Special Issue "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)

Special Issue Editor

Guest Editor
Dr. Gareth Owen

University of South Wales, School of Applied Sciences, Pontypridd, United Kingdom
Website | E-Mail
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

Manuscript Submission Information

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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 (6 papers)

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Research

Open AccessArticle
Comparing the Acidity of (R3P)2BH-Based Donor Groups in Iridium Pincer Complexes
Received: 31 March 2019 / Revised: 28 April 2019 / Accepted: 29 April 2019 / Published: 7 May 2019
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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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Graphical abstract

Open AccessArticle
Dimethyloxonium and Methoxy Derivatives of nido-Carborane and Metal Complexes Thereof
Received: 27 February 2019 / Revised: 21 March 2019 / Accepted: 22 March 2019 / Published: 27 March 2019
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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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Graphical abstract

Open AccessArticle
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)
Received: 27 February 2019 / Revised: 20 March 2019 / Accepted: 23 March 2019 / Published: 27 March 2019
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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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Graphical abstract

Open AccessArticle
Synthesis and Structural Characterization of Two New Main Group Element Carboranylamidinates
Received: 26 February 2019 / Revised: 11 March 2019 / Accepted: 11 March 2019 / Published: 13 March 2019
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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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Figure 1

Open AccessArticle
Mono- and Hexanuclear Zinc Halide Complexes with Soft Thiopyridazine Based Scorpionate Ligands
Received: 20 December 2018 / Revised: 4 February 2019 / Accepted: 5 February 2019 / Published: 19 February 2019
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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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Graphical abstract

Open AccessArticle
Synthesis of Trithia-Borinane Complexes Stabilized in Diruthenium Core: [(Cp*Ru)21-S)(η1-CS){(CH2)2S3BR}] (R = H or SMe)
Received: 12 December 2018 / Revised: 5 February 2019 / Accepted: 7 February 2019 / Published: 13 February 2019
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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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Graphical abstract

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