atom on the CO ligand. In the presence of water, phenylacetic acid and a rhenium(I) species was formed. Reaction of the acyl species with methyl triflate afforded (E)-(2-methoxyvinyl)benzene and a rhenium(I) species.
The reaction of rhenium(III) with 2,6-dimethylphenyl isocyanide was also investigated and afforded two products of where the isocyanide moiety was inserted into the rhenium-benzyl bond: 1) a kinetic product, featuring an h¹-coordination mode; and 2) a thermodynamic product, featuring an h²-coordination mode. This species was isolated and fully characterized (NMR, X-ray single crystal, and elemental analysis). DFT (B3PW91-D3) studies showed that the mechanism for this reaction starts with the initial coordination of the isonitrile ligand to rhenium, which is then followed by the insertion into the rhenium-benzyl bond. A carbene complex resulting from the reaction of the isocyanide inserted product with methyl triflate was also afforded and characterized. The possibility of performing multiple insertions of the isocyanide molecule 2,6-dimethylphenyl isocyanide into the rhenium-benzyl bond was also investigated, and the product resulting from two consecutive isocyanide insertions can be afforded.

Liana Gouveia

Appearances