25 research outputs found
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 (Cy<sub>3</sub>P)<sub>2</sub>Cl<sub>2</sub>RuC–PtCl<sub>2</sub>–L (<b>RuC–Pt–L</b>) complexes,
leading to the incipient formation of the terminal ruthenium carbide
complex, (Cy<sub>3</sub>P)<sub>2</sub>Cl<sub>2</sub>Ru<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 chromiumÂ(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 nickelÂ(II) complexes
based on an unsymmetrical
(1-(3-((di<i>tert</i>-butylphosphino)Âmethyl)Âphenyl)-<i>N</i>,<i>N</i>-dimethyl-methanamine) (PCN) pincer
ligand were synthesized and characterized by <sup>1</sup>H, <sup>31</sup>PÂ{<sup>1</sup>H}, and <sup>13</sup>CÂ{<sup>1</sup>H} NMR spectroscopy.
Their molecular structures were confirmed by X-ray diffraction. Oxidation
to high-valent paramagnetic NiÂ(III) dihalide complexes was achieved
through straightforward reaction of the corresponding diamagnetic
halide complexes with anhydrous CuX<sub>2</sub> (X = Cl, Br). In agreement
with this, the complexes are active in Kharasch addition of CCl<sub>4</sub> to olefins. The reaction of the hydroxo complex (<b>8</b>) and the amido complex (<b>11</b>) with CO<sub>2</sub> 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 CO<sub>2</sub> is sluggish
MOESM3 of Effective cleaning of rust stained marble
Additional file 3. Supplementary material for: Effective cleaning of rust stained marble
MOESM1 of Effective cleaning of rust stained marble
Additional file 1: Fig S1. ATR-FTIR spectrum of the white precipitate. The ATR-FTIR spectrum of the white precipitate identifies it as cystine
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 chromiumÂ(III)
complexes, the methyl isocyanide complex [(CH<sub>3</sub>NC)<sub>5</sub>CrOCrÂ(CNCH<sub>3</sub>)<sub>5</sub>]Â(PF<sub>6</sub>)<sub>4</sub>·2CH<sub>3</sub>CN, is reported. This constitutes only the third oxo-bridged,
dinuclear chromiumÂ(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 chromiumÂ(III) complex known.
Furthermore, we report the crystal structure and computed magnetic
properties for [(bpy)<sub>2</sub>(SCN)ÂCrOCrÂ(NCS)Â(bpy)<sub>2</sub>]Â(ClO<sub>4</sub>)<sub>2</sub>·2H<sub>2</sub>O (bpy = 2,2′-bipyridine),
which differs from other reported oxo-bridged species by featuring
a bent CrOCr<sup>4+</sup> 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 chromiumÂ(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
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><sub>2,5</sub> 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 [RuCÂ(Cl)<sub>2</sub>(PCy<sub>3</sub>)<sub>2</sub>] (<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, [RuCÂ(Cl)Â(CH<sub>3</sub>CN)Â(PCy<sub>3</sub>)<sub>2</sub>]<sup>+</sup>, is described and characterized
by NMR, MS, X-ray crystallography, and computational studies. The
experimentally observed irregular variation of the carbide <sup>13</sup>C 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>-[RuCÂ(CN)<sub>2</sub>(PCy<sub>3</sub>)<sub>2</sub>], 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<sup>–1</sup> s<sup>–1</sup>. Further reaction with cyanide
leads to loss of the carbide ligand and formation of <i>trans</i>-[RuÂ(CN)<sub>4</sub>(PCy<sub>3</sub>)<sub>2</sub>]<sup>2–</sup>, which was isolated and structurally characterized as its PPh<sub>4</sub><sup>+</sup> salt
Synthesis and Characterization of a Neutral Titanium Tris(iminosemiquinone) Complex Featuring Redox-Active Ligands
The neutral trisÂ(semiquinonate) complex [TiÂ(dmp-BIAN<sup>isq</sup>)<sub>3</sub>] [dmp-BIAN<sup>isq</sup> = <i>N</i>,<i>N</i>′-bisÂ(3,5-dimethylphenylimino)Âacenaphthenesemiquinonate]
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<sup>isq</sup> 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 trisÂ(semiquinonate) complex [TiÂ(dmp-BIAN<sup>isq</sup>)<sub>3</sub>] [dmp-BIAN<sup>isq</sup> = <i>N</i>,<i>N</i>′-bisÂ(3,5-dimethylphenylimino)Âacenaphthenesemiquinonate]
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<sup>isq</sup> 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