Synthesis and electrochemical behaviour of the cyanamide-isocyanide complexes of rhenium, trans-[ReL(CNR)(Ph2PCH2CH2PPh2)2] ( L = NCNH2 or NCNH)

Reaction of trans-[ReCl(CNR)(dppe)₂] (R = Me (Ia) or ^tBu (Ib); DPPE = Ph₂PCH₂CH₂PPh₂) in CH₂Cl₂ with cynamide in the presence of TlBF₄ forms the new cynamide-isocyanide complexes trans-[Re(CNR)(NCNH₂)(dppe)₂][BF₄] (R = Me (IIa) or ^tBu (IIb)), which upon treatment by ^tBuOK or Et₃N give trans-[Re(NCNH)(CNR)(dppe)₂] (R = Me (IIIa) or ^tBu (IIIb)). The electrochemical behaviour of these species was studied by cyclic voltammetry and controlled potential electrolysis at a Pt electrode in an aprotic solvent, and cathodic reduction of II results in the formation of III.     

The direct catalytic asymmetric alpha-aminooxylation reaction: development of stereoselective routes to 1,2-diols and 1,2-amino alcohols and density functional calculations

Proline-catalyzed direct asymmetric alpha-aminooxylation of ketones and aldehydes is described. The proline-catalyzed reactions between unmodified ketones or aldehydes and nitrosobenzene proceeded with excellent diastereo- and enantioselectivities. In all cases tested, the corresponding products were isolated with >95 % ees. Methyl alkyl ketones were regiospecifically oxidized at the methylene carbon atom to afford enantiomerically pure alpha-aminooxylated ketones. In addition, cyclic ketones could be alpha,alpha'-dioxidized with remarkably high selectivity, furnishing the corresponding diaminooxylated ketones with >99 % ees. The reaction mechanism of the proline-catalyzed direct asymmetric alpha-aminooxylation was investigated, and we performed density functional theory (DFT) calculations in order to investigate the nature of the plausible transition states further. We also screened other organocatalysts for the asymmetric alpha-oxidation reaction and found that several proline derivatives were also able to catalyze the transformation with excellent enantioselectivities. Moreover, stereoselective routes for the synthesis of monoprotected vicinal diols and hydroxyketones were found. In addition, short routes for the direct preparation of enantiomerically pure epoxides and 1,2-amino alcohols are presented. The direct catalytic alpha-oxidation is also a novel route for the stereoselective preparation of beta-adrenoreceptor antagonists.     

Mechanochemical reactions of telluric acid with alkaline fluorides

The mechanochemical reactions of telluric acid, Te(OH)₆ with alkaline fluorides (Na and K) have been studied using IR and XRD techniques. The reactions lead to the formation of hydrogen-bonding complexes, NaF.Te(OH)₆ and 2KF.Te(OH)₆. The reactions are free from side products such as alkali tellurates, alkali fluorotellurates or HF₂⁻ salts.     

New Copper(II) Complexes Containing 2-Furoic Hydrazide and 5-Nitro-2-Furoic Hydrazide Ligands: Synthesis,Thermal, Magnetic and Spectroscopic Characterization

Two new copper(II) complexes, [Cu₂(L¹)₄(H₂O)₂](SO₄)₄· 2H₂O and [Cu(L²)₂(H₂O)₂]SO₄, were isolated containing 2-furoic hydrazide and 5-nitro-2-furoic hydrazide ligands, respectively. The complexes were characterized by thermal, magnetic and spectroscopic techniques, showing a distorted tetragonal environment around the metal ion. Compound (1), containing 2-furoic hydrazide as the ligand, appears to be dimeric in the solid state, with substituted hydrazine acting as a bidentate bridging ligand. On the contrary, a monomeric species was observed with the 5-nitro-2-furoic hydrazide ligand, probably in the cis configuration, for compound (2). Magnetic measurements for the binuclear copper(II) complex (1) were carried out at low temperatures, in the 2–300 K range, and a magnetic field of 500 G, indicating that besides an intramolecular ferromagnetic interaction between the two Cu(II) centers, for which J/k = 1.07 K, further weak antiferromagnetic interactions between adjacent dimers, with Jz/k =–0.95 K, should be taken into account. However, in MeOH/H₂O solution, evidence of equilibria involving the dimer (1) and the corresponding mononuclear cis and trans species was obtained from e.p.r. spectra.     

Protic conversion of nitrile into azavinylidene complexes of rhenium, a mechanistic theoretical study

The mechanism of the protonation of the rhenium nitrile chloro-complexes [ReCl(NCCH3)(PH3)4] (2), taken as models of the real systems [ReCl(NCR)(dppe)(2)] (dppe = Ph2PCH2CH2PPh2), leading to the azavinylidene products [ReCl(NC(H)CH3)(PH3)4]+ (3) was investigated by theoretical methods at the B3LYP level of theory. Electrostatic and molecular orbital arguments and thermodynamic, kinetic, and steric factors are analyzed and indicate that the chlorine atom is the most probable site of the initial proton attack, although the direct protonation of the nitrile carbon atom is also possible as a concurrent process. For the cis-isomer of 2, the initially formed chloro-protonated species cis-[Re(ClH)(NCCH3)(PH3)4]+ further converts to the azavinylidene cis-3 via either an acid-independent 1,4-proton shift or an acid-base catalyzed pathway involving a second protonation of the nitrile carbon atom to give cis-[Re(ClH)(NC(H)CH3)(PH3)4]2+ followed by elimination of the proton from the chlorine atom.     

1,2-Didehydro[10]annulenes: structures, aromaticity, and cyclizations

The conformational space of C(10)H(8) 1,2-didehydro[10]annulenes, along with their unimolecular conversion to isonaphthalenes (cyclic allenes), has been studied computationally using DFT (B3LYP), single-reference [CCSD(T)], and multireference (MCQDPT2) post-HF methods. The introduction of the linear alkynyl moiety releases enough angle strain to make a nearly planar "heart" aromatic form the preferred conformer by more than 6 kcal/mol [CCSD(T)] over a localized C(2) "twist" structure, as opposed to the closely related C(10)H(10) [10]annulene system. Computations also show that electrocyclic ring-opening of isonaphthalenes to the heart C(10)H(8) annulene takes place through a low barrier of 15 kcal/mol, and this should be considered the working mechanism for the reported isomerizations during dehydro Diels-Alder reactions of phenylacetylenes.     

Study on the reactions of the dinitrogen complexestrans-[M(N2)2(Ph 2PCH2CH2PPh 2)2] (M=Mo or W) with ethyldiazoacetate: Formation of an Azo compound and of a phosphazene species

Complextrans-[Mo(N₂)₂(dppe)₂] (dppe=Ph ₂PCH₂CH₂PPh ₂) reacts with NN=CHCOOEt in benzene solution to afford benzene-azomethane,Ph-N=N-CH₃, as the main organic product. However, the phosphazene speciesPh ₂P(N₂CHCOOEt)(CH₂CH₂)P(N₂CHCOOEt)Ph ₂ is formed by irradiating aTHF solution oftrans-[W(N₂)₂(dppe)₂] in the presence of ethyldiazoacetate; in moist solution, the phosphazene bonds undergo a partial hydrolysis, and the phosphonium species [Ph ₂P(NHNCHCOOEt)(CH₂CH₂)P(NHNCHCOOEt)Ph ₂]²⁺ appears to be formed.

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Untersuchungen zu den Reaktionen der Distickstoff-Komplexetrans-[M(N₂)₂(Ph ₂PCH₂CH₂PPh ₂)₂] (M=Mo oder W) mit Ethyldiazoacetat: Die Bildung einer Azoverbindung und eines Phosphazens

Zusammenfassung Die Komplexetrans-[Mo(N₂)₂(dppe)₂] (dppe=Ph ₂PCH₂CH₂PPh ₂) reagieren mit NN=CHCOOEt in benzolischer Lösung zuPh-N=N-CH₃ als organischem Hauptprodukt. Andererseits wird bei der Bestrahlung vontrans-[W(N₂)₂(dppe)₂] inTHF-Lösung in der Gegenwart von Ethyldiazoacetat das PhosphazenPh ₂P(N₂CHCOOEt)(CH₂CH₂)P(N₂CHCOOEt)Ph ₂ gebildet; in feuchter Lösung erleidet die Phosphazen-Bindung eine teilweise Hydrolyse und die Phosphonium-Spezies [Ph ₂P(NHNCHCOOEt)(CH₂CH₂)P(NHNCHCOOEt)Ph ₂]²⁺ scheint gebildet zu werden.

     

Mechanochemical reactions of fluorides with hemin

Hemin has two potential sites to react with fluorides, the peripheral acid groups and the central Fe^III cation. The mechanochemical reactions of hemin with fluorides (LiF, NaF, KF, CsF, NH₄F and AgF) were monitored using X-ray diffraction (XRD), and IR and Mössbauer spectroscopies. LiF and NaF were found inert when milled with hemin, however KF, CsF, NH₄F and AgF react at both hemin sites. At the iron site Cl⁻ is replaced by F⁻ with formation of KCl, CsCl, NH₄Cl, and AgCl, as detected by XRD, while with the peripheral acid groups, fluorides collect the acidic protons to form KHF₂, CsHF₂, NH₄HF and AgHF₂. The reactions of hemin with the reactive fluorides take place first at the iron site and then at the propionic acid groups.     

Diazadiene-isonitrile complexes of molybdenum(II) and molybdenum(III)

Summary [MoCl₃(THF)₃] reacts with CNMe and diazadienes or a diamines, NN (RN=CHCH=NR, RN=CMeCMe=NR where R = 4-C6₆H₄OMe, and Me₂NCH₂CH₂NMe₂) to give molybdenum(III) complexes [MoCl₃(CNMe) NN] and molybdenum(II) complexes [MoCl₂(CNMe)₂NN]. The i.r. and magnetic data of these complexes are interpreted on the basis of the electronic properties of the ligands.     

Semicarbazones and thiosemicarbazones,XIII: Study of the hydrolysis of coordinated thiosemicarbazones

Summary The hydrolysis of coordinated thiosemicarbazones was studied. It was found that the nickel(II) ion promotes the reaction. Steric and electronic influences were found. The hydrolysis ofATSC in the trigonal bipyramid compounds [M(ATSC)₂Cl]Cl [M=Fe(II), Co(II), Ni(II)], is higher with the Ni(II) complex, the compound with the shorterM-N distance.

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Semicarbazone und Thiosemicarbazone, 13. Mitt.: Untersuchungen zur Hydrolyse koordinierter Thiosemicarbazone

Zusammenfassung Bei der Hydrolyse von koordinierten Thiosemicarbazonen wurde festgestellet, daß das Nickel(II)-Ion die Reaktion begünstigt. Es wurden sterische und elektronische Einflüsse gefunden. Die Hydrolysengeschwindigkeit desATSC im trigonal bipyramidalen Komplex [M(ATSC)₂Cl]Cl [M=Fe(II), Co(II), Ni(II)] ist höher mit dem Ni(II)-Komplex, der Verbindung mit der kürzerenM-N-Distanz.