Selective Valorization of Bio-derived Levulinic Acid and Its Derivatives into Hydrocarbons and Biochemicals by Using Hydrosilylation.

Herein we report an efficient hydrosilylation strategy to selectively defunctionalize biomass-derived levulinic acid into value-added chemicals such as pentane-1,4-diol, pentan-2-ol, 2-MTHF and C5 hydrocarbons by using cost-effective silanes and the commercially available catalyst B(C6 F5 )3 at room temperature. All reactions work well in chlorinated solvents but, as a greener alternative, most reactions can be run in toluene or solvent-less.

Ligand-Promoted [Pd]-Catalyzed α-Alkylation of Ketones through a Borrowing-Hydrogen Approach.

A new class of palladium complexes bearing bidentate 2-hydroxypyridine based ligands have been prepared and fully characterized. The applications of these new complexes towards ketone alkylation reactions with alcohols through a metal-ligand cooperative borrowing-hydrogen (BH) process were demonstrated.

A mononuclear iron(III) complex with unusual changes of color and magneto-structural properties with temperature: synthesis, structure, magnetization, multi-frequency ESR and DFT study.

From the reaction of 2-hydroxy-6-methylpyridine (L) with iron(II) tetrafluoroborate, a new mononuclear iron(III) octahedral complex [FeL6](BF4)3 has been isolated. The color of the complex reversibly changed from red at room temperature to yellow-orange at the liquid nitrogen temperature. Magnetization measurements indicate that iron(III) in [FeL6](BF4)3 is in a high-spin state S = 5/2, from room temperature to 1.8 K. The high-spin ground state of iron(III) is also confirmed by DFT calculations. Although the spin-crossover of the complex is not observed, X-band and multifrequency high-field/high-frequency electron spin resonance (ESR) spectroscopy shows rather uncommon iron(III) spectra at room temperature and an unusual change with cooling. Spectral simulations reveal that the S = 5/2 ground state multiplet of the complex can be characterized by the temperature independent axial zero-field splitting parameter of |D| = +2 GHz (0.067 cm-1) while the value of the rhombic parameter E of the order of some tenths MHz increases on lowering the temperature. Single crystal X-ray diffraction (SCXRD) shows that the iron(III) coordination geometry does not change with temperature while supramolecular interactions are temperature dependent, influencing the iron(III) rhombicity. Additionally, the DFT calculations show temperature variation of the HOMO-LUMO gap, in agreement with the changes of color and ESR-spectra of the iron(III) complex with temperature.

Ru-Catalyzed Cross-Dehydrogenative Coupling between Primary Alcohols to Guerbet Alcohol Derivatives: with Relevance for Fragrance Synthesis.

A simple method has been developed for the cross dehydrogenative coupling between two different primary alcohols using readily available RuCl2(PPh3)3 as a precatalyst through the borrowing-hydrogen approach. The present methodology is applicable to a large variety of alcohol derivatives including long chain aliphatic alcohols and heteroaryl alcohols. In addition, the methodology was applied in a straightforward protocol to synthesize commercially available fragrances such as Rosaphen and Cyclamenaldehyde in good yields.

Ru-Catalyzed Completely Deoxygenative Coupling of 2-Arylethanols through Base-Induced Net Decarbonylation.

Substituted arylethanols can be coupled by using a readily available Ru catalyst in a fully deoxygenative manner to produce hydrocarbon chains in one step. Control experiments indicate that the first deoxygenation occurs through an aldol condensation, whereas the second occurs through a base-induced net decarbonylation. This double deoxygenation enables further development in the use of alcohols as versatile and green alkylating reagents, as well as in other fields, such as deoxygenation and upgrading of overfunctionalized biomass to produce hydrocarbons.

Naphthyl Thio- and Carba-xylopyranosides for Exploration of the Active Site of ß-1,4-Galactosyltransferase 7 (ß4GalT7).

Xyloside analogues with substitution of the endocyclic oxygen atom by sulfur or carbon were investigated as substrates for ß-1,4-galactosyltransferase 7 (ß4GalT7), a key enzyme in the biosynthesis of glycosaminoglycan chains. The analogues with an endocyclic sulfur atom proved to be excellent substrates for ß4GalT7, and were galactosylated approximately fifteen times more efficiently than the corresponding xyloside. The 5a-carba-ß-xylopyranoside in the d-configuration proved to be a good substrate for ß4GalT7, whereas the enantiomer in the l-configuration showed no activity. Further investigations by X-ray crystallography, NMR spectroscopy, and molecular modeling provided a rationale for the pronounced activity of the sulfur analogues. Favorable π-π interactions between the 2-naphthyl moiety and a tyrosine side chain of the enzyme were observed for the thio analogues, which open up for the design of efficient GAG primers and inhibitors.

Regio- and Stereoselective Alkylation of Pyridine-N-oxides: Synthesis of Substituted Piperidines and Pyridines.

Regio- and stereoselective addition of alkyl Grignard reagents to pyridine-N-oxides gave C2-alkylated N-hydroxy-1,2,5,6-tetrahydropyridines and trans-2,3-disubstituted N-hydroxy-1,2,5,6-tetrahydropyridines in good to excellent yields. These intermediates were aromatized or alternatively reduced in one-pot methodologies for efficient syntheses of alkylpyridines or piperidines, respectively. These reactions have a broad substrate scope and short reaction times.

Fast and reversible insertion of carbon dioxide into zirconocene-alkoxide bonds. A mechanistic study.

In two consecutive equilibria the compound (Cp*)2Zr(OMe)2 undergoes insertion of CO2 to form the mono- and bis-hemicarbonates. Both equilibria are exothermic but entropically disfavoured. Magnetisation transfer experiments gave kinetic data for the first equilibrium showing that the rate of insertion is overall second order with a rate constant of 3.20 ± 0.12 M(-1) s(-1), which is substantially higher than those reported for other early transition metal alkoxides, which are currently the best homogeneous catalysts for dimethyl carbonate formation from methanol and CO2. Activation parameters for the insertion reaction point to a highly ordered transition state and we interpret that as there being a substantial interaction between the CO2 and the metal during the C-O bond formation. This is supported by DFT calculations showing the lateral attack by CO2 to have the lowest energy transition state.

Synthesis of an orthogonal topological analogue of helicene.

The synthesis of an orthogonal topological pentamer analogue of helicene is presented. This analogue forms a tubular structure with its aromatic systems directed parallel to the axis of propagation, which creates a cavity with the potential to function as a host molecule. The synthetic strategy reported, based on a series of repeating Friedländer condensations that utilize pyrido[3,2-d]pyrimidine moieties as protected amino aldehydes, allows for the facile access of higher generations of helical, tubular structures. As a result of the synthetic strategy, only a helical isomer of the pentamer is possible. The structure and absolute configuration of the pentamer were elucidated from a combination of NMR spectroscopic data, optical properties, X-ray structures, and by comparison of an experimental electronic circular dichroism spectrum to a calculated spectrum.

Preparation of potentially porous, chiral organometallic materials through spontaneous resolution of pincer palladium conformers.

Understanding the mechanism by which advanced materials assemble is essential for the design of new materials with desired properties. Here, we report a method to form chiral, potentially porous materials through spontaneous resolution of conformers of a PCP pincer palladium complex ({2,6-bis[(di-t-butylphosphino)methyl]phenyl}palladium(II)halide). The crystallisation is controlled by weak hydrogen bonding giving rise to chiral qtz-nets and channel structures, as shown by 16 such crystal structures for X = Cl and Br with various solvents like pentane and bromobutane. The fourth ligand (in addition to the pincer ligand) on palladium plays a crucial role; the chloride and the bromide primarily form hexagonal crystals with large 1D channels, whereas the iodide (presumably due to its inferior hydrogen bonding capacity) forms monoclinic crystals without channels. The hexagonal channels are completely hydrophobic and filled with disordered solvent molecules. Upon heating, loss of the solvent occurs and the hexagonal crystals transform into other non-porous polymorphs. Also by introducing a strong acid, the crystallisation process can be directed to a different course, giving several different non-porous polymorphs. In conclusion, a number of rules can be formulated dictating the formation of hexagonal channel structures based on pincer palladium complexes. Such rules are important for a rational design of future self-assembling materials with applications in storage and molecular recognition.

Palladium(II)-catalyzed oxidative cyclization of allylic tosylcarbamates: scope, derivatization, and mechanistic aspects.

A highly selective oxidative palladium(II)-catalyzed (Wacker-type) cyclization of readily available allylic tosylcarbamates is reported. This operationally simple catalytic reaction furnishes tosyl-protected vinyl-oxazolidinones, common precursors to syn-1,2-amino alcohols, in high yield and excellent diasteroselectivity (>20:1). It is demonstrated that both stoichiometric amounts of benzoquinone (BQ) as well as aerobic reoxidation (molecular oxygen) is suitable for this transformation. The title reaction is shown to proceed through overall trans-amidopalladation of the olefin followed by ß-hydride elimination. This process is scalable and the products are suitable for a range of subsequent transformations such as: kinetic resolution (KR) and oxidative Heck-, Wacker-, and metathesis reactions.

Neutral Organometallic Halogen Bond Acceptors: Halogen Bonding in Complexes of PCPPdX (X = Cl, Br, I) with Iodine (I(2)), 1,4-Diiodotetrafluorobenzene (F4DIBz), and 1,4-Diiodooctafluorobutane (F8DIBu).

The behavior of a sterically crowded neutral pincer {2,6-bis[(di-t-butylphosphino)methyl]-phenyl}palladium (PCPPd) halides, PCPPdX (X = Cl, Br or I), as XB acceptors with strong halogen bond (XB) donors, iodine (I(2)), 1,4-diiodotetrafluorobenzene (F4DIBz), and 1,4-diiodooctafluorobutane (F8DIBu) were studied in the solid state. The co-crystallization experiments afforded high-quality single crystals of XB complexes PCPPdCl-I(2) (1a), PCPPdBr-I(2) (2a), PCPPdI-I(2)(3a), PCPPdCl-F4DIBz (1b), PCPPdBr-F4DIBz (2b), and PCPPdBr-F8DIBu (2c). The 1:1 iodine complexes (1a, 2a, and 3a) all showed a strong halogen bonding interaction, the reduction of the sum of the van der Waals radii of halogen to iodine being 24.6 (1a), 23.9 (2a), and 19.4% (3a) with X···I-I angles of 177, 176, and 179°, respectively. While the pincer palladium chloride 1 and bromide 2 were crystallographically isomorphous and showed similar XB behavior, the palladium iodide complex, 3, exhibited markedly different properties, and unlike 1 and 2 it does not, under similar conditions, result in XB complexes with the weaker XB donors F4DIBz and F8DIBu. The results indicate that PCPPdI is not nucleophilic enough to have XB interactions with other donors than iodine. However, the weaker XB donors F4DIBz and F8DIBu form XB complexes with the chloride 1 and especially with the bromide 2. The prevalence of the halogen bonding with 2 is probably not only electronic in origin, and it seems to offer the best balance between electron poorness and steric availability. The XB interactions with F4DIBz and F8DIBu are much weaker than with iodine, the reduction of the sum of the van der Waals radii of halogen to iodine being 13.5, 12.3, and 14.6% with C-I···X angles between 163 and 179° for 1b, 2b, and 2c, respectively, and results in polymeric (···1···F4DIBz···1···F4DIBz···)(n), (···2···F4DIBz···2···F4DIBz···)(n), and (···2···F8DIBu···2···F8DIBu···)(n) one-dimensional zigzag chains in the solid state.

Bis(1,3-dimesitylimidazol-yl)gold(I) 2,4,8,10-tetra-phenyl-1,3,5,7,9,11-hexa-oxa-2,4,8,10-tetra-bora-6-borataspiro-[5.5]undeca-ne.

The Au(I) atom in the title compound, [Au(C(21)H(24)N(2))(2)](C(24)H(20)B(5)O(6)), adopts a slightly distorted linear AuC(2) coordination geometry arising from its coordination by two mesitylenic N-heterocyclic carbene ligands, forming an overall cationic complex. The dihedral angle between the imidazole rings is 57.3 (6)°. In the crystal, the components are linked by weak C-H⋯O hydrogen bonds.

[2,6-Bis(di-tert-butyl-phosphinometh-yl)phenyl-κP,C,P'](trifluoro-acetato)palladium(II).

The Pd(II) atom in the title compound, [Pd(C(2)F(3)O(2))(C(24)H(43)P(2))], adopts a distorted square-planar geometry with the P atoms in a trans arrangement, forming two five-membered chelate rings. Four intra-molecular C-H⋯O hydrogen bonds occur. The crystal packing reveals one weak inter-molecular C-H⋯O hydrogen bond, which self-assembles the mol-ecules into infinite chains parallel to the b axis.