Electronically Triggered Switchable Binding Modes of the C-Organonitroso (ArNO) Moiety on the {Ru(acac)₂} Platform

Abstract

This work evaluated the switchable binding profile of the biochemically relevant and redox non-innocent C-organonitroso (ArNO) moiety with the selective {Ru­(acac)2} (acac = acetylacetonate) metal fragment as a function of external stimuli, including the solvent medium (EtOH versus toluene) and aryl substituents (C6H5, p-OMe-C6H4, and p-Cl-C6H4) in the framework of ArNO. In this context, the reaction of ArNO (Ar = C6H5 or p-OMe-C6H4) with the metal precursor RuII(acac)2(CH3CN)2 in polar protic EtOH led to the formation of monomeric [RuII(acac)2(ArNOo)2] (1a or 1b) with η1-N-bonded terminal ArNOo and double-ArNOo-bridged dimeric [(acac)2RuII(μ-ArNOo)2RuII(acac)2], 2a or 2b, respectively. On the other hand, the use of p-Cl-substituted ArNO selectively yielded the corresponding dimeric 2c. However, the use of nonpolar toluene resulted in monomeric 1 irrespective of the nature of aryl substituents in ArNO. Molecular identities, including the redox state of ArNOo in 1 and 2, were authenticated by their single-crystal X-ray structures as well as by solution spectral features. Though monomeric 1 exhibited reversible one-electron oxidation and reduction processes, leading to the electron paramagnetic resonance active [RuIII(acac)2(ArNOo)2]+ (1 +; S = 1/2) and [RuII(acac)2(ArNO•–)­(ArNOo)]− (1 •–; S = 1/2), respectively, redox states of dimeric 2 were found to be unstable on the electrolysis time scale. Interestingly, monomeric 1 underwent transformation to dimeric 2 in the presence of a strong reducing agent, hydrazine hydrate, and the reverse process, i.e., conversion of dimeric 2 to 1, took place under the influence of external coordinating agent ArNO. The detailed experimental exploration, including kinetic investigations related to 1 → 2 and 2 → 1 transformations, revealed that the electronic aspects of ArNO (redox non-innocence of ArNOo/•–, π-accepting and coordinating features of ArNOo) had facilitated its switchable binding event in combination with the {Ru­(acac)2} metal fragment.

Generation of a Sulfinamide Species from Facile N–O Bond Cleavage of Nitrosobenzene by a Thiolate-Bridged Diiron Complex

“…The N–O bond length of 1.321(4) Å in 2a is significantly longer than that found for uncoordinated PhNO (1.240(7) Å) . In addition, this N–O bond distance is intermediate between the typical ranges observed for neutral PhNO 0 (1.257–1.32 Å) − and anionic radical PhNO •– (1.322–1.35 Å), , but shorter than anionic PhNO 2– ligands (1.37–1.49 Å) , with the same μ−η 1 :η 1 coordination mode. Notably, the phenyl ring of the bridging PhNO ligand is nearly perpendicular to the plane through C27, N1, and O1 atoms with a dihedral angle of 84.5(4)°.…”

“…This structural feature is usually regarded as a geometric marker for complexes having a PhNO 0 or PhNO 2– ligand, whereas PhNO •– often prefers a coplanar arrangement . However, it is should be noted that the PhNO 0 or PhNO 2– ligands in some metal nitrosoarene complexes are coplanar. ,,,,, …”

“…38 However, it is should be noted that the PhNO 0 or PhNO 2− ligands in some metal nitrosoarene complexes are coplanar. 22,23,25,33,34,39 Compared with 2a, the most remarkable structural feature of 3a is the existence of a bridging sulfinamide ligand derived from the N−O bond cleavage realized by unexpected thiolate insertion (Figure 1d). The S2−O2 bond possesses substantial double-bond character 40,41 as evidenced by its short distance of 1.4629(18) Å.…”

Ruthenium‐Hydride Assisted Remarkable Diversity Towards Non‐Spectator Feature of Benzodifuroxan

“…region in CH 3 CN (Figure , Experimental Section) and the band position/intensity varied to some extent based on the nature and binding mode of the transformed L 1 ‐L 6 with the metal ions including isomeric identities of the complexes. The origin of the transitions were evaluated by time‐dependent DFT (TD‐DFT) calculations (Table S38, Supporting Information) which revealed (π * )L or (π * )PPh 3 targeted mixed metal‐ligand to ligand based M/LLCT transitions in the visible region (633‐510 nm) due to metal‐ligand covalency besides intra‐ligand/inter‐ligand π‐π * transitions in the higher energy UV‐region.…”

“…Electrochemically (coulometrically) generated isomeric 1 + , 2 + and 3 b + (4 + , 5 + and 6 + were found to be unstable at coulometric time scale of~5 min) displayed anisotropic EPR responses with < g > /Δg = 2.013/0.073, 2.035/0.111, 2.048/ 0.054, respectively, which indeed signified the intermediate resonance description [16] instead of any precise configuration, in agreement with the DFT results. On the contrary, isomer 3 a + displayed a free radical type EPR with g value of 1.99 (peak to peak separation: 28 G) corresponding to selective {Ru II -L * } configuration, [17] though spin density suggested partial metal contribution.…”