Electrospray ionization mass spectrometric studies of nucleophilic carbenes derived from pyrazolium and indazolium carboxylates

Pyrazolium-3-carboxylate and indazolium-3-carboxylate, which belong to the class of pseudo-cross-conjugated mesomeric betaines and which represent the electronically relevant partial structures of the betaine alkaloid Nigellicin, were examined by electrospray ionization mass spectrometry. These compounds decarboxylate to pyrazol-3-ylidene and indazol-3-ylidene. The formation of adducts of these new nucleophilic carbenes under the measurement conditions was examined.     

[(Mes3Sn)2MoO4], ein monomeres Triorganozinnmolybdat

[(Mes₃Sn)₂MoO₄], a Monomeric Triorganotin Molybdate Mes₃SnBr (Mes = 1, 3, 5‐trimethylphenyl) reacts with (NBu₄)₂[Mo₆O₁₉] in the presence of (NBu₄)OH (in CH₃CN as solvent) to form [(Mes₃Sn)₂MoO₄]. Alternatively the title compound can be obtained from the reaction of [MoO₂(acac)₂] (acac = 2, 4‐pentadionate) with Mes₃SnOH in isopropanol. [(Mes₃Sn)₂MoO₄] forms monoclinic crystals, space group C2/c, with a = 2271.6(3) pm, b = 825.2(1) pm, c = 2739.9(5) pm, β = 90.96(2)°. The crystal structure consists of isolated molecules in which a tetrahedral MoO₄ unit is connected to two terminal Mes₃Sn groups. The Mo‐O distances range from 169.6(4) to 181.1(3) pm and the Sn‐O distance is 204.8(3) pm.     

Using ultrafast infrared multidimensional correlation spectroscopy to aid in vibrational spectral peak assignments

Ultrafast infrared heterodyne detected vibrational stimulated echoes with full phase information are used to obtain the vibrational correlation spectrum from a mixture of metal-carbonyl compounds. The linear absorption spectrum displays four peaks in the carbonyl stretching region. In the absence of knowledge of the molecules that make up the mixture, the absorption spectrum could arise from four molecules that each produces a single peak to one molecule with four peaks. In contrast, the correlation spectrum displays four peaks on the diagonal and off-diagonal peaks that make it straightforward to determine which peaks belong to a particular molecule.     

X-ray magnetic circular dichroism of Pseudomonas aeruginosa nickel(II) azurin

We show that X-ray magnetic circular dichroism (XMCD) can be employed to probe the oxidation states and other electronic structural features of nickel active sites in proteins. As a calibration standard, we have measured XMCD and X-ray absorption (XAS) spectra for the nickel(II) derivative of Pseudomonas aeruginosa azurin (NiAz). Our analysis of these spectra confirms that the electronic ground state of NiAz is high-spin (S = 1); we also find that the L(3)-centroid energy is 853.1(1) eV, the branching ratio is 0.722(4), and the magnetic moment is 1.9(4) mu(B). Density functional theory (DFT) calculations on model NiAz structures establish that orbitals 3d(x2-y2) and 3d(z2) are the two valence holes in the high-spin Ni(II) ground state, and in accord with the experimentally determined orbital magnetic moment, the DFT results also demonstrate that both holes are highly delocalized, with 3d(x2-y2) having much greater ligand character.     

Neue neutrale und kationische Mono‐Aziridin‐Komplexe des Typs [CpMn(CO)2Az], [CpCr(NO)2Az]+ und [(Ph3P)(CO)4ReAz]+ über CO‐, Hydrid‐ und Chlorid‐Abspaltungsreaktionen

Novel Neutral and Cationic Mono‐Aziridine Complexes of the Type [CpMn(CO)₂Az], [CpCr(NO)₂Az]⁺, and [(Ph₃P)(CO)₄ReAz]⁺ via CO‐, Hydride‐, and Chloride‐Elimination Reactions The monoaziridine complexes 1 — 5 are obtained by three differently induced substitution reactions. The photolytically induced CO substitution reaction of [CpMn(CO)₃] with 2, 2‐dimethylaziridine leads to the neutral N‐coordinate aziridine complex [Cp(CO)₂Mn{$\overline{N(H)CMe₂C}$ H₂}] ( 1 ). The protonation of [(Ph₃P)(CO)₄ReH] with CF₃SO₃H and consecutive treatment with 2, 2‐dimethylaziridine or 2‐ethylaziridine gives the salt‐like aziridine complexes [(Ph₃P)(CO)₄Re{$\overline{N(H)CMe₂C}$ H₂}](CF₃SO₃) ( 2 ) or [(Ph₃P)(CO)₄Re{ H₂}](CF₃SO₃) ( 3 ) by hydride elimination reactions. The like‐wise salt‐like complexes [Cp(NO)₂Cr{$\overline{N(H)CMe₂C}$ H₂}](BF₄) ( 4 ) and [Cp(NO)₂Cr{ H₂}](CF₃SO₃) ( 5 ) are synthesized from [CpCr(NO)₂Cl] by chloride elimination with AgX (X = BF₄, CF₃SO₃) in the presence of 2, 2‐dimethylaziridine or 2‐ethylaziridine, respectively. As a result of X‐ray structure analyses, the metal atoms are trigonal pyramidally ( 1, 4, 5 ) or octahedrally ( 2, 3 , cis‐position) configurated; the intact three‐membered rings coordinate through the distorted tetrahedrally configurated N atoms. All compounds 1‐5 are stable with respect to the directed thermal alkene elimination to give the corresponding nitrene complexes; the IR, ¹H‐ and ¹³C{¹H}‐NMR, and MS spectra are reported and discussed.     

Thermisches Verhalten von Caesiumchloroferraten(III) und Caesiumchloroferrat(III)-Hydraten. II. Die Rehydratation der Zersetzungsprodukte von Cs3[FeCl6] – Eine ramanspektroskopische Untersuchung unter definierter Wasserdampfatmosphäre [1]

The Thermal Behaviour of Caesiumchloroferrates(III) and Caesiumehloroferrate(III) Hydrates. II. The Rehydration of Decomposition Products of Cs₃[FeCl₆] — A Raman Spectroscopic Study under Definite Atmosphere of Water Vapour Cs₃[FeCl₆] formed by dehydration of Cs₃[FeCl₆] · H₂O at about 160°C does not change at normal atmosphere within 3 till 4 hours. Rehydration under the vapour pressure of the eliminated water yields the monohydrate in nearly the same time. In the same manner rehydration of the solid mixture of Cs[FeCl₄] and 2 CsCl formed by thermal decomposition of the metastable Cs₃[FeCl₆] (280°C) produces the intermediates Cs₃[Fe₂Cl₉] and Cs₂[Fe(H₂O)Cl₅] in mixtures with CsCl and, finally, Cs₃[FeCl₆] · H₂O. The formation of Cs₃[Fe₂Cl₉] from Cs[FeCl₄] and CsCl is accelerated by water. The reaction cycle has been studied using Raman and IR spectroscopy. The results will be discussed with respect to thermoanalytical data.     

A general organocatalyst for direct alpha-functionalization of aldehydes: stereoselective C-C, C-N, C-F, C-Br, and C-S bond-forming reactions. Scope and mechanistic insights

The development of a general organocatalyst for the alpha-functionalization of aldehydes, via an enamine intermediate, is presented. Based on optically active alpha,alpha-diarylprolinol silyl ethers, the scope and applications of this catalyst for the stereogenic formation of C-C, C-N, C-F, C-Br, and C-S bonds are outlined. The reactions all proceed in good to high yields and with excellent enantioselectivities. Furthermore, we will present mechanistic insight into the reaction course applying nonlinear effect studies, kinetic resolution, and computational investigations leading to an understanding of the properties of the alpha,alpha-diarylprolinol silyl ether catalysts.     

Charge transfer in the Cl-CO cluster induced by core ionization

Ab initio calculations of core-ionization spectra of the anion-molecule Cl-CO cluster are performed. Particular attention is paid to the investigation of charge-transfer screening processes accompanying core ionization of the CO molecule in the cluster. The charge-transfer processes are very efficient and favored by the presence of a low-lying unoccupied pi* orbital in CO capable of accepting an electron from Cl-. The O1s(-1) and C1s(-1) core-ionization spectra are calculated and compared. Both reveal a breakdown of the quasiparticle picture of core ionization caused by the charge-transfer processes. Remarkable differences between these two spectra are found which manifest themselves in distinct intensity distributions in the prominent low-energy spectral bands. The underlying reason for these differences is elucidated and linked with the preference of the pi* orbital to localize mainly on carbon. Core-ionization spectra of anion-molecule clusters are very sensitive to the type of the molecule involved as the comparative analysis of the O1s(-1) core-ionization spectra of the Cl-CO and Cl-H(2)O clusters show.     

The Dynamic Behaviour and NMR Solution structures of complexes of the type (Bisphosphine)(cycloocta-1,5-diene)iridium(I) and the X-ray crystal structure of (cycloocta-1,5-diene)((−)-norphos)iridium(I) hexafluorophosphate

A square-planar coordination geometry was found for the complex [Ir(cod){(?)-norphos}][PF₆] ( 1b [PF₆]; cod = cylcoocta-1,5-diene and (?)-norphos = [(2R,3R)-8-9-10-trinorborn-5-ene-2,3-diyl]bis(diphenylphosphine)) in the solid state by X-ray diffraction. Crystal data: monoclinic, space group P2₁, a = 10.751 (6), b = 18.669(14), c = 12.037(8) Å, β = 114.82(5)°, Z = 2. A total structural assignment including the configurational and conformational aspects of this and the related compounds [Ir(bishosphine)(cod)]X (bisphosphine = (?)-chiraphos = (2S,3S)-2,3-bis(diphenylphosphino)butane and (?)-norphos, X = Cl, CF₃SO₃, or PF₆) was carried out in solution by one- and two-dimensional NMR spectroscopy. The complexes containing the CF₃SO₃^? and PF₆^? anions are four-coordinate cations with square-planar geometry, whereas the chlorides are five-coordinate neutral compounds showing solvent-dependent dynamic behaviour. In toluene, two diastereoisomers of [IrCl(cod){(?)-norphos}] ( 2b ) exist and interconvert slowly at room temperature. This interchange is fast in CDCl₃ solution, and it is likely to involve Cl dissociation and the formation of the cation [Ir(cod){(?)-norphos}]⁺ as an intermediate.     

Synthese und Charakterisierung funktionalisierter β‐Hydroxydithiozimtsäuren und deren Ester. Komplexchemisches Verhalten gegenüber Nickel(II), Palladium(II) und Platin(II)

Synthesis and Analytical Characterization of Functionalized β‐Hydroxydithiocinnamic Acids and their Esters. Complex Chemistry towards Nickel(II), Palladium(II), and Platin(II) Starting from silyl‐protected 4‐hydroxy acetophenone ( 1 ) the 1,1‐ethenedihiolato complexes 3 – 5 were synthesised using carbon disulfide and potassium‐tert‐butylate as a base. After being deprotected, the resulting 4‐hydroxy‐substituted complexes 6 – 8 were esterified with DL‐α‐lipoic acid to obtain the compounds 9 – 11 . The resulting complexes were characterized using NMR spectroscopy, mass spectrometry and IR spectroscopy. 3‐substituted β‐hydroxydithiocinnamic acid methyl ester ( 12 ) was obtained via an analogous path of reaction using silyl‐protected 3‐hydroxy acetophenone ( 2 ), carbon disulfide and methyl iodide. After removing of the silyl group the resulting hydroxy group was esterified with DL‐α‐lipoic acid. Using the dithioacid ester 14 as a ligand the Ni^II ( 15 ), Pd^II ( 16 ) and Pt^II ( 17 ) [O,S] complexes were obtained.