Markovnikov-Selective Cobalt-Catalyzed Wacker-Type Oxidation of Styrenes into Ketones under Ambient Conditions Enabled by Hydrogen Bonding.

The replacement of palladium catalysts for Wacker-type oxidation of olefins into ketones by first-row transition metals is a relevant approach for searching more sustainable protocols. Besides highly sophisticated iron catalysts, all the other first-row transition metal complexes have only led to poor activities and selectivities. Herein, we show that the cobalt-tetraphenylporphyrin complex is a competent catalyst for the aerobic oxidation of styrenes into ketones with silanes as the hydrogen sources.

Reactivity of a Unique Si(I)-Si(I)-Based η-Bis(silylene) Iron Complex.

In this paper, we report the synthesis of a unique silicon(I)-based metalla-disilirane and report on its reactivity toward TMS-azide and benzophenone. Metal complexes containing disilylenes ((bis)silylenes with a Si-Si bond) are known, but direct ligation of the Si(I) centers to transition metals always generated dinuclear species. To overcome this problem, we targeted the formation of a mononuclear iron(0)-silicon(I)-based disilylene complex via templated synthesis, starting with ligation of two Si(II) centers to iron(II), followed by a two-step reduction.

Atypical and Asymmetric 1,3-P,N Ligands: Synthesis, Coordination and Catalytic Performance of Cycloiminophosphanes.

Novel seven-membered cyclic imine-based 1,3-P,N ligands were obtained by capturing a Beckmann nitrilium ion intermediate generated in situ from cyclohexanone with benzotriazole, and then displacing it by a secondary phosphane under triflic acid promotion. These "cycloiminophosphanes" possess flexible non-isomerizable tetrahydroazepine rings with a high basicity; this sets them apart from previously reported iminophophanes. The donor strength of the ligands was investigated by using their P-κ - and P,N-κ -tungsten(0) carbonyl complexes, by determining the IR frequency of the trans-CO ligands.

Computational Evaluation of Me TCCP as Lewis Acid.

Supramolecular adducts between dimethyl-2,2,3,3-tetracyanocyclopropane (Me TCCP) with 21 small (polar) molecules and 10 anions were computed with DFT (B3LYP-D3/def2-TZVP). Their optimized geometries were used to obtain interaction energies, and perform energy decomposition and 'atoms-in-molecules' analyses. A set of 38 other adducts were also evaluated for comparison purposes.

Effect-directed analysis and chemical identification of agonists of peroxisome proliferator-activated receptors in white button mushroom.

Obesity has a serious effect on human health. It relates to metabolic syndrome, including the associated disorders such as type 2 diabetes, heart disease, stroke and hyperemia. The peroxisome proliferator-activated receptors (PPARs) are important receptors to control fat metabolism in the human body.

Photoinduced and Thermal Single-Electron Transfer to Generate Radicals from Frustrated Lewis Pairs.

Archetypal phosphine/borane frustrated Lewis pairs (FLPs) are famed for their ability to activate small molecules. The mechanism is generally believed to involve two-electron processes. However, the detection of radical intermediates indicates that single-electron transfer (SET) generating frustrated radical pairs could also play an important role.

Performance of TDDFT Vertical Excitation Energies of Core-Substituted Naphthalene Diimides.

We have evaluated the performance of various density functionals, covering generalized gradient approximation (GGA), global hybrid (GH) and range-separated hybrid (RSH), using time dependent density functional theory (TDDFT) for computing vertical excitation energies against experimental absorption maximum (λ ) for a set of 10 different core-substituted naphthalene diimides (cNDI) recorded in dichloromethane. The computed excitation in case of GH PBE0 is most accurate while the trend is most systematic with RSH LCY-BLYP compared to λ . We highlight the importance of including solvent effects for optimal agreement with the λ .

Distortion-Controlled Redshift of Organic Dye Molecules.

It is shown, quantum chemically, how structural distortion of an aromatic dye molecule can be leveraged to rationally tune its optoelectronic properties. By using a quantitative Kohn-Sham molecular orbital (KS-MO) approach, in combination with time-dependent DFT (TD-DFT), the influence of various structural and electronic tuning parameters on the HOMO-LUMO gap of a benzenoid model dye have been investigated. These parameters include 1) out-of-plane bending of the aromatic core, 2) bending of the bridge with respect to the core, 3) the nature of the bridge itself, and 4) π-π stacking.

Pyridyl-Functionalized 1-Phosphabarrelene: Synthesis, Coordination Chemistry and Photochemical di-π-Methane Rearrangement.

The [4+2] cycloaddition of 2-(2'-pyridyl)-4,6-diphenyl-λ -phosphinine with the highly reactive dienophile hexafluoro-2-butyne has been studied and the first pyridyl-functionalized 1-phosphabarrelene was obtained and structurally characterized. Although monodentate CF -1-phosphabarrelenes show only a poor coordination ability, the chelating nature of the novel P,N-hybrid ligand gives access to various transition-metal complexes. Upon irradiation with UV light, the pyridyl-functionalized 1-phosphabarrelene undergoes a rather selective di-π-methane rearrangement in the coordination sphere of the metal center, leading to the formation of a complex based on a hitherto unknown pyridyl-functionalized 5-phosphasemibullvalene derivative.

New Insights in Frustrated Lewis Pair Chemistry with Azides.

The geminal frustrated Lewis pair (FLP) tBu PCH BPh (1) reacts with phenyl-, mesityl-, and tert-butyl azide affording, respectively, six, five, and four-membered rings as isolable products. DFT calculations revealed that the formation of all products proceeds via the six-membered ring structure, which is thermally stable with an N-phenyl group, but rearranges when sterically more encumbered Mes-N and tBu-N are used. The reaction of 1 with Me Si-N is believed to follow the same course, yet subsequent N elimination occurs to afford a four-membered heterocycle (5), which can be considered as a formal FLP-trimethylsilylnitrene adduct.

Parallels between Metal-Ligand Cooperativity and Frustrated Lewis Pairs.

Metal ligand cooperativity (MLC) and frustrated Lewis pair (FLP) chemistry both feature the cooperative action of a Lewis acidic and a Lewis basic site on a substrate. A lot of work has been carried out in the field of FLPs to prevent Lewis adduct formation, which often reduces the FLP reactivity. Parallels are drawn between the two systems by looking at their reactivity with CO, and we explore the role of steric bulk in preventing dimer formation in MLC systems.

Phosphinine-Based Ligands in Gold-Catalyzed Reactions.

A series of substituted phosphinines, 1-phosphabarrelenes and 5-phosphasemibullvalenes were synthesized and evaluated for their potential application as ligands in homogeneous catalytic reactions. While their buried volume (%V ) was calculated to get insight into the steric properties, [LNi(CO) ] complexes were prepared in order to determine the corresponding Tolman electronic parameter. ETS-NOCV (extended-transition-state natural orbital for chemical valence) calculations on [LAuCl] complexes further allowed an estimation of the σ- and π-contributions to the L-M interaction.

A New Mode of Chemical Reactivity for Metal-Free Hydrogen Activation by Lewis Acidic Boranes.

We herein explore whether tris(aryl)borane Lewis acids are capable of cleaving H outside of the usual Lewis acid/base chemistry described by the concept of frustrated Lewis pairs (FLPs). Instead of a Lewis base we use a chemical reductant to generate stable radical anions of two highly hindered boranes: tris(3,5-dinitromesityl)borane and tris(mesityl)borane. NMR spectroscopic characterization reveals that the corresponding borane radical anions activate (cleave) dihydrogen, whilst EPR spectroscopic characterization, supported by computational analysis, reveals the intermediates along the hydrogen activation pathway.

Construction of alkyl-substituted pentaphosphido ligands in the coordination sphere of cobalt.

Rare mono- and diorganopentaphosphido cobalt complexes are accessible by P-P condensation using the unprecedented, reactive cobalt-gallium tetraphosphido complex [K(dme){(BIAN)Co(μ-η:η-P)Ga(nacnac)}] (). Compound was prepared in good yield by reaction of [K(EtO){(BIAN)Co(η-1,5-cod)}] [, BIAN = bis(mesitylimino)acenaphthene diimine, cod = 1,5-cyclooctadiene] with [Ga(nacnac)(η-P)] (nacnac = CH[CMeN(2,6-iPrCH)]). Reactions with RPCl (R = iPr, Bu, and Cy) selectively afford [(BIAN)Co(-PR)] (), which feature η-coordinated 1,1-diorganopentaphosphido ligands.

Rational design of near-infrared absorbing organic dyes: Controlling the HOMO-LUMO gap using quantitative molecular orbital theory.

Principles are presented for the design of functional near-infrared (NIR) organic dye molecules composed of simple donor (D), spacer (π), and acceptor (A) building blocks in a D-π-A fashion. Quantitative Kohn-Sham molecular orbital analysis enables accurate fine-tuning of the electronic properties of the π-conjugated aromatic cores by effecting their size, including silaaromatics, adding donor and acceptor substituents, and manipulating the D-π-A torsional angle. The trends in HOMO-LUMO gaps of the model dyes correlate with the excitation energies computed with time-dependent density functional theory at CAMY-B3LYP.

Chiral Control in Pentacoordinate Systems: The Case of Organosilicates.

Chirality at the central element of pentacoordinate systems can be controlled with two identical bidentate ligands. In such cases the topological Levi-Desargues graph for all the Berry pseudorotations (BPR, max. 20) reduces to interconnected inner and outer "circles" that represent the dynamic enantiomer pair.

Synthesis of a Cyclic CoSn Cluster Using a Co Synthon.

[Ar'SnCo] (1, Ar' = CH-2,6{CH-2,6- Pr}), a rare metal-metal bonded cobalt-tin cluster with low-coordinate tin atoms, was prepared by the reaction of [K(thf)][Co(1,5-cod)] (cod = 1,5-cyclooctadiene) with [Ar'Sn(μ-Cl)]. This reaction illustrates a promising synthetic strategy to access uncommon metal clusters. The structure of 1 features a rhomboidal CoSn core with strong metal-metal bonds between tin and cobalt and a weaker tin-tin interaction.

Aryldiazonium Salts as Nitrogen-Based Lewis Acids: Facile Synthesis of Tuneable Azophosphonium Salts.

Inspired by the commercially available azoimidazolium dyes (e.g., Basic Red 51) that can be obtained from aryldiazonium salts and N-heterocyclic carbenes, we developed the synthesis of a unique set of arylazophosphonium salts.

Template-Directed Synthesis of an Inverted Spiro Architecture.

The regular bicyclic spiro motif is highly abundant given its synthetic accessibility while the diastereomer-virtually obtained through inversion at the central atom-is almost unknown. We have developed methodology to access the elusive inverted spiro architecture by employing a covalent template-directed approach. Comparison with the regular spiro bicycle analog unequivocally established the diastereomeric relationship, providing insight into the fascinating stereochemical and structural properties.

Ring-opening of Epoxides Mediated by Frustrated Lewis Pairs.

Treatment of the preorganized frustrated Lewis pairs (FLPs) tBu PCH BPh (1) and o-Ph P(C H )BCat (Cat=catechol) (4) with 2-methyloxirane, 2-phenyloxirane and 2-(trifluoromethyl)oxirane resulted in epoxide ring-opening to yield the six- and seven-membered heterocycles 2 a-c and 5 a-c, respectively. These zwitterionic products were characterized spectroscopically, and compounds 2 a, 2 b, 5 a and 5 c were structurally characterized by single-crystal X-ray structure analyses. Based on computational and kinetic studies, the mechanism of these reactions was found to proceed via activation of the epoxide by the Lewis acidic borane moiety followed by nucleophilic attack of the phosphine of a second FLP molecule.

Gold(I) Complexes of the Geminal Phosphinoborane BuPCHBPh.

In this work, we explored the coordination properties of the geminal phosphinoborane BuPCHBPh () toward different gold(I) precursors. The reaction of with an equimolar amount of the sulfur-based complex (MeS)AuCl resulted in displacement of the SMe ligand and formation of linear phosphine gold(I) chloride . Using an excess of ligand , bisligated complex was formed and showed dynamic behavior at room temperature.

Toward Asymmetric Synthesis of Pentaorganosilicates.

Introducing chiral silicon centers was explored for the asymmetric Rh-catalyzed cyclization of dihydrosilanes to enantiomerically enriched spirosilanes as targets to enable access to enantiostable pentacoordinate silicates. The steric rigidity required in such systems demands the presence of two naphthyl or benzo[b]thiophene groups. The synthetic approach to the expanded spirosilanes extends Takai's method (Kuninobu et al.

Synthesis and Reactivity of the Phosphorus Analogues of Cyclopentadienone, Tricyclopentanone, and Housene.

The phosphorus analogues of cyclopentadienone, tricyclopentanone, and housene were accessed from bis(cyclopropenyl)diphosphetanedione 3, which was prepared by mixing 1,2,3-tris-tert-butylcyclopropenium tetrafluoroborate (1) and sodium phosphaethynolate [Na(OCP)(dioxane) ]. While photolysis of 3 results in decarbonylation, yielding bis(cyclopropenyl)diphosphene 4 and after rearrangement diphosphahousene 5, thermolysis of 3 leads to phosphatricyclo[2.1.

Reactivity of the geminal phosphinoborane tBuPCHBPh towards alkynes, nitriles, and nitrilium triflates.

The reactivity of the geminal phosphinoborane tBuPCHBPh towards terminal alkynes, nitriles and nitrilium salts is investigated. Terminal alkynes react via C-H bond splitting (deprotonation) resulting in the formation of phosphonium borates. In contrast, both nitriles and nitrilium salts undergo addition reactions resulting in the formation of five-membered heterocycles.