Dieter Schaarschmidt

From {Bi22O26} to chiral ligand-protected {Bi38O45}-based bismuth oxido clusters.

The reaction of [Bi(22)O(26)(OSiMe(2)tBu)(14)] (1) in THF with salicylic acid gave [Bi(22)O(24)(HSal)(14)] (2) first, which was converted into [Bi(38)O(45)(HSal)(22)(OH)(2)(DMSO)(16.5)]·DMSO·H(2)O (3·DMSO·H(2)O) after dissolution and crystallization from DMSO. Single-crystal X-ray diffraction analysis and ESI mass spectrometry associated with infrared multi-photon dissociation (IRMPD) tandem MS experiments confirm the formation of the large and quite stable bismuth oxido cluster 3. The reaction of compound 2 with the butoxycarbonyl(BOC)-protected amino acids phenylalanine and valine (BOC-PheOH and BOC-ValOH), respectively, resulted in the formation of chiral [Bi(38)O(45)(BOC-AA)(22)(OH)(2)] (AA=deprotonated amino acid), as shown by a combination of different analytical techniques such as elemental analysis, dynamic light scattering, circular dichroism spectroscopy, and ESI mass spectrometry.

Gold nanoparticles generated by thermolysis of “all-in-one” gold(I) carboxylate complexes

Consecutive synthesis methodologies for the preparation of the gold(I) carboxylates [(Ph(3)P)AuO(2)CCH(2)(OCH(2)CH(2))(n)OCH(3)] (n = 0-6) (6a-g) are reported, whereby selective mono-alkylation of diols HO(CH(2)CH(2)O)(n)H (n = 0-6), Williamson ether synthesis and metal carboxylate (Ag, Au) formation are the key steps. Single crystal X-ray diffraction studies of 6a (n = 0) and 6b (n = 1) were carried out showing that the P-Au-O unit is essentially linear. These compounds were applied in the formation of gold nanoparticles (NP) by a thermally induced decomposition process and hence the addition of any further stabilizing and reducing reagents, respectively, is not required. The ethylene glycol functionalities, providing multiple donating capabilities, are able to stabilise the encapsulated gold colloids. The dependency of concentration, generation time and ethylene glycol chain lengths on the NP size and size distribution is discussed. Characterisation of the gold colloids was performed by TEM, UV/Vis spectroscopy and electron diffraction studies revealing that Au NP are formed with a size of 3.3 (±0.6) to 6.5 (±0.9) nm in p-xylene with a sharp size distribution. Additionally, a decomposition mechanism determined by TG-MS coupling experiments of the gold(i) precursors is reported showing that 1(st) decarboxylation occurs followed by the cleavage of the Au-PPh(3) bond and finally release of ethylene glycol fragments to give Au-NP and the appropriate organics.

Elusive ethynyl azides: trapping by 1,3-dipolar cycloaddition and decomposition to cyanocarbenes

Although they decompose rapidly to produce cyanocarbenes, ethynyl azides were generated from (chloroethynyl)arenes and trapped for the first time by 1,3-dipolar cycloaddition at cyclooctyne.

Solvatochromism and acidochromism of azobenzene-functionalized poly(vinyl amines)

Nucleophilic substitution of fluoroaromatics with poly(vinyl amine) (PVAm) is a suitable method for producing various azobenzene-functionalized PVAms. The solubility of the fluoroaromatic reagents in water was mediated by complexation with 2,6-O-dimethyl-β-cyclodextrin (DMCD). The degree of functionalization has been determined using model compounds as reference system. The solvatochromic properties of the polymers and the model compounds have been studied and interpreted using the well-established linear solvation energy relationships (LSER) of Kamlet–Taft and Catalan. The most dominant effect on the solvatochromic behavior is caused by interactions with solvents of a different dipolarity/polarizability. Also the basicity of the solvents is assumed to play an important role in the solvatochromism of the azobenzene-functionalized PVAms which shows the influence of the polymer chains. Furthermore, the UV/vis absorption spectra show a bathochromic shift with increasing acid strength of the medium. The impact of the PVAm backbone on the color of the chromophore bonded is highlighted.

Well Known or New? Synthesis and Structure Assignment of Binary C2N14 Compounds Reinvestigated

Isocyanogen tetraazide (6) was first prepared from the corresponding tetrabromide 5 in 1961 (Scheme 2). At that time, 6 was the most nitrogen-rich organic compound known. Later, 6 was also synthesized by using the multiple-step sequence 7!6. The unique product 6 was characterized by elemental analysis, a melting point of 89 8C, and more recently by a melting point of 76–77 8C as well as by HRMS, EIMS, and IR spectroscopic data. Up to now, however, structural proof by C NMR, N NMR, and N NMR spectra and by single-crystal X-ray diffraction has been lacking. In contrast to this, the isomeric compound 9 was characterized by Klapçtke et al. so thoroughly that there is no doubt of the monocyclic tetrazole structure. The C2N14 compound 9, which shows a melting point of 78 8C, was prepared from salt 8 by nitrosation followed by “dimerization” and ring closure. Surprisingly, the heterocycle 9 seems to be more susceptible toward shock and friction than the tetraazide 6. In general, aromatic tetrazoles are less sensitive than covalent azides. It is even more remarkable that 6 does not spontaneously cyclize to yield 9. Whereas imidoyl azides such as (Z)-10 are well known to undergo slow ring closure only at higher temperatures owing to their unfavorable stereochemistry, the diastereomeric azines (E)10, which have a cis orientation of the imino lone pair and the azido group, were postulated to form the tetrazoles 11 very rapidly (Scheme 3). Consequently, immediate cyclization of tetraazido-2,3-diazabuta-1,3-diene (6) could be expected and this should actually exclude the isolation of this openchain compound at room temperature.

Highly Strained 2,3-Bridged 2H-Azirines at the Borderline of Closed-Shell Molecules†

Substituted 1-azidocyclopentenes and 1-azidocyclohexenes were photolyzed to generate 2,3-bridged 2H-azirines. In the case of bridgehead azirines with a six-membered carbocycle, detection by NMR spectroscopic analysis was possible, whereas even kinetically stabilized bridgehead azirines with a five-membered ring could not be characterized by low-temperature NMR spectroscopic analysis. Thus, a recent report on the latter heterocycles was corrected. Depending on the substitution pattern, irradiation of 1-azidocyclopentenes either led to products that can be explained on the basis of short-lived 2,3-bridged 2H-azirines, or gave secondary products generated from triplet nitrenes. The diverse photoreactivity of 2,3-bridged 2H-azirines was also studied by quantum chemical methods (DFT, CCSD(T), CASSCF(6,6)) with respect to the singlet and triplet energy surfaces. The ring-opening processes leading to the corresponding vinyl nitrenes were identified as key steps for the observed reactivity.

Synthesis and Catalysis of Redox-active Bis(imino)acenaphthene (BIAN) Iron Complexes

Reactions of various substituted bis(imino)acenaphthenes (R‐BIANs) with FeCl2(thf)1.5 afforded the tetrahedral complexes (R‐BIAN)FeCl2 (2) from bulky α‐diimines and the octahedral complexes [Fe(R‐BIAN)3][FeCl4]2 (3) from less bulky ligands. The driving force for the formation of complexes 3 is the high ligand‐field stabilization of the low‐spin FeII center. The two sets of complexes exhibit distinct charge‐transfer band intensities and redox activities. (R‐BIAN)FeCl2 complexes showed reversible ligand‐centered reductions at −0.9 V (vs. FcH/FcH+; FcH: ferrocene); further reduction led to decomposition. Irreversible oxidations were observed at 0.2 and 0.4 V, associated with a reduction at −0.4 V, as well as a ligand‐centered redox event at 1.0 V. First applications of the Fe(BIAN) complexes to hydrogenations of alkenes indicated good catalytic activity under mild conditions.

1,4-Dihydro­benzo[g]quinoxaline-2,3-dione

The title compound, C12H8N2O2, was prepared by the reaction of the diethyl ester of naphthalenebis(oxamate) with tert-BuNH2. The molecule is nearly planar, with an r.m.s. deviation of 0.017 Å from the plane through all 16 non-H atoms. In the crystal, a three-dimensional network is formed, composed of layers of molecules along the b- and c-axis directions, due to the formation of intermolecular N—H⋯O hydrogen bonds, as well as of chains along the a-axis direction due to parallel displaced sandwich-type π–π interactions with average distances between the interacting molecules in the range 3.35–3.40 Å.

Crystal structure of cyclo-bis­(μ4-2,2-di­allyl­malonato-κ6O1,O3:O3:O1′,O3′:O1′)tetra­kis­(triphenyl­phosphane-κP)tetra­silver(I)

In the title compound, the silver(I) ions are coordinated by four triphenylphosphane ligands and two 2,2-diallylmalonate anions in a μ4-(κ6 O 1,O 3:O 3:O 1′,O 3′:O 1′) mode, setting up an Ag4O8P4 core.

Cationic tri(ferrocenecarbonitrile)silver(I)

Abstract The synthesis of the tri-coordinated ferrocenecarbonitrile silver(I) complex [Ag(N≡CFc)3]OTf (3) is reported. Its electrochemical behavior shows that the three ferrocenyl units are oxidized in a very close potential range. In addition, the molecular structure of 3 in the solid state is discussed, showing that silver(I) is exclusively coordinated by three ferrocenecarbonitrile molecules.