Research

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20 pages, 4077 KiB

Open AccessArticle

Investigating Ligand Sphere Perturbations on Mn^III–Alkylperoxo Complexes

by Samuel A. Brunclik, Elizabeth N. Grotemeyer, Zahra Aghaei, Mohammad Rasel Mian and Timothy A. Jackson

Molecules 2024, 29(8), 1849; https://doi.org/10.3390/molecules29081849 - 18 Apr 2024

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Abstract

Manganese catalysts that activate hydrogen peroxide carry out several different hydrocarbon oxidation reactions with high stereoselectivity. The commonly proposed mechanism for these reactions involves a key manganese(III)-hydroperoxo intermediate, which decays via O–O bond heterolysis to generate a Mn(V)–oxo species that institutes substrate oxidation. [...] Read more.

Manganese catalysts that activate hydrogen peroxide carry out several different hydrocarbon oxidation reactions with high stereoselectivity. The commonly proposed mechanism for these reactions involves a key manganese(III)-hydroperoxo intermediate, which decays via O–O bond heterolysis to generate a Mn(V)–oxo species that institutes substrate oxidation. Due to the scarcity of characterized Mn^III–hydroperoxo complexes, Mn^III–alkylperoxo complexes are employed to understand factors that affect the mechanism of the O–O cleavage. Herein, we report a series of novel complexes, including two room-temperature-stable Mn^III–alkylperoxo species, supported by a new amide-containing pentadentate ligand (^6Medpaq^5NO2). We use a combination of spectroscopic methods and density functional theory computations to probe the effects of the electronic changes in the ligand sphere trans to the hydroxo and alkylperoxo units to thermal stability and reactivity. The structural characterizations for both Mn^II(OTf)(^6Medpaq^5NO2) and [Mn^III(OH)(^6Medpaq^5NO2)](OTf) were obtained via single-crystal X-ray crystallography. A perturbation to the ligand sphere allowed for a marked increase in reactivity towards an organic substrate, a modest change in the distribution of the O–O cleavage products from homolytic and heterolytic pathways, and little change in thermal stability. Full article

(This article belongs to the Special Issue Recent Advances in Coordination Chemistry of Metal Complexes)

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15 pages, 2719 KiB

Open AccessArticle

DFT Studies of Dimethylaminophenyl-Substituted Phthalocyanine and Its Silver Complexes

by Martin Breza

Molecules 2024, 29(6), 1344; https://doi.org/10.3390/molecules29061344 - 18 Mar 2024

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Abstract

The dimethylaminophenyl-substituted silver phthalocyanine [dmaphPcAg] can be used as a UV-vis photoinitiator for in situ preparation of a silver/polymer nanocomposite. To verify early steps of the supposed mechanism of radical polymerization, we performed quantum chemical calculations of ^m[dmaphPcAg]^q complexes with charges [...] Read more.

The dimethylaminophenyl-substituted silver phthalocyanine [dmaphPcAg] can be used as a UV-vis photoinitiator for in situ preparation of a silver/polymer nanocomposite. To verify early steps of the supposed mechanism of radical polymerization, we performed quantum chemical calculations of ^m[dmaphPcAg]^q complexes with charges q = +1 to −2 in the two lowest spin states m, of a free ligand and its dehydrogenated/deprotonated products ^m[dmaphPcH_n]^q, n = 2 to 0, q = 0, −1 or −2, in the lowest spin states m. The calculated electronic structures and electron transitions of all the optimized structures in CHCl₃ solutions are compared with experimental EPR and UV-vis spectra, respectively. The unstable ³[dmaphPcAg]⁺ species deduced only from previous EPR spin trap experiments was identified. In addition to ²[dmaphPcAg]⁰, our results suggest the coexistence of both reaction intermediates ¹[dmaphPcAg]⁻ and ³[dmaphPcAg]⁻ in reaction solutions. Silver nanoparticle formation is a weak point of the supposed reaction mechanism from the energetic, stereochemistry, and electronic structure points of view. Full article

(This article belongs to the Special Issue Recent Advances in Coordination Chemistry of Metal Complexes)

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21 pages, 3284 KiB

Open AccessArticle

New Copper Complexes with N,O-Donor Ligands Based on Pyrazole Moieties Supported by 3-Substituted Acetylacetone Scaffolds

by Jo’ Del Gobbo, Carlo Santini, Alessandro Dolmella, Zhenzhen Li, Miriam Caviglia and Maura Pellei

Molecules 2024, 29(3), 621; https://doi.org/10.3390/molecules29030621 - 28 Jan 2024

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Abstract

The new 3-monosubstituted acetylacetone ligands, 3-(phenyl(1H-pyrazol-1-yl)methyl)pentane-2,4-dione (HL^acPz) and 3-((3,5-dimethyl-1H-pyrazol-1-yl)(phenyl)methyl)pentane-2,4-dione (HL^acPzMe), were synthesized and used as supporting ligands for new copper(II) and copper(I) phosphane complexes of the general formulae [Cu(HL^acX)₂(L^acX) [...] Read more.

The new 3-monosubstituted acetylacetone ligands, 3-(phenyl(1H-pyrazol-1-yl)methyl)pentane-2,4-dione (HL^acPz) and 3-((3,5-dimethyl-1H-pyrazol-1-yl)(phenyl)methyl)pentane-2,4-dione (HL^acPzMe), were synthesized and used as supporting ligands for new copper(II) and copper(I) phosphane complexes of the general formulae [Cu(HL^acX)₂(L^acX)₂] and [Cu(PPh₃)₂(HL^acX)]PF₆ (X = Pz (pyrazole) or PzMe (3,5-dimethylpyrazole)), respectively. In the syntheses of the Cu(I) complexes, the triphenylphosphine coligand (PPh₃) was used to stabilize copper in the +1 oxidation state, avoiding oxidation to Cu(II). All compounds were characterized by CHN analysis, ¹H-NMR, ¹³C-NMR, FT-IR spectroscopy, and electrospray ionization mass spectrometry (ESI-MS). The ligands HL^acPz (1) and HL^acPzMe (2) and the copper complex [Cu(PPh₃)₂(HL^acPz)]PF₆ (3) were also characterized by X-ray crystallography. The reactivity of these new compounds was investigated and the new compounds 4-phenyl-4-(1H-pyrazol-1-yl)butan-2-one (7) and 4-(3,5-dimethyl-1H-pyrazol-1-yl)-4-phenylbutan-2-one (8) were obtained in basic conditions via the retro-Claisen reaction of related 3-monosubstituted acetylacetone, providing efficient access to synthetically useful ketone compounds. Compound 8 was also characterized by X-ray crystallography. Full article

(This article belongs to the Special Issue Recent Advances in Coordination Chemistry of Metal Complexes)

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14 pages, 2746 KiB

Open AccessArticle

Luminescent Behavior of Zn(II) and Mn(II) Halide Derivatives of 4-Phenyldinaphtho[2,1-d:1′,2′-f][1,3,2]dioxaphosphepine 4-Oxide and Single-Crystal X-ray Structure Determination of the Ligand

by Valentina Ferraro, Jesús Castro and Marco Bortoluzzi

Molecules 2024, 29(1), 239; https://doi.org/10.3390/molecules29010239 - 01 Jan 2024

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Abstract

The two enantiomers of chiral phosphonate 4-phenyldinaphtho[2,1-d:1′,2′-f][1,3,2]dioxaphosphepine 4-oxide, O=PPh(BINOL), were synthesized from the proper 1,1′-bi-2-naphtol (BINOL) enantiomer and characterized. The structure of the (S)-enantiomer was elucidated by means of single-crystal X-ray diffraction. The reaction with anhydrous ZnBr₂ afforded complexes having [...] Read more.

The two enantiomers of chiral phosphonate 4-phenyldinaphtho[2,1-d:1′,2′-f][1,3,2]dioxaphosphepine 4-oxide, O=PPh(BINOL), were synthesized from the proper 1,1′-bi-2-naphtol (BINOL) enantiomer and characterized. The structure of the (S)-enantiomer was elucidated by means of single-crystal X-ray diffraction. The reaction with anhydrous ZnBr₂ afforded complexes having the general formula [ZnBr₂{O=PPh(BINOL)}₂] that showed intense fluorescence centered in the near-UV region rationalized on the basis of TD-DFT calculations. The corresponding Mn(II) complexes with the general formula [MnX₂{O=PPh(BINOL)}₂] (X = Cl, Br) exhibited dual emission upon excitation with UV light, with the relative intensity of the bands dependent upon the choice of the halide. The highest energy transition is comparable with that of the Zn(II) complex, while the lowest energy emission falls in the red region of the spectrum and is characterized by lifetimes in the hundreds of microseconds range. Although the emission at lower energy can also be achieved by direct excitation of the metal center, the luminescence decay curves suggest that the band in the red range is possibly derived from BINOL-centered excited states populated by intersystem crossing. Full article

(This article belongs to the Special Issue Recent Advances in Coordination Chemistry of Metal Complexes)

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14 pages, 1635 KiB

Open AccessArticle

Synthesis and Characterization of Iridium(III) Complexes with Substituted Phenylimidazo(4,5-f)1,10-phenanthroline Ancillary Ligands and Their Application in LEC Devices

by Bárbara Vásquez, Max Bayas, Paulina Dreyse, Juan Luis Palma, Alan R. Cabrera, Elena Rossin, Mirco Natali, Cesar Saldias and Iván González-Pavez

Molecules 2024, 29(1), 53; https://doi.org/10.3390/molecules29010053 (registering DOI) - 21 Dec 2023

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Abstract

In this work, we report on the synthesis and characterization of six new iridium(III) complexes of the type [Ir(C^N)₂(N^N)]⁺ using 2-phenylpyridine (C1–3) and its fluorinated derivative (C4–6) as cyclometalating ligands (C^N) and [...] Read more.

In this work, we report on the synthesis and characterization of six new iridium(III) complexes of the type [Ir(C^N)₂(N^N)]⁺ using 2-phenylpyridine (C1–3) and its fluorinated derivative (C4–6) as cyclometalating ligands (C^N) and R-phenylimidazo(4,5-f)1,10-phenanthroline (R = H, CH₃, F) as the ancillary ligand (N^N). These luminescent complexes have been fully characterized through optical and electrochemical studies. In solution, the C4–6 series exhibits quantum yields (Ф) twice as high as the C1–3 series, exceeding 60% in dichloromethane and where ³MLCT/³LLCT and ³LC emissions participate in the phenomenon. These complexes were employed in the active layer of light-emitting electrochemical cells (LECs). Device performance of maximum luminance values of up to 21.7 Lx at 14.7 V were observed for the C2 complex and long lifetimes for the C1–3 series. These values are counterintuitive to the quantum yields observed in solution. Thus, we established that the rigidity of the system and the structure of the solid matrix dramatically affect the electronic properties of the complex. This research contributes to understanding the effects of the modifications in the ancillary and cyclometalating ligands, the photophysics of the complexes, and their performance in LEC devices. Full article

(This article belongs to the Special Issue Recent Advances in Coordination Chemistry of Metal Complexes)

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10 pages, 1630 KiB

Open AccessCommunication

Russian Doll-like 3d–4f Cluster Wheels with Slow Relaxation of Magnetization

by Lan Liu, Panpan Yang, Zhihui Qiu, Kai Wang, Dongcheng Liu, Yuning Liang, Huancheng Hu, Huahong Zou, Fupei Liang and Zilu Chen

Molecules 2023, 28(15), 5906; https://doi.org/10.3390/molecules28155906 - 06 Aug 2023

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Abstract

The solvothermal reactions of LnCl₃·6H₂O and MCl₂·6H₂O (M = Co, Ni) with 2,2′-diphenol (H₂L¹) and 5,7-dichloro-8-hydroxyquinoline (HL²) gave three 3d–4f heterometallic wheel-like nano-clusters [Ln₇M₆(L¹ [...] Read more.

The solvothermal reactions of LnCl₃·6H₂O and MCl₂·6H₂O (M = Co, Ni) with 2,2′-diphenol (H₂L¹) and 5,7-dichloro-8-hydroxyquinoline (HL²) gave three 3d–4f heterometallic wheel-like nano-clusters [Ln₇M₆(L¹)₆(L²)₆(µ₃-OH)₆(OCH₃)₆Cl(CH₃CN)₆]Cl₂·xH₂O (Ln = Dy, M = Co, x = 3 for 1; Ln = Dy, M = Ni, x = 0 for 2; Ln = Tb, M = Ni, x = 0 for 3) with similar cluster structure. The innermost Ln(III) ion is encapsulated in a planar Ln₆ ring which is further embedded in a chair-conformation M₆ ring, constructing a Russian doll-like 3d–4f cluster wheel Ln(III)⸦Ln₆⸦M₆. 2 and 3 show obvious slow magnetic relaxation behavior with negligible opening of the magnetic hysteresis loop. Such a Russian doll-like 3d–4f cluster wheel with the lanthanide disc isolated by transition metallo-ring is rarely reported. Full article

(This article belongs to the Special Issue Recent Advances in Coordination Chemistry of Metal Complexes)

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12 pages, 2170 KiB

Open AccessArticle

Synthesis and Characterization of Iron Bispyridine Bisdicyanamide, Fe[C₅H₅N]₂[N(CN)₂]₂

by Laura Henrich, Peter C. Müller, Jan Hempelmann, Markus Mann, Jan van Leusen, Simon Steinberg and Richard Dronskowski

Molecules 2023, 28(13), 4886; https://doi.org/10.3390/molecules28134886 - 21 Jun 2023

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Abstract

Fe[C₅H₅N]₂[N(CN)₂]₂ (1) was synthesized from a reaction of stoichiometric amounts of NaN(CN)₂ and FeCl₂·4H₂O in a methanol/pyridine solution. Single-crystal and powder diffraction show that 1 crystallizes in [...] Read more.

Fe[C₅H₅N]₂[N(CN)₂]₂ (1) was synthesized from a reaction of stoichiometric amounts of NaN(CN)₂ and FeCl₂·4H₂O in a methanol/pyridine solution. Single-crystal and powder diffraction show that 1 crystallizes in the monoclinic space group I2/m (no. 12), different from Mn[C₅H₅N]₂[N(CN)₂]₂ (P2₁/c, no. 14) due to tilted pyridine rings, with a = 7.453(7) Å, b = 13.167(13) Å, c = 8.522(6) Å, β = 114.98(6)° and Z = 2. ATR-IR, AAS, and CHN measurements confirm the presence of dicyanamide and pyridine. Thermogravimetric analysis shows that π-stacking interactions of the pyridine rings play an important role in structural stabilization. Based on DFT-optimized structures, a chemical bonding analysis was performed using a local-orbital framework by projection from a plane-wave basis. The resulting bond orders and atomic charges are in good agreement with the expectations based on the structure analysis. SQUID magnetic susceptibility measurements show a high-spin state Fe^II compound with predominantly antiferromagnetic exchange interactions at lower temperatures. Full article

(This article belongs to the Special Issue Recent Advances in Coordination Chemistry of Metal Complexes)

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Review

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14 pages, 6281 KiB

Open AccessReview

Metal Complexes of Redox Non-Innocent Ligand N,N′-Bis(3,5-di-tertbutyl-2-hydroxy-phenyl)-1,2-phenylenediamine

by Ari Lehtonen

Molecules 2024, 29(5), 1088; https://doi.org/10.3390/molecules29051088 - 29 Feb 2024

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Abstract

Redox non-innocent ligands react with metal precursors to form complexes where the oxidation states of the ligand and thus the metal atom cannot be easily defined. A well-known example of such ligands is bis(o-aminophenol) N,N′-bis(3,5-di-tertbutyl-2-hydroxy-phenyl)-1,2-phenylenediamine, previously [...] Read more.

Redox non-innocent ligands react with metal precursors to form complexes where the oxidation states of the ligand and thus the metal atom cannot be easily defined. A well-known example of such ligands is bis(o-aminophenol) N,N′-bis(3,5-di-tertbutyl-2-hydroxy-phenyl)-1,2-phenylenediamine, previously developed by the Wieghardt group, which has a potentially tetradentate coordination mode and four distinct protonation states, whereas its electrochemical behavior allows for five distinct oxidation states. This rich redox chemistry, as well as the ability to coordinate to various transition metals, has been utilized in the syntheses of metal complexes with M₂L, ML and ML₂ stoichiometries, sometimes supported with other ligands. Different oxidation states of the ligand can adopt different coordination modes. For example, in the fully oxidized form, two N donors are sp²-hybridized, which makes the ligand planar, whereas in the fully reduced form, the sp³-hybridized N donors allow the formation of more flexible chelate structures. In general, the metal can be reduced during complexation, but redox processes of the isolated complexes typically occur on the ligand. Combination of this non-innocent ligand with redox-active transition metals may lead to complexes with interesting magnetic, electrochemical, photonic and catalytic properties. Full article

(This article belongs to the Special Issue Recent Advances in Coordination Chemistry of Metal Complexes)

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40 pages, 14175 KiB

Open AccessReview

Advances for Triangular and Sandwich-Shaped All-Metal Aromatics

by Miaomiao Wang and Yanlan Wang

Molecules 2024, 29(4), 763; https://doi.org/10.3390/molecules29040763 - 07 Feb 2024

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Abstract

Much experimental work has been contributed to all-metal σ, π and δ-aromaticity among transition metals, semimetallics and other metals in the past two decades. Before our focused investigations on the properties of triangular and sandwich-shaped all-metal aromatics, A. I. Boldyrev presented general [...] Read more.

Much experimental work has been contributed to all-metal σ, π and δ-aromaticity among transition metals, semimetallics and other metals in the past two decades. Before our focused investigations on the properties of triangular and sandwich-shaped all-metal aromatics, A. I. Boldyrev presented general discussions on the concepts of all-metal σ-aromaticity and σ-antiaromaticity for metallo-clusters. Schleyer illustrated that Nucleus-Independent Chemical Shifts (NICS) were among the most authoritative criteria for aromaticity. Ugalde discussed the earlier developments of all-metal aromatic compounds with all possible shapes. Besides the theoretical predictions, many stable all-metal aromatic trinuclear clusters have been isolated as the metallic analogues of either the σ-aromatic molecule’s [H₃]⁺ ion or the π-aromatic molecule’s [C₃H₃]⁺ ion. Different from Hoffman’s opinion on all-metal aromaticity, triangular all-metal aromatics were found to hold great potential in applications in coordination chemistry, catalysis, and material science. Triangular all-metal aromatics, which were theoretically proved to conform to the Hückel (4n + 2) rule and possess the smallest aromatic ring, could also play roles as stable ligands during the formation of all-metal sandwiches. The triangular and sandwich-shaped all-metal aromatics have not yet been specifically summarized despite their diversity of existence, puissant developments and various interesting applications. These findings are different from the public opinion that all-metal aromatics would be limited to further applications due to their overstated difficulties in synthesis and uncertain stabilities. Our review will specifically focus on the summarization of theoretical predictions, feasible syntheses and isolations, and multiple applications of triangular and sandwich shaped all-metal aromatics. The appropriateness and necessities of this review will emphasize and disseminate their importance and applications forcefully and in a timely manner. Full article

(This article belongs to the Special Issue Recent Advances in Coordination Chemistry of Metal Complexes)

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