Luminescent metal complexes. Part 3. Electrochemical potentials of ground and excited states of ring-substituted 2,2′-bipyridyl and 1,10-phenanthroline tris-complexes of ruthenium

Skarda, Vladimir; Cook, Michael J.; Lewis, Anthony P.; McAuliffe, Glenn S. G.; Thomson, Andrew J.; Robbins, David J.

doi:10.1039/p29840001309

Cited by 38 publications

(22 citation statements)

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“…This comparison suggests that the substituents on the pyridine rings of TPA can exert larger electronic effects on reactivity at the metal center. The ρ value of +0.150 of the Ru TPA complexes is comparable to that of the Ru bpy complexes ( ρ =+0.175 for ∑ σ ) 30. The relationship between the redox potentials of Ru II /Ru III and Ru III /Ru IV couples is shown in Figure 4 b, and the linear relationship indicates that the structural change is very small.…”

Section: Resultsmentioning

confidence: 70%

Synthesis and Characterization of Mononuclear Ruthenium(III) Pyridylamine Complexes and Mechanistic Insights into Their Catalytic Alkane Functionalization with m‐Chloroperbenzoic Acid

Kojima

Hayashi

Iizuka

et al. 2007

Chemistry A European J

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A series of mononuclear RuIII complexes [RuCl2(L)]+, where L is tris(2-pyridylmethyl)amine (TPA) or one of four TPA derivatives as tetradentate ligand, were prepared and characterized by spectroscopic methods, X-ray crystallography, and electrochemical measurements. The geometry of a RuIII complex having a non-threefold-symmetric TPA ligand bearing one dimethylnicotinamide moiety was determined to show that the nicotine moiety resides trans to a pyridine group, but not to the chlorido ligand. The substituents of the TPA ligands were shown to regulate the redox potential of the ruthenium center, as indicated by a linear Hammett plot in the range of 200 mV for RuIII/RuIV couples with a relatively large rho value (+0.150). These complexes act as effective catalysts for alkane functionalization in acetonitrile with m-chloroperbenzoic acid (mCPBA) as terminal oxidant at room temperature. They exhibited fairly good reactivity for oxidation of cyclohexane (C--H bond energy 94 kcal mol(-1)), and the reactivity can be altered significantly by the electronic effects of substituents on TPA ligands in terms of initial rates and turnover numbers. Catalytic oxygenation of cyclohexane by a RuIII complex with 16O-mCPBA in the presence of H2 18O gave 18O-labeled cyclohexanol with 100% inclusion of the 18O atom from the water molecule. Resonance Raman spectra under catalytic conditions without the substrate indicate formation of a RuIV==O intermediate with lower bonding energy. Kinetic isotope effects (KIEs) in the oxidation of cyclohexane suggest that hydrogen abstraction is the rate-determining step and the KIE values depend on the substituents of the TPA ligands. Thus, the reaction mechanism of catalytic cyclohexane oxygenation depends on the electronic effects of the ligands.

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Section: Resultsmentioning

confidence: 70%

Synthesis and Characterization of Mononuclear Ruthenium(III) Pyridylamine Complexes and Mechanistic Insights into Their Catalytic Alkane Functionalization with m‐Chloroperbenzoic Acid

Kojima

Hayashi

Iizuka

et al. 2007

Chemistry A European J

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“…Because direct reduction of CF 3 I (at a potential of −1.52 V versus the saturated calomel electrode, SCE, in cyclic voltammetry) 18 by visible-light-excited photocatalyst *Ru(phen) 3 2+ 2 (Fig. 2; −0.90 V versus SCE) 19 is thermodynamically challenging, we questioned whether the incorporation of an electron-deficient system such as SO 2 within CF 3 X might enable more facile reduction 20 . Our investigations led us to the use of trifluoromethanesulphonyl chloride (known as triflyl chloride, TfCl), which has been employed in a non-general sense to effect aryl trifluoromethylation of benzene and other simple arenes via atom transfer catalysis 21–23 .…”

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confidence: 99%

Trifluoromethylation of arenes and heteroarenes by means of photoredox catalysis

Nagib

MacMillan

2011

Nature

1,195

616

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Modern drug discovery relies on the continual development of synthetic methodology to address the many challenges associated with the design of new pharmaceutical agents1. One such challenge arises from the enzymatic metabolism of drugs in vivo by cytochrome P450 oxidases, which use single-electron oxidative mechanisms to rapidly modify small molecules to facilitate their excretion2. A commonly used synthetic strategy to protect against in vivo metabolism involves the incorporation of electron-withdrawing functionality, such as the trifluoromethyl (CF3) group, into drug candidates3. The CF3 group enjoys a privileged role in the realm of medicinal chemistry because its incorporation into small molecules often enhances efficacy by promoting electrostatic interactions with targets, improving cellular membrane permeability, and increasing robustness towards oxidative metabolism of the drug4–6. Although common pharmacophores often bear CF3 motifs in an aromatic system, access to such analogues typically requires the incorporation of the CF3 group, or a surrogate moiety, at the start of a multi-step synthetic sequence. Here we report a mild, operationally simple strategy for the direct trifluoromethylation of unactivated arenes and heteroarenes through a radical-mediated mechanism using commercial photocatalysts and a household light bulb. We demonstrate the broad utility of this transformation through addition of CF3 to a number of heteroaromatic and aromatic systems. The benefit to medicinal chemistry and applicability to late-stage drug development is also shown through examples of the direct trifluoromethylation of widely prescribed pharmaceutical agents.

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“…An early study on Ru(bpyX2)3 2+ systems showed a linear relationship between emission energy and difference between electrochemical potentials for first oxidation and first reduction (E½). [17] Furthermore the E½ showed a linear relationship to the Hammett σ constants for the substituents.…”

Section: Mlct Statesmentioning

confidence: 99%

Probing the excited state nature of coordination complexes with blended organic and inorganic chromophores using vibrational spectroscopy

Horvath

Huff

Gordon

et al. 2016

Coordination Chemistry Reviews

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Luminescent metal complexes. Part 3. Electrochemical potentials of ground and excited states of ring-substituted 2,2′-bipyridyl and 1,10-phenanthroline tris-complexes of ruthenium

Cited by 38 publications

References 1 publication

Synthesis and Characterization of Mononuclear Ruthenium(III) Pyridylamine Complexes and Mechanistic Insights into Their Catalytic Alkane Functionalization with m‐Chloroperbenzoic Acid

Synthesis and Characterization of Mononuclear Ruthenium(III) Pyridylamine Complexes and Mechanistic Insights into Their Catalytic Alkane Functionalization with m‐Chloroperbenzoic Acid

Trifluoromethylation of arenes and heteroarenes by means of photoredox catalysis

Probing the excited state nature of coordination complexes with blended organic and inorganic chromophores using vibrational spectroscopy

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