Prabir Ghosh

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).

Ru-Complex Framework toward Aerobic Oxidative Transformations of β-Diketiminate and α-Ketodiimine

The impact of the {Ru(acac)2} (acac- = acetylacetonate) framework on the transformations of C-H and C-H/C-C bonds of coordinated β-diketiminate and ketodiimine scaffolds, respectively, has been addressed. It includes the following transformations involving {Ru(acac)2} coordinated β-diketiminate in 1 and ketodiimine in 2 with the simultaneous change in metal oxidation state: (i) insertion of oxygen into the C(sp2)-H bond of β-diketiminate in 1, leading to the metalated ketodiimine in 2 and (ii) Bronsted acid (CH3COOH) assisted cleavage of unstrained C(sp2)-C(sp2)/C═N bonds of chelated ketodiimine (2) with the concomitant formation of intramolecular C-N bond in 3, as well as insertion of oxygen into the C(sp3)-H bond of 2 to yield -CHO function in 4 (-CH3 → -CHO). The aforesaid transformation processes have been authenticated via structural elucidation of representative complexes and spectroscopic and electrochemical investigations.

Solvent-Mediated Functionalization of Benzofuroxan on Electron-Rich Ruthenium Complex Platform

An unprecedented reactivity profile of biochemically relevant R-benzofuroxan (R=H, Me, Cl), with high structural diversity and molecular complexity on a selective {Ru(acac)2 } (acac=acetylacetonate) platform, in conjugation with EtOH solvent mediation, is revealed. This led to the development of monomeric [RuIII (acac)2 (L1R )] (1 a-1 c; L1R =2-nitrosoanilido derivatives) and dimeric [{RuII (acac)2 }2 (L2R )] (2 a-2 b; L2R =(1E,2E)-N1 ,N2 -bis(2-nitrosophenyl)ethane-1,2-diimine derivatives) complexes in one pot with a change in the metal redox conditions. The functionalization of benzofuroxan in 1 and 2 implied in situ reduction of N=O to NH- in the former and solvent-assisted multiple N-C coupling in the latter. The aforesaid transformation processes were authenticated through structural elucidation of representative complexes, and evaluated by their spectroscopic/electrochemical features, along with C2 D5 OD labeling and monitoring of the impact of substituents (R) in the benzofuroxan framework on the product distribution process. The noninnocent potential of newly developed L1 and L2 in 1 and 2, respectively, was also probed by spectroelectrochemistry in combination with DFT calculations.