Phosphaniminato‐Komplexe von Rhenium(VII). Synthesen und Kristallstrukturen von [ReO3(NPR3)] (R = Ph,Et) sowie von [ReO(OSiMe3)3(Me3SiNPEt3)]

Phosphoraneiminato Complexes of Rhenium(VII). Syntheses and Crystal Structures of [ReO₃(NPR₃)] (R = Ph, Et) and of [ReO(OSiMe₃)₃(Me₃SiNPEt₃)] The phosphoraneiminato complexes [ReO₃(NPR₃)] with R = Ph ( 1 ) and R = Et ( 2 ) are made from dirhenium heptaoxide and the silylated phosphoraneimines Me₃SiNPR₃. The complexes 1 and 2 as well as the red silanolate [ReO(OSiMe₃)₃(Me₃SiNPEt₃)] ( 3 ), which is formed as a by‐product in the synthesis of 2 , are characterized crystallographically. 1 and 2 are monomeric molecules, in which the phosphoraneiminato ligands NPR₃^– realize short ReN bonds of 179.3 pm ( 1 ) and 178.6 pm ( 2 ), respectively, with large ReNP bond angles of 162.0° ( 1 ) and 160.6° ( 2 ), respectively. In the rhenium(V) complex 3 the oxoligand occupies the apical position of the tetragonal pyramidal coordination of the rhenium atom, while the oxygen atoms of the Me₃SiO^– groups take the basic positions along with the nitrogen atom of the phosphaneimine molecule.     

Phosphoraneiminato Complexes of Manganese and Cobalt with Heterocubane Structure

The phosphoraneiminato complexes [MnBr(NPEt₃)]₄ ( 1 ) and [M₄Br₅{NP(NMe₂)₃}₃] with M = Mn ( 2 ) and M = Co ( 3 ) are prepared by melting reactions from the anhydrous metal dibromides with the silylated phosphaneimines Me₃SiNPR₃ (R = Et, NMe₂) in the presence of potassium fluoride. All complexes are characterized by crystal structure analyses. 1 forms an only slightly distorted Mn₄N₄ heterocubane skeleton with an approximate T_d symmetry and short Mn…Mn distances of average 295.7 pm. In the structures of 2 and 3 one μ₃-NPEt₃ ligand of 1 is replaced by one bromine atom with μ₃-function. This leads to the novel heterocubane type M₄N₃Br with approximate C₃ symmetry. The deformation of the cubic skeleton leads to metal-metal distances of different lengths, i. e. 292.7 and 323.6 pm in 2 and 274.4 and 306.2 pm in 3 . Temperature dependent magnetic susceptibility measurements between 300 and 5 K on 1 have shown that strong antiferromagnetic coupling exists between the Mn(II) ions with S = 5/2, with a large negative Weiss constant of Θ = –694 K.     

Die Deprotonierung silylierter Amido-Komplexe von Seltenerdelementen

Deprotonation Reactions of Silylated Amido Complexes of Rare Earth Elements The deprotonation of the rare earth element-tris(bistrimethylsilyl)amides Ln[N(SiMe₃)₂]₃ of scandium, ytterbium, and lutetium with sodium-bis(trimethylsilyl)amide in THF leads to the complexes [Na(THF)₃LnCH₂SiMe₂NSiMe₃{N(SiMe₃)₂}₂] [Ln = Sc ( 1 ), Yb ( 2 ), and Lu ( 3 )]. According to crystal structure analyses of 1 and 2 the metal atoms Sc and Yb are constituents of planar LnCSiN four-membered rings. At the same time, the C atom of the CH₂ group is coordinated with the sodium ion in a linear axis Ln–C–Na; the sodium ion obtains a distorted tetrahedral arrangement by three THF molecules. The equatorial positions of the methylene-C atom, which is coordinated in a trigonal bipyramidal fashion, are occupied by the two H atoms and the Si atom of the four-membered ring. 2.6-dimethylbenzoisonitrile can be inserted into the Yb–CH₂ bond of 2 and the new five-membered heterocylce YbNCSiN originates, the exocyclic CH₂ group of which enters into a C–C coupling with the centrosymmetric dimer 4 while the ytterbium undergoes reduction. At the same time, sodium-7-methyl indolate is formed, which together with [NaN(SiMe₃)₂(THF)₂] forms the centrosymmetric dimeric molecular aggregate [NaN(SiMe₃)₂(THF)₂Na(C₉H₁₆N)]₂ ( 5 ). 1 : Space group P2₁/n, Z = 8, lattice dimensions at –80 °C: a = 2941.4(2), b = 1205.5(1), c = 2952.4(3) pm; β = 113.455(8)°; R₁ = 0.0625. 2 : Space group P2₁/n, Z = 8, lattice dimensions at –80 °C: a = 2943.9(1), b = 1219.5(1), c = 2944.3(1) pm; β = 113.372(4)°; R₁ = 0.0361. 4 : Space group P 1, Z = 4, lattice dimensions at –80 °C: a = 1117.0(1), b = 1207.5(1), c = 1614.3(2) pm; α = 73.634(10)°, β = 82.091(10)°, γ = 74.391(10)°; R₁ = 0.0525. 5 : Space group P2₁/n, Z = 2, lattice dimensions at –80 °C: a = 1126.7(1), b = 1459.3(1), c = 1741.1(1) pm; β = 96.461(8)°; R₁ = 0.0458. Quantum chemical DFT calculations of the scandium model compound [Na(Me₂O)₃ScCH₂SiMe₂NSiH₃{N(SiH₃)₂}₂] ( 1 M ) give a very large negative charge at the pentacoordinated carbon atom of the four-membered ring that is concentrated in a lone-pair orbital which has mainly p character. The carbon atom interacts with the positively charged scandium atom mainly by Coulombic interactions.     

A Five-Membered Ring with Three Negative Charges and Solvent-Free Lithium Counterions

Remarkably short distances to the ring plane are shown by the η⁵-bound lithium ions in the first compound with a triply negatively charged five-membered ring, 1 , which was obtained by reduction of 2 with lithium. R=CH(SiMe₃)₂, Dur=2,3,5,6-tetramethylphenyl.     

Molybdenum Complexes Supported by Mixed NHC/Phosphine Ligands: Activation of N2 and Reaction With P(OMe)3 to the First Meta‐Phosphite Complex

Molybdenum(0) dinitrogen complexes, supported by the mixed NHC/phosphine pincer ligand PCP, exhibit an extreme activation of the N₂ ligand due to a very π‐electron‐rich metal center. The low thermal stability of these compounds can be increased using phosphites instead of phosphines as coligands. Through an amalgam reduction of [MoCl₃(PCP)] in the presence of trimethyl phosphite and N₂ the highly activated and room‐temperature stable dinitrogen complex [Mo(N₂)(PCP)(P(OMe)₃)₂] is obtained. As a second product, the first transition metal complex containing the meta‐phosphite ligand P(O)(OMe) originates from this reaction.     

Octahedral Chiral‐at‐Metal Iridium Catalysts: Versatile Chiral Lewis Acids for Asymmetric Conjugate Additions

Octahedral iridium(III) complexes containing two bidentate cyclometalating 5‐tert‐butyl‐2‐phenylbenzoxazole ( IrO ) or 5‐tert‐butyl‐2‐phenylbenzothiazole ( IrS ) ligands in addition to two labile acetonitrile ligands are demonstrated to constitute a highly versatile class of asymmetric Lewis acid catalysts. These complexes feature the metal center as the exclusive source of chirality and serve as effective asymmetric catalysts (0.5–5.0 mol % catalyst loading) for a variety of reactions with α,β‐unsaturated carbonyl compounds, namely Friedel–Crafts alkylations (94–99 % ee), Michael additions with CH‐acidic compounds (81–97 % ee), and a variety of cycloadditions (92–99 % ee with high d.r.). Mechanistic investigations and crystal structures of an iridium‐coordinated substrates and iridium‐coordinated products are consistent with a mechanistic picture in which the α,β‐unsaturated carbonyl compounds are activated by two‐point binding (bidentate coordination) to the chiral Lewis acid.     

A Rhodium Catalyst Superior to Iridium Congeners for Enantioselective Radical Amination Activated by Visible Light

A bis‐cyclometalated rhodium(III) complex catalyzes a visible‐light‐activated enantioselective α‐amination of 2‐acyl imidazoles with up to 99 % yield and 98 % ee. The rhodium catalyst is ascribed a dual function as a chiral Lewis acid and, simultaneously, as a light‐activated smart initiator of a radical‐chain process through intermediate aminyl radicals. Notably, related iridium‐based photoredox catalysts reported before were unsuccessful in this enantioselective radical C?N bond formation. The surprising preference for rhodium over iridium is attributed to much faster ligand‐exchange kinetics of the rhodium complexes involved in the catalytic cycle, which is crucial to keep pace with the highly reactive and thus short‐lived nitrogen‐centered radical intermediate.     

Evaluation of recombinant invasive, non-pathogenic Eschericia coli as a vaccine vector against the intracellular pathogen, Brucella

Background  

There is no safe, effective human vaccine against brucellosis. Live attenuated Brucella strains are widely used to vaccinate animals. However these live Brucella vaccines can cause disease and are unsafe for humans. Killed Brucella or subunit vaccines are not effective in eliciting long term protection. In this study, we evaluate an approach using a live, non-pathogenic bacteria (E. coli) genetically engineered to mimic the brucellae pathway of infection and present antigens for an appropriate cytolitic T cell response.     

Re-investigation of ortho-metalated N,N-dialkylbenzylamine complexes of rare-earth metals. First structurally characterized arylates of neodymium and gadolinium Li[LnAr4]

The influence of the ether ligand in [LnCl₃(solv)_n], solv = THF, DME; n = 1–3 in reactions with ortho-lithiated dimethyl-benzylamine Li(dmba) has been studied. An improved protocol towards homoleptic tris-aryl complexes of the type [Ln(dmba)₃], Ln = Y, Er and Yb has been developed and molecular structures of these complexes have been established by X-ray crystallography. For the first time stable homoleptic lithium ate-complexes of the type Li[Ln(dmba)₄] (Ln = Gd, Nd) have been isolated and structurally characterized. The success in their synthesis strongly depends on the choice of the appropriate [LnCl₃(solv)_n] precursor, such as [GdCl₃(dme)₂], [NdCl₃(dme)], and THF-free reaction conditions. Factors influencing on possible degradation pathways of lanthanide tris-aryl complexes with dmba-type ligands are discussed.     

High performance liquid chromatography/electrospray ionization mass spectrometry for simultaneous analysis of alkamides and caffeic acid derivatives from Echinacea purpurea extracts

Extracts of the plant Echinacea purpurea are widely used for medicinal purposes. Effective quality control of these extracts requires rapid methods to determine their chemical composition. A new method for analysis of caffeic acid derivatives and alkamides from Echinacea extracts has been developed. With this method, isomeric isobutylamides and 2-methylbutylamides can be distinguished, a capability that previously published methods have lacked. Quantitative analyses carried out with this method on E. purpurea extracts that have been stored for 18 months indicate that they contain caftaric acid, cichoric acid, and undeca-2Z,4E-diene-8,10-diynoic acid isobutylamide at concentrations of 0.7, 0.71 and 2.0mg/mL, respectively.