Metal-Free Decarboxylative Allylation of Oxime Esters under Light Irradiation.

Allylation reactions, often used as a key step for constructing complex molecules and drug candidates, typically rely on transition-metal (TM) catalysts. Even though TM-free radical allylations have been developed using allyl-stannanes, -sulfides, -silanes or -sulfones, much less procedures have been reported using simple and commercially available allyl halides, that are used for the preparation of the before-mentioned allyl derivatives. Here, we present a straightforward photocatalytic protocol for the decarboxylative allylation of oxime esters using allyl bromide derivatives under metal-free and mild conditions.

N Functionalization via Molybdenum-Nitride Complex: Stepwise BH Bond Additions.

Reactivity of (triphosphine)Mo-nitrido complex generated by N splitting, toward boranes is reported. The simple adduct Mo≡N→BH is observed with BH.SMe while 1,2 addition is evidenced with 9-BBN leading to H-Mo=NBR.

Assessing Combinations of B(C F ) and N -Derived Molybdenum Nitrido Complexes for Heterolytic Bond Activation.

Two different dinitrogen-derived molybdenum nitrido complexes varying by their geometry, ligand spheres and oxidations states were shown to engage their N ligand in dative bonding with the strong Lewis acid B(C F ) . The stable adducts were assessed for frustrated Lewis pair-type heterolytic E-H bond splitting of hydrosilanes (E=Si) and HB(C F ) . Whereas Si-H bond activation was achieved, HB(C F ) was shown to substitute B(C F ) in a quantitative or equilibrated fashion, depending on the nature of the nitrido complex.

Ammonia Synthesis at Room Temperature and Atmospheric Pressure from N : A Boron-Radical Approach.

Ammonia, NH , is an essential molecule, being part of fertilizers. It is currently synthesized via the Haber-Bosch process, from the very stable dinitrogen molecule, N and dihydrogen, H . This process requires high temperatures and pressures, thereby generating ca 1.

Molecular Electrochemical Reductive Splitting of Dinitrogen with a Molybdenum Complex.

Nitrogen reduction under mild conditions (room T and atmospheric P), using a non-fossil source of hydrogen remains a challenge. Molecular metal complexes, notably Mo based, have recently been shown to be active for such nitrogen fixation. We report electrochemical N splitting with a Mo triphosphino complex [(PPP)MoI ], at room temperature and a moderately negative potential.

Chirogenesis in Zinc Porphyrins: Theoretical Evaluation of Electronic Transitions, Controlling Structural Factors and Axial Ligation.

In the present work, sixteen different zinc porphyrins (possessing different meso substituents) with and without a chiral guest were modelled using DFT and TD-DFT approaches in order to understand the influence of various controlling factors on electronic circular dichroism (ECD) spectra. Two major aspects are influenced by these factors: excitation energy of the electronic transitions and their intensity. In the case of excitation energy, the influence increases in the following order: orientation of the peripheral substituents View Article and Find Full Text PDF

Benchmarking computational methods and influence of guest conformation on chirogenesis in zinc porphyrin complexes.

Circular dichroism (CD) is a convenient and widely used tool for investigating structures of chiral molecules. However, the unambiguous simulation of CD spectra is not a trivial task, because the accuracy of theoretical calculations depends on the nature of the system. In the present work, the induced CD spectra of six zinc porphyrin complexes with chiral guests were simulated by using different DFT methods.

Efficient alkene hydrosilation with bis(8-quinolyl)phosphine (NPN) nickel catalysts. The dominant role of silyl-over hydrido-nickel catalytic intermediates.

A cationic nickel complex of the bis(8-quinolyl)(3,5-di--butylphenoxy)phosphine (NPN) ligand, [(NPN)NiCl], is a precursor to efficient catalysts for the hydrosilation of alkenes with a variety of hydrosilanes under mild conditions and low catalyst loadings. DFT studies reveal the presence of two coupled catalytic cycles based on [(NPN)NiH] and [(NPN)NiSiR] active species, with the latter being more efficient for producing the product. The preferred silyl-based catalysis is not due to a more facile insertion of alkene into the Ni-Si ( Ni-H) bond, but by consistent and efficient conversions of the hydride to the silyl complex.

Aerobic and Ligand-Free Manganese-Catalyzed Homocoupling of Arenes or Aryl Halides via in Situ Formation of Aryllithiums.

Ligand-free manganese-catalyzed homocoupling of arenes or aryl halides can be carried out under aerobic conditions via the in situ formation of the corresponding aryllithiums. A wide range of biaryls and derivatives has been obtained, and a mechanism involving monomeric manganese-oxo complexes has been proposed on the basis of DFT calculations.

Room-Temperature Functionalization of N to Borylamine at a Molybdenum Complex.

Intermolecular, stepwise functionalization by BH bonds of a (triphosphine)Mo -nitrido complex generated by N splitting is reported. The imido-hydride and di-hydride-amido Mo complexes have been isolated and characterized. Addition of PinBH to the [Mo(H) (N(BPin) )] complex at room temperature results in the liberation of borylamines from the metal center.

Domino Pd -Catalyzed C(sp )-H Arylation/Electrocyclic Reactions via Benzazetidine Intermediates.

The Pd -catalyzed C(sp )-H arylation of 2-bromo-N-methylanilides leads to unstable benzazetidine intermediates that rearrange to benzoxazines through 4π electrocyclic ring-opening and 6π electrocyclization. The introduction of a bulky, non-activatable amide group on the nitrogen atom was key to favor the challenging reductive elimination step and disfavor undesired reaction pathways.

Dehydrogenative coupling of 4-substituted pyridines mediated by a zirconium(ii) synthon: reaction pathways and dead ends.

The mechanism of the reductive homocoupling of pyridine derivatives mediated by the Zr synthon [(PNP)Zr(η-toluene)Cl] () has been investigated. Selective transformation into three different types of product complexes has been observed, depending on the N-heterocyclic substrate employed: the bipyridyl complexes (R = Me, Et, Bu, Bn, Ph, CHCHPh), which are the homocoupling products, the η-((4-dimethylamino)pyridyl) complex as well as the bis(isoquinolinyl) complex . By deuterium labelling experiments the participation of the ligand backbone in the pyridine coupling reaction potential cyclometallation steps was ruled out.

Isolation and structural characterization of a titanacyclopropane as key intermediate in the double aryl Grignard addition to 2-(arylethynyl)pyridine derivatives.

A titanacyclopropane species, which is a key reaction intermediate in the Ti(OiPr)-mediated double aryl Grignard addition to 1,2-di(pyridin-2-yl)ethyne and related alkynes, was isolated and fully characterized. Based on this observation a one-pot synthesis of diarylated 1,2-di(pyridin-2-yl)ethanes and 2-(1,2,2-triarylvinyl)-pyridines was developed, including the tetraarylation of V-shaped 2,6-bis(arylethynyl)pyridines.

A mechanochemical approach to access the proline-proline diketopiperazine framework.

Ball milling was exploited to prepare a substituted proline building block by mechanochemical nucleophilic substitution. Subsequently, the mechanocoupling of hindered proline amino acid derivatives was developed to provide proline-proline dipeptides under solvent-free conditions. A deprotection-cyclization sequence yielded the corresponding diketopiperazines that were obtained with a high stereoselectivity which could be explained by DFT calculations.

Mild Decarboxylative C-H Alkylation: Computational Insights for Solvent-Robust Ruthenium(II) Domino Manifold.

Computational studies on decarboxylative C-H alkenylations provided key insights into the solvent-robust nature of C-H activation/decarboxylation domino reactions. These properties were exploited for ruthenium(II)-catalyzed C-H alkylations by a decarboxylative process with ample scope under copper-free and silver-free reaction conditions.

New Titanium Borylimido Compounds: Synthesis, Structure, and Bonding.

We report a combined experimental and computational study of the synthesis and electronic structure of titanium borylimido compounds. Three new synthetic routes to this hitherto almost unknown class of Group 4 imide are presented. The double-deprotonation reaction of the borylamine HNB(NAr'CH) (Ar' = 2,6-CHPr) with Ti(NMe)Cl gave Ti{NB(NAr'CH)}Cl(NHMe), which was easily converted to Ti{NB(NAr'CH)}Cl(py).

New Scandium Borylimido Chemistry: Synthesis, Bonding, and Reactivity.

We report a combined synthetic, mechanistic, and theoretical study of the first borylimido complex of a rare earth metal, (NacNac)Sc{NB(NAr'CH)} (25, Ar' = 2,6-CHPr, NacNac = Ar'NC(Me)CHC(Me)NCHCHNMe). Thermolysis of the methyl-borylamide (NacNac)Sc(Me){NHB(NAr'CH)} (18) generated transient imide 25 via rate-determining, first-order methane elimination (KIE ≈ 8.7).

η(6) -Arene-Zirconium-PNP-Pincer Complexes: Mechanism of Their Hydrogenolytic Formation and Their Reactivity as Zirconium(II) Synthons.

The cyclometalated monobenzyl complexes [(Cbzdiphos(R) -CH)ZrBnX] 1 (iPr) Cl and 1 (Ph) I reacted with dihydrogen (10 bar) to yield the η(6) -toluene complexes [(Cbzdiphos(R) )Zr(η(6) -tol)X] 2 (iPr) Cl and 2 (Ph) I (cbzdiphos=1,8-bis(phosphino)-3,6-di-tert-butyl-9H-carbazole). The arene complexes were also found to be directly accessible from the triiodide [(Cbzdiphos(Ph) )ZrI3 ] through an in situ reaction with a dibenzylmagnesium reagent and subsequent hydrogenolysis, as exemplified for the η(6) -mesitylene complex [(Cbzdiphos(Ph) )Zr(η(6) -mes)I] (3 (Ph) I). The tolyl-ring in 2 (iPr) Cl adopts a puckered arrangement (fold angle 23.

Deciphering Selectivity in Organic Reactions: A Multifaceted Problem.

Computational chemistry has made a sustained contribution to the understanding of chemical reactions. In earlier times, half a century ago, the goal was to distinguish allowed from forbidden reactions (e.g.

Azaphilic versus Carbophilic Coupling at C=N Bonds: Key Steps in Titanium-Assisted Multicomponent Reactions.

Consecutive C- and N-arylation of N-heterocyclic nitriles is mediated by titanium(IV) alkoxides. The carbo- and azaphilic arylation step may be separated by choosing the order in which the two equivalents of aryl transfer reagent are added. In the course of this transformation, the ancillary N-heterocycle acts as both a directing anchor group and electron reservoir.

Reactions of Titanium Hydrazides with Silanes and Boranes: N-N Bond Cleavage and N Atom Functionalization.

Reaction of Ti(N2(iPr)N)(NNPh2)(py) with Ph(R)SiH2 (R = H, Ph) or 9-BBN gave reductive cleavage of the N(α)-N(β) bond and formation of new silyl- or boryl-amido ligands. The corresponding reactions of Cp*Ti{MeC(N(i)Pr)2}(NNR2) (R = Me or Ph) with HBPin or 9-BBN gave borylhydrazido-hydride or borylimido products, respectively. N(α) and N(β) atom transfer and dehydrogenative coupling reactions are also reported.

A Highly Effective Ruthenium System for the Catalyzed Dehydrogenative Cyclization of Amine-Boranes to Cyclic Boranes under Mild Conditions.

We recently disclosed a new ruthenium-catalyzed dehydrogenative cyclization process (CDC) of diamine-monoboranes leading to cyclic diaminoboranes. In the present study, the CDC reaction has been successfully extended to a larger number of diamine-monoboranes (4-7) and to one amine-borane alcohol precursor (8). The corresponding NB(H)N- and NB(H)O-containing cyclic diaminoboranes (12-15) and oxazaborolidine (16) were obtained in good to high yields.

Mechanistic study of the selectivity of olefin versus cyclobutene formation by palladium(0)-catalyzed intramolecular C(sp3)-H activation.

This study describes the mechanism and selectivity pattern of the Pd(0)-catalyzed C(sp(3))-H activation of a prototypical substrate bearing two linear alkyl groups. Experimentally, the use of the Pd/P(t-Bu)3 catalytic system leads to a ca. 7:3 mixture of olefin and benzocyclobutene (BCB) products.

Linear-selective hydroarylation of unactivated terminal and internal olefins with trifluoromethyl-substituted arenes.

We report a series of hydroarylations of unactivated olefins with trifluoromethyl-substituted arenes that occur with high selectivity for the linear product without directing groups on the arene. We also show that hydroarylations occur with internal, acyclic olefins to yield linear alkylarene products. Experimental mechanistic data provide evidence for reversible formation of an alkylnickel-aryl intermediate and rate-determining reductive elimination to form the carbon-carbon bond.