The impact of metal-to-ligand charge transfer towards the redox noninnocence of 2,2'-azobis(benzothiazole) (abbt) has been highlighted on coordination to {Ru II (acac) 2 } (acac = 2,4-pentanedionato). It led to the authentication of a series of mononuclear and dinuclear complexes incorporating variable oxidation states of abbt (abbt 0/ C À/2À ). Mononuclear 1 was identified as [Ru III (abbtC À )], a MLCT excited state of [Ru II (abbt)]. Dinuclear 2 was however recognized as two discrete redox isomers: (i) radical bridged mixed-valent meso-[Ru 2.5 (m-abbtC À )Ru 2.5 ] (2a) and (ii) dianionic ligand bridged isovalent meso-[Ru III (m-abbt 2À )Ru III ] (2b), demonstrating unprecedented structural confirmation of valence tautomerism in azo-based ligand systems. A crystal structure of [2]ClO 4 validated the formation of [Ru III (m-abbtC À ) Ru III ]ClO 4 . Analysis of electronic structural forms of 1 and 2 in accessible redox states via spectroelectrochemistry and DFT revealed their electron reservoir feature.

The Fujiwara-Moritani reaction has had a profound contribution in the emergence of contemporary C-H activation protocols. Despite the applicability of the traditional approach in different elds, the associated reactivity and regioselectivity issues had rendered it redundant. The revival of this exemplary reaction requires the development of a mechanistic paradigm that would have simultaneous control on both the reactivity and regioselectivity. Often high thermal energy required to promote ole nation leads to multiple site functionalization. To this aim we established a photoredoxcatalytic system constituting a merger of palladium/organo-photocatalyst that forges oxidative ole nation in an explicit regioselective fashion of diverse arenes and heteroarenes. Visible light plays a signi cant role in executing 'regio-resolved' Fuijiwara-Moritani reaction without the requirement of silver salts and thermal energy. The catalytic system is also amenable towards proximal and distal ole nation aided by respective directing groups (DGs), which entails the versatility of the protocol in engaging the entire spectrum of C(sp2)-H ole nation.Furthermore, streamlining the synthesis of natural products, chiral molecules, drugs and diversi cation through late-stage functionalizations underscore the importance of this sustainable protocol. The photoinduced attainment of this regioselective transformation is mechanistically established through control reactions, kinetic studies and theoretical calculations.

The paper deals with the electronic impact of ancillary ligands on the varying redox features of azobis(benzothiazole) (abbt) in the newly introduced mononuclear ruthenium complexes [Ru(pap) 2 (abbt)] n (1 n ) and [Ru(bpy) 2 (abbt)] n (2 n ), where pap = 2phenylazopyridine and bpy = 2,2′-bipyridine. In this regard, the complexes [Ru II (pap) 2 (abbt •− )]ClO 4 ([1]ClO 4 ), [Ru II (pap) 2 (abbt 0 )](ClO 4 ) 2 ([1](ClO 4 ) 2 ), [Ru II (bpy) 2 (abbt 0 )](ClO 4 ) 2 ([2](ClO 4 ) 2 ), and [Ru II (bpy) 2 (abbt •− )]ClO 4 ([2]ClO 4 ) were structurally and spectroscopically characterized. Unambiguous assignments of the aforestated radical and nonradical forms of abbt in 1 + /2 + and 1 2+ /2 2+ , respectively, were made primarily based on their redox-sensitive azo (NN) bond distances as well as by their characteristic electron paramagnetic resonance (EPR)/NMR signatures. Although the radical form of abbt •− was isolated as an exclusive product in the case of strongly π-acidic pap-derived 1 + , the corresponding moderately π-acidic bpy ancillary ligand primarily delivered an oxidized form of abbt 0 in 2 2+ , along with the radical form in 2 + as a minor (<10%) component. The oxidized abbt 0 -derived [1](ClO 4 ) 2 was, however, obtained via the chemical oxidation of [1]ClO 4 . Both 1 + and 2 2+ displayed multiple closed by reversible redox processes (one oxidation O1 and four successive reductions R1−R4) within the potential window of ±2.0 V versus saturated calomel electrode. The involvement of metal-, ligand-, or metal/ligand-based frontier molecular orbitals along the redox chain was assigned based on the combined experimental (structure, EPR, and spectroelectrochemisry) and theoretical [density functional theory (DFT): molecular orbitals, Mulliken spin densities/time-dependent DFT] investigations. It revealed primarily ligand (abbt/pap or bpy)-based redox activities, keeping the metal ion as a simple spectator. Moreover, frontier molecular orbital analysis corroborated the initial isolation of the radical and nonradical species for the pap-derived 1 + and bpy-derived 2 2+ as well as facile reduction of pap and abbt in 1 + and 2 + , respectively.

Chemical noninnocence" of metal-coordinated 2-picolylamine (PA) derivatives has been introduced upon its reaction with the metal precursor [Ru II (Cl)-(H)(CO)(PPh 3 ) 3 ] under basic conditions. This in effect leads to the facile formation of metalated amide, imine, ring-cyclized pyrrole, and an N-dealkylated congener based on the fine-tuning of an amine nitrogen (N amine ) and a methylene center (C α ) at the PA backbone. It develops oxygenated L1′ in 1 and cyclized L4′ in 4 upon switching of the N amine substituent of PA from aryl to an electrophilic pent-3-en-2-one moiety. On the other hand, imposing the substituent at the C α position of PA modifies its reactivity profile, leading to a dehydrogenation (2/3) or N-dealkylation (6) process. The divergent reactivity profile of metalated PA is considered to proceed through a common dianionic intermediate. Further, a competitive scenario of C−H bond functionalization of coordinated PA versus the ligand-exchange process has been exemplified in the presence of external electrophile such as benzyl bromide or methylene iodide. Authentication of the product formation as well as elucidation of the reaction pathway has been addressed by their crystal structures and spectroscopic features in conjunction with the transition-state (TS) theory.

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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.

The reaction of R-benzofuroxan (R = H, Me, Cl) with the metal precursor [Ru(Cl)(H)(CO)(PPh)] (A) or [Ru(Cl)(H)(CHCN)(CO)(PPh)] (B) in CHCN at 298 K resulted in the intermediate complex [Ru(Cl)(L)(CHCN)(CO)(PPh)] (L = monodentate 2-nitroanilido) (1, pink), which however underwent slow transformation to the final product [Ru(Cl)(L)(CO)(PPh)] (L = bidentate 2-nitroanilido) (2, green). On the contrary, the same reaction in refluxing CHCN 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) in the former and bidentate 2-nitroanilido (L) 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 CHCN 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 (L) or (L).

The paper documents redox-triggered C–C coupling of acyclic N,N′-bis­(2-pyridylmethylene)­ethylenediamine (BPE) to yield 2,3-bis­(2-pyridyl)­pyrazine (DPP) upon coordination to an electron-rich {Ru­(acac)2} (acac = acetylacetonate) unit. This led to DPP-bridged [{Ru­(acac)2}2(DPP)]0/+ (2 and [2]­ClO4) along with the unperturbed BPE-bridged [{Ru­(acac)2}2(BPE)] (1). On the contrary, electron-poor {Ru­(Cl)­(H)­(CO)­(PPh3)3} yielded BPE-bridged [3]­(ClO4)2 as an exclusive product. Synergistic metal (Ru)–ligand (BPE) redox participation toward chemical noninnocence of the Schiff base ligand and DPP-mediated electronic communication in RuIIRuIII-derived [2]­ClO4 are addressed.