Research

17 pages, 3866 KiB

Open AccessArticle

The Identification of Structural Changes in the Lithium Hexamethyldisilazide–Toluene System via Ultrasonic Relaxation Spectroscopy and Theoretical Calculations

by Constantine Kouderis, Afrodite Tryfon, Themistoklis A. Kabanos and Angelos G. Kalampounias

Molecules 2024, 29(4), 813; https://doi.org/10.3390/molecules29040813 - 09 Feb 2024

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Abstract

Ultrasonic absorption measurements were carried out over a wide concentration and temperature range by means of a pulse technique to examine the structural mechanisms and the dynamical properties in lithium hexamethyldisilazide (LiHMDS)–toluene solutions. Acoustic spectra [...] Read more.

Ultrasonic absorption measurements were carried out over a wide concentration and temperature range by means of a pulse technique to examine the structural mechanisms and the dynamical properties in lithium hexamethyldisilazide (LiHMDS)–toluene solutions. Acoustic spectra revealed two distinct Debye-type relaxational absorptions attributed to the formation of trimers from dimeric and monomer units and to the formation of aggregates between a LiHMDS dimer and one toluene molecule in low and high frequencies, respectively. The formation of aggregates was clarified by means of molecular docking and DFT methodologies. The aggregation number, the rate constants and the thermodynamic properties of these structural changes were determined by analyzing in detail the concentration-dependent relaxation parameters. The low-frequency relaxation mechanism dominates the acoustic spectra in the high LiHMDS mole fractions, while the high-frequency relaxation influences the spectra in the low LiHMDS mole fractions. In the intermediate mole fraction region (0.25 to 0.46), both relaxations prevail in the spectra. The adiabatic compressibility, the excess adiabatic compressibility and the theoretically estimated mean free length revealed a crossover in the 0.25 to 0.46 LiHMDS mole fractions that signified the transition from one structural mechanism related with the hetero-association of LiHMDS dimers with toluene molecules to the other structural mechanism assigned to the formation of LiHMDS trimers. The combined use of acoustic spectroscopy with theoretical calculations permitted us to disentangle the underlying structural mechanisms and evaluate the volume changes associated with each reaction. The results were compared with the corresponding theoretically predicted volume changes and discussed in the context of the concentration effect on intermolecular bonding. Full article

(This article belongs to the Special Issue Featured Papers in Organometallic Chemistry)

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13 pages, 3957 KiB

Open AccessArticle

Role of the Environment Polarity on the Photophysical Properties of Mesogenic Hetero-Polymetallic Complexes

by Adelina A. Andelescu, Angela Candreva, Evelyn Popa, Alexandru Visan, Carmen Cretu, Massimo La Deda and Elisabeta I. Szerb

Molecules 2024, 29(4), 750; https://doi.org/10.3390/molecules29040750 - 06 Feb 2024

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Abstract

New hetero-polynuclear coordination complexes based on a pentacoordinated Zn(II) metal center with tridentate terpyridine-based ligands and monoanionic gallates functionalized with long alkyl chains containing ferrocene units were designed, synthesized and characterized using spectroscopic and analytical methods. The complexes are mesomorphic, exhibiting columnar hexagonal [...] Read more.

New hetero-polynuclear coordination complexes based on a pentacoordinated Zn(II) metal center with tridentate terpyridine-based ligands and monoanionic gallates functionalized with long alkyl chains containing ferrocene units were designed, synthesized and characterized using spectroscopic and analytical methods. The complexes are mesomorphic, exhibiting columnar hexagonal mesophases. The photophysical properties in a solution and in an ordered condensed state were accurately investigated and the influence of the polarity of the solvent was evidenced. Full article

(This article belongs to the Special Issue Featured Papers in Organometallic Chemistry)

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14 pages, 2345 KiB

Open AccessArticle

Aminoquinoline-Based Tridentate (NNN)-Copper Catalyst for C–N Bond-Forming Reactions from Aniline and Diazo Compounds

by Mohsen Teimouri, Selvam Raju, Edward Acheampong, Allison N. Schmittou, Bruno Donnadieu, David O. Wipf, Brad S. Pierce, Sean L. Stokes and Joseph P. Emerson

Molecules 2024, 29(3), 730; https://doi.org/10.3390/molecules29030730 - 05 Feb 2024

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Abstract

A new tridentate Cu²⁺ complex based on (E)-1-(pyridin-2-yl)-N-(quinolin-8-yl)methanimine (PQM) was generated and characterized to support the activation of diazo compounds for the formation of new C–N bonds. This neutral Schiff base ligand was structurally characterized to coordinate with [...] Read more.

A new tridentate Cu²⁺ complex based on (E)-1-(pyridin-2-yl)-N-(quinolin-8-yl)methanimine (PQM) was generated and characterized to support the activation of diazo compounds for the formation of new C–N bonds. This neutral Schiff base ligand was structurally characterized to coordinate with copper(II) in an equatorial fashion, yielding a distorted octahedral complex. Upon characterization, this copper(II) complex was used to catalyze an efficient and cost-effective protocol for C–N bond formation between N-nucleophiles and copper carbene complexes arising from the activation of diazo carbonyl compounds. A substrate scope of approximately 15 different amine-based substrates was screened, yielding 2° or 3° amine products with acceptable to good yields under mild reaction conditions. Reactivity towards phenol and thiophenol were also screened, showing relatively weak C–O or C–S bond formation under optimized conditions. Full article

(This article belongs to the Special Issue Featured Papers in Organometallic Chemistry)

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15 pages, 2173 KiB

Open AccessArticle

Ruthenium–Cyclopentadienyl–Cycloparaphenylene Complexes: Sizable Multicharged Cations Exhibiting High DNA-Binding Affinity and Remarkable Cytotoxicity

by Konstantinos Ypsilantis, Evangelia Sifnaiou, Antonia Garypidou, Dimitrios Kordias, Angeliki Magklara and Achilleas Garoufis

Molecules 2024, 29(2), 514; https://doi.org/10.3390/molecules29020514 - 19 Jan 2024

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Abstract

Two novel sizable multicharged cationic complexes, of the formulae [(η⁶–-[12]CPP)[Ru(η⁵–-Cp)]₁₂]Χ₁₂ and [(η⁶–-[11]CPP)[Ru(η⁵–-Cp)]₁₁]Χ₁₁, CPP = cycloparaphenylene, Cp = cyclopentadienyl, X = [PF₆]⁻ [...] Read more.

Two novel sizable multicharged cationic complexes, of the formulae [(η⁶–-[12]CPP)[Ru(η⁵–-Cp)]₁₂]Χ₁₂ and [(η⁶–-[11]CPP)[Ru(η⁵–-Cp)]₁₁]Χ₁₁, CPP = cycloparaphenylene, Cp = cyclopentadienyl, X = [PF₆]⁻, (1), (3) and [Cl]⁻, (2), (4), were synthesized and characterized using NMR techniques, high-resolution mass spectrometry, and elemental analyses. Complexes (1) and (3) were stable in acetone and acetonitrile solutions over 48 h. In contrast, the water-soluble (2) and (4) begin to decompose in aqueous media after 1 h, due to the [Cl]⁻ tendency for nucleophilic attack on ruthenium of the {Ru(η⁵–-Cp)} units. Fluorescence quenching experiments conducted during the stability window of (2) with the d(5′-CGCGAATTCGCG-3′)₂-EtBr adducts revealed remarkably high values for K_sv = 1.185 × 10⁴ ± 0.025 M⁻¹ and K_b = 3.162 × 10⁵ ± 0.001 M⁻¹. Furthermore, the cytotoxic activity of (2) against A2780, A2780res, and MCF-7 cancer cell lines shows that it is highly cytotoxic with IC₅₀ values in the range of 4.76 ± 1.85 to 16 ± 0.81 μΜ. Full article

(This article belongs to the Special Issue Featured Papers in Organometallic Chemistry)

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24 pages, 3009 KiB

Open AccessArticle

Rational Design of Palladium(II) Indenyl and Allyl Complexes Bearing Phosphine and Isocyanide Ancillary Ligands with Promising Antitumor Activity

by Enrica Bortolamiol, Eleonora Botter, Enrico Cavarzerani, Matteo Mauceri, Nicola Demitri, Flavio Rizzolio, Fabiano Visentin and Thomas Scattolin

Molecules 2024, 29(2), 345; https://doi.org/10.3390/molecules29020345 - 10 Jan 2024

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Abstract

A new class of palladium–indenyl complexes characterized by the presence of one bulky alkyl isocyanide and one aryl phosphine serving as ancillary ligands has been prepared, presenting high yields and selectivity. All the new products were completely characterized using spectroscopic and spectrometric techniques [...] Read more.

A new class of palladium–indenyl complexes characterized by the presence of one bulky alkyl isocyanide and one aryl phosphine serving as ancillary ligands has been prepared, presenting high yields and selectivity. All the new products were completely characterized using spectroscopic and spectrometric techniques (NMR, FT-IR, and HRMS), and, for most of them, it was also possible to define their solid-state structures via X-ray diffractometry, revealing that the indenyl fragment always binds to the metal centre with a hapticity intermediate between ƞ³ and ƞ⁵. A reactivity study carried out using piperidine as a nucleophilic agent proved that the indenyl moiety is the eligible site of attack rather than the isocyanide ligand or the metal centre. All complexes were tested as potential anticancer agents against three ovarian cancer cell lines (A2780, A2780cis, and OVCAR-5) and one breast cancer cell line (MDA-MB-231), displaying comparable activity with respect to cisplatin, which was used as a positive control. Moreover, the similar cytotoxicity observed towards A2780 and A2780cis cells (cisplatin-sensitive and cisplatin-resistant, respectively) suggests that our palladium derivatives presumably act with a mechanism of action different than that of the clinically approved platinum drugs. For comparison, we also synthesized Pd-ƞ³-allyl derivatives, which generally showed a slightly higher activity towards ovarian cancer cells and lower activity towards breast cancer cells with respect to their Pd-indenyl congeners. Full article

(This article belongs to the Special Issue Featured Papers in Organometallic Chemistry)

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18 pages, 5401 KiB

Open AccessArticle

DFT Exploration of Metal Ion–Ligand Binding: Toward Rational Design of Chelating Agent in Semiconductor Manufacturing

by Wenyuan Wang, Junli Zhu, Qi Huang, Lei Zhu, Ding Wang, Weimin Li and Wenjie Yu

Molecules 2024, 29(2), 308; https://doi.org/10.3390/molecules29020308 - 08 Jan 2024

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Abstract

Chelating agents are commonly employed in microelectronic processes to prevent metal ion contamination. The ligand fragments of a chelating agent largely determine its binding strength to metal ions. Identification of ligands with suitable characteristics will facilitate the design of chelating agents to enhance [...] Read more.

Chelating agents are commonly employed in microelectronic processes to prevent metal ion contamination. The ligand fragments of a chelating agent largely determine its binding strength to metal ions. Identification of ligands with suitable characteristics will facilitate the design of chelating agents to enhance the capture and removal of metal ions from the substrate in microelectronic processes. This study employed quantum chemical calculations to simulate the binding process between eleven ligands and the hydrated forms of Ni²⁺, Cu²⁺, Al³⁺, and Fe³⁺ ions. The binding strength between the metal ions and ligands was quantified using binding energy and binding enthalpy. Additionally, we explored the binding interaction mechanisms and explained the differences in binding abilities of the eleven ligands using frontier molecular orbitals, nucleophilic indexes, electrostatic potentials, and energy decomposition calculations based on molecular force fields. Based on our computational results, promising chelating agent structures are proposed, aiming to guide the design of new chelating agents to address metal ion contamination issues in integrated circuit processes. Full article

(This article belongs to the Special Issue Featured Papers in Organometallic Chemistry)

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24 pages, 4133 KiB

Open AccessArticle

Synthesis and Characterization of Ruthenium-Paraphenylene-Cyclopentadienyl Full-Sandwich Complexes: Cytotoxic Activity against A549 Lung Cancer Cell Line and DNA Binding Properties

by Evangelia Sifnaiou, Theodoros Tsolis, Konstantinos Ypsilantis, Eugenia Roupakia, Evangelos Kolettas, John C. Plakatouras and Achilleas Garoufis

Molecules 2024, 29(1), 17; https://doi.org/10.3390/molecules29010017 - 19 Dec 2023

Cited by 1 | Viewed by 804

Abstract

Novel full-sandwich (η⁵-Cp)-Ru-paraphenylene complexes with the general formula [(η⁵-Cp)_nRu(η⁶-L)](PF₆)_n where n = 1–3 and L = biphenyl, p-terphenyl and p-quaterphenyl, were synthesized and characterized by means of [...] Read more.

Novel full-sandwich (η⁵-Cp)-Ru-paraphenylene complexes with the general formula [(η⁵-Cp)_nRu(η⁶-L)](PF₆)_n where n = 1–3 and L = biphenyl, p-terphenyl and p-quaterphenyl, were synthesized and characterized by means of spectroscopic and analytical techniques. The structures of the complexes [(η⁵-Cp)Ru(η⁶-biphenyl)](PF₆) (1), [(η⁵-Cp)Ru(η⁶-terphenyl)](PF₆) (3) and [(η⁵-Cp)₂Ru(η⁶-terphenyl)](PF₆)₂ (4) was determined by X-ray single crystal methods. The interaction of the complexes [(η⁵-Cp)Ru(η⁶-quaterphenyl)]Cl, (6)Cl, and [(η⁵-Cp)₂Ru(η⁶-quaterphenyl)]Cl₂, (7)Cl₂, with the DNA duplex d(5′-CGCGAATTCGCG-3′)₂ was studied using NMR techniques. The results showed that both complexes interacted non-specifically with both the minor and major grooves of the helix. Specifically, (6)Cl exhibited partial binding through intercalation between the T7 and T8 bases of the sequence without disrupting the C–G and A–T hydrogen bonds. Fluorometric determination of the complexes’ binding constants revealed a significant influence of the number of connected phenyl rings in the paraphenylene ligand (L) on the binding affinity of their complexes with the d(5′-CGCGAATTCGCG-3′)₂. The complexes (6)Cl and (7)Cl₂ were found to be highly cytotoxic against the A549 lung cancer cell line, with complex (6) being more effective than (7) (IC₅₀ for (6)Cl: 17.45 ± 2.1 μΜ, IC₅₀ for (7)Cl₂: 65.83 ± 1.8 μΜ) and with a selectivity index (SI) (SI for (6)Cl: 1.1 and SI for (7)Cl₂: 4.8). Full article

(This article belongs to the Special Issue Featured Papers in Organometallic Chemistry)

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13 pages, 4143 KiB

Open AccessArticle

[IPr^#–PEPPSI]: A Well-Defined, Highly Hindered and Broadly Applicable Pd(II)–NHC (NHC = N-Heterocyclic Carbene) Precatalyst for Cross-Coupling Reactions

by Md. Mahbubur Rahman, Qun Zhao, Guangrong Meng, Roger Lalancette, Roman Szostak and Michal Szostak

Molecules 2023, 28(15), 5833; https://doi.org/10.3390/molecules28155833 - 02 Aug 2023

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Abstract

In this Special Issue, “Featured Papers in Organometallic Chemistry”, we report on the synthesis and characterization of [IPr^#–PEPPSI], a new, well-defined, highly hindered Pd(II)–NHC precatalyst for cross-coupling reactions. This catalyst was commercialized in collaboration with MilliporeSigma, Burlington, ON, Canada (no. 925489) [...] Read more.

In this Special Issue, “Featured Papers in Organometallic Chemistry”, we report on the synthesis and characterization of [IPr^#–PEPPSI], a new, well-defined, highly hindered Pd(II)–NHC precatalyst for cross-coupling reactions. This catalyst was commercialized in collaboration with MilliporeSigma, Burlington, ON, Canada (no. 925489) to provide academic and industrial researchers with broad access to reaction screening and optimization. The broad activity of [IPr^#–PEPPSI] in cross-coupling reactions in a range of bond activations with C–N, C–O, C–Cl, C–Br, C–S and C–H cleavage is presented. A comprehensive evaluation of the steric and electronic properties is provided. Easy access to the [IPr^#–PEPPSI] class of precatalysts based on modular pyridine ligands, together with the steric impact of the IPr^# peralkylation framework, will facilitate the implementation of well-defined, air- and moisture-stable Pd(II)–NHC precatalysts in chemistry research. Full article

(This article belongs to the Special Issue Featured Papers in Organometallic Chemistry)

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12 pages, 1675 KiB

Open AccessArticle

Rhodium-Catalyzed Trans-Bis-Silylation Reactions of 2-Ethynyl-3-pentamethyldisilanylpyridines

by Akinobu Naka and Hisayoshi Kobayashi

Molecules 2023, 28(8), 3284; https://doi.org/10.3390/molecules28083284 - 07 Apr 2023

Cited by 3 | Viewed by 1821

Abstract

Rhodium-catalyzed reactions of 2-ethynyl-3-pentamethyldisilanylpyridine derivatives (1 and 2) are reported. The reactions of compounds 1 and 2 in the presence of catalytic amounts of rhodium complexes at 110 °C gave the corresponding pyridine-fused siloles (3) and (4) [...] Read more.

Rhodium-catalyzed reactions of 2-ethynyl-3-pentamethyldisilanylpyridine derivatives (1 and 2) are reported. The reactions of compounds 1 and 2 in the presence of catalytic amounts of rhodium complexes at 110 °C gave the corresponding pyridine-fused siloles (3) and (4) through intramolecular trans-bis-silylation cyclization. The reaction of 2-bromo-3-(1,1,2,2,2-pentamethyldisilanyl)pyridine with 3-phenyl-1-propyne in the presence of PdCl₂(PPh₃)₂-CuI catalysts afforded 1:2 bis-silylation adduct 6. DFT calculations were also performed to understand the reaction mechanism for the production of compound 3 from compound 1. Full article

(This article belongs to the Special Issue Featured Papers in Organometallic Chemistry)

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11 pages, 2016 KiB

Open AccessArticle

Niobium Complexes Supported by Chalcogen-Bridged [OEO]-Type Bis(phenolate) Ligands (E = S, Se): Synthesis, Characterization, and Phenylacetylene Polymerization

by Jing An, Akihiko Ishii and Norio Nakata

Molecules 2023, 28(6), 2573; https://doi.org/10.3390/molecules28062573 - 12 Mar 2023

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Abstract

Trichloro niobium(V) complexes 3 and 4 with the sulfur- or selenium-bridged [OEO]-type bis(phenolate) ligands (E = S, Se) were synthesized and fully characterized on the basis of their NMR spectroscopic data and X-ray crystallographic analysis. In the crystalline state of 4, the [...] Read more.

Trichloro niobium(V) complexes 3 and 4 with the sulfur- or selenium-bridged [OEO]-type bis(phenolate) ligands (E = S, Se) were synthesized and fully characterized on the basis of their NMR spectroscopic data and X-ray crystallographic analysis. In the crystalline state of 4, the [OSeO]-core of the ligand was coordinated to the niobium center in a fac-fashion. The corresponding tribenzyl niobium(V) complexes 5 and 6 were also prepared by the reactions of 3 and 4 with 3 equivalents of PhCH₂MgCl in toluene. The X-ray diffraction analysis of 6 revealed that the distorted six-coordinated niobium center incorporated in the [OSeO]-type ligand took a mer-fashion, and one benzyl ligand was coordinated to the niobium center by η²-fashion. Complexes 5 and 6 were tested for the phenylacetylene polymerization that produced poly(phenylacetylene)s (PPAs), oligomers, and triphenylbenzenes (TPBs) depending on the chalcogen atom in the [OEO]-type ligand. Full article

(This article belongs to the Special Issue Featured Papers in Organometallic Chemistry)

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12 pages, 2328 KiB

Open AccessArticle

Novel NHC-Based Au(I) Complexes as Precursors of Highly Pure Au(0) Nuggets under Oxidative Conditions

by Pau Font, Nikolaos V. Tzouras, Argyro T. Papastavrou, Georgios C. Vougioukalakis and Xavi Ribas

Molecules 2023, 28(5), 2302; https://doi.org/10.3390/molecules28052302 - 01 Mar 2023

Cited by 1 | Viewed by 1815

Abstract

The Lewis-acidic character and robustness of NHC-Au(I) complexes enable them to catalyze a large number of reactions, and they are enthroned as the catalysts of choice for many transformations among polyunsaturated substrates. More recently, Au(I)/Au(III) catalysis has been explored either by utilizing external [...] Read more.

The Lewis-acidic character and robustness of NHC-Au(I) complexes enable them to catalyze a large number of reactions, and they are enthroned as the catalysts of choice for many transformations among polyunsaturated substrates. More recently, Au(I)/Au(III) catalysis has been explored either by utilizing external oxidants or by seeking oxidative addition processes with catalysts featuring pendant coordinating groups. Herein, we describe the synthesis and characterization of N-heterocyclic carbene (NHC)-based Au(I) complexes, with and without pendant coordinating groups, and their reactivity in the presence of different oxidants. We demonstrate that when using iodosylbenzene-type oxidants, the NHC ligand undergoes oxidation to afford the corresponding NHC=O azolone products concomitantly with quantitative gold recovery in the form of Au(0) nuggets ~0.5 mm in size. The latter were characterized by SEM and EDX-SEM showing purities above 90%. This study shows that NHC-Au complexes can follow decomposition pathways under certain experimental conditions, thus challenging the believed robustness of the NHC-Au bond and providing a novel methodology to produce Au(0) nuggets. Full article

(This article belongs to the Special Issue Featured Papers in Organometallic Chemistry)

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