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Grams RJ, Santos WL, Scorei IR, Abad-García A, Rosenblum CA, Bita A, Cerecetto H, Viñas C, Soriano-Ursúa MA. The Rise of Boron-Containing Compounds: Advancements in Synthesis, Medicinal Chemistry, and Emerging Pharmacology. Chem Rev 2024; 124:2441-2511. [PMID: 38382032 DOI: 10.1021/acs.chemrev.3c00663] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/23/2024]
Abstract
Boron-containing compounds (BCC) have emerged as important pharmacophores. To date, five BCC drugs (including boronic acids and boroles) have been approved by the FDA for the treatment of cancer, infections, and atopic dermatitis, while some natural BCC are included in dietary supplements. Boron's Lewis acidity facilitates a mechanism of action via formation of reversible covalent bonds within the active site of target proteins. Boron has also been employed in the development of fluorophores, such as BODIPY for imaging, and in carboranes that are potential neutron capture therapy agents as well as novel agents in diagnostics and therapy. The utility of natural and synthetic BCC has become multifaceted, and the breadth of their applications continues to expand. This review covers the many uses and targets of boron in medicinal chemistry.
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Affiliation(s)
- R Justin Grams
- Department of Chemistry and Virginia Tech Center for Drug Discovery, Virginia Tech, 900 West Campus Drive, Blacksburg, Virginia 24061, United States
| | - Webster L Santos
- Department of Chemistry and Virginia Tech Center for Drug Discovery, Virginia Tech, 900 West Campus Drive, Blacksburg, Virginia 24061, United States
| | | | - Antonio Abad-García
- Academia de Fisiología y Sección de Estudios de Posgrado e Investigación, Escuela Superior de Medicina del Instituto Politécnico Nacional, Plan de San Luis y Díaz Mirón s/n, 11340 Mexico City, Mexico
| | - Carol Ann Rosenblum
- Department of Chemistry and Virginia Tech Center for Drug Discovery, Virginia Tech, 900 West Campus Drive, Blacksburg, Virginia 24061, United States
| | - Andrei Bita
- Department of Pharmacognosy & Phytotherapy, Faculty of Pharmacy, University of Medicine and Pharmacy of Craiova, 2 Petru Rareş Street, 200349 Craiova, Romania
| | - Hugo Cerecetto
- Centro de Investigaciones Nucleares, Facultad de Ciencias, Universidad de la República, Mataojo 2055, 11400 Montevideo, Uruguay
| | - Clara Viñas
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus UAB, 08193 Bellaterra, Spain
| | - Marvin A Soriano-Ursúa
- Academia de Fisiología y Sección de Estudios de Posgrado e Investigación, Escuela Superior de Medicina del Instituto Politécnico Nacional, Plan de San Luis y Díaz Mirón s/n, 11340 Mexico City, Mexico
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2
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Kaltenberg AA, Somov NV, Malysheva YB, Vorozhtsov DL, Grishin ID. Synthesis of Novel
Pseudocloso
Ruthenacarboranes based on an Unsubstituted
nido
‐C
2
B
9
H
11
2−
Ligand. Eur J Inorg Chem 2021. [DOI: 10.1002/ejic.202100765] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Alexander A. Kaltenberg
- Lobachevsky State University of Nizhny Novgorod 603950 Gagarin prospect 23 Nizhny Novgorod Russia
| | - Nikolay V. Somov
- Lobachevsky State University of Nizhny Novgorod 603950 Gagarin prospect 23 Nizhny Novgorod Russia
| | - Yulia B. Malysheva
- Lobachevsky State University of Nizhny Novgorod 603950 Gagarin prospect 23 Nizhny Novgorod Russia
| | - Dmitry L. Vorozhtsov
- Lobachevsky State University of Nizhny Novgorod 603950 Gagarin prospect 23 Nizhny Novgorod Russia
| | - Ivan D. Grishin
- Lobachevsky State University of Nizhny Novgorod 603950 Gagarin prospect 23 Nizhny Novgorod Russia
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3
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Nuez-Martínez M, Pedrosa L, Martinez-Rovira I, Yousef I, Diao D, Teixidor F, Stanzani E, Martínez-Soler F, Tortosa A, Sierra À, Gonzalez JJ, Viñas C. Synchrotron-Based Fourier-Transform Infrared Micro-Spectroscopy (SR-FTIRM) Fingerprint of the Small Anionic Molecule Cobaltabis(dicarbollide) Uptake in Glioma Stem Cells. Int J Mol Sci 2021; 22:9937. [PMID: 34576098 PMCID: PMC8466526 DOI: 10.3390/ijms22189937] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Revised: 09/07/2021] [Accepted: 09/10/2021] [Indexed: 12/16/2022] Open
Abstract
The anionic cobaltabis (dicarbollide) [3,3'-Co(1,2-C2B9H11)2]-, [o-COSAN]-, is the most studied icosahedral metallacarborane. The sodium salts of [o-COSAN]- could be an ideal candidate for the anti-cancer treatment Boron Neutron Capture Therapy (BNCT) as it possesses the ability to readily cross biological membranes thereby producing cell cycle arrest in cancer cells. BNCT is a cancer therapy based on the potential of 10B atoms to produce α particles that cross tissues in which the 10B is accumulated without damaging the surrounding healthy tissues, after being irradiated with low energy thermal neutrons. Since Na[o-COSAN] displays a strong and characteristic ν(B-H) frequency in the infrared range 2.600-2.500 cm-1, we studied the uptake of Na[o-COSAN] followed by its interaction with biomolecules and its cellular biodistribution in two different glioma initiating cells (GICs), mesenchymal and proneural respectively, by using Synchrotron Radiation-Fourier Transform Infrared (FTIR) micro-spectroscopy (SR-FTIRM) facilities at the MIRAS Beamline of ALBA synchrotron light source. The spectroscopic data analysis from the bands in the regions of DNA, proteins, and lipids permitted to suggest that after its cellular uptake, Na[o-COSAN] strongly interacts with DNA strings, modifies proteins secondary structure and also leads to lipid saturation. The mapping suggests the nuclear localization of [o-COSAN]-, which according to reported Monte Carlo simulations may result in a more efficient cell-killing effect compared to that in a uniform distribution within the entire cell. In conclusion, we show pieces of evidence that at low doses, [o-COSAN]- translocates GIC cells' membranes and it alters the physiology of the cells, suggesting that Na[o-COSAN] is a promising agent to BNCT for glioblastoma cells.
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Affiliation(s)
- Miquel Nuez-Martínez
- Institut de Ciència de Materials de Barcelona, ICMAB-CSIC, Campus Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain; (M.N.-M.); (F.T.)
| | - Leire Pedrosa
- Laboratory of Experimental Oncological Neurosurgery, Neurosurgery Service, Hospital Clinic de Barcelona—FCRB, 08036 Barcelona, Spain; (L.P.); (D.D.); (J.J.G.)
| | - Immaculada Martinez-Rovira
- Ionizing Radiation Research Group (GRRI), Physics Department, Universitat Autònoma de Barcelona (UAB), Avinguda de l’Eix Central, Edifici C. Campus de la UAB, 08193 Cerdanyola del Vallès, Spain;
- ALBA-CELLS Synchrotron, MIRAS Beamline, Carrer de la Llum 2-26, 08290 Cerdanyola del Vallès, Spain;
| | - Ibraheem Yousef
- ALBA-CELLS Synchrotron, MIRAS Beamline, Carrer de la Llum 2-26, 08290 Cerdanyola del Vallès, Spain;
| | - Diouldé Diao
- Laboratory of Experimental Oncological Neurosurgery, Neurosurgery Service, Hospital Clinic de Barcelona—FCRB, 08036 Barcelona, Spain; (L.P.); (D.D.); (J.J.G.)
| | - Francesc Teixidor
- Institut de Ciència de Materials de Barcelona, ICMAB-CSIC, Campus Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain; (M.N.-M.); (F.T.)
| | - Elisabetta Stanzani
- Laboratory of Pharmacology and Brain Pathology, IRCCS Humanitas Research Hospital, 20089 Rozzano, Italy;
| | - Fina Martínez-Soler
- Apoptosis and Cancer Unit, Department of Physiological Sciences, IDIBELL, Faculty of Medicine and Health Sciences, Universitat de Barcelona, 08907 L’Hospitalet del Llobregat, Spain; (F.M.-S.); (A.T.)
| | - Avelina Tortosa
- Apoptosis and Cancer Unit, Department of Physiological Sciences, IDIBELL, Faculty of Medicine and Health Sciences, Universitat de Barcelona, 08907 L’Hospitalet del Llobregat, Spain; (F.M.-S.); (A.T.)
| | - Àngels Sierra
- Laboratory of Experimental Oncological Neurosurgery, Neurosurgery Service, Hospital Clinic de Barcelona—FCRB, 08036 Barcelona, Spain; (L.P.); (D.D.); (J.J.G.)
| | - José Juan Gonzalez
- Laboratory of Experimental Oncological Neurosurgery, Neurosurgery Service, Hospital Clinic de Barcelona—FCRB, 08036 Barcelona, Spain; (L.P.); (D.D.); (J.J.G.)
| | - Clara Viñas
- Institut de Ciència de Materials de Barcelona, ICMAB-CSIC, Campus Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain; (M.N.-M.); (F.T.)
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4
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Kellert M, Sárosi I, Rajaratnam R, Meggers E, Lönnecke P, Hey-Hawkins E. Ruthenacarborane-Phenanthroline Derivatives as Potential Metallodrugs. Molecules 2020; 25:molecules25102322. [PMID: 32429279 PMCID: PMC7287719 DOI: 10.3390/molecules25102322] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2020] [Revised: 05/04/2020] [Accepted: 05/12/2020] [Indexed: 01/28/2023] Open
Abstract
Ruthenium-based complexes have received much interest as potential metallodrugs. In this work, four RuII complexes bearing a dicarbollide moiety, a carbonyl ligand, and a phenanthroline-based ligand were synthesized and characterized, including single crystal diffraction analysis of compounds 2, 4, and 5 and an observed side product SP1. Complexes 2-5 are air and moisture stable under ambient conditions. They show excellent solubility in organic solvents, but low solubility in water.
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Affiliation(s)
- Martin Kellert
- Institute of Inorganic Chemistry, Faculty of Chemistry and Mineralogy, Leipzig University, Johannisallee 29, 04103 Leipzig, Germany; (M.K.); (I.S.); (P.L.)
| | - Imola Sárosi
- Institute of Inorganic Chemistry, Faculty of Chemistry and Mineralogy, Leipzig University, Johannisallee 29, 04103 Leipzig, Germany; (M.K.); (I.S.); (P.L.)
| | - Rajathees Rajaratnam
- Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein Straße 4, 35043 Marburg, Germany; (R.R.); (E.M.)
| | - Eric Meggers
- Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein Straße 4, 35043 Marburg, Germany; (R.R.); (E.M.)
| | - Peter Lönnecke
- Institute of Inorganic Chemistry, Faculty of Chemistry and Mineralogy, Leipzig University, Johannisallee 29, 04103 Leipzig, Germany; (M.K.); (I.S.); (P.L.)
| | - Evamarie Hey-Hawkins
- Institute of Inorganic Chemistry, Faculty of Chemistry and Mineralogy, Leipzig University, Johannisallee 29, 04103 Leipzig, Germany; (M.K.); (I.S.); (P.L.)
- Correspondence: ; Tel.: +49-341-97-36151
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5
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Teixeira RG, Marques F, Robalo MP, Fontrodona X, Garcia MH, Geninatti Crich S, Viñas C, Valente A. Ruthenium carboranyl complexes with 2,2′-bipyridine derivatives for potential bimodal therapy application. RSC Adv 2020; 10:16266-16276. [PMID: 35498822 PMCID: PMC9053089 DOI: 10.1039/d0ra01522a] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2020] [Accepted: 04/06/2020] [Indexed: 11/21/2022] Open
Abstract
The substituents at the bipyridine lead to different cell uptake and stability.
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Affiliation(s)
- Ricardo G. Teixeira
- Centro de Química Estrutural
- Departamento de Química e Bioquímica
- Faculdade de Ciências
- Universidade de Lisboa
- 1749-016 Lisboa
| | - Fernanda Marques
- Centro de Ciências e Tecnologias Nucleares
- Instituto Superior Técnico
- Universidade de Lisboa
- 2695-006 Bobadela LRS
- Portugal
| | - M. Paula Robalo
- Área Departamental de Engenharia Química
- Instituto Superior de Engenharia de Lisboa
- Instituto Politécnico de Lisboa
- 1959-007 Lisboa
- Portugal
| | - Xavier Fontrodona
- Departament de Química and Serveis Tècnics de Recerca
- Universitat de Girona
- 17071 Girona
- Spain
| | - M. Helena Garcia
- Centro de Química Estrutural
- Departamento de Química e Bioquímica
- Faculdade de Ciências
- Universidade de Lisboa
- 1749-016 Lisboa
| | - Simonetta Geninatti Crich
- Dipartimento di Biotecnologie Molecolari e Scienze per la Salute
- Università di Torino
- 10126 Torino
- Italy
| | - Clara Viñas
- Institut de Ciència de Materials de Barcelona (ICMAB-CSIC)
- 08193 Bellaterra
- Spain
| | - Andreia Valente
- Centro de Química Estrutural
- Departamento de Química e Bioquímica
- Faculdade de Ciências
- Universidade de Lisboa
- 1749-016 Lisboa
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6
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Schwarze B, Sobottka S, Schiewe R, Sarkar B, Hey-Hawkins E. Spectroscopic and Electronic Properties of Molybdacarborane Complexes with Non-innocently Acting Ligands. Chemistry 2019; 25:8550-8559. [PMID: 31002195 DOI: 10.1002/chem.201900504] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Indexed: 11/12/2022]
Abstract
The molybdacarboranes [3-{L-κ2 N,N}-3-(CO)2 -closo-3,1,2-MoC2 B9 H11 ] (L=2,2'-bipyridine (2,2'-bpy, 1 a) or 1,10-phenanthroline (1,10-phen, 1 b)) incorporating well-known potentially non-innocent ligands (CO, 2,2'-bpy, 1,10-phen) and the "non-spectator" nido-carborane ([η5 -C2 B9 H11 ]2- ) ligand were prepared and fully characterised. High-resolution mass spectrometry, single-crystal X-ray diffraction methods, spectroscopy (IR, (resonance) Raman, NMR), cyclic voltammetry and spectroelectrochemistry (electrochemical properties) were supported by theoretical investigations of the electronic structure (DFT, CAS-SCF, TD-DFT).
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Affiliation(s)
- Benedikt Schwarze
- Leipzig University, Faculty of Chemistry and Mineralogy, Institute of Inorganic Chemistry, Johannisallee 29, 04103, Leipzig, Germany
| | - Sebastian Sobottka
- Institut für Chemie und Biochemie, Anorganische Chemie, Freie Universität Berlin, Fabeckstraße 34-36, 14195, Berlin, Germany
| | - Robert Schiewe
- Leipzig University, Faculty of Chemistry and Mineralogy, Institute of Inorganic Chemistry, Johannisallee 29, 04103, Leipzig, Germany
| | - Biprajit Sarkar
- Institut für Chemie und Biochemie, Anorganische Chemie, Freie Universität Berlin, Fabeckstraße 34-36, 14195, Berlin, Germany
| | - Evamarie Hey-Hawkins
- Leipzig University, Faculty of Chemistry and Mineralogy, Institute of Inorganic Chemistry, Johannisallee 29, 04103, Leipzig, Germany
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7
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8
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Kirlikovali KO, Axtell JC, Gonzalez A, Phung AC, Khan SI, Spokoyny AM. Luminescent Metal Complexes Featuring Photophysically Innocent Boron Cluster Ligands. Chem Sci 2016; 7:5132-5138. [PMID: 28191302 PMCID: PMC5300762 DOI: 10.1039/c6sc01146b] [Citation(s) in RCA: 125] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2016] [Accepted: 04/18/2016] [Indexed: 12/23/2022] Open
Abstract
We report the synthesis and characterization of a series of d8 metal complexes featuring robust and photophysically innocent strong-field chelating 1,1'-bis(o-carborane) (bc) ligand frameworks. A combination of UV-Vis spectroscopy, single crystal X-ray structural analysis, and DFT calculations of these species suggest that the dianionic bc ligand does not contribute to any visible metal-to-ligand charge transfer (MLCT) transitions, yet it provides a strong ligand field in these complexes. Furthermore, a bc-based Pt(II) complex containing a 4,4'-di-tert-butyl-2,2'-bipyridine ligand (dtb-bpy) has been prepared and was found to display blue phosphorescent emission dominated by MLCT from the Pt(II) center to the dtb-bpy ligand. Importantly, the bulky three-dimensional nature of the bc ligand precludes intermolecular Pt(II)⋯Pt(II) interactions in the solid state where the resulting compounds retain their emission properties. This study opens a potentially new avenue for designing organic light-emitting diode (OLED) materials with tunable properties featuring photophysically innocent boron-rich cluster ligands.
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Affiliation(s)
- Kent O. Kirlikovali
- Department of Chemistry and Biochemistry
, University of California
,
607 Charles E. Young Drive East
, Los Angeles
, California 90025-1569
, USA
.
; https://www.organomimetic.com
| | - Jonathan C. Axtell
- Department of Chemistry and Biochemistry
, University of California
,
607 Charles E. Young Drive East
, Los Angeles
, California 90025-1569
, USA
.
; https://www.organomimetic.com
| | - Alejandra Gonzalez
- Department of Chemistry and Biochemistry
, University of California
,
607 Charles E. Young Drive East
, Los Angeles
, California 90025-1569
, USA
.
; https://www.organomimetic.com
| | - Alice C. Phung
- Department of Chemistry and Biochemistry
, University of California
,
607 Charles E. Young Drive East
, Los Angeles
, California 90025-1569
, USA
.
; https://www.organomimetic.com
| | - Saeed I. Khan
- Department of Chemistry and Biochemistry
, University of California
,
607 Charles E. Young Drive East
, Los Angeles
, California 90025-1569
, USA
.
; https://www.organomimetic.com
| | - Alexander M. Spokoyny
- Department of Chemistry and Biochemistry
, University of California
,
607 Charles E. Young Drive East
, Los Angeles
, California 90025-1569
, USA
.
; https://www.organomimetic.com
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9
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12-vertex ruthenacarborane half-sandwich complexes: Redox properties and second-order nonlinear optical responses. J Organomet Chem 2016. [DOI: 10.1016/j.jorganchem.2015.10.018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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10
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Dash BP, Satapathy R, Maguire JA, Hosmane NS. Polyhedral boron clusters in materials science. NEW J CHEM 2011. [DOI: 10.1039/c1nj20228f] [Citation(s) in RCA: 148] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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11
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Prokhorov AM, Slepukhin PA, Rusinov VL, Kalinin VN, Kozhevnikov DN. 2,2′-Bipyridinyl carboranes as B,N,N-ligands in cyclometallated complexes of platinum(ii). Chem Commun (Camb) 2011; 47:7713-5. [DOI: 10.1039/c1cc12230d] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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12
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Ligand-displacement reactions as a powerful route to closo-ruthenacarboranes incorporating bidentate N-donor ligands. MENDELEEV COMMUNICATIONS 2010. [DOI: 10.1016/j.mencom.2010.05.018] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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13
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14
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Bernard R, Cornu D, Scharff JP, Chiriac R, Miele P, Baldeck PL, Caslavský J. Synthesis, Characterization, and UV−vis Linear Absorption of Centrosymmetric π-Systems Incorporating closo-Dodecaborate Clusters. Inorg Chem 2006; 45:8743-8. [PMID: 17029386 DOI: 10.1021/ic060563x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Single- and multibranched centrosymmetric derivatives incorporating B12 clusters [B12H11-N(H)=C(H)-C6H4-C6H4-C(H)=(H)N-B12H11]2- (3) and [1,3,5-(4-(B12H11-N(H)=C(H))-C6H4)-C6H3]3- (5) have been synthesized. Both derivatives were characterized by multinuclear NMR and ESI-MS analyses. To the best of our knowledge, compound 5 is the first example of a multicage derivative bearing three B12 units. Compounds 3 and 5 are only slightly yellowish colored. The UV-vis absorption curves of 3 and 5 show intense absorption bands at 360 and 314 nm, respectively. This result permits us to confirm the strong donor effect of the B12 cluster. The hypsochrome effect observed for compound 5 compared to that of compound 3 confirms the interest in multibranched derivatives for the preparation of two-photon absorption materials active in the visible range.
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Affiliation(s)
- Rémy Bernard
- Laboratoire des Multimatériaux et Interfaces, UMR 5615 CNRS-Université Claude Bernard Lyon 1, 43 Boulevard du 11 Novembre 1918, F-69622 Villeurbanne Cedex, France
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15
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Buckner SW, Fischer MJ, Jelliss PA, Luo R, Minteer SD, Rath NP, Siemiarczuk A. Dual fluorescence from an isonido ReIII rhenacarborane phosphine complex, [7,10-mu-H-7-CO-7,7-(PPh3)2-isonido-7,8,9-ReC2B7H9]. Inorg Chem 2006; 45:7339-47. [PMID: 16933936 DOI: 10.1021/ic061071n] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The complex [7,10-mu-H-7-CO-7,7-(PPh3)2-isonido-7,8,9-ReC2B7H9] has been synthesized by treatment of the complex salt [NHMe3][3,3-Cl2-3,3-(CO)2-closo-3,1,2-ReC2B9H11] with PPh3 in refluxing THF (tetrahydrofuran) and isolated as intensely colored orange-red microcrystals. Spectroscopic NMR and IR data have suggested that the product has a highly asymmetric structure with two inequivalent PPh3 ligands and a single CO ligand. Measurement of 11B NMR spectra in particular have indicated seven distinct boron vertexes, although the resulting cage degradation by removal of two BH vertexes was confirmed only following X-ray crystallographic analysis, which revealed the pentadecahedral isonido-7,8,9-ReC2B7 architecture. The 11B NMR resonances span an enormous chemical shift range (Deltadelta = 113), and this appears to be a direct consequence of the deshielding of the boron vertex directly opposite the quadrilateral |ReCCB| aperture. The new complex has been shown by electrochemical measurements to undergo a reversible one-electron oxidation. Digitally simulated cyclic voltammograms support a proposed square scheme (E(1/2) = 0.58, 0.69 V vs ferrocene) involving a reversible isonido-closo transition of the metallacarborane cage. Most unusually for a metallacarborane complex, ambient temperature solutions in CH2Cl2 and DMF have been shown to be intensely turquoise-blue fluorescent (lambda(em) = 442 nm, Phi = 0.012). Fluorescence spectroscopy measurements in MeTHF (2-methyltetrahydrofuran) glass at 77 K have indicated that the likely cause of such a broad emission is dual fluorescence (lambda(em) = 404, 505 nm), with both emissions displaying vibronic structure. Following excited-state lifetime decay analysis, the emissive behavior has been accredited to metal-perturbed 1IL states, with the lower energy emission arising from a slight geometric distortion of the initially excited complex.
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Affiliation(s)
- Steven W Buckner
- Department of Chemistry, Saint Louis University, St. Louis, MO 63103, USA
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