Net charge effects in N-heterocyclic carbene–ruthenium complexes with similar oxidation states and coordination geometries

Mangalum, Anshuman; Htet, Yamin; Roe, Dallas A.; McMillen, Colin D.; Tennyson, Andrew G.

doi:10.1016/j.ica.2015.06.025

Cited by 8 publications

(8 citation statements)

References 34 publications

(13 reference statements)

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“… 29 Based on this catalytic chemical reactivity observed with Ru1 and previous reports of other Ru complexes with chelating carboxylate ligands exerting antioxidant effects in cells, which derived from irreversible stoichiometric reactions with nitric oxide, 30 , 31 we hypothesized that Ru1 would function as a catalytic antioxidant, reducing radicals using non-tertiary alcohols as terminal reductants. Using methods previously reported by our group, 29 , 32 the N-heterocyclic carbene (NHC) ligand precursor [ 1 H 2 ][Br] was treated with Ag 2 O to afford the Ag–NHC complex [Ag( 1 )] n ( 2 ). The NHC ligand was subsequently transferred to Ru via the reaction of 2 with [{RuCl(η 6 -cymene)} 2 (μ-Cl) 2 ], which yielded the Ru–NHC complex [RuCl( 1 )(η 6 -cymene)] ( Ru1 ).…”

Section: Resultsmentioning

confidence: 99%

Catalytic radical reduction in aqueous solution via oxidation of biologically-relevant alcohols

Htet

Tennyson

2016

Chem. Sci.

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Section: Resultsmentioning

confidence: 99%

Catalytic radical reduction in aqueous solution via oxidation of biologically-relevant alcohols

Htet

Tennyson

2016

Chem. Sci.

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“…There are several review articles reported in the past decade, which are dedicated to NHC ligands bearing one additional donor group [ 7 , 8 , 9 , 10 ]. Included in these review articles are bidentate NHC ligands with phosphorous tether [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ], nitrogen [ 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 ], and oxygen tethers [ 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 ,…”

Section: Introductionmentioning

confidence: 99%

Recent Advances in Catalysis Involving Bidentate N-Heterocyclic Carbene Ligands

2021

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Since the discovery of persistent carbenes by the isolation of 1,3-di-l-adamantylimidazol-2-ylidene by Arduengo and coworkers, we witnessed a fast growth in the design and applications of this class of ligands and their metal complexes. Modular synthesis and ease of electronic and steric adjustability made this class of sigma donors highly popular among chemists. While the nature of the metal-carbon bond in transition metal complexes bearing N-heterocyclic carbenes (NHCs) is predominantly considered to be neutral sigma or dative bonds, the strength of the bond is highly dependent on the energy match between the highest occupied molecular orbital (HOMO) of the NHC ligand and that of the metal ion. Because of their versatility, the coordination chemistry of NHC ligands with was explored with almost all transition metal ions. Other than the transition metals, NHCs are also capable of establishing a chemical bond with the main group elements. The advances in the catalytic applications of the NHC ligands linked with a second tether are discussed. For clarity, more frequently targeted catalytic reactions are considered first. Carbon–carbon coupling reactions, transfer hydrogenation of alkenes and carbonyl compounds, ketone hydrosilylation, and chiral catalysis are among highly popular reactions. Areas where the efficacy of the NHC based catalytic systems were explored to a lesser extent include CO2 reduction, C-H borylation, alkyl amination, and hydroamination reactions. Furthermore, the synthesis and applications of transition metal complexes are covered.

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“…We find few complexes in the literature that have a similar coordination sphere for comparison, but we note that Tennyson and co-workers report an absorption maximum of 496 nm for a [Ru(bpy) 2 ] 2+ center with a chelating benzimidazolylidene carboxylate (C, O coordination mode). 41 Methylation of this complex yields the ester, and the subsequent coordination of the ketone. In that case, the absorption maximum is observed at 454 nm.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Slow ³MLCT Formation Prior to Isomerization in Ruthenium Carbene Sulfoxide Complexes

et al. 2021

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A series of photochromic complexes with general formulas of [Ru(bpy) 2 (NHC-SR)] 2+ and [Ru(bpy) 2 (NHC-S(O)R)] 2+ were prepared and investigated by X-ray crystallography, electrochemistry, and ultrafast transient absorption spectroscopy {where bpy is 2,2′-bipyridine and NHC-SR and NHC-S(O)R are chelating thioether (-SR) and chelating sulfoxide [-S(O)R] N-heterocyclic carbene (NHC) ligands}. The only differences between these complexes are the nature of the R group on the sulfur (Me vs Ph), the identity of the carbene (imidazole vs benzimidazole), and the number of linker atoms in the chelate (CH 2 vs C 2 H 4 ). A total of 13 structures are presented {four [Ru(bpy) 2 (NHC-SR)] 2+ complexes, four [Ru(bpy) 2 (NHC-S(O)R)] 2+ complexes, and five uncomplexed ligands}, and these reveal the expected coordination geometry as predicted from other spectroscopy data. The data do not provide insight into the photochemical reactivity of these compounds. These carbene ligands do impart stability with respect to ground state and excited state ligand substitution reactions. Bulk photolysis reveals that these complexes undergo efficient S → O isomerization, with quantum yields ranging from 0.24 to 0.87. The excited state reaction occurs with a time constant ranging from 570 ps to 1.9 ns. Electrochemical studies reveal an electron transfer-triggered isomerization, and voltammograms are consistent with an ECEC (electrochemical−chemical electrochemical−chemical) reaction mechanism. The carbene facilitates an unusually slow S → O isomerization and an unusally fast O → S isomerization. Temperature studies reveal a small and negative entropy of activation for the O → S isomerization, suggesting an associative transition state in which the sulfoxide simply slides along the S−O bond during isomerization. Ultrafast studies provide evidence of an active role of the carbene in the excited state dynamics of these complexes.

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Net charge effects in N-heterocyclic carbene–ruthenium complexes with similar oxidation states and coordination geometries

Cited by 8 publications

References 34 publications

Catalytic radical reduction in aqueous solution via oxidation of biologically-relevant alcohols

Catalytic radical reduction in aqueous solution via oxidation of biologically-relevant alcohols

Recent Advances in Catalysis Involving Bidentate N-Heterocyclic Carbene Ligands

Slow ³MLCT Formation Prior to Isomerization in Ruthenium Carbene Sulfoxide Complexes

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Net charge effects in N-heterocyclic carbene–ruthenium complexes with similar oxidation states and coordination geometries

Cited by 8 publications

References 34 publications

Catalytic radical reduction in aqueous solution via oxidation of biologically-relevant alcohols

Catalytic radical reduction in aqueous solution via oxidation of biologically-relevant alcohols

Recent Advances in Catalysis Involving Bidentate N-Heterocyclic Carbene Ligands

Slow 3MLCT Formation Prior to Isomerization in Ruthenium Carbene Sulfoxide Complexes

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Slow ³MLCT Formation Prior to Isomerization in Ruthenium Carbene Sulfoxide Complexes