Effect of the bipyridine substituents nature on the reactivity of Re(I) or Mo(II) carbonyl complexes

Resumen del trabajo presentado al 6th EuCheMS Chemistry Congres, celebrado en Sevilla (España) del 11 al 15 de septiembre de 2016.Dearomatization of pyridines and other six-membered N-heterocycles is a challenging task that can provide a route to the synthesis of functionalized molecules present in many natural products and pharmaceuticals. In our previous studies, focused on the deprotonation of N-alkylimidazole (N-RIm) ligands coordinated to the fac-{Re(CO)3} fragment, we achieved the dearomatization of one pyridine ring of a 2,2’-bipyridine (bipy) ligand from the intramolecular nucleophilic attack at a bipy Cortho atom by the deprotonated imidazole. A subsequent protonation step occurs on the nitrogen atom of the dearomatized ring, transforming it from an amido to an amino-like N (Scheme 1a).1 Herein we describe the results obtained for the analogous compounds bearing 4,4’-dimethoxy-2,2’-bipyridine, in which the deprotonation/protonation sequence leads to the protonation of a CH group of the dearomatized pyridyl ring affording a CH2 moiety (Scheme 1b). Furthermore, the nature of the substituents at the backbone of the bipy ligand has been found to have a dramatic effect on the reactivity of [Mo(η3-allyl)(4,4’-R2-bipy)(CO)2(N-RIm)]OTf compounds towards a strong base. For non-substituted2 or tBu bipy ligands, the imidazole, once has been deprotonated, isomerizes from N- to C- coordinated affording an imidazole-2-yl ligand (Scheme 2a). In contrast, for the [Mo(η3-allyl)(4,4’-Br2-bipy)(CO)2(N-MesIm)]OTf compound a dearomatized complex is obtained by C-C coupling between the imidazole central C atom and C2 of the bipy ligand (Scheme 2b).Peer Reviewe