Experimental and computational studies on ruthenium(<scp>ii</scp>) bis-diimine complexes of <i>N</i>,<i>N</i>′-chelate ligands: the origin of changes in absorption spectra upon oxidation and reduction

Tan, Siew San; Yanagisawa, Susumu; Inagaki, Kouji; Kassim, Mohammad B.; Morikawa, Yoshitada

doi:10.1039/c8cp05016c

Cited by 12 publications

(8 citation statements)

References 21 publications

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“…Irrespective of the [Rh(Cp*)Cl]-center being present or not, the ground-state bleach, reflecting the 1 MLCT absorption band, is accompanied by a broad and unstructured excited state absorption at wavelengths longer than ~500 nm, which stems from ligand-to-metal charge transfer transitions, characteristic for 3 MLCT states in [(bpy) 2 Ru(phen)] 2+ complexes 41 , 63 , 64 . The more intense excited state absorption at ~360 nm is due to ππ* transitions of the reduced phen-sphere—also characteristic for [(bpy) 2 Ru(phen)] 2+ complexes 41 , 65 . The transient absorption data – irrespective of solvent and excitation wavelength – show that excited state relaxation in 3 and 4 does not involve the peripheral phen motif or the [(phen)Rh(Cp*)Cl]-center, respectively.…”

Section: Resultsmentioning

confidence: 93%

Outpacing conventional nicotinamide hydrogenation catalysis by a strongly communicating heterodinuclear photocatalyst

et al. 2022

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Unequivocal assignment of rate-limiting steps in supramolecular photocatalysts is of utmost importance to rationally optimize photocatalytic activity. By spectroscopic and catalytic analysis of a series of three structurally similar [(tbbpy)2Ru-BL-Rh(Cp*)Cl]3+ photocatalysts just differing in the central part (alkynyl, triazole or phenazine) of the bridging ligand (BL) we are able to derive design strategies for improved photocatalytic activity of this class of compounds (tbbpy = 4,4´-tert-butyl-2,2´-bipyridine, Cp* = pentamethylcyclopentadienyl). Most importantly, not the rate of the transfer of the first electron towards the RhIII center but rather the rate at which a two-fold reduced RhI species is generated can directly be correlated with the observed photocatalytic formation of NADH from NAD+. Interestingly, the complex which exhibits the fastest intramolecular electron transfer kinetics for the first electron is not the one that allows the fastest photocatalysis. With the photocatalytically most efficient alkynyl linked system, it is even possible to overcome the rate of thermal NADH formation by avoiding the rate-determining β-hydride elimination step. Moreover, for this photocatalyst loss of the alkynyl functionality under photocatalytic conditions is identified as an important deactivation pathway.

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Section: Resultsmentioning

confidence: 93%

Outpacing conventional nicotinamide hydrogenation catalysis by a strongly communicating heterodinuclear photocatalyst

et al. 2022

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“…The LUMO area was mainly distributed on the oxygen-doped graphene. This HOMO–LUMO transition meant an electron-transfer state from PPh 3 /NaI to O 4 /C. − As such, the hot electrons were able to transfer from adsorbed PPh 3 /NaI to O 4 /C after Fe 1 O 4 /C–PPh 3 /NaI being excited, which was unrelated to Fe single atoms. The transfer of photogenerated electrons significantly enhanced the separation efficiency of electron–hole pairs.…”

Section: Results and Discussionmentioning

confidence: 99%

Fe Single-Atom Catalyst for Visible-Light-Driven Photofixation of Nitrogen Sensitized by Triphenylphosphine and Sodium Iodide

et al. 2020

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Photosensitizers with charge-separated excited states are commonly introduced into photocatalytic systems to accomplish photon-to-electron transformation. Unfortunately, the photosensitizers in current use are mostly precious metal complexes and synthetically elaborate organic dyes. Herein, we successfully applied a low-cost triphenylphosphine (PPh3)/sodium iodide (NaI)-based photosensitizer to heterogeneous catalysis using Fe single-atom catalysts (Fe1/C) toward N2 photofixation. PPh3 molecules mainly adsorbed on the active carbon to form Fe1/C–PPh3/NaI. During N2 photofixation, Fe1/C–PPh3/NaI exhibited an NH3 production rate of 98 μmol/(gcat.·h) without any sacrificial agents, even 1.5 times as high as that for Fe1/C using tris(2,2′-bipyridyl)dichlororuthenium(II) ([Ru(bpy)3]Cl2) as the photosensitizer. Further mechanistic studies revealed that Fe1/C–PPh3/NaI effectively harvested photons by delivering hot electrons from adsorbed PPh3/NaI to Fe single atoms under light irradiation, together with the generation of PPh3-I• radicals. The hot electrons reduced N2 to NH3 over Fe single atoms, while PPh3-I• radicals were regarded to oxidize H2O to O2.

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“…It is proved that the higher redox potential indicates the good stability of the complexes, whereas the lower redox potential of the complex should increase the interconversion [35]. The higher redox potential observed for the present G-CLRu(II) confirmed the greater stability of the Ru(II)complexes upon coordination of the chiral thiourea ligand [35,36]. In order to investigate the redox behavior and stability of G-CLRu(II), CV curves were recorded.…”

Section: Characterization Of G-clru(ii)mentioning

confidence: 68%

“…In general, the Rucomplexes possibly undergo one-electron redox reaction between Ru(II) and Ru(III). The present G-CLRu(II) showsquasi-reversible (I pa /I pc = 1) (at 0.57 vs. SCE) waves correspondingto the one-electron oxidation of Ru(II) to Ru(III)(Figure 5a)[35]. The waves corresponding to Ru(II)Catalysts 2020, 10, x FOR PEER REVIEW 8 of 21…”

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confidence: 87%

Stepwise Construction of Ru(II)Center Containing Chiral Thiourea Ligand on Graphene Oxide: First Efficient, Reusable, and Stable Catalyst for Asymmetric Transfer Hydrogenation of Ketones

2020

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Heterogenization of homogenous catalysts on solid support has attracted tremendous attention in organic synthesis due to the key benefits of heterogenized catalysts such as easy recovery and reusability. Although a considerable number of heterogenized catalysts are available, to the best of our knowledge, there is no efficient and reusable heterogenized catalyst reported for asymmetric reactions to date. Herein, we prepared a [RuCl2(η6-p-cymene)]/chiralthiourea ligand covalently bonded to graphene nanosheets (G-CLRu(II), where G represents graphene oxide (GO), CL denotes chiral N-((1-phenylethyl)carbamothioyl)acetamide and Ru(II) symbolizes [RuCl2(η6-p-cymene)]), for the asymmetric transfer hydrogenation of ketones. Five simple steps were involved in the preparation of the G-CLRu(II) catalyst. The structure of G-CLRu(II) was investigated by means of various spectroscopic and microscopic techniques. Coordination mode and covalent bonding involved in the G-CLRu(II) structure we reconfirmed. G-CLRu(II) demonstrated good catalytic performance towards the asymmetric transfer hydrogenation of ketones (conversion of up to 95%, enantiomeric excesses (ee) of up to 99%, and turnover number (TON) and turnover frequency (TOF) values of 535.9 and 22.3 h−1, respectively). A possible mechanism is proposed for the G-CLRu(II)-catalyzed asymmetric transfer hydrogenation of ketones. Recovery (~95%), reusability (fifth cycle, yield of 89% and ee of 81%), and stability of G-CLRu(II) were found to be good. We believe that the present stepwise preparation of G-CLRu(II) opens a new door for designing various metal-centered heterogenized chiral catalysts for asymmetric synthesis.

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Experimental and computational studies on ruthenium(ii) bis-diimine complexes of N,N′-chelate ligands: the origin of changes in absorption spectra upon oxidation and reduction

Abstract: The first report seeking to determine the origin of the observed spectral changes by investigating the frontier MOs and electronic structures of the ligands.

Cited by 12 publications

References 21 publications

Outpacing conventional nicotinamide hydrogenation catalysis by a strongly communicating heterodinuclear photocatalyst

Outpacing conventional nicotinamide hydrogenation catalysis by a strongly communicating heterodinuclear photocatalyst

Fe Single-Atom Catalyst for Visible-Light-Driven Photofixation of Nitrogen Sensitized by Triphenylphosphine and Sodium Iodide

Stepwise Construction of Ru(II)Center Containing Chiral Thiourea Ligand on Graphene Oxide: First Efficient, Reusable, and Stable Catalyst for Asymmetric Transfer Hydrogenation of Ketones

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