Sviluppo di nuovi complessi di rutenio(II) con leganti bis(carbene N-eterociclici) come piattaforma per lo sviluppo di catalizzatori in fase omogenea

N-heterocyclic carbenes rapidly emerged as versatile ligands in coordination chemistry due to their adaptable stereoelectronic properties, enhanced stability, and strong σ-donating power, presenting an appealing alternative to conventional ligands like phosphines. Moreover, integrating NHCs into polydentate ligands has resulted in more robust coordination compounds, which, for instance, has led to decreased catalyst-to-substrate ratios in catalysis. Remarkably, limited examples exist of ruthenium(II) complexes bearing bis(NHC) ligands, despite the blooming field of ruthenium(II) coordination chemistry, prompting further investigation. Our research led to the development of a novel synthetic pathway giving access to a branch of ruthenium(II) bis(NHC) dicationic organonitrile complexes, successfully functionalized with diverse bidentate ligands of the amino, bipyridine, and phosphine types. The reaction mechanism was thoroughly studied, identifying a key reactive intermediate species, the dicationic tetrakis(acetonitrile)[bis(NHC)]ruthenium(II), which was isolated. Additionally, our investigation unveiled the pivotal role of triethylamine, revealing its function as an internal base in the formation of a ruthenium(II)-triethylamino complex, which then reacts with the bis(NHC) precursor. The synthesized catalysts have been tested in the transfer hydrogenation reaction, displaying moderate reactivity, with the exception of the dicationic cis-bis(acetonitrile)(2,2’-bipyridine) [bis(NHC)]ruthenium(II) complex, which reached a TOF of 50,000 h-1. A significant result for catalysts in an early stage of development. In conclusion, the developed synthetic protocol is remarkably efficient, demanding mild reaction conditions and minimal workup. It relies on commercially available reagents and consistently returns high yields. The nearly unlimited range of ligands that can be accommodated in the coordination sphere of these complexes - whether novel bis(NHC) ligands, mixed bidentate ligands, or even pincer ligands - enables the tailored synthesis of catalysts for specific applications. This versatility makes of the dicationic tetrakis(acetonitrile)[bis(NHC)]ruthenium(II) a critical platform for catalyst development.