Methyl Bond Research Articles

Density Functional Theory Study of Oxygen-Atom Insertion into Metal–Methyl Bonds of Iron(II), Ruthenium(II), and Osmium(II) Complexes: Study of Metal-Mediated C–O Bond Formation

Metal-mediated C-O bond formation is a key step in hydrocarbon oxygenation catalytic cycles; however, few examples of this reaction have been reported for low-oxidation-state complexes. Oxygen insertion into a metal-carbon bond of Cp*M(CO)(OPy)R (Cp* = η(5)-pentamethylcyclopentadienyl; R = Me, Ph; OPy = pyridine-N-oxide; M = Fe, Ru, Os) was analyzed via density functional theory calculations. Oxygen-atom insertions through a concerted single-step organometallic Baeyer-Villiger pathway and a two-step pathway via a metal-oxo intermediate were studied; calculations predict that the former pathway was lower in energy. The results indicated that functionalization of M-R to M-OR (R = Me, Ph) is plausible using iron(II) complexes. Starting from Cp*Fe(CO)(OPy)Ph, the intermediate Fe-oxo showed oxyl character and, thus, is best considered an Fe(III)O(•-) complex. Oxidation of the π-acid ancillary ligand CO was facile. Substitutions of CO with dimethylamide and NH3 were calculated to lower the activation barrier by ∼1-2 kcal/mol for formation of the Fe(III)O(•-) intermediate, whereas a chloride ligand raised the activation barrier to 26 kcal/mol from 22.9 kcal/mol.

Nickel-Catalyzed Site-Selective Alkylation of Unactivated C(sp3)–H Bonds

The direct alkylation of unactivated sp(3) C-H bonds of aliphatic amides was achieved via nickel catalysis with the assist of a bidentate directing group. The reaction favors the C-H bonds of methyl groups over the methylene C-H bonds and tolerates various functional groups. Moreover, this reaction shows a predominant preference for sp(3) C-H bonds of methyl groups via a five-membered ring intermediate over the sp(2) C-H bonds of arenes in the cyclometalation step.

Nickel-Catalyzed Direct Arylation of C(sp3)–H Bonds in Aliphatic Amides via Bidentate-Chelation Assistance

The Ni-catalyzed, direct arylation of C(sp(3))-H (methyl and methylene) bonds in aliphatic amides containing an 8-aminoquinoline moiety as a bidentate directing group with aryl halides is described. Deuterium-labeling experiments indicate that the C-H bond cleavage step is fast and reversible. Various nickel complexes including both Ni(II) and Ni(0) show a high catalytic activity. The results of a series of mechanistic experiments indicate that the catalytic reaction does not proceed through a Ni(0)/Ni(II) catalytic cycle, but probably through a Ni(II)/Ni(IV) catalytic cycle.

TG/FTIR analysis on co-pyrolysis behavior of PE, PVC and PS

The pyrolysis and co-pyrolysis behaviors of polyethylene (PE), polystyrene (PS) and polyvinyl chloride (PVC) under N2 atmosphere were analyzed by Thermal gravimetric/Fourier transform infrared (TG/FTIR). The volatile products were analyzed to investigate the interaction of the plastic blends during the thermal decomposition process. The TGA results showed that the thermal stability increased followed by PVC, PS and PE. The pyrolysis process of PE was enhanced when mixed with PS. However, PS was postponed when mixed with PVC. As for PE and PVC, mutual block was happened when mixed together. The FTIR results showed that the free radical of the decomposition could combine into a stable compound. When PE mixed with PVC or PS, large amount of unsaturated hydrocarbon groups existed in products while the content of alkynes was decreased. The methyl (CH3) and methylene (CH2) bonds were disappeared while PVC mixed with PE.

Reductive functionalization of a rhodium(iii)–methyl bond by electronic modification of the supporting ligand

Net reductive elimination (RE) of MeX (X = halide or pseudo-halide: Cl(-), CF3CO2(-), HSO4(-), OH(-)) is an important step during Pt-catalyzed hydrocarbon functionalization. Developing Rh(I/III)-based catalysts for alkane functionalization is an attractive alternative to Pt-based systems, but very few examples of RE of alkyl halides and/or pseudo-halides from Rh(III) complexes have been reported. Here, we compare the influence of the ligand donor strength on the thermodynamic potentials for oxidative addition and reductive functionalization using [(t)Bu3terpy]RhCl (1) {(t)Bu3terpy = 4,4',4''-tri-tert-butylpyridine} and [(NO2)3terpy]RhCl (2) {(NO2)3terpy = 4,4',4''-trinitroterpyridine}. Complex 1 oxidatively adds MeX {X = I(-), Cl(-), CF3CO2(-) (TFA(-))} to afford [(t)Bu3terpy]RhMe(Cl)(X) {X = I(-) (3), Cl(-) (4), TFA(-) (5)}. By having three electron-withdrawing NO2 groups, complex 2 does not react with MeCl or MeTFA, but reacts with MeI to yield [(NO2)3terpy]RhMe(Cl)(I) (6). Heating 6 expels MeCl along with a small quantity of MeI. Repeating this experiment but with excess [Bu4N]Cl exclusively yields MeCl, while adding [Bu4N]TFA yields a mixture of MeTFA and MeCl. In contrast, 3 does not reductively eliminate MeX under similar conditions. DFT calculations successfully predict the reaction outcome by complexes 1 and 2. Calorimetric measurements of [(t)Bu3terpy]RhI (7) and [(t)Bu3terpy]RhMe(I)2 (8) were used to corroborate computational models. Finally, the mechanism of MeCl RE from 6 was investigated via DFT calculations, which supports a nucleophilic attack by either I(-) or Cl(-) on the Rh-CH3 bond of a five-coordinate Rh complex.

Inside Cover: Chemoselective Oxidative C(CO)C(methyl) Bond Cleavage of Methyl Ketones to Aldehydes Catalyzed by CuI with Molecular Oxygen (Angew. Chem. Int. Ed. 43/2013)

Inside Cover: Chemoselective Oxidative C(CO)C(methyl) Bond Cleavage of Methyl Ketones to Aldehydes Catalyzed by CuI with Molecular Oxygen (Angew. Chem. Int. Ed. 43/2013)

On the physical interpretation of ab initio normal-mode coordinates for the three C–H stretching vibrations of methanol along the internal-rotation path

Graphical representations are presented for variation along the steepest-descent internal-rotation path in methanol of the normal mode frequencies and their associated eigenvectors in several sets of internal coordinates and in Cartesian atomic displacement vectors di(γ), as determined for the three CH stretching vibrations (ν3, ν2, and ν9) by projected-frequency calculations from the Gaussian suite of programs. The methyl-group CH stretching modes are interesting because the symmetry environment of each C–H bond changes significantly during the internal rotation, i.e., each of the methyl bonds takes turns passing (twice for a complete torsional revolution) through the plane of symmetry of the COH frame of the molecule. No accumulation of geometric phase is observed in any of these plots, and all quantities return to their original values after the internal rotation angle γ increases by 2π. A simple two-vibrational-state, three-parameter model, closely based on earlier models from the literature, can be used to understand nearly quantitatively much of the γ-variation observed in the Gaussian plots, including a number of cusp-like features. In particular, when the three parameters in the model are determined from a fit to the Gaussian projected frequencies for ν2 and ν9 at the top and bottom of the internal rotation path, it is found that the Renner–Teller-like torsion–vibration interaction term is slightly larger in magnitude than the Jahn–Teller-like term, which is consistent with no accumulation of geometric phase in the various plots. Finally, a highly simplified computation is presented to illustrate the changes that will be necessary in order to move from the usual diabatic torsion–vibration treatments in the literature to adiabatic treatments, in which the normal-mode Cartesian displacement vectors given at each point along the internal rotation path by the Gaussian projected frequency calculation are used directly in the torsion–vibration energy level calculation.

Chemoselective Oxidative C(CO)C(methyl) Bond Cleavage of Methyl Ketones to Aldehydes Catalyzed by CuI with Molecular Oxygen

Bis zum Aldehyd: Eine kupferkatalysierte Umsetzung von Methylketonen zu Aldehyden wurde entwickelt. Die Methode kann für eine Vielzahl aromatischer und aliphatischer Methylketone verwendet werden und führt chemoselektiv zu Aldehyden, wobei lediglich Wasserstoff (H2) und Kohlendioxid (CO2) als Beiprodukte entstehen. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Chemoselective Oxidative C(CO)C(methyl) Bond Cleavage of Methyl Ketones to Aldehydes Catalyzed by CuI with Molecular Oxygen

Aldehyde Termination: A novel copper-catalyzed transformation from methyl ketones into aldehydes has been accomplished. This method is applicable to a wide range of aromatic and aliphatic methyl ketones and chemoselectively produces aldehydes, accompanied by the release of hydrogen (H2 ) and carbon dioxide (CO2 ) as by-products.

Ruthenium-catalyzed cyclocarbonylation of aliphatic amides through the regioselective activation of unactivated C(sp3)–H bonds

The regioselective carbonylation of unactivated C(sp3)–H bonds of aliphatic amides, using 2-pyridinylmethylamine as a directing group in conjunction with Ru3(CO)12 as a catalyst is described. The presence of a 2-pyridinylmethylamine moiety in the amides is crucial for the success of the reaction. Although ethylene is not incorporated into the products, its presence is also essential for the reaction to proceed. Furthermore, the addition of H2O is important for the reaction to proceed efficiently. The reaction shows a high preference for the C–H bonds of methyl groups, compared to methylene C–H bonds, even the methylene C–H bonds are activated by the presence of an oxygen atom or an aryl group. In addition, the reaction tolerates various functional groups, such as MeO, Cl, CF3, CN, and even Br substituents. The reaction of α-mono-substituted aliphatic amides gave the corresponding carbonylation products in lower yields, although the use of α,α-di-substituted aliphatic amides resulted in high product yields. The use of a sterically demanding directing group, such as 1-(2-pyridinylethyl)amine moiety, in α-mono-substituted aliphatic amides improved the yields of the products. The stoichiometric reaction of an amide with Ru3(CO)12 gave a stable di-nuclear ruthenium complex as a single ruthenium complex in which the 2-pyridinylmethylamino moiety is coordinated to the ruthenium center in a N,N-manner and an amide carbonyl oxygen binds to the other ruthenium center, but C–H bond activation is not involved. The complex itself does not show catalytic activity, but is activated in the presence of H2O under the catalytic reaction conditions employed.

Mechanism of Hydrogenolysis of an Iridium–Methyl Bond: Evidence for a Methane Complex Intermediate

Evidence for key σ-complex intermediates in the hydrogenolysis of the iridium-methyl bond of (PONOP)Ir(H)(Me)(+) (1) [PONOP = 2,6-bis(di-tert-butylphosphinito)pyridine] has been obtained. The initially formed η(2)-H(2) complex, 2, was directly observed upon treatment of 1 with H(2), and evidence for reversible formation of a σ-methane complex, 5, was obtained through deuterium scrambling from η(2)-D(2) in 2-d(2) into the methyl group of 2 prior to methane loss. This sequence of reactions was modeled by density functional theory calculations. The transition state for formation of 5 from 2 showed significant shortening of the Ir-H bond for the hydrogen being transferred; no true Ir(V) trihydride intermediate could be located. Barriers to methane loss from 2 were compared to those of 1 and the six-coordinate species (PONOP)Ir(H)(Me)(CO)(+) and (PONOP)Ir(H)(Me)(Cl).

Manganese(III) acetate induced radical addition of azide to unsaturated fatty compounds

AbstractNitrogen functionalities can be introduced in the alkyl chain of unsaturated fatty compounds by addition of azide mediated by manganese(III) acetate. The respective reaction of methyl oleate 1 containing an internal C,C double bond gave allyl azide 3 as a mixture of 4 regioisomers while the addition of azide to the terminal C,C double bond of methyl 10‐undecenoate 2 afforded the vicinal diazide 6. Azide 3 could be easily converted to the saturated amine 4 by catalytic hydrogenation and to the allyl amines 5 by the Staudinger reaction.

Toward the Characterization of Fractional Stochastic Processes Underlying Methyl Dynamics in Proteins

In this article, we investigate the multiple-scale structure of methyl side chain dynamics in proteins. We show that the orientational correlation functions of CH(3) methyl groups are well described by a fractional Brownian dynamics model. Typical angular correlation functions involved in NMR relaxation were computed from MD simulations performed on two different proteins. These correlation functions were shown to be very well fitted by a fractional Ornstein-Uhlenbeck process in the presence of effective local potentials at the C-H and C-C methyl bonds. In addition, our analysis highlights the presence of the asymptotic power law decay of the waiting time probability density of the stochastic process involved, thereby illustrating the connection between approaches based on fractional diffusion equations and the continuous time random walk.

Flavin-Catalyzed Insertion of Oxygen into Rhenium–Methyl Bonds

Flavins and related molecules catalyze organic Baeyer-Villiger reactions. Combined experimental and DFT studies indicate that these molecules also catalyze the insertion of oxygen into metal-carbon bonds through a Baeyer-Villiger-like transition state.

Computational Investigation of the Mechanism for the Activation of CO by Oxorhenium Complexes

In this paper a computational analysis (B3PW91) of the previously reported reaction of (O)Re(Me)(DAAm) (1; DAAm = N,N-bis(2-arylaminoethyl)methylamine, aryl = C6F5) with CO to produce (CO)Re(OAc)(DAAm) (2) is described. The data suggest that this transformation proceeds by two novel elementary steps that are of fundamental interest to the broader organometallic/inorganic community: (a) direct insertion of CO into the rhenium–methyl bond in 1 to yield the acyl intermediate (O)Re(Ac)(DAAm) (3) and (b) 1,2-migration, in the presence of CO, of the acyl fragment in 3 to the oxo ligand to yield 2. Evidence is provided for the first example of an insertion reaction where CO inserts directly into a M–R bond without prior formation of a CO adduct. In addition, it was shown that the addition of CO is necessary for the 1,2-migration of the acyl ligand. The data suggest that the addition of CO effectively weakens the Re–Cacyl bond in 3 and enables the facile migration of the acyl ligand.

Kinetics and Thermochemistry of 2,5-Dimethyltetrahydrofuran and Related Oxolanes: Next Next-Generation Biofuels

The enthalpies of formation, entropies, specific heats at constant pressure, enthalpy functions, and all carbon-hydrogen and carbon-methyl bond dissociation energies have been computed using high-level methods for the cyclic ethers (oxolanes) tetrahydrofuran, 2-methyltetrahydrofuran, and 2,5-dimethyltetrahydrofuran. Barrier heights for hydrogen-abstraction reactions by hydrogen atoms and the methyl radical are also computed and shown to correlate with reaction energy change. The results show a pleasing consistency and considerably expands the available data for these important compounds. Abstraction by ȮH is accompanied by formation of both pre- and postreaction weakly bound complexes. The resulting radicals formed after abstraction undergo ring-opening reactions leading to readily recognizable intermediates, while competitive H-elimination reactions result in formation of dihydrofurans. Formation enthalpies of all 2,3- and 2,5-dihydrofurans and associated radicals are also reported. It is probable that the compounds at the center of this study will be relatively clean-burning biofuels, although formation of intermediate aldehydes might be problematic.

Comparative Study of Thermal Degradation Behavior of High Char Yield Phenolic Resin and Commercial Resin

The thermal degradation behavior of high char yield phenolic resin (PF1.2) synthesized by us was investigated, in comparison with that of commercial resin (PF1.5), using TGA and13C-NMR techniques. It was found that the degradation process of PF1.2behaved very similar to that of PF1.5during heat treatment up to 700 °C under N2atmosphere, but resulted in a somewhat different extent of some specific reactions. That was, although the reactions occurring up to 700 °C were dominated by crosslinking and/or polyaromatization, fewer methyl bonds from breaking of methylene bridges were formed in PF1.2than in PF1.5. As a consequence, a higher char yield of 73.8% of PF1.2than that of PF1.5(57.5%) up to 700 °C under N2atmosphere was attached, with better thermal properties.

Comparative Study of Thermal Degradation Behavior of High Char Yield Phenolic Resin and Commercial Resin

The thermal degradation behavior of high char yield phenolic resin (PF1.2) synthesized by us was investigated, in comparison with that of commercial resin (PF1.5), using TGA and 13C-NMR techniques. It was found that the degradation process of PF1.2 behaved very similar to that of PF1.5 during heat treatment up to 700 °C under N2 atmosphere, but resulted in a somewhat different extent of some specific reactions. That was, although the reactions occurring up to 700 °C were dominated by crosslinking and/or polyaromatization, fewer methyl bonds from breaking of methylene bridges were formed in PF1.2 than in PF1.5. As a consequence, a higher char yield of 73.8% of PF1.2 than that of PF1.5 (57.5%) up to 700 °C under N2 atmosphere was attached, with better thermal properties.

Large Kinetic Isotope Effects for the Protonolysis of Metal–Methyl Complexes Are Not Reliable Mechanistic Indicators

Earlier work on protonolyses of several palladium and platinum methyl complexes (with release of methane) had suggested the possibility that observation of an unusually large kinetic isotope effect, consistent with significant contributions from quantum mechanical tunneling, might be diagnostic of a mechanism involving direct protonation of the metal–methyl bond, as opposed to one proceeding via a metal hydride intermediate. By extension of these measurements to a wider set of complexes, we find no support for the proposed correlation.

Breaking the regioselectivity rule for acrylate insertion in the Mizoroki–Heck reaction

In modern methods for the preparation of small molecules and polymers, the insertion of substrate carbon-carbon double bonds into metal-carbon bonds is a fundamental step of paramount importance. This issue is illustrated by Mizoroki-Heck coupling as the most prominent example in organic synthesis and also by catalytic insertion polymerization. For unsymmetric substrates H(2)C = CHX the regioselectivity of insertion is decisive for the nature of the product formed. Electron-deficient olefins insert selectively in a 2,1-fashion for electronic reasons. A means for controlling this regioselectivity is lacking to date. In a combined experimental and theoretical study, we now report that, by destabilizing the transition state of 2,1-insertion via steric interactions, the regioselectivity of methyl acrylate insertion into palladium-methyl and phenyl bonds can be inverted entirely to yield the opposite "regioirregular" products in stoichiometric reactions. Insights from these experiments will aid the rational design of complexes which enable a catalytic and regioirregular Mizoroki-Heck reaction of electron-deficient olefins.