1
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Leung JN, Mondori Y, Ogoshi S, Hoshimoto Y, Huynh HV. Electronic Profiling of N-Phosphine Oxide-Substituted Imidazolin-2-ylidenes (PoxIms) and Imidazolidin-2-ylidenes (SPoxIms). Inorg Chem 2024; 63:4344-4354. [PMID: 38387056 DOI: 10.1021/acs.inorgchem.3c04600] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/24/2024]
Abstract
A detailed electronic study of the N-phosphine oxide functionalized imidazolin-2-ylidenes (PoxIms) and imidazolidin-2-ylidenes (SPoxIms) has been performed experimentally using IR, 13C, and 77Se NMR spectroscopies. While the net donor/acceptor properties of the (S)PoxIms could not be differentiated via IR spectroscopy (TEP), NMR spectroscopic methods (HEP, Se) reveal that the (S)PoxIms are slightly weaker σ-donors but stronger π-acceptors compared to common NHCs. Moreover, backbone and substituent-effects could also be resolved by the latter, allowing for a ranking of their electronic properties. Finally, the donicities of these well-designed NHC ligands in their bidentate κ2-C,O modes were evaluated using HEP2 and compared to those of classical chelators.
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Affiliation(s)
- Jia Nuo Leung
- Department of Chemistry, Faculty of Science, National University of Singapore, 3 Science Drive 3, Singapore 117453, Republic of Singapore
| | - Yutaka Mondori
- Department of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
| | - Sensuke Ogoshi
- Department of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
| | - Yoichi Hoshimoto
- Department of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
- Center for Future Innovation (CFi), Division of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
| | - Han Vinh Huynh
- Department of Chemistry, Faculty of Science, National University of Singapore, 3 Science Drive 3, Singapore 117453, Republic of Singapore
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2
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Leung JN, Luong HTT, Huynh HV. Stereoelectronic Profiling of Neutral and Monoanionic Biimidazoles and Mixed Diimines. Inorg Chem 2023; 62:4606-4617. [PMID: 36872911 DOI: 10.1021/acs.inorgchem.3c00017] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/07/2023]
Abstract
14 mono-, di-, and tetranuclear palladium complexes were prepared to study the coordination chemistry of symmetrical and unsymmetrical azole-derived diimines and their anions. The diverse range of complexes obtained highlights the structural and electronic diversities imposed by these ligands. Using the monopalladium species, the electronic properties of selected bidentate ligands were determined, ranked, and compared by 13C NMR spectroscopy, extending the scope of the HEP2 (Huynh electronic parameter 2) scale, which can detect even subtle differences. Moreover, the %Vbur (percentage volume buried) values as an estimate for the steric bulk of some ligands were determined using the solid-state molecular structures of their complexes, and a preliminary stereoelectronic map was established.
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Affiliation(s)
- Jia Nuo Leung
- Department of Chemistry, Faculty of Science, National University of Singapore, 3 Science Drive 3, Singapore 117453, Republic of Singapore
| | - Huyen T T Luong
- Department of Chemistry, Faculty of Science, National University of Singapore, 3 Science Drive 3, Singapore 117453, Republic of Singapore
| | - Han Vinh Huynh
- Department of Chemistry, Faculty of Science, National University of Singapore, 3 Science Drive 3, Singapore 117453, Republic of Singapore
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3
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Teng Q, Liu Z, Song H, Liu J, Zhao Y, Jiang W, Huynh HV, Meng Q. Versatile halogenation via a C NHC^C sp3 palladacycle intermediate. Dalton Trans 2023; 52:2223-2226. [PMID: 36779836 DOI: 10.1039/d3dt00113j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Stable cyclopalladated complexes containing an (sp3)C-Pd bond were synthesized via α-CH2 deprotonation and palladation of N-alkyl groups of carbene ligands bearing electron-withdrawing substituents. The strong electron donating strengths of the resulting CNHC^Csp3 chelators were experimentally identified, and the palladacycle underwent template-directed, versatile C-halogenation with X2.
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Affiliation(s)
- Qiaoqiao Teng
- Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology, School of Petrochemical Engineering, Changzhou University, Changzhou, 213164, China.
| | - Ziwei Liu
- Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology, School of Petrochemical Engineering, Changzhou University, Changzhou, 213164, China.
| | - Haobin Song
- Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology, School of Petrochemical Engineering, Changzhou University, Changzhou, 213164, China.
| | - Jiayu Liu
- Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology, School of Petrochemical Engineering, Changzhou University, Changzhou, 213164, China.
| | - Yaru Zhao
- Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology, School of Petrochemical Engineering, Changzhou University, Changzhou, 213164, China.
| | - Weihua Jiang
- Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology, School of Petrochemical Engineering, Changzhou University, Changzhou, 213164, China.
| | - Han Vinh Huynh
- Department of Chemistry, National University of Singapore, 117543 Singapore, Republic of Singapore.
| | - Qi Meng
- Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology, School of Petrochemical Engineering, Changzhou University, Changzhou, 213164, China.
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4
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Abstract
A library of 12 palladium(II) complexes of the type [PdBr(iPr2-bimy)(L∧X)] comprising 10 dithiocarbamato (R2NCS2-) and two xanthato (ROCS2-) ligands have been prepared and fully characterized. With these complexes in hand, the electronic and steric properties of the bidentate, monoanionic ligands were evaluated using the HEP2 and %Vbur methodologies. Moreover, the construction of the first stereoelectronic map for dithiocarbamates enabled the in-principle identification of optimal ligand parameters for enhanced cytotoxic activities of their gold(III) complexes. This application of the stereoelectronic map showcases its viability as a useful tool to establish structure-activity relationships for rational ligand design.
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Affiliation(s)
- Jia Nuo Leung
- Department of Chemistry, Faculty of Science, National University of Singapore, 3 Science Drive 3, Singapore 117453, Singapore
| | - Han Vinh Huynh
- Department of Chemistry, Faculty of Science, National University of Singapore, 3 Science Drive 3, Singapore 117453, Singapore
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5
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Do DCH, Huynh HV. Controlled Access to Four- and Six-Membered Palladacycles via Modifying Donor Abilities of β-Ketiminato Ligands ("NacAcs"). Inorg Chem 2022; 61:20087-20094. [PMID: 36419368 DOI: 10.1021/acs.inorgchem.2c03515] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The synthesis of Pd complexes of the type [PdBr(iPr2-bimy)(NacAc)] (NacAc = β-ketiminate, iPr2-bimy = 1,3-diisopropylbenzimidazolin-2-ylidene) was attempted, in a continuing effort to quantify donor abilities of chelating β-ketiminate ligands using the Huynh electronic parameter for bidentate donors (HEP2). Subtle variation of N-substituents on the NacAc backbone was discovered to induce a drastic change in the preferred chelating mode, in that the commonly encountered κ2-N,O-six-membered palladacycles were observed with R = Me and Et, while the unusual κ2-C,N-four-membered palladacycles were isolated with R = iPr, Cy, and tBu. Computational studies subsequently corroborated these findings, in the form of an overall exergonic six-to-four-membered ring contraction process and a lower associated activation energy for the three more electron-donating alkyl moieties. This trend in the established energy profiles can be attributed to a reduced HOMO-LUMO gap in the corresponding optimized structures of the six-membered ring complexes.
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Affiliation(s)
- Dinh Cao Huan Do
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543
| | - Han Vinh Huynh
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543
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6
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Abstract
Recent synthetic achievements have led to 4,4-disubstituted-4-bora-3a,4a-diaza-s-indacenes (BODIPYs) with varying substituents at the meso, pyrrolic and/or boron sites, with each influencing photophysical properties and utility. This Feature article gives an overview of chemistry at the boron atom in BODIPYs, highlighting our contributions that evolved from synthetic curiosities and now offer this dipyrrolic skeleton potential across a wider range of applications. We first summarise preparative routes to BODIPYs through complexation of boron with the dipyrrinato ligand. The role of boron in protecting dipyrrins is then discussed, followed by strategies by which to achieve facile substitution at the boron atom.
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Affiliation(s)
- Rosinah Liandrah Gapare
- Department of Chemistry, Dalhousie University, P.O. Box 15000, Halifax, NS, B3H 4R2, Canada.
| | - Alison Thompson
- Department of Chemistry, Dalhousie University, P.O. Box 15000, Halifax, NS, B3H 4R2, Canada.
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7
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Affiliation(s)
- Han Vinh Huynh
- Department of Chemistry, National University of Singapore, 3 Science Drive 3, 117543 Singapore, Republic of Singapore
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8
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Curtis CJ, Astashkin AV, Conradie J, Ghosh A, Tomat E. Ligand-Centered Triplet Diradical Supported by a Binuclear Palladium(II) Dipyrrindione. Inorg Chem 2021; 60:12457-12466. [PMID: 34347474 PMCID: PMC8389801 DOI: 10.1021/acs.inorgchem.1c01691] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
Oligopyrroles
form
a versatile class of redox-active ligands and
electron reservoirs. Although the stabilization of radicals within
oligopyrrolic π systems is more common for macrocyclic ligands,
bidentate dipyrrindiones are emerging as compact platforms for one-electron
redox chemistry in transition-metal complexes. We report the synthesis
of a bis(aqua) palladium(II) dipyrrindione complex and its deprotonation-driven
dimerization to form a hydroxo-bridged binuclear complex in the presence
of water or triethylamine. Electrochemical, spectroelectrochemical,
and computational analyses of the binuclear complex indicate the accessibility
of two quasi-reversible ligand-centered reduction processes. The product
of a two-electron chemical reduction by cobaltocene was isolated and
characterized. In the solid state, this cobaltocenium salt features
a folded dianionic complex that maintains the hydroxo bridges between
the divalent palladium centers. X-band and Q-band EPR spectroscopic
experiments and DFT computational analysis allow assignment of the
dianionic species as a diradical with spin density almost entirely
located on the two dipyrrindione ligands. As established from the
EPR temperature dependence, the associated exchange coupling is weak
and antiferromagnetic (J ≈ −2.5 K),
which results in a predominantly triplet state at the temperatures
at which the measurements have been performed. The coordination and redox chemistry of the dipyrrindione
scaffold, which is found in several heme metabolites, is investigated
in heteroleptic palladium(II) complexes. The bis(aqua) complex undergoes
a deprotonation-driven dimerization to form a hydroxo-bridged binuclear
species. Crystallographic, electrochemical, and spectroscopic data,
as well as computational analysis, demonstrate that a two-electron
reduction of the binuclear complex leads to a diradical dianion with
spin density delocalized over the two dipyrrindione ligands.
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Affiliation(s)
- Clayton J Curtis
- Department of Chemistry and Biochemistry, The University of Arizona, 1306 East University Blvd., Tucson, Arizona 85721, United States
| | - Andrei V Astashkin
- Department of Chemistry and Biochemistry, The University of Arizona, 1306 East University Blvd., Tucson, Arizona 85721, United States
| | - Jeanet Conradie
- Department of Chemistry, University of the Free State, P.O. Box 339, Bloemfontein 9300, Republic of South Africa.,Department of Chemistry, UiT - The Arctic University of Norway, N-9037 Tromsø, Norway
| | - Abhik Ghosh
- Department of Chemistry, UiT - The Arctic University of Norway, N-9037 Tromsø, Norway
| | - Elisa Tomat
- Department of Chemistry and Biochemistry, The University of Arizona, 1306 East University Blvd., Tucson, Arizona 85721, United States
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van Rees K, Love JB. Synthesis and complexes of a constrained-cavity Schiff-base dipyrrin macrocycle. Dalton Trans 2021; 50:1610-1613. [PMID: 33508062 DOI: 10.1039/d1dt00175b] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A new constrained-cavity [1 + 1] Schiff-base dipyrrin macrocycle comprising an N4 donor-pocket has been synthesised by spontaneous oxidation and in situ crystallisation. Access to Fe(ii) and Zn(ii) complexes is achieved by salt elimination reactions of the lithium salt. All compounds have been characterised by NMR and UV-vis spectroscopy, X-ray crystallography, and DFT analysis.
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Affiliation(s)
- Karlotta van Rees
- EaStCHEM School of Chemistry, University of Edinburgh, Joseph Black Building, David Brewster Road, The King's Buildings, Edinburgh, EH9 3FJ, UK.
| | - Jason B Love
- EaStCHEM School of Chemistry, University of Edinburgh, Joseph Black Building, David Brewster Road, The King's Buildings, Edinburgh, EH9 3FJ, UK.
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10
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Evaluating the electronic properties of ditopic and hetero-ditopic ligands derived from benzimidazole and pyrazole by 13C NMR spectroscopy. J Organomet Chem 2020. [DOI: 10.1016/j.jorganchem.2020.121409] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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11
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Smith CD, Thompson A. Facile deprotection of F-BODIPYs using methylboronic acid. RSC Adv 2020; 10:24273-24279. [PMID: 35516207 PMCID: PMC9055154 DOI: 10.1039/d0ra05151a] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2020] [Accepted: 06/12/2020] [Indexed: 11/21/2022] Open
Abstract
4,4-Difluoro-4-bora-3a,4a-diaza-s-indacenes (F-BODIPYs) are deprotected through removal of the -BF2 moiety upon treatment with methylboronic acid. The tolerance of various substitution patterns about the dipyrrinato core is demonstrated via the deprotection of thirteen F-BODIPYs and an F-aza-BODIPY. Work-up with aq. HBr affords the desired dipyrin HBr salt in quantitative yield without need for purification.
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Affiliation(s)
- Craig D Smith
- Department of Chemistry, Dalhousie University PO BOX 15000 Halifax NS B3H 4R2 Canada
| | - Alison Thompson
- Department of Chemistry, Dalhousie University PO BOX 15000 Halifax NS B3H 4R2 Canada
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12
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Abstract
Sometimes named half-porphyrins, bis-pyrrolic dipyrrin ligands endow their metal complexes with unique properties such as the potential to functionalize the heterocyclic backbone or the meso position and the ability to catalyze interesting chemical transformations. Thus, strategies towards the derivatization of or at the meso group and the use of dipyrrin metal complexes for the formation of a broad range of polypyrrolic derivatives such as 2,2'-bis-dipyrrins, nor-/hetero-corroles and porphynoids have been elaborated. Furthermore, the chelating ability of dipyrrins and the possibility of modifying their steric and electronic characteristics by functionalization can be exploited for the development of numerous complexes featuring appealing properties. Hence, C-H activation/amination, polymerization or oxidation reactions can be catalyzed by dipyrrin metal complexes and classical reagents such as Grignard species, Rh-based or Suzuki-Miyaura catalysts have been revisited by incorporation of dipyrrins in the coordination sphere of the metal cations. This contribution aims to review and illustrate all these aspects, highlighting the potential of these complexes for the design and synthesis of valuable organic compounds and metallo-organic architectures.
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Affiliation(s)
- Stéphane A Baudron
- Université de Strasbourg, CNRS, CMC UMR 7140, 4 rue Blaise Pascal, F-67000, Strasbourg, France.
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13
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Diaz-Rodriguez RM, Burke L, Robertson KN, Thompson A. Synthesis, properties and reactivity of BCl 2 aza-BODIPY complexes and salts of the aza-dipyrrinato scaffold. Org Biomol Chem 2020; 18:2139-2147. [PMID: 32134102 DOI: 10.1039/d0ob00272k] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The synthesis and characterisation of the BCl2-chelated complexes of both archetypal aza-dipyrrin sub-types are presented. A stepwise halogen exchange, leading to a mixed-halide Cl-B-F intermediate, is implicated in the conversion of F-aza-BODIPYs to Cl-aza-BODIPYs upon treatment with BCl3. The utility of the Cl-aza-BODIPY scaffold to facilitate substitutions at boron is demonstrated under mild conditions through treatment with aryl Grignard reagents. Additionally, the lability of the B-Cl bond enables facile removal of the BCl2 group, i.e. deprotection of F-aza-BODIPYs, under aqueous conditions. Three aza-dipyrrin HX salts were also synthesised and characterised. The pKa of the protonated aza-dipyrrin was determined to be 4, thereby providing insight regarding the storage and stability of such species.
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Curtis CJ, Tomat E. Heteroleptic palladium(II) complexes of dipyrrin-1,9-dione supported by intramolecular hydrogen bonding. J PORPHYR PHTHALOCYA 2020. [DOI: 10.1142/s1088424619501062] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The dipyrrin-1,9-dione framework, which is characteristic of the propentdyopent pigments deriving from heme metabolism, coordinates metal ions as monoanionic bidentate donors. The resulting analogs of dipyrrinato complexes undergo reversible ligand-based reductions, thus showcasing the ability of the dipyrrindione scaffold to act as an electron reservoir. Herein we report the synthesis and characterization of three heteroleptic palladium complexes of the redox-active dipyrrindione ligand. Primary amines were chosen as additional ligands so as to assemble complexes of planar geometries with complementary interligand hydrogen-bonding. Full chemical characterization confirms the hydrogen bonding interactions between the primary amine ligands and the acceptor carbonyl groups on the dipyrrolic ligand. The resulting heteroleptic compounds display reversible one-electron reduction events that are centered on the dipyrrindione ligand as revealed by voltammetry and spectroelectrochemistry data. Within these planar Pd(II) complexes, the propentdyopent motif therefore combines reversible ligand-based redox chemistry with interligand hydrogen bonding in the primary coordination sphere of the metal center.
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Affiliation(s)
- Clayton J. Curtis
- The University of Arizona, Department of Chemistry and Biochemistry, 1306 E. University Blvd., Tucson AZ 85721, USA
| | - Elisa Tomat
- The University of Arizona, Department of Chemistry and Biochemistry, 1306 E. University Blvd., Tucson AZ 85721, USA
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