Structural diversity and versatility for organoaluminum complexes supported by mono- and di-anionic aminophenolate bidentate ligands

The present contribution describes the synthesis and structural characterization of structurally diverse organoaluminum species supported by variously substituted aminophenolate-type ligands: these Al complexes are all derived from the reaction of AlMe₃ with aminophenols 2-CH₂NH(R)-C₆H₃OH (1a, R = mesityl (Mes); 1b, R = 2,6-di-isopropylphenyl (Diip)) and 2-CH₂NH(R)-4,6-^tBu₂-C₆H₂OH (1c, R = Mes; 1d, R = Diip). The low temperature reaction of AlMe₃ with 1a–b readily affords the corresponding Al dimeric species [μ-η¹,η¹-N,O-{2-CH₂NH(R)-C₆H₄O}]₂Al₂Me₄ (2a–b), consisting of twelve-membered ring aluminacycles with two μ-η¹,η¹-N,O-aminophenolate units, as determined by X-ray crystallographic studies. Heating a toluene solution of 2a (80 °C, 3 h) affords the quantitative and direct formation of the dinuclear aluminium complex Al[η²-N; μ,η²-O-{2-CH₂N(Mes)-C₆H₄O}](AlMe₂) (4a) while species 2b, under the aforementioned conditions, affords the formation of the Al dimeric species [η²-N,O-{2-CH₂N(Dipp)-C₆H₄O}AlMe]₂ (3b), as deduced from X-ray crystallography for both 3b and 4a. In contrast, the reaction of bulky aminophenol pro-ligands 1c–d with AlMe₃ afford the corresponding monomeric Al aminophenolate chelate complexes η²-N,O-{2-CH₂NH(R)-4,6-^tBu₂-C₆H₂O}AlMe₂ (5c–d; R = Mes, Diip; Scheme 3) as confirmed by X-ray crystallographic analysis in the case of 5d. Subsequent heating of species 5c–d yields, via a methane elimination route, the corresponding Al-THF amido species η²-N,O-{2-CH₂N(R)-4,6-^tBu₂-C₆H₂O}Al(Me)(THF) (6c–d; R = Mes, Diip). Compounds 6c–6d, which are of the type {X₂}Al(R)(L) (L labile), may well be useful as novel well-defined Lewis acid species of potential use for various chemical transformations. Overall, the sterics of the aminophenol backbone and, to a lesser extent, the reaction conditions that are used for a given ligand/AlMe₃ set essentially govern the rather diverse “structural” outcome in these reactions, with a preference toward the formation of mononuclear Al species (i.e. species 5c–d and 6c–d) as the steric demand of the chelating N,O-ligand increases.     

Hexacyanometalate molecular chemistry: di-, tri-, tetra-, hexa- and heptanuclear heterobimetallic complexes; control of nuclearity and structural anisotropy

Following a bottom-up approach to nanomaterials, we present a rational synthetic route to high-spin and anisotropic molecules based on hexacyanometalate [M(CN)(6)](3-) cores. Part 1 of this series was devoted to isotropic heptanuclear clusters; herein, we discuss the nuclearity and the structural anisotropy of nickel(II) derivatives. By changing either the stoichiometry, the nature of the terminal ligand, or the counterion, it is possible to tune the nuclearity of the polynuclear compounds and therefore to control the structural anisotropy. We present the synthesis and the characterisation by mass spectrometry, X-ray crystallography and magnetic susceptibility of bi-, tri-, tetra-, hexa- and heptanuclear species [M(CN)(n)(CN-M'L)(6-n)](m+) (with n=0-5; M=Cr(III), Co(III), M'=Ni(II); L=pentadentate ligand). Thus, with M=Cr(III), d(3), S=3/2, a dinuclear complex [Cr(III)(CN)(5)(CN-NiL(n))](9+), (L(n)=polydentate ligand) was built and characterised, showing a spin ground state, S(G)=5/2, with a ferromagnetic interaction J(Cr,Cu)=+18.5 cm(-1). With M=Co(III) (d(6), S=0) were built di-, tri-, tetra-, hexa and hepanuclear CoNi species: CoNi, CoNi(2), CoNi(3), CoNi(5) and CoNi(6). By a first approximation, they behave as one, two, three, five and six isolated nickel(II) complexes, respectively, but more accurate studies allow us to evaluate the weak antiferromagnetic coupling constant between two next-nearest neighbours M'-Co-M'.     

Zaubervorlesung mit Salvador Dalí. Chemie‐Edutainment

During the past 10 years the “Magic chemistry” lecture was conducted in Erlangen. Due to an increasing professionalization of the lecture and especially the underlying information concept, we could emphasize the seriousness of this event. We combine scientific education and entertainment to an “edutainment” concept. We hope to show in an exemplary way, how fun and experimental natural sciences can be combined in a big live event.     

Metabolism of synthetic cannabinoids PB-22 and its 5-fluoro analog, 5F-PB-22, by human hepatocyte incubation and high-resolution mass spectrometry

Background

PB-22 (1-pentyl-8-quinolinyl ester-1H-indole-3-carboxylic acid) and 5F-PB-22 (1-(5-fluoropentyl)-8-quinolinyl ester-1H-indole-3-carboxylic acid) are new synthetic cannabinoids with a quinoline substructure and the first marketed substances with an ester bond linkage. No human metabolism data are currently available, making it difficult to document PB-22 and 5F-PB-22 intake from urine analysis, and complicating assessment of the drugs’ pharmacodynamic and toxicological properties.

Methods

We incubated 10 μmol/l PB-22 and 5F-PB-22 with pooled cryopreserved human hepatocytes up to 3 h and analyzed samples on a TripleTOF 5600+ high-resolution mass spectrometer. Data were acquired via TOF scan, followed by information-dependent acquisition triggered product ion scans with mass defect filtering (MDF). The accurate mass full scan MS and MS/MS metabolite datasets were analyzed with multiple data processing techniques, including MDF, neutral loss and product ion filtering.

Results

The predominant metabolic pathway for PB-22 and 5F-PB-22 was ester hydrolysis yielding a wide variety of (5-fluoro)pentylindole-3-carboxylic acid metabolites. Twenty metabolites for PB-22 and 22 metabolites for 5F-PB-22 were identified, with the majority generated by oxidation with or without glucuronidation. For 5F-PB-22, oxidative defluorination occurred forming PB-22 metabolites. Both compounds underwent epoxide formation followed by internal hydrolysis and also produced a cysteine conjugate.

Conclusion

Human hepatic metabolic profiles were generated for PB-22 and 5F-PB-22. Pentylindole-3-carboxylic acid, hydroxypentyl-PB-22 and PB-22 pentanoic acid for PB-22, and 5′-fluoropentylindole-3-carboxylic acid, PB-22 pentanoic acid and the hydroxy-5F-PB-22 metabolite with oxidation at the quinoline system for 5F-PB-22 are likely the best targets to incorporate into analytical methods for urine to document PB-22 and 5F-PB-22 intake.

Influence of chlorine substitution on the self-assembly of zinc phthalocyanine

The adsorption and ordering of zinc phthalocyanine (ZnPc) and octachloro zinc phthalocyanine (ZnPcCl(8)) on an Ag(111) surface is studied in situ by scanning tunneling microscopy under ultrahigh vacuum. Two-dimensional self-assembled supramolecular domains are observed for these two molecules. We show how substituting chlorine atoms for half of the peripheral hydrogen atoms on ZnPc influences the self-assembly mechanisms. While intermolecular interactions are dominated by van der Waals forces in ZnPc molecular networks, ZnPcCl(8) molecular packing undergoes a sequential phase evolution driven by the creation of C-Cl...H-C hydrogen bonds between adjacent molecules. At the end of this evolution, the final molecular assembly involves all possible hydrogen bonds. Our study also reveals the influence of molecule-substrate interactions through the presence of fault lines generating a stripe structure in the molecular film.     

MALDI-TOF-MS Directly Combined with TLC: A Review of the Current State

Thin-layer chromatography (TLC) is a widely used, fast and inexpensive method for separating complex mixtures. Unfortunately, the quality of achievable separation represents only one side. An additional problem is the unambiguous assignment of the obtained spots to defined compounds. Clear identification of spots is often not possible by common staining methods and comparison with a known reference compound. Therefore, further analytical techniques are mostly required for further structural elucidation. Mass spectrometry (MS) is a suitable method due to its high sensitivity. In particular, matrix-assisted laser desorption and ionization time-of-flight (MALDI-TOF) MS is a modern soft-ionization technique that may be easily combined with TLC. This review summarizes the so far available knowledge about direct TLC–MALDI combination and gives an overview about different molecule classes that have already been successfully analyzed by this approach. This review critically summarizes the capabilities and limitations of the direct MALDI–TLC combination and highlights in particular the problems related to sample preparation and instrumentation.

     

Halogenation of Lewis acid/base stabilised phosphanylboranes

The reaction pattern of the Lewis-acid/base stabilised phosphanylborane [(CO)₅W(H₂PBH₂ · NMe₃)] (1) with elemental halogens is comprehensively studied. The reaction with iodine and bromine leads to a selective halogenation at the tungstencarbonyl moiety under formation of [WX₂(CO)₄(H₂PBH₂ · NMe₃)] (X = I (2), Br (3)). Whereas 2 is a stable product the brominated compound 3 dimerises easily to [WBr₂(CO)₃(H₂PBH₂ · NMe₃)]₂ (4) under lost of CO. The CO elimination reaction of 3 is extensively studied. If 3 is reacted with [Et₄N][Br] the ionic compound [Et₄N][WBr₃(CO)₃(H₂PBH₂ · NMe₃)] (5) is formed. Otherwise, if 3 is combined with the donor ligand [H₂PBH₂ · NMe₃], the complex [WBr₂(CO)₃(H₂PBH₂ · NMe₃)₂] (6) is obtained. Compounds 2–6 are comprehensively characterised by X-ray diffraction analysis, NMR, and IR spectroscopy.     

Sol gel synthesis of 3-n-propyl(4-aminomethyl)pyridinium silsesquioxane chloride and the enhanced electrocatalytic activity of LbL films

Journal of Sol-Gel Science and Technology - A silsesquioxane based on a silica matrix and 4-(aminomethyl)pyridine group was successfully synthesized using the sol–gel process with the...