Neue Synthese für Tellurocarbonyl-difluorid

Reaction between CF3TeTeCF3 and (CH3)3SnH in Et2O provides (CH3)3SnTeCF3 in 75% yield. This is a good starting material for the preparation of TeCF2 and its cyclic dimer, because pyrolysis of (CH3)3SnTeCF3 at 280° (10-3 Torr) yields TeCF2 in 60% yield. On warming from -196° to 20°, TeCF2 dimerizes quantitatively to the corresponding tetrafluoro-l,3-ditelluretane

NMR spectroscopic investigations on the successive implementation of nickel and zinc ions to a NacNac-dibenzofuran-Br ligand precursor

The ligand precursor HNacNac-dibenzofuran-Br, LH, was synthesized by the condensation of 6-bromo-4-dibenzofuranamine and 4-(N-(mesityl)amino)pent-3-en-2-one with the aim of preparing heterodinuclear nickel/zinc complexes in two successive steps. Reacting LH with Zn(HMDS)2, Zn(C6F5)2 and Zn(C2H5)2 led to the respective X-Zn-NacNac-dibenzofuran-Br complexes (X=HMDS (2), C6F5 (3), Et (4)). However, in case of 2 and 3 the subsequent treatment with Ni(COD)2/TMEDA did not lead to any conversion, probably as the steric bulk imposed by the NacNac-Zn-X entities was too high. 4 did react with Ni(COD)2/TMEDA, likely in the envisaged manner, but apparently the targeted product complex Et-Zn-NacNac-dibenzofuran-Ni(TMEDA)Br, once formed, immediately reacts further via a Negishi coupling reaction, so that Br-Zn-NacNac-dibenzofuran-Et (5) is formed. The reaction of 4 with triethylammonium bromide led to the formation of the Br-Zn-NacNac-dibenzofuran-Br (6) complex that could be reacted with Ni(COD)2/TMEDA successfully. All attempts to purify the product led to Zn(NacNac-dibenzofuran-Ni(TMEDA)Br)2, which is insoluble in THF and thus drives a dismutation reaction.Peer Reviewe

Cationic Tetrylene‐Iron(0) Complexes: Access Points for Cooperative, Reversible Bond Activation and Open‐Shell Iron(−I) Ferrato‐Tetrylenes

The open-shell cationic stannylene-iron(0) complex 4 (4=[PhiPDippSn⋅Fe⋅IPr]+; PhiPDipp={[Ph2PCH2Si(iPr)2](Dipp)N}; Dipp=2,6-iPr2C6H3; IPr=[(Dipp)NC(H)]2C:) cooperatively and reversibly cleaves dihydrogen at the Sn−Fe interface under mild conditions (1.5 bar, 298 K), in forming bridging hydrido-complex 6. The One-electron oreduction of the related GeII−Fe0 complex 3 leads to oxidative addition of one C−P linkage of the PhiPDipp ligand in an intermediary Fe−I complex, leading to FeI phosphide species 7. One-electron reduction reaction of 4 gives access to the iron(−I) ferrato-stannylene, 8, giving evidence for the transient formation of such a species in the reduction of 3. The covalently bound tin(II)-iron(−I) compound 8 has been characterised through EPR spectroscopy, SQUID magnetometry, and supporting computational analysis, which strongly indicate a high localization of electron spin density at Fe−I in this unique d9-iron complex.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Verband der Chemischen Industrie http://dx.doi.org/10.13039/100007215Peer Reviewe

Mimicking of the histidine brace structural motif in molecular copper(I) compounds

L-Nτ-methylhistidine methyl ester, MeHisOMe, has been employed as a potential ligand to mimic the histidine brace-type coordination of copper ions in enzymes such as the particulate methane monoxygenase or lytic polysaccharide monooxygenases. MeHisOMe was prepared by double-methylation of histidine methyl ester. Subsequently, its complexation by diphosphine copper(I) precursors [Cu(P^P)(MeCN)2]BF4 was tested, which led to the complexes [Cu(P^P)(MeHisOMe)]BF4 (P^P=dpePhos: 1, P^P=XantPhos: 2, P^P=dppf: 3). 1–3 were fully characterized, also by single crystal X-ray analysis, thus providing first structural data for copper complexes with a synthetic, authentic histidine brace. The complexes proved inert in contact with dioxygen. To improve the biomimetic character attempts were made to formally replace the diphosphine ligands by bis(pyrazolyl)methanes, Bpm. Correspondingly, [BpmCu(NCMe)x]BF4 precursors were synthesized, with different substituents at the 3-positions of the pyrazolyl (i. e. Bpm=di(3-(phenyl)-1H-pyrazol-1-yl)diphenylmethane, di(3-(mesityl)-1H-pyrazol-1-yl)methane and di(3-(tert-butyl)-1H-pyrazol-1-yl)diphenylmethane). Addition of MeHisOMe to these complexes led to products that were so sensitive towards oxidation by the environment that they eluded isolation. One experiment provided blue crystals as a product of such a reaction. They belonged to a salt with a complex cation consisting of a Cu(μ-OH)2Cu core ligated by two MeHisOMe ligands, which dimerises in the solid state to give [Cu4(OH)4(MeHisOMe)4]4+.Peer Reviewe

Controlling the Activation at NiII−CO22− Moieties through Lewis Acid Interactions in the Second Coordination Sphere

Nickel complexes with a two-electron reduced CO2 ligand (CO22−, “carbonite”) are investigated with regard to the influence alkali metal (AM) ions have as Lewis acids on the activation of the CO2 entity. For this purpose complexes with NiII(CO2)AM (AM=Li, Na, K) moieties were accessed via deprotonation of nickel-formate compounds with (AM)N(iPr)2. It was found that not only the nature of the AM ions in vicinity to CO2 affect the activation, but also the number and the ligation of a given AM. To this end the effects of added (AM)N(R)2, THF, open and closed polyethers as well as cryptands were systematically studied. In 14 cases the products were characterized by X-ray diffraction and correlations with the situation in solution were made. The more the AM ions get detached from the carbonite ligand, the lower is the degree of aggregation. At the same time the extent of CO2 activation is decreased as indicated by the structural and spectroscopic analysis and reactivity studies. Accompanying DFT studies showed that the coordinating AM Lewis acidic fragment withdraws only a small amount of charge from the carbonite moiety, but it also affects the internal charge equilibration between the LtBuNi and carbonite moieties.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Peer Reviewe

Unravelling the Role of the Pentafluoroorthotellurate Group as a Ligand in Nickel Chemistry

The pentafluoroorthotellurate group (teflate, OTeF5) 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 [NiCl4]2− and neat ClOTeF5, we have synthesized the homoleptic [Ni(OTeF5)4]2− anion, which presents a distorted tetrahedral structure, unlike the polymeric [NiF4]2−. This high‐spin 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 [NEt4]2[Ni(OTeF5)4] are easily substituted, as shown by the formation of [Ni(NCMe)6][OTeF5]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. [NEt4]2[trans‐Ni(OEt2)2(OTeF5)4] or [NEt4][Ni(bpyMe2)(OTeF5)3].Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Peer Reviewe

Iron–molybdenum-oxo complexes as initiators for olefin autoxidation with O2

The reaction between [(TPA)Fe(MeCN)2](OTf)2 and [nBu4N](Cp*MoO3) yields the novel tetranuclear complex [(TPA)Fe(μ-Cp*MoO3)]2(OTf)2, 1, with a rectangular [Mo–O–Fe–O–]2 core containing high-spin iron(II) centres. 1 proved to be an efficient initiator/(pre)catalyst for the autoxidation of cis-cyclooctene with O2 to give cyclooctene epoxide. To test, which features of 1 are essential in this regard, analogues with zinc(II) and cobalt(II) central atoms, namely [(TPA)Zn(Cp*MoO3)](OTf), 3, and [(TPA)Co(Cp*MoO3)](OTf), 4, were prepared, which proved to be inactive. The precursor compounds of 1, [(TPA)Fe(MeCN)2](OTf)2 and [nBu4N](Cp*MoO3) as well as Cp2*Mo2O5, were found to be inactive, too. Reactivity studies in the absence of cyclooctene revealed that 1 reacts both with O2 and PhIO via loss of the Cp* ligands to give the triflate salt 2 of the known cation [((TPA)Fe)2(μ-O)(μ-MoO4)]2+. The cobalt analogue 4 reacts with O2 in a different way yielding [((TPA)Co)2(μ-Mo2O8)](OTf)2, 5, featuring a Mo2O84− structural unit which is novel in coordination chemistry. The compound [(TPA)Fe(μ-MoO4)]2, 6, being related to 1, but lacking Cp* ligands failed to trigger autoxidation of cyclooctene. However, initiation of autoxidation by Cp* radicals was excluded via experiments including thermal dissociation of Cp2*

Unravelling the Role of the Pentafluoroorthotellurate Group as a Ligand in Nickel Chemistry

The pentafluoroorthotellurate group (teflate, OTeF5) 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 [NiCl4]2− and neat ClOTeF5, we have synthesized the homoleptic [Ni(OTeF5)4]2− anion, which presents a distorted tetrahedral structure, unlike the polymeric [NiF4]2−. This high‐spin 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 [NEt4]2[Ni(OTeF5)4] are easily substituted, as shown by the formation of [Ni(NCMe)6][OTeF5]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. [NEt4]2[trans‐Ni(OEt2)2(OTeF5)4] or [NEt4][Ni(bpyMe2)(OTeF5)3]

Biomimetic mono- and dinuclear Ni(I) and Ni(II) complexes studied by X-ray absorption and emission spectroscopy and quantum chemical calculations

Five biomimetic mono- or dinuclear nickel complexes featuring Ni(I) or Ni(II) sites were studied by X-ray absorption and emission spectroscopy and DFT calculations. Ni K-edge XANES spectra and Kβ main and satellite emission lines were collected on powder samples. The pre-edge absorption transitions (core-to-valence excitation) and Kβ2,5 emission transitions (valence-to-core decay) were calculated using DFT (TPSSh/TZVP) on crystal structures. This yielded theoretical ctv and vtc spectra in near-quantitative agreement with the experiment, showing the adequacy of the DFT approach for electronic structure description, emphasizing the sensitivity of the XAS/XES spectra for ligation/redox changes at nickel, and revealing the configuration of unoccupied and occupied valence levels, as well as the spin-coupling modes in the dinuclear complexes. XAS/XES-DFT is valuable for molecular and electronic structure analysis of synthetic complexes and of nickel centers in H2 or COx converting metalloenzymes.Peer Reviewe

Examination of Protonation-Induced Dinitrogen Splitting by in Situ EXAFS Spectroscopy

The splitting of dinitrogen into nitride complexes emerged as a key reaction for nitrogen fixation strategies at ambient conditions. However, the impact of auxiliary ligands or accessible spin states on the thermodynamics and kinetics of N-N cleavage is yet to be examined in detail. We recently reported N-N bond splitting of a {Mo(μ2:η1:η1-N2)Mo}-complex upon protonation of the diphosphinoamide auxiliary ligands. The reactivity was associated with a low-spin to high-spin transition that was induced by the protonation reaction in the coordination periphery, mainly based on computational results. Here, this proposal is evaluated by an XAS study of a series of linearly N2 bridged Mo pincer complexes. Structural characterization of the transient protonation product by EXAFS spectroscopy confirms the proposed spin transition prior to N-N bond cleavage