Enantioselective Addition-Alkylation of α,β-Unsaturated Carbonyls via Bisguanidinium Silicate Ion Pair Catalysis.

Silicon hydrides, alkynylsilanes, and alkoxylsilanes were activated by fluoride in the presence of bisguanidinium catalyst to form hypervalent silicate ion pairs. These activated silicates undergo 1,4-additions with chromones, coumarins, and α-cyanocinnamic esters generating enolsilicate intermediates, for a consequent stereoselective alkylation reaction. The reduction-alkylation reaction proceeded under mild conditions using polymethylhydrosiloxane, a cheap and environmentally friendly hydride source.

Halogen-Bonding-Induced Conjugate Addition of Thiophenes to Enones and Enals.

Herein, we report the conjugate addition of α,β-unsaturated carbonyl compounds to thiophene derivatives. We used a 2-iodoimidazolinium triflate salt as a halogen-bonding donor, which afforded moderate-to-excellent yields of the corresponding alkylated thiophenes. Insight into the catalytic process was obtained from H NMR spectroscopy studies and DFT calculations, which indicated a halogen-bonding-supported mechanism with limited Brønsted acid catalysis.

Direct air capture of CO- - topological analysis of the experimental electron density (QTAIM) of the highly insoluble carbonate salt of a 2,6-pyridine-bis(iminoguanidine), (PyBIGH)(CO)(HO).

Chemical bonding and all intermolecular interactions in the highly insoluble carbonate salt of a 2,6-pyridine-bis(iminoguanidine), (PyBIGH)(CO)(HO), recently employed in the direct air capture of CO via crystallization, have been analyzed within the framework of the quantum theory of atoms in molecules (QTAIM) based on the experimental electron density derived from X-ray diffraction data obtained at 20 K. Accurate hydrogen positions were included based on an analogous neutron diffraction study at 100 K. Topological features of the covalent bonds demonstrate the presence of multiple bonds of various orders within the PyBIGH cation.

Revisiting the charge density analysis of 2,5-dichloro-1,4-benzoquinone at 20 K.

A high-resolution X-ray diffraction measurement of 2,5-dichloro-1,4-benzoquinone (DCBQ) at 20 K was carried out. The experimental charge density was modeled using the Hansen-Coppens multipolar expansion and the topology of the electron density was analyzed in terms of the quantum theory of atoms in molecules (QTAIM). Two different multipole models, predominantly differentiated by the treatment of the chlorine atom, were obtained.

Seven-Membered Ring Nucleoside Analogues: Stereoselective Synthesis and Studies on Their Conformational Properties.

The synthesis of a novel series of seven-membered ring nucleoside analogues as candidates for biological screening and gene silencing applications is described. The key step in the synthetic approach is a stereoselective synthesis of an epoxide that is used as a common synthetic intermediate to prepare functionalized oxepane nucleoside derivatives. The conformational landscape and preferred ring-puckering of selected oxepane nucleosides was also studied by NMR, X-ray crystallography, and quantum mechanical calculations.

Stabilizing and Activating Nitrogen Catenates.

The remarkably stable catenated hexa-nitrogen chain in bis(benzotriazene-4-one) is structurally, theoretically, and spectroscopically characterized to illustrate the durability of the central N-N bond in this hexaazo chain. The reactions of this species illustrate the potential of these nitrogen catenates for the preparation of other condensed heterocycles, such as bispyrazolones, by thermal nitrogen exclusion or by trapping the single ring-opened Dimroth intermediates. In these latter reactions, 2-naphtholate anion condenses with bis(benzotriazene-4-one) to trap and retain a zwitterionic diazonium intermediate as an isolated diazo product, whereas transition metals ring effect ring-extrusion of dinitrogen from the Dimroth intermediate to generate chelating σ-aryls.

Activation of nitrogen Brønsted acids: synthesis and reactivity of a new class of nitrogen acid complexes.

The nitrogen acids RC(O)NHNO2, N-nitroamide, R = CH3 (1), C2H5 (2) and N-nitrocarbamate, R'OC(O)NHNO2, R' = CH3 (3), C2H5 (4) are a class of primary N-nitrocarboxamide compounds that oxidatively add to trans-Ir((I))(Cl)(N2)(PPh3)2 to give six-coordinate Ir((III))(η(2)-(NO2)-nitrogen acid)(H)(Cl)(PPh3)2 complexes 5-8. Unexpected fluxional behavior of the complexes in solution is observed by (1)H NMR spectroscopy. Reaction intermediates of the oxidative addition reactions were also observed and monitored using (31)P and (1)H NMR and solution IR spectroscopies.

Facile NN Activation in Benzotriazole: Capturing the Dimroth Azo/Triazole Intermediate by Complexation to Iridium.

The in situ observation of benzotriazole ring and ring-opened isomers, which result from the Dimroth equilibrium for 1-[(nonafluorobutane)sulfonyl]benzotriazole, 1, in solution by F NMR and UV/Vis spectroscopy is reported. Two benzotriazoles, compound 1 and 1,1'-sulfonylbis(benzotriazole) (3), undergo Dimroth triazole ring opening and coordination to an iridium(I) metal center to give either linear diazo [Ir (η -NNPhNSO C F )(Cl)(PPh ) ] (2) or an unusual double bent diazene [Ir (η -NNPhNSO Btz)(Cl)(PPh ) ] (4; Btz=benzotriazole) complex.

E/Z oxime isomerism in PhC(NOH)CN.

The reaction of nitric oxide with benzyl cyanide in the presence of potassium methoxide at low temperature gave the dipotassium salt of a bis-diazeniumdiolate 2 in excellent yield. Two new stereospecific syntheses of E or Z 2-(hydroxyimino)-2-phenylacetonitrile from 2 have been found. The thermodynamics of the E/Z isomerization has been investigated spectroscopically in solution, in the solid state by differential scanning calorimetry (DSC), and theoretically in the gas phase.

N-H activation in N-nitropropionamide: coordination chemistry of a primary nitroamide.

N-nitropropionamide, EtC(O)NHNO(2), oxidatively adds to Ir(Cl)(N(2))(PPh(3))(2) to give a η(2)-(N,O)-N-nitropropionamide anion bound to an Ir hydride complex. Single-crystal X-ray diffraction of the product indicates that it forms an unusual O-bound chelate through the nitro group. Density functional calculations for a model nickel complex, [Ni(MeC(O)NNO(2))(CN)(2)](-), are used to help distinguish the observed IR bands for the four possible conformations and binding geometries of this ligand.