Development of ruthenium(II) bis(N-Heterocyclic Carbene) complexes for homogeneous catalysis

A tetrakis(acetonitrile) complex bearing a bidentate bis(N-Heterocyclic Carbene) ligand was synthesized, and its formation was extensively studied. Triethylamine played a pivotal role in the reaction, initially forming a ruthenium(II)-triethylamino complex with the precursor. It then functioned as a base to produce the ruthenium(II) bis(NHC) complex, which was found to be very active in catalyzing the direct ortho-arylation of 2-phenylpyridine, with loadings as low as 2 % (a significant result considering that most reported examples in the literature require loadings as high as 10 % and are typically limited to monoarylations). Additionally, the reactive complex was successfully functionalized with various bidentate ligands of the amino, pyridine, and phosphine types, yielding a series of novel ruthenium(II) bis(NHC) dicationic organonitrile complexes. These complexes were evaluated in the catalytic transfer hydrogenation reaction, demonstrating notable activity (TOF of 50,000 h-1). It is notable that within the pool of reported ruthenium(II) complexes featuring bidentate bis(NHC) ligands, cis- [Ru(CH3CN)2(1,1′-bis(3-methyl-imidazol-2-ylidene)methylene))(2–2′Bipyridine)](PF6)2 demonstrates exceptional high rate, marking it as one of the fastest known. Overall, the synthesized tetrakis(acetonitrile) complex proves to be a promising platform for the development of future catalysts.