Superior electrocatalytic hydrogen evolution activity of a triply bridged diruthenium(II) complex on a carbon cloth support.

This article describes the structural authentication of a unique triply bridged [1](ClO4)2 and monomeric [2]ClO4/[3]ClO4. Electrochemical HER on a carbon cloth support demonstrated the superior performance of [1](ClO4)2 with high TON (>105) and its long-term stability. The primary kinetic isotope effect of [1](ClO4)2 revealed the involvement of PCET in the rate-determining step.

Tetracoordinated 15-Electron Ruthenium(I) in a Discrete Triruthenium Framework.

This paper highlights the unique case of a tetracoordinated Ru(I) (15-electron) component in a structurally characterized discrete triruthenium setup, [(acac)2RuIIIL1(µ-RuI)L1RuII (acac)2](ClO4)2 ([3](ClO4)2, where acac = acetylacetonate; S = 1), which was formed along with the monomeric [(acac)2RuIII(L1)] ([1]ClO4; S = 1/2) and dimeric [{(acac)2RuIII}2(µ-L1)](ClO4)2 ([2](ClO4)2; S = 1) counterparts upon interaction of {Ru(acac)2} and L1 = 3,3'-dipyridin-2-yl-1,1'-bis(imidazo[1,5-a]pyridinyl).

Azo Appended Modified Lawsone Derived Ru-Systems with Multi-Redox Entities. Competitive Electronic Form and the Question of Azo Reduction.

The article dealt with the ruthenium complexes of redox active azo appended modified lawsone L1 - (HL1 : (E)-2-hydroxy-3-(p-tolyldiazenyl)naphthalene-1,4-dione))/L2 - (HL2 :5-hydroxy-6-p-tolylazobenzo[a]phenazine) derived [RuIII (acac)2 (L1 - )]/[RuIII (acac)2 (L2 - )] 1/5, [RuII (bpy)2 (L1 - )]ClO4 /[RuII (bpy)2 (L2 - )]ClO4 [2]ClO4 /[6]ClO4 , ctc-[RuII (pap)2 (L1 - )]ClO4 /ctc-[RuII (pap)2 (L2 - )]ClO4 [3]ClO4 /[7]ClO4 and [RuII (CO)(H)(PPh3 )2 (L1 - )]/[RuII (CO)(Cl)(PPh3 )2 (L2 - )] 4/8 (acac=acetylacetonate, bpy=2,2'-bipyridine, pap=2-phenylazopyridine). The ligands L1 - and L2 - differed with respect to the para-quinone versus phenazine moieties linked to the azo function. Structural analysis of the complexes established unreduced state of the azo (N=N) group of coordinated L1 - /L2 - or pap as well as unprecedented para-quinone form of L1 - . The involvement of selective redox center(s) towards the accessible redox steps of the complexes encompassing multiple redox active entities i. e. Ru, phenolate (L1 - /L2 - ), para-quinone (L1 - ), phenazine (L2 - ), azo (L1 - /L2 - , pap), diimine (bpy) was analyzed by combined experimental and DFT calculations. It revealed that under the prevailing competitive scenario oxidation was mostly dominated by the phenolate group of L1 - /L2 - (phenolate→phenoxide), while successive reductions were taken place either at the para-quinone/phenazine units of L1 - /L2 - or azo/diimine functions of pap/bpy. Though the azo function of pap in 3+ /7+ underwent facile reduction, the same azo function associated with L1 - /L2 - conspicuously remained unreduced in all occasions. The frontier molecular orbital analysis revealed that the propensity of pap for the azo reduction with special reference to that in L1 - /L2 - could be correlated with its relatively lower energy π* orbital (LUMO). Complexes displayed intense LMCT (1/5) and bpy (2+ /6+ ), pap (3+ /7+ ), L (4/8) targeted MLCT transitions in the visible region.

Bidirectional noninnocence of hinge-like deprotonated bis-lawsone on selective ruthenium platform: a function of varying ancillary ligands.

The present work aimed to obtain discrete heavier metal complexes of unperturbed deprotonated bis-lawsone (hinge-like H2L = 2,2'-bis(3-hydroxy-1,4-napthoquinone). This is primarily due to its limited examples with lighter metal ions (Co, Zn, and Ga) and the fact that our earlier approach with the osmium ion facilitated its functionalisation. Herein, we demonstrated the successful synthesis and structural characterisation of L2--derived diruthenium [(bpy)2RuII(µ-L2-)RuII(bpy)2](ClO4)2 [1](ClO4)2 (S = 0), (acac)2RuIII(µ-L2-)RuIII(acac)22 (S = 1) and monoruthenium (pap)2Ru(L2-) 3 (S = 0) derivatives (bpy = 2,2'-bipyridine, acac = acetylacetonate, and pap = 2-phenylazopyridine). The crystal structures established that (i) O,O-/O,O- donating five-membered bis-bidentate and O-,O- donating seven-membered bidentate chelating modes of deprotonated L2- in rac (ΔΔ/ΛΛ) diastereomeric [1](ClO4)2, 2 and 3, respectively. (ii) The L2- bridging unit in [1](ClO4)2, 2 and 3 underwent twisting its two naphthoquinone rings with respect to the ring connecting C-C bond by 73.01°, 62.15° and 59.12°, respectively. (iii) Intermolecular π-π interactions (∼3.5 Å) between the neighbouring molecules. The paramagnetic complex 2 (S = 1) with two non-interacting Ru(III) (S = 1/2) ions exhibited weak antiferromagnetic coupling only at very low temperatures. In agreement with the magnetic results, 2 displayed typical RuIII-based anisotropic EPR in CH3CN (/Δg: 2.314/0.564) but without any forbidden g1/2 signal at 120 K. The complexes exhibited multiple redox processes in CH3CN in the experimental potential window of ± 2.0 V versus SCE. The analysis of the redox steps via a combined experimental and theoretical (DFT/TD-DFT) approach revealed the involvement of L2- to varying extents in both the oxidative and reductive processes as a consequence of its bidirectional redox non-innocent feature. The mixing of the frontier orbitals of the metal ion and L2- due to their closeness in energy indeed led to the resonating electronic form in certain redox states instead of any precise electronic structural state.

Osmium(II)-Coordination Induced C-C Bond Functionalization of Bis-lawsone.

Metal-coordination-driven C-C bond functionalization without involvement of the traditional route of oxidative addition, insertion, and reductive elimination has gained immense importance. In this context, the present Communication highlights the facile ring contraction process of the deprotonated bis-lawsone (L2-) to functionalized L12- upon coordination to {Os(bpy)2} or isomeric {Os(pap)2} (bpy = 2,2'-bipyridine and pap = 2-phenylazopyridine) in 1-3. Further, recognition of fractional redox noninnocence of L1 in 1+-3+ via experimental and theoretical events facilitated its inclusion in the redox noninnocent family.