Two novel bis(triazolyl)carbazole ligands Hbtc1 (3,6-di(tert-butyl)-1,8-bis[(1-(3,5-di(tert-butyl)phenyl)-1,2,3-triazol-4-yl)]-9H-carbazole) and Hbtc2 (3,6-di(tert-butyl)-1,8-bis[(4-(3,5-di(tert-butyl)phenyl)-1,2,3-triazol-1-yl)]-9H-carbazole), differing in the regiochemistry of triazole attachment, have been synthesized by Cu-catalyzed azide-alkyne cycloaddition, the so-called "click-reactions". Metalation with Ru, Zn, and Ni precursors led to the formation of M(btc) complexes (M=Ru, Zn, Ni), with two deprotonated ligands coordinating to the metal center in tridentate fashion, forming almost perfectly octahedral coordination spheres. The redox properties of M(btc) complexes have been investigated by cyclic voltammetry, UV/Vis spectroscopy, spectroelectrochemistry, and chemically. The CV of the ruthenium complexes revealed three quasi-reversible one-electron oxidation processes, one assigned as the Ru couple and two originating from ligand-based oxidations. The CVs of both Zn and Ni complexes contained only two oxidation waves corresponding to the oxidation of the two ligands. The oxidation potentials of complexes derived from Hbtc1 ligands were found to be 300-400 mV lower than those of the corresponding complexes derived from Hbtc2, reflecting the significant difference in donation through the N(2) or N(3) atom of the triazole moiety.
The pentafluoroorthotellurate group (teflate, OTeF 5 ) is able to form species, for which only the fluoride analogues are known. Despite nickel fluorides being widely investigated, nickel teflates have remained elusive for decades. By reaction of [NiCl 4 ] 2À and neat ClOTeF 5 , we have synthesized the homoleptic [Ni(OTeF 5 ) 4 ] 2À anion, which presents a distorted tetrahedral structure, unlike the polymeric [NiF 4 ] 2À . This highspin complex has allowed the study of the electronic properties of the teflate group, which can be classified as a weak/ medium-field ligand, and therefore behaves as the fluoride analogue also in ligand-field terms. The teflate ligands in [NEt 4 ] 2 [Ni(OTeF 5 ) 4 ] are easily substituted, as shown by the formation of [Ni(NCMe) 6 ][OTeF 5 ] 2 by dissolving it in acetonitrile. Nevertheless, careful reactions with other conventional ligands have enabled the crystallization of nickel teflate complexes with different coordination geometries, i.e. [NEt 4 ] 2 [trans-Ni(OEt 2 ) 2 (OTeF 5 ) 4 ] or [NEt 4 ][Ni(bpyMe 2 )(OTeF 5 ) 3 ].
Complexes [L 2 Fe][Li(DME)] 2 , 1(DME), {[L 2 Fe][Na 2 (DME) 3 ]} 1 , 2(DME) and [L 2 Fe][K(DME) 2 ] 2 , 3(DME) were synthesized by deprotonation of LH 2 (LH 2 = O(SiPh 2 OH) 2 ) with the respective alkali metal tert-butoxides followed by recrystallization from DME. It turned out that upon crossing over from Li + via Na + to K + counterions the structures of the high-spin iron(II) complexes are increasingly distorted from a square planar towards a tetrahedral structure so that 3(DME) represents a borderline case, as indicated by the τ-values. The distortions are also reflected in the Mössbauer spectra through the quadrupole splittings. The compounds behave inert in contact with O atom transfer reagents but react rapidly with dioxygen. The reaction rates are too high to be determined even by stopped-flow measurements quantitatively, but qualitatively it emerged that the rates increase from Li to Na to K. Using NO as an O 2 surrogate an NO adduct with an S = 3/2 ground state was isolated where NO is coordinated in an end-on binding mode, formally as a NO À ligand, with a significantly weakened NO bond.
Open-shell molecules with unpaired electrons and a high-spin S ≥ 1 con guration are of fundamental importance in chemistry, biology and towards molecular electronics. Among metal-free systems, carbon-and silicon-based triplet diradicals with two unpaired electrons and strong ferromagnetic coupling are proposed as key intermediates in many organic and elementorganic transformations but their isolation remains challenging due to their very high reactivity. Herein, we report the facile synthesis of the rst isolable 1,3-disilapyrroles which represent organosilicon-based delocalized triplet diradicals. They result from click chemistry of two divalent silicon atoms in a 1,1-bis(silylenyl)aniline to the carbon-carbon triple bond of diphenylacetylenes. Remarkably, the spin-density distribution of these triplet diradicals exhibits an asymmetric delocalization due to steric congestion. The unpaired electrons in the 1,3-disilapyrroles enable an unprecedented reactivity, including cyclotetramerization and complete cleavage of the carbon-oxygen triple bond of CO at ambient temperature with subsequent C(sp3)-H bond activation to give a new bicyclic product.Prof. Yitzhak Apeloig (Technion, Israel) for his contribution to the peer review of this work. Reprints and permissions information is available at www.nature.com/reprints.
The pentafluoroorthotellurate group (teflate, OTeF 5 ) is considered as a bulky analogue of fluoride, yet its coordination behavior in transition metal complexes is not fully understood. By reaction of [CoCl 4 ] 2− and neat ClOTeF 5 , we synthesized the first cobalt teflate complex, [Co(OTeF 5 ) 4 ] 2− , which exhibits moisture-resistant Co−OTeF 5 bonds. Through a combined experimental and theoretical (DFT and NEVPT2) study, the properties and electronic structure of this species have been investigated. It exhibits a distorted tetrahedral structure around the cobalt center and can be described as a d 7 system with a quartet (S = 3/2) ground state. A comparative bonding analysis of the (pseudo)tetrahedral [CoX 4 ] 2− anions (X = OTeF 5 , F, Cl) revealed that the strength of the Co−X interaction is similar in the three cases, being the strongest in [Co(OTeF 5 ) 4 ] 2− . In addition, an analysis of the charge of the Co center reinforced the similar electronwithdrawing properties of the teflate and fluoride ligands. Therefore, the [Co(OTeF 5 ) 4 ] 2− anion constitutes an analogue of the polymeric [CoF 4 ] 2− in terms of electronic properties, but with a monomeric structure.
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