Inorganic Chemistry, Vol.56, No.17, 10735-10747, 2017
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)(L-1)(CH3CN)(CO)(PPh3)(2)] (L-1 = monodentate 2-nitroanilido) (1, pink), which however underwent slow transformation to the final product [Ru(Cl)(L-2)(CO)(PPh3)(2)] (L-2 = 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 (L-1) in the former and bidentate 2-nitroanilido (L-2) 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 UVvis) 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 (L-1) or (L-2).