Reversible Switching of the Coordination Modes of a Pyridine-Functionalized Quinonoid Zwitterion; Its Di- and Tetranuclear Palladium Complexes

Coupled Polymethine Dyes: Six Decades of Discoveries

This review provides a comprehensive examination of the applications of the seminal coupling principle introduced by Siegfried Dähne and Dieter Leupold in 1966. Their heuristic and groundbreaking work proposed that combining multiple polymethine subunits within a single chromophore enables orbital coupling, consequently narrowing the HOMO-LUMO gap, and yielding redshifted optical properties. These outcomes are particularly valuable for developing organic dyes tailored for visible-to-near-infrared applications. Despite their potential, coupled polymethines remain relatively underexplored, with most reported instances being serendipitous discoveries over the last six decades. In light of this, our review compiles and discusses the reported coupled polymethine structures, covering synthetic, spectroscopic, theoretical and applicative aspects, offering insights into the structure-property relationships of this unique class of dyes and perspectives for their future applications.

Charge frustration in ligand design and functional group transfer

Molecules with different resonance structures of similar importance, such as heterocumulenes and mesoionics, are prominent in many applications of chemistry, including 'click chemistry', photochemistry, switching and sensing. In coordination chemistry, similar chameleonic/schizophrenic entities are referred to as ambidentate/ambiphilic or cooperative ligands. Examples of these had remained, for a long time, limited to a handful of archetypal compounds that were mere curiosities. In this Review, we describe ambiphilicity - or, rather, 'charge frustration' - as a general guiding principle for ligand design and functional group transfer. We first give a historical account of organic zwitterions and discuss their electronic structures and applications. Our discussion then focuses on zwitterionic ligands and their metal complexes, such as those of ylidic and redox-active ligands. Finally, we present new approaches to single-atom transfer using cumulated small molecules and outline emerging areas, such as bond activation and stable donor-acceptor ligand systems for reversible 1e^- chemistry or switching.

Single-Pot Self-Assembly of Heteroleptic Mn(I)-Based Aminoquinonato-Bridged Ester/Amide-Functionalized Dinuclear Metallastirrups: Potential Anticancer and Visible-Light-Triggered CORMs

Multicomponent self-assembly of Mn₂(CO)₁₀, a bis-chelating aminoquinonato (ON∩ON) bridge (L), and an ester/amide-functionalized flexible neutral ditopic linker (L') has resulted into the formation of M₂LL'-type manganese(I)-based dinuclear metallastirrups of general formula [{(CO)₃Mn(μ-η⁴-L)Mn(CO)₃}(μ-L')] (1-10). Compounds 1-10 were accomplished via orthogonal bonding of the aminoquinone ligand (2,5-bis(n-butylamino)-1,4-benzoquinone/2,5-bis(phenethylamino)-1,4-benzoquinone) and ditopic pyridyl ligand to manganese carbonyl. The resultant metallastirrups were characterized using elemental analyses and IR, UV-vis, ¹H NMR, and electrospray ionization-mass spectroscopic techniques. The molecular structure of 6 was confirmed by single-crystal X-ray diffraction methods. Furthermore, molecular recognition capabilities of 1, 5, 7, and 9 were evaluated with aromatic compounds containing hydroxy/amine functionalities. Anticancer activities of compounds 1-3, 5-7, 9, and 10 were investigated against three cancer cell lines, that is, lung (A549), colon (HCT-15), and cervical (HeLa) as well as on normal cells (HEK 293). Compound 9 showed a broad-spectrum inhibition toward these cancer cells upon exposure to visible light. The myoglobin assay was performed using UV-vis absorption spectroscopy to investigate the visible-light-triggered CO release from 5 and 9 that could be related to their ability to effectively inhibit cancer cells. In addition, morphological studies confirmed the induction of autophagy due to the treatment of cancer cells using compound 9.

Regioselective addition of DDQ on a quinoid ring: an entry into chiral zwitterionic bridging ligands

The Michael-type addition of DDQ on a zwitterionic ligand is described together with the chiral separation and full characterization of the two enantiomers of one derivative. These adducts offer a novel entry into chiral zwitterionic quinoidal ligands.

1,2,3-Triazole based bisphosphine, 5-(diphenylphosphanyl)-1-(2-(diphenylphosphanyl)-phenyl)-4-phenyl-1H-1,2,3-triazole: an ambidentate ligand with switchable coordination modes

The reaction of 1-(2-bromophenyl)-4-phenyl-1H-1,2,3-triazole (1) with Ph₂PCl yielded bisphosphine, 5-(diphenylphosphanyl)-1-(2-(diphenylphosphanyl)phenyl)-4-phenyl-1H-1,2,3-triazole (2). Bisphosphine 2 exhibits ambidentate character in either the κ²-P,N or κ²-P,P coordination mode. Treatment of 2 with [M(CO)₄(piperidine)₂] (M = Mo and W) yielded κ²-P,N and κ²-P,P coordinated Mo⁰ and W⁰ complexes [M(CO)₄(2)] [M = W-κ²-P,N (4); Mo-κ²-P,P (5); W-κ²-P,P (6)] depending on the reaction conditions. Formation and stability of κ²-P,P coordinated Mo⁰ and W⁰ complexes were assessed by time dependent ³¹P{¹H} NMR experiments and DFT studies. The complex 4 on treatment with [AuCl(SMe₂)] afforded the hetero-bimetallic complex [μ-PN,P-{o-Ph₂P(C₆H₄){1,2,3-N₃C(Ph)C(PPh₂AuCl)}-κ²-P,N}W(CO)₄] (7). The 1 : 1 reaction between 2 and [CpRu(PPh₃)₂Cl] yielded [(η⁵-C₅H₅)RuCl{o-Ph₂P(C₆H₄){1,2,3-N₃C(Ph)C(PPh₂)}}-κ²-P,P] (8), whereas the similar reaction with [Ru(η⁶-p-cymene)Cl₂]₂ in a 2 : 1 molar ratio produced a cationic complex [(η⁶-p-cymene)RuCl{o-Ph₂P(C₆H₄){1,2,3-N₃C(Ph)C(PPh₂)}}-κ²-P,N]Cl (9). Similarly, treatment of 2 with [M(COD)(Cl)₂] (M = Pd and Pt) in a 1 : 1 molar ratio yielded Pd^II and Pt^II complexes [{o-Ph₂P(C₆H₄){1,2,3-N₃C(Ph)C(PPh₂)}-κ²-P,P}PdCl₂] (10) and [{o-Ph₂P(C₆H₄){1,2,3-N₃C(Ph)C(PPh₂)}-κ²-P,P}PtCl₂] (11). The reaction of 2 with 2 equiv. of [AuCl(SMe₂)] afforded [Au₂Cl₂{o-Ph₂P(C₆H₄){1,2,3-N₃C(Ph)C(PPh₂)}}-μ-P,P] (12). Most of the complexes have been structurally characterized. Palladium complex 10 shows excellent catalytic activity towards Cu-free Sonogashira alkynylation/cyclization reactions.

This paper describes the synthesis of a triazole based bisphosphine and its transition metal chemistry and catalytic utility in Cu-free Sonogashira alkynylation/cyclization reaction.

Changes in molecular film metallicity with minor modifications of the constitutive quinonoid zwitterions

The electronic properties of molecular films formed by quinonoid zwitterions deposited on gold are highly dependent on the nature of the N-substituent.

Influence of steric hindrance on the molecular packing and the anchoring of quinonoid zwitterions on gold surfaces

The N-substituent on quinonoid zwitterions influences the molecules packing and impacts their anchoring on gold surfaces.

Colour tuning by the stepwise synthesis of mononuclear and homo- and hetero-dinuclear platinum(ii) complexes using a zwitterionic quinonoid ligand

The colour of a mononuclear Pt(ii) complex bearing a [O,N,N,O] quinonoid ligand is judiciously tuned by stepwise deprotonation and successive homo- and hetero-metalation.

Counter-ligand control of the electronic structure in dinuclear copper-tetrakisguanidine complexes

Decision-making counter-ligands: a bridging redox-active ligand in a dinuclear copper complex could be either neutral (complex type [Cu^II-GFA-Cu^II]) or dicationic (complex type [Cu^I-GFA-Cu^I]), depending on the nature of the counter-ligands X.

Metal ion promoted tautomerization and C-N bond cleavage: conversion of catechol to a p-benzoquinone derivative

Metal ion promoted tautomerization of p-iminoquinone to o-diiminoquinone and a C-N bond cleavage of 2,5-bis(p-tolylamino)-4-p-tolyliminobenzoquinone leading to the conversion of catechol to a p-benzoquinone derivative are reported.