Metal Complexes Containing Boron Based Ligands

A special issue of Inorganics (ISSN 2304-6740). This special issue belongs to the section "Organometallic Chemistry".

Deadline for manuscript submissions: closed (31 May 2019) | Viewed by 26017

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Special Issue Editor

School of Applied Sciences, University of South Wales, Pontypridd, UK
Interests: complexes containing boron-based ligands; Z-type ligands; borohydride ligands; hydrogen shuttle processes within complexes; element-element activation across metal-boron bonds; boron-based ligands for hydrogen atom storage and ligand cooperation catalysis

Special Issue Information

Dear Colleagues,

Boron-based compounds have been utilized as ligands for many decades now, during which time there has been a fascinating array of compounds reported. Boron is most notable for its potential to be modified with an extraordinarily broad range of functional groups and for the diverse way in which these groups interact with metal centres. For this reason, they remain curiosities and there is still much to understand. There have been plenty of ground-breaking developments along the way. For example, an enduring interest in Trofimenko-type scorpionate ligands as well as in cluster type borane- and carborane-based ligands. In addition to interstitial boron atoms within metal clusters, the coordination chemistry of boron containing heterocycles has also been established. In recent times, there have been some very exciting developments which have further reinvigorated the field. Pioneering work by outstanding leaders have led to the discovery of yet more ways in which novel boron functional groups can interact with metal centres. Alongside this, there has been a significant growth in the chemistry of metal-boryl, -borane and borohydride compounds and their interconversions via migrations of hydrogen and other groups between boron and metal centres. These have found application within element-hydrogen bond activations and ligand cooperation catalysis. The nature of the metal-boron interaction has also been of great interest. Boron-based ligands have been shown to act as X- and Z-type ligands and, in some cases, even as L-type (acting as a Lewis Base). Furthermore, the way in which they influence other ligands within the complex has also attracted significant attention. This Special Issue aims to bring together a collection of research and review contributions highlighting recent advances in all areas involving boron based ligands. I invite you to submit your manuscript to this Special Issue.

Dr. Gareth Owen
Guest Editor

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Keywords

  • Boryl, borane and borohydride based ligands
  • Trofimenko-type and flexible-scorpionate ligands
  • Boranes, carboranes and related species as ligands
  • Boron containing heterocycles
  • Interstitial boron
  • Reactivity involving metal-boron cooperation

Published Papers (8 papers)

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Research

11 pages, 1385 KiB  
Article
Adding to the Family of Copper Complexes Featuring Borohydride Ligands Based on 2-Mercaptopyridyl Units
by Joseph Goldsworthy, Simon D. Thomas, Graham J. Tizzard, Simon J. Coles and Gareth R. Owen
Inorganics 2019, 7(8), 93; https://doi.org/10.3390/inorganics7080093 - 24 Jul 2019
Cited by 2 | Viewed by 3441
Abstract
Borohydride ligands featuring multiple pendant donor functionalities have been prevalent in the chemical literature for many decades now. More recent times has seen their development into new families of so-called soft scorpionates, for example, those featuring sulfur based donors. Despite all of these [...] Read more.
Borohydride ligands featuring multiple pendant donor functionalities have been prevalent in the chemical literature for many decades now. More recent times has seen their development into new families of so-called soft scorpionates, for example, those featuring sulfur based donors. Despite all of these developments, those ligands containing just one pendant group are rare. This article explores one ligand family based on the 2-mercaptopyridine heterocycle. The coordination chemistry of the monosubstituted ligand, [H3B(mp)] (mp = 2-mercaptopyridyl), has been explored. Reaction of Na[BH3(mp)] with one equivalent of Cu(I)Cl in the presence of either triphenylphosphine or tricyclohexylphosphine co-ligands leads to the formation of [Cu{H3B(mp)}(PR3)] (R = Ph, 1; Cy, 2), respectively. Structural characterization confirms a κ3-S,H,H coordination mode for the borohydride-based ligand within 1 and 2, involving a dihydroborate bridging interaction (BH2Cu) with the copper centers. Full article
(This article belongs to the Special Issue Metal Complexes Containing Boron Based Ligands)
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14 pages, 1585 KiB  
Article
On the Aqueous Solution Behavior of C-Substituted 3,1,2-Ruthenadicarbadodecaboranes
by Marta Gozzi, Benedikt Schwarze, Peter Coburger and Evamarie Hey-Hawkins
Inorganics 2019, 7(7), 91; https://doi.org/10.3390/inorganics7070091 - 22 Jul 2019
Cited by 8 | Viewed by 2879
Abstract
3,1,2-Ruthenadicarbadodecaborane complexes bearing the [C2B9H11]2− (dicarbollide) ligand are robust scaffolds, with exceptional thermal and chemical stability. Our previous work has shown that these complexes possess promising anti-tumor activities in vitro, and tend to form aggregates (or [...] Read more.
3,1,2-Ruthenadicarbadodecaborane complexes bearing the [C2B9H11]2− (dicarbollide) ligand are robust scaffolds, with exceptional thermal and chemical stability. Our previous work has shown that these complexes possess promising anti-tumor activities in vitro, and tend to form aggregates (or self-assemblies) in aqueous solutions. Here, we report on the synthesis and characterization of four ruthenium(II) complexes of the type [3-(η6-arene)-1,2-R2-3,1,2-RuC2B9H9], bearing either non-polar (R = Me (24)) or polar (R = CO2Me (7)) substituents at the cluster carbon atoms. The behavior in aqueous solution of complexes 2, 7 and the parent unsubstituted [3-(η6-p-cymene)-3,1,2-RuC2B9H11] (8) was investigated via UV-Vis spectroscopy, mass spectrometry and nanoparticle tracking analysis (NTA). All complexes showed spontaneous formation of self-assemblies (108–109 particles mL−1), at low micromolar concentration, with high polydispersity. For perspective applications in medicine, there is thus a strong need for further characterization of the spontaneous self-assembly behavior in aqueous solutions for the class of neutral metallacarboranes, with the ultimate scope of finding the optimal conditions for exploiting this self-assembling behavior for improved biological performance. Full article
(This article belongs to the Special Issue Metal Complexes Containing Boron Based Ligands)
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11 pages, 3260 KiB  
Article
Comparing the Acidity of (R3P)2BH-Based Donor Groups in Iridium Pincer Complexes
by Leon Maser, Christian Schneider, Lukas Alig and Robert Langer
Inorganics 2019, 7(5), 61; https://doi.org/10.3390/inorganics7050061 - 07 May 2019
Cited by 8 | Viewed by 2981
Abstract
In the current manuscript, we describe the reactivity of a series of iridium(III) pincer complexes with the general formulae [(PEP)IrCl(CO)(H)]n (n = +1, +2) towards base, where PEP is a pincer-type ligand with different central donor groups, and E is the [...] Read more.
In the current manuscript, we describe the reactivity of a series of iridium(III) pincer complexes with the general formulae [(PEP)IrCl(CO)(H)]n (n = +1, +2) towards base, where PEP is a pincer-type ligand with different central donor groups, and E is the ligating atom of this group (E = B, C, N). The donor groups encompass a secondary amine, a phosphine-stabilised borylene and a protonated carbodiphosphorane. As all ligating atoms E exhibit an E–H bond, we addressed the question of wether the coordinated donor group can be deprotonated in competition to the reductive elimination of HCl from the iridium(III) centre. Based on experimental and quantum chemical investigations, it is shown that the ability for deprotonation of the coordinated ligand decreases in the order of (R3P)2CH+ > R2NH > (R3P)2BH. The initial product of the reductive elimination of HCl from [(PBP)IrCl(CO)(H)]n (1c), the square planar iridium(I) complex, [(PBP)Ir(CO)]+ (3c), was found to be unstable and further reacts to [(PBP)Ir(CO)2]+ (5c). Comparing the C–O stretching vibrations of the latter with those of related complexes, it is demonstrated that neutral ligands based on tricoordinate boron are very strong donors. Full article
(This article belongs to the Special Issue Metal Complexes Containing Boron Based Ligands)
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13 pages, 1578 KiB  
Article
Dimethyloxonium and Methoxy Derivatives of nido-Carborane and Metal Complexes Thereof
by Marina Yu. Stogniy, Svetlana A. Erokhina, Irina D. Kosenko, Andrey A. Semioshkin and Igor B. Sivaev
Inorganics 2019, 7(4), 46; https://doi.org/10.3390/inorganics7040046 - 27 Mar 2019
Cited by 13 | Viewed by 3135
Abstract
9-Dimethyloxonium, 10-dimethyloxonium, 9-methoxy and 10-methoxy derivatives of nido-carborane (9-Me2O-7,8-C2B9H11, 10-Me2O-7,8-C2B9H11, [9-MeO-7,8-C2B9H11], and [10-MeO-7,8-C2B9H11 [...] Read more.
9-Dimethyloxonium, 10-dimethyloxonium, 9-methoxy and 10-methoxy derivatives of nido-carborane (9-Me2O-7,8-C2B9H11, 10-Me2O-7,8-C2B9H11, [9-MeO-7,8-C2B9H11], and [10-MeO-7,8-C2B9H11], respectively) were prepared by the reaction of the parent nido-carborane [7,8-C2B9H12] with mercury(II) chloride in a mixture of benzene and dimethoxymethane. Reactions of the 9 and 10-dimethyloxonium derivatives with triethylamine, pyridine, and 3-methyl-6-nitro-1H-indazole result in their N-methylation with the formation of the corresponding salts with 9 and 10-methoxy-nido-carborane anions. The reaction of the symmetrical methoxy derivative [10-MeO-7,8-C2B9H11] with anhydrous FeCl2 in tetrahydrofuran in the presence of t-BuOK results in the corresponding paramagnetic iron bis(dicarbollide) complex [8,8′-(MeO)2-3,3′-Fe(1,2-C2B9H10)2], whereas the similar reactions of the asymmetrical methoxy derivative [9-MeO-7,8-C2B9H11] with FeCl2 and CoCl2 presumably produce the 4,7′-isomers [4,7′-(MeO)2-3,3′-M(1,2-C2B9H10)2] (M = Fe, Co) rather than a mixture of rac-4,7′- and meso-4,4′-isomers. Full article
(This article belongs to the Special Issue Metal Complexes Containing Boron Based Ligands)
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12 pages, 3047 KiB  
Article
Hexaborate(2−) and Dodecaborate(6−) Anions as Ligands to Zinc(II) Centres: Self-Assembly and Single-Crystal XRD Characterization of [Zn{κ3O-B6O7(OH)6}(κ3N-dien)]·0.5H2O (dien = NH(CH2–CH2NH2)2), (NH4)2[Zn{κ2O-B6O7(OH)6}2 (H2O)2]·2H2O and (1,3-pnH2)3[(κ1N-H3N{CH2}3NH2) Zn{κ3O-B12O18(OH)6}]2·14H2O (1,3-pn = 1,3-diaminopropane)
by Mohammed A. Altahan, Michael A. Beckett, Simon J. Coles and Peter N. Horton
Inorganics 2019, 7(4), 44; https://doi.org/10.3390/inorganics7040044 - 27 Mar 2019
Cited by 10 | Viewed by 3589
Abstract
Two zinc(II) hexaborate(2−) complexes, [Zn{κ3O-B6O7(OH)6}(κ3N-dien)]·0.5H2O (dien = NH(CH2CH2NH2)2) (1) and (NH4)2[Zn{κ2O-B6O [...] Read more.
Two zinc(II) hexaborate(2−) complexes, [Zn{κ3O-B6O7(OH)6}(κ3N-dien)]·0.5H2O (dien = NH(CH2CH2NH2)2) (1) and (NH4)2[Zn{κ2O-B6O7(OH)6}2(H2O)2]·2H2O (2), and a zinc(II) dodecaborate(6−) complex, (1,3-pnH2)3[(κ1N-H3N{CH2}3NH2)Zn{κ3O-B12O18(OH)6}]2·14H2O (1,3-pn = 1,3-diaminopropane) (3), have been synthesized and characterized by single-crystal XRD studies. The complexes crystallized through self-assembly processes, from aqueous solutions containing 10:1 ratios of B(OH)3 and appropriate Zn(II) amine complex: [Zn(dien)2](OH)2, [Zn(NH3)4](OH)2, and [Zn(pn)3](OH)2. The hexaborate(2−) anions in 1 and 2 are coordinated to octahedral Zn(II) centres as tridentate (1) or bidentate ligands (2) and the dodecaborate(6−) ligand in 3 is tridentate to a tetrahedral Zn(II) centre. Full article
(This article belongs to the Special Issue Metal Complexes Containing Boron Based Ligands)
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8 pages, 1678 KiB  
Article
Synthesis and Structural Characterization of Two New Main Group Element Carboranylamidinates
by Phil Liebing, Nicole Harmgarth, Florian Zörner, Felix Engelhardt, Liane Hilfert, Sabine Busse and Frank T. Edelmann
Inorganics 2019, 7(3), 41; https://doi.org/10.3390/inorganics7030041 - 13 Mar 2019
Cited by 5 | Viewed by 3057
Abstract
Two new main group element carboranylamidinates were synthesized using a bottom-up approach starting from o-carborane, ortho-C2B10H12 (1, = 1,2-dicarba-closo-dodecaborane). The first divalent germanium carboranylamidinate, GeCl[HLCy] (3, [HLCy [...] Read more.
Two new main group element carboranylamidinates were synthesized using a bottom-up approach starting from o-carborane, ortho-C2B10H12 (1, = 1,2-dicarba-closo-dodecaborane). The first divalent germanium carboranylamidinate, GeCl[HLCy] (3, [HLCy] = [o-C2B10H10C(NCy)(NHCy)], Cy = cyclohexyl), was synthesized by treatment of GeCl2(dioxane) with 1 equiv. of in situ-prepared Li[HLCy] (2a) in THF and isolated in 47% yield. In a similar manner, the first antimony(III) carboranylamidinate, SbCl2[HLiPr] (4, [HLiPr] = [o-C2B10H10C(NiPr)(NHiPr)]), was obtained from a reaction of SbCl3 with 1 equiv. of Li[HLiPr] in THF (56% yield). The title compounds were fully characterized by analytical and spectroscopic methods as well as single-crystal X-ray diffraction. Both compounds 3 and 4 are monomeric species in the solid state, and the molecular geometries are governed by a stereo-active lone pair at the metal centers. Full article
(This article belongs to the Special Issue Metal Complexes Containing Boron Based Ligands)
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14 pages, 2429 KiB  
Article
Mono- and Hexanuclear Zinc Halide Complexes with Soft Thiopyridazine Based Scorpionate Ligands
by Michael Tüchler, Melanie Ramböck, Simon Glanzer, Klaus Zangger, Ferdinand Belaj and Nadia C. Mösch-Zanetti
Inorganics 2019, 7(2), 24; https://doi.org/10.3390/inorganics7020024 - 19 Feb 2019
Cited by 2 | Viewed by 3021
Abstract
Scorpionate ligands with three soft sulfur donor sites have become very important in coordination chemistry. Despite its ability to form highly electrophilic species, electron-deficient thiopyridazines have rarely been used, whereas the chemistry of electron-rich thioheterocycles has been explored rather intensively. Here, the unusual [...] Read more.
Scorpionate ligands with three soft sulfur donor sites have become very important in coordination chemistry. Despite its ability to form highly electrophilic species, electron-deficient thiopyridazines have rarely been used, whereas the chemistry of electron-rich thioheterocycles has been explored rather intensively. Here, the unusual chemical behavior of a thiopyridazine (6-tert-butylpyridazine-3-thione, HtBuPn) based scorpionate ligand towards zinc is reported. Thus, the reaction of zinc halides with tris(6-tert-butyl-3-thiopyridazinyl)borate Na[TntBu] leads to the formation of discrete torus-shaped hexameric zinc complexes [TntBuZnX]6 (X = Br, I) with uncommonly long zinc halide bonds. In contrast, reaction of the sterically more demanding ligand K[TnMe,tBu] leads to decomposition, forming Zn(HPnMe,tBu)2X2 (X = Br, I). The latter can be prepared independently by reaction of the respective zinc halides and two equiv of HPnMe,tBu. The bromide compound was used as precursor which further reacts with K[TnMe,tBu] forming the mononuclear complex [TnMe,tBu]ZnBr(HPnMe,tBu). The molecular structures of all compounds were elucidated by single-crystal X-ray diffraction analysis. Characterization in solution was performed by means of 1H, 13C and DOSY NMR spectroscopy which revealed the hexameric constitution of [TntBuZnBr]6 to be predominant. In contrast, [TnMe,tBu]ZnBr(HPnMe,tBu) was found to be dynamic in solution. Full article
(This article belongs to the Special Issue Metal Complexes Containing Boron Based Ligands)
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14 pages, 2694 KiB  
Article
Synthesis of Trithia-Borinane Complexes Stabilized in Diruthenium Core: [(Cp*Ru)21-S)(η1-CS){(CH2)2S3BR}] (R = H or SMe)
by Koushik Saha, Urminder Kaur, Rosmita Borthakur and Sundargopal Ghosh
Inorganics 2019, 7(2), 21; https://doi.org/10.3390/inorganics7020021 - 13 Feb 2019
Cited by 3 | Viewed by 3268
Abstract
The thermolysis of arachno-1 [(Cp*Ru)2(B3H8)(CS2H)] in the presence of tellurium powder yielded a series of ruthenium trithia-borinane complexes: [(Cp*Ru)21-S)(η1-CS){(CH2)2S3BH}] 2, [...] Read more.
The thermolysis of arachno-1 [(Cp*Ru)2(B3H8)(CS2H)] in the presence of tellurium powder yielded a series of ruthenium trithia-borinane complexes: [(Cp*Ru)21-S)(η1-CS){(CH2)2S3BH}] 2, [(Cp*Ru)21-S)(η1-CS){(CH2)2S3B(SMe)}] 3, and [(Cp*Ru)21-S)(η1-CS){(CH2)2S3BH}] 4. Compounds 24 were considered as ruthenium trithia-borinane complexes, where the central six-membered ring {C2BS3} adopted a boat conformation. Compounds 24 were similar to our recently reported ruthenium diborinane complex [(Cp*Ru){(η2-SCHS)CH2S2(BH2)2}]. Unlike diborinane, where the central six-membered ring {CB2S3} adopted a chair conformation, compounds 24 adopted a boat conformation. In an attempt to convert arachno-1 into a closo or nido cluster, we pyrolyzed it in toluene. Interestingly, the reaction led to the isolation of a capped butterfly cluster, [(Cp*Ru)2(B3H5)(CS2H2)] 5. All the compounds were characterized by 1H, 11B{1H}, and 13C{1H} NMR spectroscopy and mass spectrometry. The molecular structures of complexes 2, 3, and 5 were also determined by single-crystal X-ray diffraction analysis. Full article
(This article belongs to the Special Issue Metal Complexes Containing Boron Based Ligands)
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