Ruthenium-Hydride Mediated Unsymmetrical Cleavage of Benzofuroxan to 2-Nitroanilido with Varying Coordination Mode.

The reaction of R-benzofuroxan (R = H, Me, Cl) with the metal precursor [Ru(Cl)(H)(CO)(PPh3)3] (A) or [Ru(Cl)(H)(CH3CN)(CO)(PPh3)2] (B) in CH3CN at 298 K resulted in the intermediate complex [Ru(Cl)(L1)(CH3CN)(CO)(PPh3)2] (L1 = monodentate 2-nitroanilido) (1, pink), which however underwent slow transformation to the final product [Ru(Cl)(L2)(CO)(PPh3)2] (L2 = bidentate 2-nitroanilido) (2, green). On the contrary, the same reaction in refluxing CH3CN directly yielded 2 without any tractable intermediate 1. Structural characterization of the intermediates 1a-1c and the corresponding final products 2a-2c (R = H, Me, Cl) authenticated their identities, revealing ruthenium-hydride mediated unsymmetrical cleavage of benzofuroxan to hydrogen bonded monodentate 2-nitroanilido (L1) in the former and bidentate 2-nitroanilido (L2) in the latter. The spectrophotometric monitoring of the transformations of B → 1 as well as 1 → 2 with time and temperature established the first order rate process with associatively activated pathway for both cases. Both 1 and 2 exhibited one reversible oxidation and an irreversible reduction within ±1.5 V versus saturated calomel reference electrode in CH3CN with slight variation in potential based on substituents in the benzofuroxan framework (R = H, Me, Cl). Spectroscopic (electron paramagnetic resonance and UV-vis) and density functional theory calculations collectively suggested varying contribution of metal based orbitals along with the ligand in the singly occupied molecular orbital of 1+ or 2+, ascertaining the noninnocent potential of the in situ generated (L1) or (L2).