Structural, Electrochemical, and Photochemical Properties of Mono- and Digold(I) Complexes Containing Mesoionic Carbenes

Triazolylidenes are a prominent class of mesoionic carbenes (MICs) that are currently widely used in organometallic chemistry. Usually the metal complexes of such ligands are used as homogeneous catalysts even though they have vast potential in other branches of chemistry. We present here three related gold(I) complexes with MIC ligands: a neutral mononuclear chlorido complex [AuCl(MIC)], a cationic mononuclear complex containing two MIC ligands [Au(MIC)2]BF4, and a dicationic digold(I) complex containing two di-MIC ligands [Au2(κ1,κ1,µ-di-MIC)2](BF4)2. The complexes were characterized by 1H and 13C{1H} NMR spectroscopy, mass spectrometry, and single-crystal X-ray diffraction. The gold(I) centers are linearly coordinated through either one MIC-C and chlorido donors or through two MIC-C donors. The triazolylidenes display a delocalized bonding situation within the ring. Additionally, a short Au–Au distance of about 3 Å is observed for the digold(I) complex. All complexes display reduction steps in their cyclic voltammograms, and these are assigned to the reduction of the MIC ligands, as opposed to the generation of gold(0). The complexes emit at ca. 500 nm, with lifetimes of several microseconds in deoxygenated solutions; the emission intensity and lifetime are strongly decreased by the presence of oxygen, supporting the triplet origin of the emissive state. The present results display the utility of MIC ligands for generating electro- and photoactive molecules

Use of ring-expanded diamino- and diamidocarbene ligands in copper catalyzed azide-alkyne "click" reactions

The two-coordinate ring-expanded N-heterocyclic carbene copper­(I) complexes [Cu­(RE-NHC)₂]⁺ (RE-NHC = 6-Mes, 7-<i>o</i>-Tol, 7-Mes) have been prepared and shown to be effective catalysts under neat conditions for the 1,3-dipolar cycloaddition of alkynes and azides. In contrast, the cationic diamidocarbene analogue [Cu­(6-MesDAC)₂]⁺ and the neutral species [(6-MesDAC)­CuCl]₂ and [(6-MesDAC)₂(CuCl)₃] show good activity when the catalysis is performed on water

Homoleptic U(iii) and U(iv) amidate complexes.

The syntheses of the first homoleptic U(iii) and U(iv) amidate complexes are described. These can be interconverted by chemical reduction/oxidation, showing an unusual change in coordination number from four in the U(iii) complex to eight in the U(iv) complex in the solid state structures

Homoleptic U(iii) and U(iv) amidate complexes.

The syntheses of the first homoleptic U(iii) and U(iv) amidate complexes are described. These can be interconverted by chemical reduction/oxidation, showing an unusual change in coordination number from four in the U(iii) complex to eight in the U(iv) complex in the solid state structures

Infection of DR4 mice with wt MHV-68 primes T cells for enhanced interferon-γ production.

<p>Mice were infected at an age of 10–13 weeks. Splenocytes from uninfected and infected DR4 mice were isolated 8–11.75 months after infection, re-stimulated with PMA/ionomycin (stim) or left unstimulated (unstim), and were subsequently analyzed by multicolor FACS analysis for intracellular IFN-γ production. A) Representative Dot Plots of one mouse per group are shown. B) Summary of three mice per group. Each symbol represents an individual mouse, and the bars represent the mean. n.i.: not-infected (n = 3); wt: infected with wt MHV-68 (n = 3); Δ73: infected with latency-deficient MHV-68, carrying a deletion in ORF73 (n = 3).</p

Infection of DR4 mice with wt MHV-68 prevents tumor development but does not improve overall survival.

<p>A) Frequency of tumors. B) Overall survival. Mice were infected at an age of 10–13 weeks and monitored up to an age of 15 months. n.i.: not-infected; wt: infected with wt MHV-68; Δ73: infected with latency-deficient MHV-68, carrying a deletion in ORF73; nto: no tumors observed; numbers in brackets (n): number of mice analysed.</p

The Ligand Field of the Azido Ligand: Insights into Bonding Parameters and Magnetic Anisotropy in a Co(II)–Azido Complex

The azido ligand is one of the most investigated ligands in magnetochemistry. Despite its importance, not much is known about the ligand field of the azido ligand and its influence on magnetic anisotropy. Here we present the electronic structure of a novel five-coordinate Co(II)–azido complex (1), which has been characterized experimentally (magnetically and by electronic d–d absorption spectroscopy) and theoretically (by means of multireference electronic structure methods). Static and dynamic magnetic data on 1 have been collected, and the latter demonstrate slow relaxation of the magnetization in an applied external magnetic field of H = 3000 Oe. The zero-field splitting parameters deduced from static susceptibility and magnetizations (D = −10.7 cm–1, E/D = 0.22) are in excellent agreement with the value of D inferred from an Arrhenius plot of the magnetic relaxation time versus the temperature. Application of the so-called N-electron valence second-order perturbation theory (NEVPT2) resulted in excellent agreement between experimental and computed energies of low-lying d–d transitions. Calculations were performed on 1 and a related four-coordinate Co(II)–azido complex lacking a fifth axial ligand (2). On the basis of these results and contrary to previous suggestions, the N3– ligand is shown to behave as a strong σ and π donor. Magnetostructural correlations show a strong increase in the negative D with increasing Lewis basicity (shortening of the Co–N bond distances) of the axial ligand on the N3– site. The effect on the change in sign of D in going from four-coordinate Co(II) (positive D) to five-coordinate Co(II) (negative D) is discussed in the light of the bonding scheme derived from ligand field analysis of the ab initio results

Infection of DR4 mice with wt MHV-68 results in hypospleny.

<p>A) Photomicrographs showing examples of normal spleens, of a very tiny spleen and of tumor spleens. B) Quantitative analysis of hyposplenism. Mice were infected at an age of 10–13 weeks. The spleen sizes of all individual mice, independent of the time point of analysis, are summarized for each group. An analysis over time after infection is shown in panel C. Each symbol represents an individual mouse, and the means ± SD are shown. Spleens with tumors were excluded from this analysis. C) Analysis of hyposplenism over time after infection. Spleens with tumors were excluded from this analysis. Means + SD of the following numbers of mice are shown: 4–5,5 months after infection: n.i. (n = 2), wt (n = 4), Δ73 (n = 2); 6–7,5 months after infection: n.i. (n = 2), wt (n = 6), Δ73 (n = 3); 8–12 months after infection: n.i. (n = 2), wt (n = 9), Δ73 (n = 3). n.i.: not-infected; wt: infected with wt MHV-68; Δ73: infected with latency-deficient MHV-68, carrying a deletion in ORF73; wo tumor: without tumor; *: P = 0.032; **: P = 0.009.</p