Khai-Nghi Truong

Divergent Reactivity of a Dinuclear (NHC)Nickel(I) Catalyst versus Nickel(0) Enables Chemoselective Trifluoromethylselenolation

Abstract We herein showcase the ability of NHC‐coordinated dinuclear NiI–NiI complexes to override fundamental reactivity limits of mononuclear (NHC)Ni0 catalysts in cross‐couplings. This is demonstrated with the development of a chemoselective trifluoromethylselenolation of aryl iodides catalyzed by a NiI dimer. A novel SeCF3‐bridged NiI dimer was isolated and shown to selectively react with Ar−I bonds. Our computational and experimental reactivity data suggest dinuclear NiI catalysis to be operative. The corresponding Ni0 species, on the other hand, suffers from preferred reaction with the product, ArSeCF3, over productive cross‐coupling and is hence inactive.

An epoxy thiolactone on stage: four component reactions, synthesis of poly(thioether urethane)s and the respective hydrogels

The synthesis of an epoxy thiolactone is described. The reactivity of this epoxy thiolactone towards amines is evaluated and presented in a four component reaction. Upon ring opening of the thiolactone with an amine an AB-type epoxy thiol monomer is generated which in situ starts a thiol–epoxy polymerization. The polymerization mechanism and kinetics are investigated: the influence of different parameters such as solvent, substrate concentration, and catalyst on the reaction course is explored. Finally, concepts for the formation of reactive hydrogels are presented.

3-(4-pyridyl)-acetylacetone--a fully featured substituted pyridine and a flexible linker for complex materials.

3-(4-Pyridyl)-acetylacetone (HacacPy) acts as a pyridine-type ligand towards CdX2 (X = Cl, Br, I). Chain polymers with six-coordinated metal cations are obtained from CdCl2 and with alternating five- and six-coordinated Cd centers from CdBr2. In either case, the formation of these compounds does not depend on the precise stoichiometry. In contrast, two different reaction products form with the heavier congener CdI2, namely a ligand-rich molecular complex CdI2(HacacPy)2 and a ligand-deficient one-dimensional polymer [CdI2(HacacPy)](1)(∞). Interconversion between these two iodo derivatives is possible via thermal degradation and mechanochemical synthesis. The acetylacetone moiety in HacacPy may be deprotonated and chelated to Fe(III), and the resulting complex Fe(acacPy)3 reacts analogously to a bridging polypyridine ligand towards the same Cd halides as the molecule HacacPy itself. With CdCl2 and CdBr2, isomorphous chain polymers are obtained in which the Cd cations adopt distorted octahedral coordination and one of the peripheric pyridyl groups remains uncoordinated. With CdI2, the iron complex acts as a mu3Fe(acacPy)3 bridge between tetrahedral Cd centers and gives rise to a ladder structure.

Interplay Between Microwave Spectroscopy and X-ray Diffraction: The Molecular Structure and Large Amplitude Motions of 2,3-Dimethylanisole

To determine the structural properties of 2,3-dimethylanisole, a multidisciplinary approach was carried out where gas phase rotational spectroscopy recording a spectrum from 2 to 26.5 GHz using a pulsed molecular jet Fourier transform microwave spectrometer was combined with solid-state X-ray diffraction. Both methods revealed that only one conformer with a planar heavy-atom structure exists. In the solid state, the packing in the monoclinic space group is P21 /n with Z=4. In the gas phase spectrum, torsional splittings due to the internal rotations of two methyl groups attached to the phenyl ring were resolved and analyzed, providing an estimate of the barriers to methyl internal rotation of V3 =26.9047(5) and 518.7(12) cm-1 for the methyl groups at the ortho- and meta-position, respectively. The coupling between the two internal rotations is modeled on a two-dimensional potential energy surface, which was obtained by quantum chemical calculations at the B3LYP/6-311++G(d,p) level of theory.

A whole zoo of hydrogen bonds in one crystal structure: tris(isonicotinium) hydrogensulfate sulfate monohydrate

Depending on the reaction partner, the organic ditopic molecule isonicotinic acid (Hina) can act either as a Brønsted acid or base. With sulfuric acid, the pyridine ring is protonated to become a pyridinium cation. Crystallization from ethanol affords the title compound tris(4-carboxypyridinium) hydrogensulfate sulfate monohydrate, 3C6H6NO2+·HSO4-·SO42-·H2O or [(H2ina)3(HSO4)(SO4)(H2O)]. This solid contains 11 classical hydrogen bonds of very different flavour and nonclassical C-H...O contacts. All N-H and O-H donors find at least one acceptor within a suitable distance range, with one of the three pyridinium H atoms engaged in bifurcated N-H...O hydrogen bonds. The shortest hydrogen-bonding O...O distance is subtended by hydrogensulfate and sulfate anions, viz. 2.4752 (19) Å, and represents one of the shortest hydrogen bonds ever reported between these residues.

3-(Pyridin-4-yl)acetylacetone: a donor ligand towards mercury(II) halides and a versatile linker for complex materials

The ditopic organic molecule 3-(pyridin-4-yl)acetylacetone (HacacPy) acts as a pyridine-type ligand towards HgX2 (X = Cl, Br, I). The nature of the anion and the ligand-to-cation ratio dominate the outcome of the reaction. Two different coordination compounds form with HgCl2, namely a ligand-rich mononuclear complex, HgCl2(HacacPy)2, and a ligand-deficient one-dimensional chain polymer, [Hg(μ-Cl)2(HacacPy)]1∞, with five-coordinated HgII cations. Two compounds are also observed for HgBr2, a molecular complex isomorphous to the chloride derivative and a chain polymer with the composition [Hg(μ-Br)Br(HacacPy)]1∞, in which the cations are four-coordinated. The ligand-rich mononuclear and ligand-deficient polymeric chloride and bromide complexes may be interconverted via thermal degradation and mechanochemical synthesis. In contrast to the chloride and bromide compounds, the reaction product with HgI2 does not depend on the ligand-to-cation ratio but corresponds to [Hg(μ-I)I(HacacPy)]1∞, isomorphous to the bromide derivative. The N-coordinated HacacPy complexes could not be deprotonated and further crosslinked with a second cation. Synthesis of mixed-metal products could be achieved, however, by deprotonation of the acetylacetone moiety in HacacPy and formation of tris-chelated Fe(acacPy)3 and Al(acacPy)3 complexes in the first step. These mononuclear building blocks act as bridging poly(pyridine) ligands towards HgII halides and form two structure types. The first represents a one-dimensional ladder, with the tris(ligand) complexes acting as triconnected nodes and the HgII halides acting as linkers. In the alternative unprecedented product, both the tris(ligand) complexes and the [HgX2(μ-X)HgX] groups act as equivalent triconnected nodes. They form a uninodal two-dimensional coordination network with vertex symbol 4.82 and fes topology.

Mononuclear Alkali Metal Organoperoxides Stabilized by an NNNN-Macrocycle and Short Hydrogen Bonds from ROOH Molecules

A series of light alkali metal organoperoxides [MOOR] (M=Li, Na, K; R=tBu, CMe2 Ph) were isolated in mononuclear form, aided by the tetradentate and neutral NNNN-type macrocycle Me4 TACD (L; Me4 [12]aneN4 =1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane) and strong hydrogen bonds from additional ROOH molecules. The Na and K compounds are characterized by short O-H⋅⋅⋅O contacts, in the case of the Na derivative as short as 2.41 Å.

Favored Conformations of Carbonyl Compounds: A Structural Study of n -Octanal

We report on the molecular structures of the two most abundant conformers of n-octanal observed by molecular beam Fourier transform microwave spectroscopy. Next to limonene, which is the main component of citrus-oil, octanal and other n-alkyl aldehydes strongly enhance the typical fresh smell of lemon-oil. Due to the high flexibility of its n-alkyl chain and the high number of possible conformers, different semi-empirical methods (AM1, PM3, MMFF94) were used to sample the conformational space of octanal before performing more sophisticated quantum chemical calculations at the MP2 level of theory. This technique has previously been shown to be an ideal tool to characterize relevant odorant structures in fragrance chemistry. The structure of octanal and structurally related molecules is discussed in the context of the most abundant chain conformations and the potential use of the microwave validated structures for further studies in biological media.