Cyclometalated Ruthenium(II) NHC Complexes with Imidazo[1,5‐<i>a</i>]pyridine‐Based (C<sup>^</sup>C*) Ligands – Synthesis and Characterization

Schleicher, D. G.; Tronnier, Alexander; Soellner, Johannes; Straßner, Thomas

doi:10.1002/ejic.201900108

Cited by 11 publications

(4 citation statements)

References 53 publications

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“…Notwithstanding the widespread interest in this class of compounds, we found that the synthetic aspects leading to their preparation are still amenable to being improved. The synthetic procedures leading to Ru(II) polypyridyl complexes bearing three equal or different diimine chelating ligands (L) were thoroughly reviewed by Spiccia and co-workers in 2004 .…”

Section: Introductionmentioning

confidence: 99%

cis-Locked Ru(II)-DMSO Precursors for the Microwave-Assisted Synthesis of Bis-Heteroleptic Polypyridyl Compounds

et al. 2021

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We describe a synthetic strategy for the preparation of bis-heteroleptic polypyridyl Ru(II) complexes of the type [Ru(L1) 2 (L2)] 2+ (L1 and L2 = diimine ligands) from well-defined Ru(II) precursors. For this purpose, a series of six neutral, anionic, and cationic cis -locked Ru(II)-DMSO complexes ( 2 – 7 ) of the general formula [Y] fac -[RuX(DMSO–S) 3 (O–O)] n (where O–O is a symmetrical chelating anion: oxalate (ox), malonate (mal), acetylacetonate (acac); X = DMSO–O or Cl – ; n = −1/0/+1 depending on the nature and charge of X and O–O; when present, Y = K + or PF 6 – ) were efficiently prepared from the well-known cis -[RuCl 2 (DMSO) 4 ] ( 1 ). When treated with diimine chelating ligands (L1 = bpy, phen, dpphen), the compounds 2 – 7 afforded the target [Ru(L1) 2 (O–O)] 0/+ complex together with the undesired (and unexpected) [Ru(L1) 3 ] 2+ species. Nevertheless, we found that the formation of [Ru(L1) 3 ] 2+ can be minimized by carefully adjusting the reaction conditions: in particular, high selectivity toward [Ru(L1) 2 (O–O)] 0/+ and almost complete conversion of the precursor was obtained within minutes, also on a 100–200 mg scale, when the reactions were performed in absolute ethanol at 150 °C in a microwave reactor. Depending on the nature of L1 and concentration, with the oxalate and malonate precursors, the neutral product [Ru(L1) 2 (O–O)] can precipitate spontaneously from the final mixture, in pure form and acceptable-to-good yields. When spontaneous precipitation of the disubstituted product does not occur, purification from [Ru(L1) 3 ] 2+ can be rather easily accomplished by column chromatography or solvent extraction. By comparison, under the same conditions, compound 1 is much less selective, thus demonstrating that locking the geometry of the precursor through the introduction of O–O in the coordination sphere of Ru is a valid strategic approach. By virtue of its proton-sensitive nature, facile and quantitative replacement of O–O in [Ru(L1) 2 (O–O)] 0/+ by L2, selectively affording [Ru(L1) 2 (L2)] 2+ , was accomplished in refluxing ethanol in the presence of a slight excess of trifluoroacetic acid or HPF 6 .

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Section: Introductionmentioning

confidence: 99%

cis-Locked Ru(II)-DMSO Precursors for the Microwave-Assisted Synthesis of Bis-Heteroleptic Polypyridyl Compounds

et al. 2021

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“…They allow the formation of C^C* cyclometalated complexes with Ir(III), 36 Pt(II), 37 and Ru-(II). 38 We prepared the chloride salts of the pro-ligands (H 2 L tBu ) + and (H 2 L OMe ) + which associate a fused imidazo [1,5a] pyridinium ring and an electron-rich 2,4-(di-tert-butyl)phenol or 2-(tert-butyl)-4-methoxyphenol, respectively (Scheme 1). The Ni(II) complexes of H 2 L tBu and H 2 L OMe were isolated (Scheme 2), and their electrochemical behavior was investigated.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Imidazo [1,5- a ] pyridinium ligands bearing N -aryl substituents are an example of unusual NHC structures derived from imidazoliums. They allow the formation of C^C* cyclometalated complexes with Ir(III), Pt(II), and Ru(II) . We prepared the chloride salts of the pro-ligands (H 2 L tBu ) + and (H 2 L OMe ) + which associate a fused imidazo [1,5- a ] pyridinium ring and an electron-rich 2,4-(di- tert -butyl)phenol or 2-( tert -butyl)-4-methoxyphenol, respectively (Scheme ).…”

Section: Introductionmentioning

confidence: 99%

Single-Oxidation of Ni(II) Complexes of Bidentate Fused N-Heterocyclic Carbene–Phenol Conjugates

et al. 2023

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The pro-ligands (H 2 L tBu ) + and (H 2 L OMe ) + were synthesized as chloride salts. They associate an imidazo [1,5-a] pyridinium ring and an electron-rich 2,4-(ditert-butyl)phenol or 2-(tert-butyl)-4-methoxyphenol, respectively. The homoleptic Ni(II) complexes of H 2 L tBu (1) and H 2 L OMe (2) were prepared and structurally characterized, showing a four-coordinate nickel center with two ligands bound by one phenolate oxygen and one carbene each. Complexes 1 and 2 show two reversible oxidation waves in their cyclic voltammetry curve, at E 1/2 1 = 0.19 V and E 1/2 2 = 0.59 V, and E 1/2 1 = 0.03 V and E 1/2 2 = 0.32 V, respectively. The one-electron oxidized forms were generated and characterized by spectroscopy, while 2 + could be isolated as single crystals. They both demonstrate two remarkable NIR bands indicating radical species in CH 2 Cl 2 . The EPR parameters are 2.097, 2.023, and 1.997 (g average = 2.039) for 1 + and 2.030, 2.016, and 1.994 (g average = 2.013) for 2 + . Both g average values are slightly higher than those reported for genuine phenoxyl radicals but far below those of Ni(III) complexes, supporting a metalloradical character of 1 + and 2 + , whereby one metal d-orbital contributes to the singly occupied molecular orbital (SOMO). A very good agreement is found between DFT calculated and experimental vis−NIR and EPR data. Both metalloradical cations could be converted into Ni(III) species by addition of pyridine. The redox isomerism could be monitored by EPR spectroscopy: the [1•Py] + species exhibits for instance the g-values 2.157, 2.136, and 2.014 (g average = 2.103). The Ni(III) adducts are thermally unstable and undergo reduction back to the neutral precursor at room temperature.

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“…[18][19][20][21][22][23] Replacement of one or several pyridine ligand sites by Nheterocyclic carbenes (NHCs) has received surprisingly little attention. [24][25][26][27] To gain an insight into the photochemical reactions of carbene complexes, it is necessary to characterize the lowest-lying electronic excited states and their photophysical deactivation mechanisms. After the first successful isolation of N-heterocyclic carbene (NHC) by Arduengo et al [28] in 1991, there has been an immense growth in the field of chemical, [14,[29][30][31] structural, [32][33][34][35] biomedical [36][37][38][39] and photophysical properties.…”

Section: Introductionmentioning

confidence: 99%

2,2/-Bipyridyl Chelated Ru(II)-Annulated NHC Complex of 1-Methyl-2-Pyridin-2-Yl-2H-Imidazo[1,5-a]Pyridin-4-Ylidene: Synthesis, Structure, Optical Properties, and DFT Interpretation

Rana¹,

Dinda²,

Mahapatra³

et al. 2022

Eng. Sci.

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This article depicts the synthesis of Ru(II)-NHC complex, [Ru(bpy)(NHC)(CH 3 CN) 2 ][PF 6 ] 2 (2); [NHC = 1-methyl-2-(pyridyl)imidazo[1,5-a]pyridine-2-yiledene, bpy = 2,2 ' -bipyridine] via Ag(I)-carbene trans-metallation process. X-ray diffraction studies of the compound 2 elucidate the triclinic crystal system of single crystal with a distorted octahedral geometry. To insight into the structure and optoelectronic properties, density functional theory (DFT) and time-dependent density functional theory (TDDFT) studies were performed, and the absorption spectra were of intra-ligand charge transfer transitions (ILCT) character along with large contribution of (metal-ligand charge transfer (MLCT) transition in complexes. The compound 2 is fluorescent active and it is expected that the source of fluorescence is due to the presence of 2,2 ' -bipyridine fluorophore. Hirshfeld model studies were also performed of the crystal structure to illustrate the nature of intermolecular interactions present in the structure in the crystalline environment, and the molecule possess several C-H…Fweak H-bonding interactions. The molecule paves the way towards a new pro-apoptotic and antimicrobial compound against various cancer cells and is also a useful pre-catalyst for different types of hydrogenation reactions.

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Cyclometalated Ruthenium(II) NHC Complexes with Imidazo[1,5‐a]pyridine‐Based (C^{^}C*) Ligands – Synthesis and Characterization

Cited by 11 publications

References 53 publications

cis-Locked Ru(II)-DMSO Precursors for the Microwave-Assisted Synthesis of Bis-Heteroleptic Polypyridyl Compounds

cis-Locked Ru(II)-DMSO Precursors for the Microwave-Assisted Synthesis of Bis-Heteroleptic Polypyridyl Compounds

Single-Oxidation of Ni(II) Complexes of Bidentate Fused N-Heterocyclic Carbene–Phenol Conjugates

2,2/-Bipyridyl Chelated Ru(II)-Annulated NHC Complex of 1-Methyl-2-Pyridin-2-Yl-2H-Imidazo[1,5-a]Pyridin-4-Ylidene: Synthesis, Structure, Optical Properties, and DFT Interpretation

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Cyclometalated Ruthenium(II) NHC Complexes with Imidazo[1,5‐a]pyridine‐Based (C^C*) Ligands – Synthesis and Characterization

Cited by 11 publications

References 53 publications

cis-Locked Ru(II)-DMSO Precursors for the Microwave-Assisted Synthesis of Bis-Heteroleptic Polypyridyl Compounds

cis-Locked Ru(II)-DMSO Precursors for the Microwave-Assisted Synthesis of Bis-Heteroleptic Polypyridyl Compounds

Single-Oxidation of Ni(II) Complexes of Bidentate Fused N-Heterocyclic Carbene–Phenol Conjugates

2,2/-Bipyridyl Chelated Ru(II)-Annulated NHC Complex of 1-Methyl-2-Pyridin-2-Yl-2H-Imidazo[1,5-a]Pyridin-4-Ylidene: Synthesis, Structure, Optical Properties, and DFT Interpretation

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Cyclometalated Ruthenium(II) NHC Complexes with Imidazo[1,5‐a]pyridine‐Based (C^{^}C*) Ligands – Synthesis and Characterization