Weakening of Carbide–Platinum Bonds as a Probe for Ligand Donor Strengths

We report the observation of the weakening of the RuC–Pt single bond in (Cy₃P)₂Cl₂RuC–PtCl₂–L (<b>RuC–Pt–L</b>) complexes, leading to the incipient formation of the terminal ruthenium carbide complex, (Cy₃P)₂Cl₂Ru<b></b>C (<b>RuC</b>). In the solid state, elongation of RuC–Pt bonds illustrates the degree of weakening, and in solution, decreasing platinum–carbide coupling constants and increasing carbide chemical shifts reveal weaker interaction through the carbide bridge, as the electron donating ability of L becomes progressively stronger. For the bridging carbide ligands, the chemical shifts and coupling constants to platinum are linearly dependent, and NMR data for parent <b>RuC</b> conform to this relationship, providing a spectroscopic means of determining the strength of the RuC–Pt linkages relative to dissociated <b>RuC</b>. The pliancy of the <b>RuC–Pt–L</b> fragment with regard to the identity of L establishes the carbide-bridged complexes as remarkably wide-ranging and sensitive probes for ligand donor abilities

Probing Effective Hamiltonian Operators by Single-Crystal EPR: A Case Study Using Dinuclear Cr(III) Complexes

The use of a simple two-center model to describe exchange-coupled systems of various complexities is common in the field of coordination chemistry and molecular magnetism. In this work we investigate the applicability of this model experimentally, employing multifrequency, single-crystal EPR on axial dinuclear chromium­(III) systems amenable to accurate parametrizations. The very high confidence with which zero-field splitting parameters can be determined by this technique, applied to the systems in question, allows for an in-depth analysis of the modeling. We experimentally demonstrate and qualitatively account for the energy-dependent modification of the spin-multiplet anisotropies, which is introduced by the exchange interaction. Even for the simple systems under consideration, we find that the standard modeling provides an inadequate parametrization of experimental data, and we present a convenient model extension, which improves the description

Synthesis, Characterization, and Reactivity of PCN Pincer Nickel Complexes

New diamagnetic nickel­(II) complexes based on an unsymmetrical (1-(3-((di<i>tert</i>-butylphosphino)­methyl)­phenyl)-<i>N</i>,<i>N</i>-dimethyl-methanamine) (PCN) pincer ligand were synthesized and characterized by ¹H, ³¹P­{¹H}, and ¹³C­{¹H} NMR spectroscopy. Their molecular structures were confirmed by X-ray diffraction. Oxidation to high-valent paramagnetic Ni­(III) dihalide complexes was achieved through straightforward reaction of the corresponding diamagnetic halide complexes with anhydrous CuX₂ (X = Cl, Br). In agreement with this, the complexes are active in Kharasch addition of CCl₄ to olefins. The reaction of the hydroxo complex (<b>8</b>) and the amido complex (<b>11</b>) with CO₂ produced the hydrogen carbonate and carbamate complexes, respectively. The hydrogen carbonate complex was converted to the dinuclear nickel carbonate complex (<b>10</b>). The methyl (<b>13</b>), phenyl (<b>14</b>), and <i>p</i>-tolylacetylide (<b>15</b>) complexes are also described in the current study providing the first example of the hydrocarbyl nickel complexes based on an unsymmetric aromatic pincer ligand. Furthermore, the reactivity of the methyl complex toward different electrophiles has been investigated, showing that C–C bond formation is possible with aryl halides, whereas the reaction with CO₂ is sluggish

MOESM3 of Effective cleaning of rust stained marble

Additional file 3. Supplementary material for: Effective cleaning of rust stained marble

Oxo-Bridged Dinuclear Chromium(III) Complexes: Correlation between the Optical and Magnetic Properties and the Basicity of the Oxo Bridge

The synthesis and X-ray structure of a new member of the series of oxo-bridged, dinuclear chromium­(III) complexes, the methyl isocyanide complex [(CH₃NC)₅CrOCr­(CNCH₃)₅]­(PF₆)₄·2CH₃CN, is reported. This constitutes only the third oxo-bridged, dinuclear chromium­(III) complex with a homoleptic auxillay ligand sphere. Experimentally, the system shows unshifted narrow nuclear magnetic resonance (NMR) spectra that are consistent with calculations using broken symmetry density functional theory (DFT), which suggests it to be the strongest coupled, dinuclear chromium­(III) complex known. Furthermore, we report the crystal structure and computed magnetic properties for [(bpy)₂(SCN)­CrOCr­(NCS)­(bpy)₂]­(ClO₄)₂·2H₂O (bpy = 2,2′-bipyridine), which differs from other reported oxo-bridged species by featuring a bent CrOCr⁴⁺ core. We also interpret the spectacular 10-orders-of-magnitude variation in acid dissociation constant of the bridging hydroxo ligand in mono hydroxo-bridged dinuclear chromium­(III) complexes, in terms of a valence bond model parametrized by metal-to-metal charge transfer (MMCT) and ligand-to-metal charge transfer (LMCT) energies

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Additional file 1: Fig S1. ATR-FTIR spectrum of the white precipitate. The ATR-FTIR spectrum of the white precipitate identifies it as cystine

β‑Selective Mannosylation with a 4,6-Silylene-Tethered Thiomannosyl Donor

Mannosylations using the new conformationally restricted donor phenyl 2,3-di-<i>O</i>-benzyl-4,6-<i>O</i>-(di-<i>tert</i>-butylsilylene)-1-thio-α-d-mannopyranoside (<b>6</b>) have been found to be β-selective with a variety of activation conditions. The simplest activation conditions were NIS/TfOH, in which case it is proposed that the β-mannoside is formed from β-selective glycosylation of the oxocarbenium ion <b>25</b> in a <i>B</i>_2,5 conformation

Ligand Sphere Conversions in Terminal Carbide Complexes

Metathesis is introduced as a preparative route to terminal carbide complexes. The chloride ligands of the terminal carbide complex [RuC­(Cl)₂(PCy₃)₂] (<b>RuC</b>) can be exchanged, paving the way for a systematic variation of the ligand sphere. A series of substituted complexes, including the first example of a cationic terminal carbide complex, [RuC­(Cl)­(CH₃CN)­(PCy₃)₂]⁺, is described and characterized by NMR, MS, X-ray crystallography, and computational studies. The experimentally observed irregular variation of the carbide ¹³C chemical shift is shown to be accurately reproduced by DFT, which also demonstrates that details of the coordination geometry affect the carbide chemical shift equally as much as variations in the nature of the auxiliary ligands. Furthermore, the kinetics of formation of the sqaure pyramidal dicyano complex, <i>trans</i>-[RuC­(CN)₂(PCy₃)₂], from <b>RuC</b> has been examined and the reaction found to be quite sluggish and of first order in both <b>RuC</b> and cyanide with a rate constant of <i>k</i> = 0.0104(6) M^–1 s^–1. Further reaction with cyanide leads to loss of the carbide ligand and formation of <i>trans</i>-[Ru­(CN)₄(PCy₃)₂]^2–, which was isolated and structurally characterized as its PPh₄⁺ salt

Synthesis and Characterization of a Neutral Titanium Tris(iminosemiquinone) Complex Featuring Redox-Active Ligands

The neutral tris­(semiquinonate) complex [Ti­(dmp-BIAN^isq)₃] [dmp-BIAN^isq = <i>N</i>,<i>N</i>′-bis­(3,5-dimethylphenylimino)­acenaphthenesemiquinonate] was structurally, spectroscopically, and electrochemically characterized. Solid-state magnetism experiments reveal field-quenchable, enhanced temperature-independent paramagnetism (TIP). Density functional theory calculations employing the experimental geometry predicts a strong antiferromagnetic coupling, leading to an <i>S</i> = 0 ground state, but they also hint at spin frustration and concomitant close-lying, excited states, which cause the observed large TIP by admixture into the ground state. The dmp-BIAN^isq ligand, which facilitates intramolecular electron transfer, was shown to undergo four quasi-reversible redox processes, demonstrating the ability of the ligand to act as an electron reservoir in complexes of early metals

Synthesis and Characterization of a Neutral Titanium Tris(iminosemiquinone) Complex Featuring Redox-Active Ligands

The neutral tris­(semiquinonate) complex [Ti­(dmp-BIAN^isq)₃] [dmp-BIAN^isq = <i>N</i>,<i>N</i>′-bis­(3,5-dimethylphenylimino)­acenaphthenesemiquinonate] was structurally, spectroscopically, and electrochemically characterized. Solid-state magnetism experiments reveal field-quenchable, enhanced temperature-independent paramagnetism (TIP). Density functional theory calculations employing the experimental geometry predicts a strong antiferromagnetic coupling, leading to an <i>S</i> = 0 ground state, but they also hint at spin frustration and concomitant close-lying, excited states, which cause the observed large TIP by admixture into the ground state. The dmp-BIAN^isq ligand, which facilitates intramolecular electron transfer, was shown to undergo four quasi-reversible redox processes, demonstrating the ability of the ligand to act as an electron reservoir in complexes of early metals