53 research outputs found
NONâLigated NâHeterocyclic Tetrylenes
We report on the synthesis of N-heterocyclic tetrylenes ligated by the NON-donor framework 4,5-bis(2,6-diisopropylphenyl-amino)-2,7-di-tert-butyl-9,9-dimethylxanthene. The molecular structures of the germylene (3), stannylene (4) and plumbylene (5) where determined by X-ray diffraction studies. Furthermore, we present quantum chemical studies on the sigma-donor and pi-acceptor properties of 3-5. Additionally, we report on the reactivity of the tetrylenes towards the transition metal carbonyls [Rh(CO)(2)Cl](2), [W(CO)(6)] and [Ni(CO)(4)]. The isolated complexes (6 and 7) show the differing reactivity of NHTs compared to NHCs. Instead of just forming the anticipated complex [(NON)Sn-Rh(CO)(2)Cl], 4 inserts into the Rh-Cl bond to afford [(NON)Sn(Cl)Rh(CO)(C6H6)] (6, additional CO/C6H6 exchange) and [(NON)Sn(Cl)Rh-2(CO)(4)Cl] (7). By avoiding halogenated transition metal precursors in order to prevent insertion reactions, germylene 3 shows "classical" coordination chemistry towards {Ni(CO)(3)} forming the complex [(NON)Ge-Ni(CO)(3)] (8)
Ein neutrales 1,4âDiborabenzol als ÏâLigand in Actinoidkomplexen
Die ÏâKoordination von Arenâ und anionischen Heteroarenliganden ist ein allgegenwĂ€rtiges Strukturmotiv in der metallorganischen Chemie der dâ und fâBlockâElemente. Im Gegensatz dazu sind vergleichbare ÏâWechselwirkungen neutraler Heteroarene, darunter auch solche neutraler, aromatischer Borheterocyclen, fĂŒr den fâBlock weit weniger verbreitet, was z.âT. mit einer geringeren EffektivitĂ€t der MetallâzuâLigandâRĂŒckbindung in Zusammenhang gebracht werden kann. FĂŒr die Actinoide sind ÏâKomplexe mit neutralen Heteroarenliganden sogar gĂ€nzlich unbekannt. Durch Ausnutzung der auĂergewöhnlichen ÏâDonorstĂ€rke eines 1,4âDiborabenzols ist es uns nun gelungen, eine Reihe stabiler ÏâHalbsandwichkomplexe des Thoriums(IV) und des Urans(IV) ĂŒber einen erstaunlich einfachen Zugang zu generieren: Umsetzung eines 1,4âDiborabenzols mit ThCl4(dme)2 bzw. UCl4 in Gegenwart einer LewisâBase. Hierdurch konnten die ersten Beispiele fĂŒr Actinoidkomplexe mit einem neutralen Borheterocyclus als Sandwichâartigem Liganden erhalten werden. Laut experimentellen und theoretischen Studien ist die starke ActinoidâHeteroarenâWechselwirkung in diesen MolekĂŒlen im Wesentlichen von elektrostatischer Natur. Der kovalente Hauptbeitrag wird hingegen von der LigandâzuâMetallâÏâWechselwirkung geleistet, wĂ€hrend Ï/ÎŽâRĂŒckbindungsanteile kaum eine Rolle spielen.EC/H2020/669054/EU/Boron-boron multiple bonding/multiBBDFG, 390540038, EXC 2008: Unifying Systems in Catalysis "UniSysCat
The value of plantation forests for plant, invertebrate and bird diversity and the potential for cross-taxon surrogacy
As the area of plantation forest expands worldwide and natural, unmanaged forests decline there is much interest in the potential for planted forests to provide habitat for biodiversity. In regions where little semi-natural woodland remains, the biodiversity supported by forest plantations, typically non-native conifers, may be particularly important. Few studies provide detailed comparisons between the species diversity of native woodlands which are being depleted and non-native plantation forests, which are now expanding, based on data collected from multiple taxa in the same study sites. Here we compare the species diversity and community composition of plants, invertebrates and birds in Sitka spruce- (Picea sitchensis-) dominated and Norway spruce- (Picea abies-) dominated plantations, which have expanded significantly in recent decades in the study area in Ireland, with that of oak- and ash-dominated semi-natural woodlands in the same area. The results show that species richness in spruce plantations can be as high as semi-natural woodlands, but that the two forest types support different assemblages of species. In areas where non-native conifer plantations are the principle forest type, their role in the provision of habitat for biodiversity conservation should not be overlooked. Appropriate management should target the introduction of semi-natural woodland characteristics, and on the extension of existing semi-natural woodlands to maintain and enhance forest species diversity. Our data show that although some relatively easily surveyed groups, such as vascular plants and birds, were congruent with many of the other taxa when looking across all study sites, the similarities in response were not strong enough to warrant use of these taxa as surrogates of the others. In order to capture a wide range of biotic variation, assessments of forest biodiversity should either encompass several taxonomic groups, or rely on the use of indicators of diversity that are not species based
Cationic Nickel dâMetalloradicals [Ni(NHC)]
A series of five new homoleptic, linear nickel dâcomplexes of the type [Ni(NHC)] is reported. Starting from the literature known Ni(0) complexes [Ni(MesIm)] 1, [Ni(MesIm)2] 2, [Ni(DippIm)] 3, [Ni(DippIm)] 4 and [Ni(cAAC)] 5 (MesIm=1,3âbis(2,4,6âtrimethylphenyl)âimidazolinâ2âylidene, MesIm=1,3âbis(2,4,6âtrimethylphenyl)âimidazolidinâ2âylidene, DippIm=1,3âbis(2,6âdiisopropylphenyl)âimidazolinâ2âylidene, DippIm=1,3âbis(2,6âdiisopropylphenyl)âimidazolidinâ2âylidene, cAAC=1â(2,6âdiisopropylphenyl)â3,3,5,5âtetramethylpyrrolidinâ2âyliden), their oxidized Ni(I) analogues [Ni(MesIm)][BPh] 1, [Ni(MesIm)][BPh] 2, [Ni(DippIm)][BPh] 3, [Ni(DippIm)][BPh] 4 and [Ni(cAAC)][BPh] 5 were synthesized by oneâelectron oxidation with ferrocenium tetraphenylâborate. The complexes 1â5 were fully characterized including Xâray structure analysis. The complex cations reveal linear geometries in the solid state and NMR spectra with extremely broad, paramagnetically shifted resonances. DFT calculations predicted an orbitally degenerate ground state leading to large magnetic anisotropy, which was verified by EPR measurements in solution and on solid samples. The magnetic anisotropy of the complexes is highly dependent from the steric protection of the metal atom, which results in a noticeable decrease of the gâtensor anisotropy for the NâMes substituted complexes 1 and 2 in solution due to the formation of Tâshaped THF adducts
Ein neutrales 1,4âDiborabenzol als âLigand in Actinoidkomplexen
Die -Koordination von Aren- und anionischen Heteroarenliganden ist ein allgegenwĂ€rtiges Strukturmotiv in der metallorganischen Chemie der d- und f-Block-Elemente. Im Gegensatz dazu sind vergleichbare -Wechselwirkungen neutraler Heteroarene, darunter auch solche neutraler, aromatischer Borheterocyclen, fĂŒr den f-Block weit weniger verbreitet, was z.âT. mit einer geringeren EffektivitĂ€t der Metall-zu-Ligand-RĂŒckbindung in Zusammenhang gebracht werden kann. FĂŒr die Actinoide sind Ï-Komplexe mit neutralen Heteroarenliganden sogar gĂ€nzlich unbekannt. Durch Ausnutzung der auĂergewöhnlichen -DonorstĂ€rke eines 1,4-Diborabenzols ist es uns nun gelungen, eine Reihe stabiler Ï-Halbsandwichkomplexe des Thoriums(IV) und des Urans(IV) ĂŒber einen erstaunlich einfachen Zugang zu generieren: Umsetzung eines 1,4-Diborabenzols mit ThCl(dme) bzw. UCl in Gegenwart einer Lewis-Base. Hierdurch konnten die ersten Beispiele fĂŒr Actinoidkomplexe mit einem neutralen Borheterocyclus als Sandwich-artigem Liganden erhalten werden. Laut experimentellen und theoretischen Studien ist die starke Actinoid-Heteroaren-Wechselwirkung in diesen MolekĂŒlen im Wesentlichen von elektrostatischer Natur. Der kovalente Hauptbeitrag wird hingegen von der Ligand-zu-Metall--Wechselwirkung geleistet, wĂ€hrend /ÎŽ-RĂŒckbindungsanteile kaum eine Rolle spielen
Stable Actinide Ï Complexes of a Neutral 1,4-Diborabenzene
The Ï coordination of arene and anionic heteroarene ligands is a ubiquitous bonding motif in the organometallic chemistry of d-block and f-block elements. By contrast, related Ï interactions of neutral heteroarenes including neutral bora-Ï-aromatics are less prevalent particularly for the f-block, due to less effective metal-to-ligand backbonding. In fact, Ï complexes with neutral heteroarene ligands are essentially unknown for the actinides. We have now overcome these limitations by exploiting the exceptionally strong Ï donor capabilities of a neutral 1,4-diborabenzene. A series of remarkably robust, Ï-coordinated thorium(IV) and uranium(IV) half-sandwich complexes were synthesized by simply combining the bora-Ï-aromatic with ThCl4(dme)2 or UCl4, representing the first examples of actinide complexes with a neutral boracycle as sandwich-type ligand. Experimental and computational studies showed that the strong actinideâheteroarene interactions are predominately electrostatic in nature with distinct ligand-to-metal Ï donation and without significant Ï/ÎŽ backbonding contributions.DFG, 390540038, EXC 2008: Unifying Systems in Catalysis "UniSysCat"EC/H2020/669054/EU/Boron-boron multiple bonding/multiBBEC/H2020/752285/EU/Towards Highly-Efficient Two-Photon Absorbing Sensitizers within a Confined Chromophore Space:From Computer-Aided Design to New Concepts and Applications/TWOSEN
Nickel(II) Cyanoborates and Cyanoborate-Ligated Nickel(II) Complexes
Nickel(II) cyanoborates Ni[BH2(CN)2]2·H2O (1b·H2O),
Ni[BH(CN)3]2·0.5H2O (1c·0.5H2O), and Ni[B(CN)4]2·0.5H2O (1d·0.5H2O) were synthesized,
and their reactivity with respect to dppeO2 (=1,2-bis-(diphenylphosphinoethane dioxide)), pyNO (=pyridine-N-oxide), dppe (=1,2-bis-(diphenylphosphinoethane),
and DMSO (=dimethyl sulfoxide) was examined. Using these ligands,
either cyanoborate (CB) complex salts of [Ni(dppe)2]2+ (2bâd) and [Ni(pyNO)6]2+ (3câd) were
isolated or complexes [Ni(DMSO)4{NC-B(CN)3}2] (1dDMSO) and [Ni(dppeO2)2{NC-B(CN)3}2] (1ddppeO2) were formed. Salt metathesis of [Ni(dppe)Cl2] with alkali metal cyanoborates resulted in mono- and disubstituted
coordination compounds [Ni(dppe){NC-BH(CN)2}Cl] (5c) and [Ni(dppe){NC-BH2CN)2}] (4b), which decomposed to salts 2bâd. The synthetical pathways explored offer convenient routes
to nickel(II) cyanoborates, nickel(II) complexes ligated with cyanoborates,
and nickel(II) complex salts of cyanoborates. Further, our studies
demonstrate the diverse character of cyanoborates in coordination
chemistry as noncoordinating counteranions and also as medium coordinating
anions forming novel transition-metal complexes and salts
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