NON‐Ligated N‐Heterocyclic 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 1,4‐Diborabenzol als π‐Ligand in Actinoidkomplexen

Die π‐Koordination von Aren‐ und anionischen Heteroarenliganden ist ein allgegenwärtiges Strukturmotiv in der metallorganischen Chemie der d‐ und f‐Block‐Elemente. Im Gegensatz dazu sind vergleichbare π‐Wechselwirkungen neutraler Heteroarene, darunter auch solche neutraler, aromatischer Borheterocyclen, für den f‐Block weit weniger verbreitet, was z. T. mit einer geringeren Effektivität der Metall‐zu‐Ligand‐Rückbindung in Zusammenhang gebracht werden kann. Für die Actinoide sind π‐Komplexe mit neutralen Heteroarenliganden sogar gänzlich unbekannt. Durch Ausnutzung der außergewöhnlichen π‐Donorstärke eines 1,4‐Diborabenzols ist es uns nun gelungen, eine Reihe stabiler π‐Halbsandwichkomplexe des Thoriums(IV) und des Urans(IV) über einen erstaunlich einfachen Zugang zu generieren: Umsetzung eines 1,4‐Diborabenzols mit ThCl4(dme)2 bzw. UCl4 in Gegenwart einer Lewis‐Base. Hierdurch konnten die ersten Beispiele für Actinoidkomplexe mit einem neutralen Borheterocyclus als Sandwich‐artigem Liganden erhalten werden. Laut experimentellen und theoretischen Studien ist die starke Actinoid‐Heteroaren‐Wechselwirkung in diesen Molekülen im Wesentlichen von elektrostatischer Natur. Der kovalente Hauptbeitrag wird hingegen von der Ligand‐zu‐Metall‐π‐Wechselwirkung geleistet, während π/δ‐Rückbindungsanteile 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 d9^{9}‐Metalloradicals [Ni(NHC)2_{2}]+^{+}

A series of five new homoleptic, linear nickel d$^{9}$‐complexes of the type [Ni$^{I}$(NHC)$_{2}$]$^{+}$ is reported. Starting from the literature known Ni(0) complexes [Ni(Mes$_{2}$Im)$_{2}$] 1, [Ni(Mes$_{2}$Im$^{H2}$)2] 2, [Ni(Dipp$_{2}$Im)$_{2}$] 3, [Ni(Dipp$_{2}$Im$^{H2}$)$_{2}$] 4 and [Ni(cAAC$^{Me}$)$_{2}$] 5 (Mes$_{2}$Im=1,3‐bis(2,4,6‐trimethylphenyl)‐imidazolin‐2‐ylidene, Mes$_{2}$Im$^{H2}$=1,3‐bis(2,4,6‐trimethylphenyl)‐imidazolidin‐2‐ylidene, Dipp$_{2}$Im=1,3‐bis(2,6‐diisopropylphenyl)‐imidazolin‐2‐ylidene, Dipp$_{2}$Im$^{H2}$=1,3‐bis(2,6‐diisopropylphenyl)‐imidazolidin‐2‐ylidene, cAAC$^{Me}$=1‐(2,6‐diisopropylphenyl)‐3,3,5,5‐tetramethylpyrrolidin‐2‐yliden), their oxidized Ni(I) analogues [Ni$^{I}$(Mes$_{2}$Im)$_{2}$][BPh$_{4}$] 1$^{+}$, [Ni$^{I}$(Mes$_{2}$Im$^{H2}$)$_{2}$][BPh$_{4}$] 2$^{+}$, [Ni$^{I}$(Dipp$_{2}$Im)$_{2}$][BPh$_{4}$] 3$^{+}$, [Ni$^{I}$(Dipp$_{2}$Im$^{H2}$)$_{2}$][BPh$_{4}$] 4$^{+}$ and [Ni$^{I}$(cAAC$^{Me}$)$_{2}$][BPh$_{4}$] 5$^{+}$ were synthesized by one‐electron oxidation with ferrocenium tetraphenyl‐borate. The complexes 1$^{+}$–5$^{+}$ were fully characterized including X‐ray 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 g‐tensor anisotropy for the N‐Mes substituted complexes 1$^{+}$ and 2$^{+}$ in solution due to the formation of T‐shaped THF adducts

Ein neutrales 1,4‐Diborabenzol als π\pi‐Ligand in Actinoidkomplexen

Die $\pi$-Koordination von Aren- und anionischen Heteroarenliganden ist ein allgegenwärtiges Strukturmotiv in der metallorganischen Chemie der d- und f-Block-Elemente. Im Gegensatz dazu sind vergleichbare $\pi$-Wechselwirkungen neutraler Heteroarene, darunter auch solche neutraler, aromatischer Borheterocyclen, für den f-Block weit weniger verbreitet, was z. T. mit einer geringeren Effektivität der Metall-zu-Ligand-Rückbindung in Zusammenhang gebracht werden kann. Für die Actinoide sind π-Komplexe mit neutralen Heteroarenliganden sogar gänzlich unbekannt. Durch Ausnutzung der außergewöhnlichen $\pi$-Donorstärke eines 1,4-Diborabenzols ist es uns nun gelungen, eine Reihe stabiler π-Halbsandwichkomplexe des Thoriums(IV) und des Urans(IV) über einen erstaunlich einfachen Zugang zu generieren: Umsetzung eines 1,4-Diborabenzols mit ThCl$_{4}$(dme)$_{2}$ bzw. UCl$_{4}$ in Gegenwart einer Lewis-Base. Hierdurch konnten die ersten Beispiele für Actinoidkomplexe mit einem neutralen Borheterocyclus als Sandwich-artigem Liganden erhalten werden. Laut experimentellen und theoretischen Studien ist die starke Actinoid-Heteroaren-Wechselwirkung in diesen Molekülen im Wesentlichen von elektrostatischer Natur. Der kovalente Hauptbeitrag wird hingegen von der Ligand-zu-Metall-$\pi$-Wechselwirkung geleistet, während $\pi$/δ-Rückbindungsanteile kaum eine Rolle spielen

Stable Actinide π Complexes of a Neutral 1,4-Diborabenzene

The π 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 π interactions of neutral heteroarenes including neutral bora-π-aromatics are less prevalent particularly for the f-block, due to less effective metal-to-ligand backbonding. In fact, π complexes with neutral heteroarene ligands are essentially unknown for the actinides. We have now overcome these limitations by exploiting the exceptionally strong π donor capabilities of a neutral 1,4-diborabenzene. A series of remarkably robust, π-coordinated thorium(IV) and uranium(IV) half-sandwich complexes were synthesized by simply combining the bora-π-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 actinide–heteroarene interactions are predominately electrostatic in nature with distinct ligand-to-metal π donation and without significant π/δ 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+ (2b–d) and [Ni(pyNO)6]2+ (3c–d) 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 2b–d. 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