Ruthenium-Chelated Non-Innocent Bis(heterocyclo)methanides: A Mimicked β-Diketiminate

The unexplored substrate-based reactivity profile of newly designed bis(heterocyclo)methanide (BHM, L1-L3), a structural mimic of ubiquitous β-diketiminate, was demonstrated on an electronically rich {Ru(acac)₂} platform (acac = σ-donating acetylacetonate). In this regard, this work deals with structurally characterized [Ru(L)(acac)₂] complexes 1A-3A incorporating electronically varying heterocycles {1A, L1 = bis(imidazo[1,5-a]pyridin-3-yl)methanide; 2A, L2 = (Z)-4-[(6,7-dihydrothieno[3,2-c]pyridin-4-yl)methylene]-6,7-dihydro-4H-thieno[3,2-c]pyridin-5-ide; 3A, L3 = (Z)-6-chloro-1-[(6-chloro-3,4-dihydroisoquinolin-1-yl)methylene]-3,4-dihydro-1H-isoquinolin-2-ide}. The significant impact of electronic modification at the BHM backbone (L1-L3) on its redox tunability at the metal-ligand interface in 1A-3A and its subsequent oxygenation profile to yield bis(heterocyclo)methanone (BMO, analogue of α-ketodiimine) in the corresponding [Ru(BMO)(acac)₂] (1B-3B) via a radical pathway were rationalized. In addition, oxidative dehydrogenation of metalated BMO in 1B-3B to BAM [bis(heteroaryl)methanone] in [Ru(BAM))(acac)₂] (1C-3C) was illustrated in support of the nonspectator behavior of α-ketodiimine. A combined experimental and theoretical investigation extended mechanistic outlines of the aforementioned transformation processes, which in effect provided a new dimension relating to the analogous β-diketiminate as well as α-ketodiimine chemistry.