Methylene Insertion Reaction Research Articles

Stereochemistry of oxidative addition reactions of cycloneophyl complexes of Platinum(II): A methylene insertion reaction from dichloromethane

Unusual features are observed in studies of oxidative addition to cycloneophylplatinum(II) complexes [Pt(CH2CMe2C6H4)(NN)], 2, NN = 3,4,7,8-tetramethyl-1,10-phenanthroline (phen*) or 3, NN = 4,4′-di-t-butyl-2,2′-bipyridine (bubipy). The oxidative addition of 4-nitrobenzyl bromide to 2 or of HgCl2 to 3 occurs with cis stereochemistry to give [PtBr(CH2-4-C6H4NO2)(CH2CMe2C6H4)(phen*)] or [PtCl(HgCl)(CH2CMe2C6H4)(bubipy)], whereas similar reactions with dimethylplatinum(II) complexes occur with trans stereochemistry. The reaction of 2 with CH2Cl2 occurs, with formal insertion of methylene into the arylplatinum bond, to give [PtCl2(CH2CMe2C6H4CH2)(phen*)], the first time such a reaction has been observed with the reagent CH2Cl2. Hydrogen peroxide reacts with 2 to give oxidative addition with trans stereochemistry to give [Pt(OH)2(CH2CMe2C6H4)(phen*)] and reaction with chlorinated solvent then gives [PtCl(OH)(CH2CMe2C6H4)(phen*)]. Depending on the reaction conditions, the peroxyacid m-ClC6H4CO3H reacts with 2 to give [Pt(OH2)2(CH2CMe2C6H4)(phen*)](m-ClC6H4CO2)2, [{Pt(OH2)2(CH2CMe2C6H4)(phen*)}.{Pt(OH)(OH2)(CH2CMe2C6H4)(phen*)}](m-ClC6H4CO2)3, or [PtCl{OOC(=O)C6H4Cl-m}(CH2CMe2C6H4)(phen*)]. Computational studies indicate that the stereochemistry of oxidative addition may be determined by kinetic or thermodynamic factors in different cases, and that the unique CH2 insertion reaction with CH2Cl2 occurs by a radical mechanism. X-ray structure determinations are reported for eight of the platinum(IV) complexes.

Equivalent chain lengths of all C4– C23 saturated monomethyl branched fatty acid methyl esters on methylsilicone OV-1 stationary phase

Isomer mixtures of monomethyl branched saturated C7– C23 fatty acid methyl esters (FAME) were prepared by performing a methylene insertion reaction to the straight chain FAME and this study model was completed by using commercially available standards of C4– C7 FAME. The equivalent chain lengths ( ECL) of all 220 C4– C23 monomethyl branched FAME on OV-1 stationary phase were measured, achieving an average repeatability of ±0.0004 ECL units. The monomethyl branched FAME was identified by GC on the basis of regularity of the fractional chain lengths ( FCL) dependence on the number of carbon atoms ( C z ) of individual homologous series of methyl 2-, 3-, …, 21-FAME. The prediction of retention of the first homologues, having the new position of methyl group beginning at higher carbon atoms number, and analogously for the second, third, fourth, and other members of the homologous series, allowed the dependence FCL = f( C z ) for the first and subsequent members of beginning homologous of monomethyl derivatives of FAME. The identification was confirmed by mass spectrometry. All of the methyl isomers of FAME, which could not be completely separated by gas chromatography due to having a methyl group in surroundings of the middle of the carbon chain, were resolved by mass spectrometry using deconvolution in a SIM-mode. Measured gas chromatographic and mass spectrometric data were applied for identification of the monomethyl branched saturated FAME in tongue coating.

ChemInform Abstract: Selective Multiple Methylene Insertion Reactions Mediated by Iodomethylzinc Iodide: Mechanistic Considerations and Synthetic Applications.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Temperature-programmed gas chromatography linear retention indices of all C 4–C 30 monomethylalkanes on methylsilicone OV-1 stationary phase : Contribution towards a better understanding of volatile organic compounds in exhaled breath

Monomethylated alkanes have been proposed to be contained in exhaled breath, their concentration pattern serving for identification of lung carcinoma, breast carcinoma and rejection of foreign tissue after heart transplant rejection. Improving the accuracy of identification for monomethylated alkanes will enhance work on their biochemical background which presently is unknown. The programmed temperature linear retention indices of all 196 C 4–C 30 monomethylalkanes on OV-1 stationary phase were measured with an average repeatability of ±0.07 index units (i.u.). The mixture of C 9–C 30 monomethylalkanes was prepared by methylene insertion reaction to C 8–C 29 n-alkanes mixture. The preliminary identification of monomethylalkanes was performed on the basis of the dependence of homomorphy factors on the number of carbon atoms of individual homologous series of monomethylalkanes (retention indices extrapolated with s = 0.15 i.u.). The prediction of retention of isomers with new position of methyl group beginning at higher carbon atoms number, as well as for second, third, fourth, etc., member of homologous series allowed the dependence H P = f( C n ) for first, second, third, etc., members of beginning homologous of monomethylalkane series (retention indices extrapolated with s = 0.17 i.u.). The identification was confirmed by mass spectrometry. All gas chromatographic unseparated monomethylalkane isomers with methyl-group near the middle of molecule carbon chain were resoluted by mass spectrometric deconvolution. Obtained regular dependences H P = f( C n ) allow precise retention prediction of monomethylalkanes C 30.

The Chemistry of CH2I2 on MoAl Alloy Thin Films Formed on Dehydroxylated Alumina: Insight into Methylene Insertion Reactions

The chemistry of diiodomethane is explored in ultrahigh vacuum on a MoAl alloy film grown on planar, dehydroxylated alumina by reaction with molybdenum hexacarbonyl. The majority of the diiodomethane forms methylene species below approximately 250 K, although a small proportion forms CH(2)I((ads)), which hydrogenates to form iodomethane. The majority ( approximately 90%) of the adsorbed methylene species thermally decomposes to carbon and hydrogen. The remainder undergoes several reactions, including partial hydrogenation to form adsorbed methyl species or total hydrogenation to form methane. The methyl species can couple forming ethane or undergo methylene insertion reactions to form alkyl species up to C(4). These form alkenes via a beta-hydride elimination reaction. This chemistry is relatively unique, only having been found previously for Ni(110) surfaces. No such chemistry is found on Ni(100) and Ni(111).

Evidence of carbon–carbon bond formation on GaAs(100)via Fischer–Tropsch methylene insertion reaction mechanism

Sequential multiple methylene (CH2) insertions into adsorbed methyl species on clean gallium-rich GaAs(100)-(4 x 1) occurs to form higher alkenes (ethene, propene, butene) and two higher alkyl iodides (iodoethane, iodopropane), not reported for a semiconductor surface previously.

A Spectroscopic Investigation of Carbon−Carbon Bond Formation by Methylene Insertion on a Ag(111) Surface: Mechanism and Kinetics

Using reflection-absorption infrared spectroscopy (RAIRS) and temperature-programmed reaction spectroscopy (TPRS), we have investigated the cross-coupling reaction between CH(2)(a) and CF(3)(a) on a Ag(111) surface. CH(2)(a) and CF(3)(a) are generated by thermal decomposition of adsorbed CH(2)I(2) and CF(3)I. RAIRS results unambiguously demonstrate that CH(2)(a) inserts into the Ag-CF(3) bond to produce adsorbed CF(3)CH(2)(a), which upon heating selectively undergoes beta-fluorine elimination to form CH(2)=CF(2). Increasing the CH(2)(a) and CF(3)(a) coverage leads to the sequential insertion of CH(2)(a) into Ag-CF(3), as evidenced by CH(2)CH(2)CF(3)(a) formation detected with RAIRS. Prior to the insertion reaction, the evidence favors islanding of fragments. The methylene insertion reaction is so facile that it occurs at cryogenic temperatures (120 K). Time-resolved RAIRS (TR-RAIRS) results at selected temperatures reveal an activation energy of 5.8 kJ/mol. Our results provide, for the first time, direct spectroscopic information about the mechanism and kinetics of the methylene insertion reaction.

Synthesis of Bis(Alkyltelluro)Methanes and their Complexation with Cadmium(II)

A novel and convenient route for the synthesis of a series of bis(alkyltelluro)methanes (alkyl─ethyl, isopropyl, n-butyl and n-hexyl) is described by one pot methylene insertion reaction using dialkyl ditellurides, sodium borohydride and chloroform. The cadmium(II) complexes of bis(isopropyltelluro)methane were also synthesized. The bis(alkyltelluro)meth-anes were characterized by elemental analysis, 1H and 125Te NMR. The product of the complexation of bis(isopropyl telluro)methane with Cd(II) have been characterized by elemental analysis, 1H, TGA and FAB mass spectrometry. The dialkyltelluroether ligands may be useful in organic synthesis and their complexes with cadmium(II) can be considered a potential single source of metal-organic chemical vapor deposition (MOCVD) precursors for advanced electronic materials.

Theoretical study of the fluorine effect on the methylene insertion reaction in the hydrogen molecule, hydrogen fluoride, and the fluorine molecule

Complete ab initio studies were performed with the goal of determining the reactivity of methylene and fluorinated methylene in an insertion reaction with the hydrogen molecule, hydrogen fluoride, and fluorine molecules. An energy profile for these reactions was computed, elucidating the reactants’ complex and the transition state structures. The complexation energies, activation barriers, and enthalpies of the reactions were used comparatively to determine the relative carbene stability and reactivity, as well as the influence of fluorine as a substituent on the reaction potential energy surface.

A New Efficient Method for S–CH2–S Bond Formation and Its Application to a Djenkolic Acid-Containing Cyclic Enkephalin Analog

Abstract An efficient methylene insertion reaction to construct an S–CH2–S bridge between two cysteine residues occurred when the thiol-protecting dimethylphosphinothioyl (Mpt) group of Z–Cys(Mpt)–OMe was removed with tetrabutylammonium fluoride hydrate in CH2Cl2. The thiol-free form gave similar results, albeit the yields were somewhat lower. In both cases, the best yields were obtained using 2 molar amounts of the reagent. Higher amounts of the reagent reduced the yield because of dehydroalanine formation. In the case of penicillamine, the thiol-free form was better in reactivity than the S-Mpt form, which required double the amount of the reagent to give the same yield. The reaction was successfully used in a synthesis of a cyclic enkephalin analog with the S–CH2–S bridge.

Effects of Fluorination on Methylene Insertion Reactions

The potential energy surfaces for the insertion reactions of methylene and fluorinated methylenes into the H2, HF, and F2 molecules were studied by density functional, many body perturbation, and coupled-cluster theories. These methods predict the barrier for the CF2 insertion into the hydrogen molecule to be about 33 kcal/mol, that is, significantly lower than previous estimates. A new transition state was found in this system for the reaction path which leads to CHF + HF. However the transition state for this metathesis channel is about 25 kcal/mol higher than that of the insertion channel. For the fluoromethylene insertion into H2 the predicted activation energy is about 8 kcal/mol. The CH2 insertion into F2 proceeds without a barrier. The peculiarity of the insertion reactions between carbenes and HF involves formation of a hydrogen-bonded complex. The CH2···HF complex is bound by about 10 kcal/mol relative to CH2 + HF. Coupled-cluster methods predict a small (ca. 3 kcal/mol) barrier for transformatio...

ChemInform Abstract: Methylene Insertion Reactions of Samarium Carbenoids into Boron‐ Hydrogen and Phosphorus‐Hydrogen Bonds.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Methylene Insertion Reactions of Samarium Carbenoids into Boron–Hydrogen and Phosphorus–Hydrogen Bonds

Abstract A samarium carbenoid, generated from diiodomethane and samarium metal, reacts with phosphine–boranes to afford phosphine–monomethylborane in good yields. The P–H bonds of secondary phosphine–boranes or secondary phosphine oxides are subjected to methylene insertion with the same carbenoid to give the corresponding P-methylated derivatives.

Alkyl Chain Propagation by Methylene Insertion on Cu(100)

One of the mechanisms proposed for formation of carboncarbon bonds in the Fischer-Tropsch synthesis, the so-called carbide/methylene mechanism, involves the propagation of alkyl chains on the catalyst surface by methylene insertion. The studies reported here provide evidence for this reaction on single crystal copper surfaces under ultra-high vacuum conditions. Alkyl iodides are used as molecular precursors to generate adsorbed methylene and alkyl groups on a Cu(100) surface. High-resolution electron energy loss spectroscopy and work function change measurements show that CI bond dissociation occurs below 200 K in iodoalkanes to form alkyl groups on the surface. Indirect evidence supports the formation of adsorbed methylene groups via CH2I2 dissociation. Temperature-programmed reaction studies of the CH2 + CD3 reaction show that sequential CH2 insertion followed by β-hydride elimination produces ethylene-d2 and propylene-d3. Similarly, reaction of CH2 with C2D5 produces propylene-d4. All of these reactions are extremely facile, occurring at 230-250 K with activation energies of 12-20 kcal/mol. Similar studies on Cu(110) show that the methylene insertion reaction is structure sensitive, being approximately two orders of magnitude faster on Cu(100) than on Cu(110). The source of this difference appears to be slow diffusion of methylene across the corrugated Cu(110) surface.

Selective multiple methylene insertion reactions mediated by iodomethylzine iodide: Mechanistic considerations and synthetic applications

The reaction of alkynylcoppers 1 with an excess of iodomethylzinc iodide selectively furnishes the quadruple methylene insertion copper organometallics 2 in fair to good yields. The mechanism of the reaction has been investigated and postulated intermediates such as 4 or 8 have been trapped with electrophiles like aldehydes or ketones in excellent yields. A new in situ preparation of propargylic copper derivatives 4 starting from readily available alkynylcopper compounds has been developed leading to homopropargylic alcohols in 80–95% yield.

Ab initio spin-coupled description of the reactions CH2(1A1) + H2 .fwdarw. CH4 and CH4 .fwdarw. CH3(2A1') + H

Spin-coupled theory, which represents the modern development of valence bond theory, is applied to the singlet methylene insertion reaction CH{sub 2}({sup 1}A{sub 1}) + H{sub 2} {yields} CH{sub 4} and to the hydrogen atom abstraction reaction CH{sub 4} {yields} CH{sub 3}({sup 2}A{sub 1}{prime}) + H. The spin-coupled wave function provides a highly visual model of the behavior of correlated electrons. Concepts such as directed covalent bonds, formed from the overlap of sp{sub x}-like hybrids on carbon and 1s functions on hydrogen, are shown to arise naturally from minimizing the total energy without preconceptions. There are, however, some important differences from the ideas of classical VB theory. A new non-least-motion pathway with no activation barrier is proposed for the singlet methylene insertion reaction.

2′,2′]-(+)-Catechin-(+)-taxifolin from commercial willow bark: structure, bonding positions and oxidative cleavage

[2′,2′]-(+)-Catechin-(+)-taxifolin, a novel biflavonoid from commercial willow bark (Salix spp.), is characterized by spectrometric methods. The bonding positions are established by nuclear Overhauser effect difference spectroscopy of the methyl ether acetates of the bi-(+)-taxifolin analogues, which represent products of oxidation of the methylene function of the (+)-catechin moiety and which undergo methylene insertion reactions with diazomethane. Photoinduced oxidative cleavage of the biphenyl-type interflavonoid linkage involving singlet oxygen, accompanied by intermolecular transfer of an acetyl group of the peracetate, yielding a range of flavan-3-ols and dihydroflavonols, provides the first example of this type of biflavonoid photofragmentation.

The first natural biflavonoid with flavanol and dihydroflavonol constituent units coupled at the B-ring

[2′,2′]-(+)-Catechin-(+)-taxifolin, a novel biflavonoid from commercial willow bark (Salix spp.), is characterized by spectrometric methods, the bonding positions being established by nuclear Overhauser effect difference spectroscopy of the methyl ether acetate of the bi-(+)-taxifolin analogue, which represents a product of oxidation and which undergoes methylene insertion reactions with diazomethane.

Multiple methylene insertion reactions: the crystal structure of a complex formed by insertion of methylene into a Pt–P bond

Up to three methylene groups from diazomethane may be incorporated into hydridodiplatinum(I) complexes by insertion into Pt–Pt. Pt–H and, in one case, a Pt–P bond; X-ray structure determination establishes the an M2(µ-CH2) group with no M–M bond are reported.

Metabolites from the purple heartwood of Mimosoideae. Part 2. Acacia carnei maiden: isolation, synthesis, and reactions of crombeone

The range of natural peltogynoid-type chalcone, flavonol, and dihydroflavonol analogues is extended by the recognition of carnein, β-photomethylquercitin, and (+)-2,3-trans-crombeone in the purple heartwood of Acacia carnei.The first synthesis of a 2,3-trans-peltogynone, crombeone tetramethyl ether, is effected and its catalytic reduction leads to a 2,3-trans-3,4-cis-peltogynol analogue. Crombeone itself is subject to a variety of methylene insertion reactions with diazomethane.