Allyldialkyl complexes of ruthenium(IV): Preparation and reductive CC bond formation followed by CH bond activation

New η³-allyldimethyl complexes Ru(η⁵-C₅R₅)(η³-C₃H₅)(CH₃)₂, where R = H or CH₃, are prepared from Ru(η⁵-C₅R₅)(η³-C₃H₅)Br₂ by alkylation with trimethyl-aluminium. The Ru^IV dimethyl complex is thermally converted to the Ru^II 1-methylallyl compound, Ru(η⁵-C₅R₅)(η³-CH₂CHCHCH₃)L, where L = CO or t-C₄H₉NC, with evolution of methane. Kinetic and deuteration studies on the reductive process are also discussed.     

Rhodium-catalyzed CC bond formation by ring-opening of alkylidenecyclopropanes and insertion of 3-butenoic acid

Diphenylmethylenecyclopropane reacts with 3-butenoic acid in the presence of RhCl(PPh₃)₃ to give products resulting from insertion of one or two molecules of butenoic acid. Insertion of the first molecule of butenoic acid is not regioselective, whereas insertion of the second is highly regioselective.     

Dissociation potential for breaking a CH bond in methane

The potential energy along the dissociation coordinate for CH₄ → CH₃ + H is calculated by the multi-reference configuration interaction method, including all single and double excitations, with a triple-split-plus-diffuse-and-extended-polarization basis set. The three-parameter Lippincott and Varshni potential curves provide better approximations to the dissociation potential than does the Morse model.     

Novel carboncarbon bond formation induced by depalladation of organometallic compounds

Two internal alkynes undergo insertion at 20°C into the PdC bond of the cyclopalladated derivative of dimethylaminomethylferrocene to give new organometallic compounds. When the reaction with diphenylacetylene is performed at higher temperatures, depalladation occurs readily to give six- and seven-membered ortho-fused rings through new annulation reactions of phenyl groups, formation of one of these involving also the cleavage of a CN bond.     

Enantioselective synthesis of allenecarboxylates from phenyl acetates through CC bond forming reactions

A variety of optically active 4,4-disubstituted allenecarboxylic acid methyl esters were prepared from simple α,α-disubstituted phenyl acetate through base treatment of the esters to generate ketenes, followed by successive Horner–Wadsworth–Emmons reaction. The transformation was further developed as a one-pot procedure with satisfactory yields and high enantioselectivity.     

Formation of keto-carbeniums from 1,2,2-triarylacenaphthen-1-ols by breaking a long CC bond: unusual alcohol protonolysis accompanied by formal hydride abstraction

Oxidation of 1,2,2-tris(4-dimethylaminophenyl)- and 2,2-bis(4-dimethylaminophenyl)-1-phenylacenaphthen-1-ols 1a,b with I₂ induced the C₁C₂ bond fission to give 8-aroylnaphthalen-1-yl-bis(4-dimethylaminophenyl)carbenium derivatives 2a,b⁺, the intramolecular Lewis acid-base pairs. Treatment of 1 with HBF₄ did not induce the expected COH bond heterolysis but caused fission of COH and C₁C₂ bonds to give exactly the same carbenium 2⁺.     

The CF bond as a tool in the conformational control of amides

The conformation of 2-fluoro-N-(2-fluoroethyl)-propionamide 4 in the solid state indicates the influence of both a β-fluorine-amide gauche effect and an α-fluoroamide effect. The structure reveals the influence of two recently observed stereoelectronic effects associated with the CF bond, which has resulted in the successful prediction of the solid state conformation of amide 4. A gauche relationship (−69.9°) was observed for atoms N(1)C(4)C(5)F and a syn planar (2.0°) relationship was observed for N(1)C(3)C(2)F. The paper demonstrates the predictive power of using the CF bond as a tool in influencing the conformation of amides and peptides.     

A novel CC bond forming reaction of aryl-and alkenylsilanols. A halogen-free Mizoroki-Heck type reaction

When dimethyl(phenyl)silanol is subjected to on electron-deficient olefin in the presence of a stoichiometric amount of Pd(OAc)₂, substitution of the CH bond of the olefin by a phenyl group on the silanol occurs in 52–86% yields. The reactions of several aryl- and alkenylsilanols with several olefins are also found to proceed in the system of 10 mol% of Pd(OAc)₂, Cu(OAc)₂ (3 mol), LiOAc (2 mol) to give the corresponding products in up to 69% yield.     

Copper(I) promoted CC bond forming reactions: direct activation of allyl alcohols

Allylic alcohols, acetates, carbonates and chlorides can be activated by copper(I) salts towards nucleophilic substitution by carbon nucleophiles under relatively mild conditions.     

Trapping of the coordinatively unsaturated organosilicon anion radical Me3SiCCCCSiMe3− by double ate-complex formation with AIR3

Reaction of 1,4-bis(trimethylsilyl)-1,3-butadiyne with AIR₃ and potassium in THF has led to observation of the first examples of persistent radical di-ate complexes, [(R₃Al)(Me₃Si)CCCC(SiMe₃)(AIR₃)]⁻, which have been characterized by ESR spectroscopy.     

Stepwise TiCl,TiCH3, and TiC6H5 bond dissociation enthalpies in bis(pentamethylcyclopentadienyl)titanium complexes

Reaction-solution calorimetric studies involving the complexes Ti[η⁵-C₅(CH₃)₅]₂-(CH₃)₂, Ti[η⁵-C₅(CH₃)₅]₂(CH₃), Ti[η⁵-C₅(CH₃)₅]₂(C₆H₅), Ti[η⁵-C₅(CH₃)₅]₂Cl₂, and Ti[η⁵-C₅(CH₃)₅]₂Cl, have enabled derivation of titaniumcarbon and titaniumchlorine stepwise bond dissociation enthalpies in these species.     

Catalytic enantioselective carboncarbon bond formation by addition of dialkylzinc reagents to cyclic 1,3-diene monoepoxides

Chiral copper complexes of 2,2′-binaphthyl-based phosphorus amidites are shown to be highly effective catalysts for the conjugate addition of dialkylzinc reagents to vinyloxiranes. The corresponding allylic alcohol reaction products (S_N2′-pathway) were obtained with moderate to high regioselectivity. Both direct- (S_N2-pathway) and conjugate-opening addition (S_N2′-pathway) seem to proceed with complete anti stereoselectivity. The enantioselectivity of these addition reactions according to a kinetic resolution protocol turned out to be high (>90% ee) with 1,3-cyclohexadiene and 1,3-cycloheptadiene monoepoxides.     

Catalyst-free,radical-mediated intermolecular 1,2-arylheteroarylation of alkenes by cleaving inert C–C bond

A novel photoinduced intermolecular 1,2-arylheteroarylation of alkenes and the efficient synthesis of valuable polyarylalkanes are reported. The reaction is operationally simple, proceeds under mild conditions and with no additional catalyst and reagents.The strategically designed radical cascade reaction is enabled by electron transfer, and involves cleavage of an inert C–C bond.The process features broad functional group compatibility as well as high product transformability.     

Enhancement of SiH bond reactivity in pentacoordinated structures

The reactions of pentacoordinated silicon dihydrides with alcohols, carboxylic acids and carbonyl compounds have been studied. The dihydrides are markedly more reactive than the corresponding tetracoordinated species.     

Thermodynamics of the URuC system

Thermodynamic measurements by the electromotive force method were made on the binary intermetallic phases URu₃ and U₃Ru₅ and on the ternary carbides URu₃C_0.7 and U₂RuC₂ of the URu and the URuC systems between 950 and 1200 K using galvanic cells with CaF₂ single crystal electrolytes: U, UF₃¦CaF₂¦UF₃, URu₃, Ru; U, UF₃¦CaF₂¦UF₃, U₃Ru₅, URu₃; Ru, URu₃, UF₃¦CaF₂¦UF₃, URu₃C_0.7, Ru, C; U, UF₃¦CaF₂¦UF₃, URu₃C_0.7, U₂RuC₂, C. The Gibbs energies of formation of URu₃, U₃Ru₅, URu₃C_0.7 and U₂RuC₂ were evaluated from the measured electromotive force which give ^fΔG^o〈URu₃〉 = −199 100 + 35.9 T J mol^−1fΔG^o〈U₃Ru₅〉 = −398 600 + 43.6 T J mol^−1fΔG^o〈URu₃C_0.7〉 = −192 600 + 2.5 T J mol^−1fΔG^o〈U₂RuC₂〉 = −380 200 + 52.5 T J mol⁻¹ The implications of these thermodynamic data for the behaviour of the fission product ruthenium in irradiated carbide fuels are discussed.     

Stereoselective synthesis of C15C24 and C25C30 fragments of dolabelides

The stereocontrolled synthesis of a C15C24 fragment of dolabelides is reported. The C19 and C21 hydroxyl-bearing stereocenters were installed using ruthenium-mediated asymmetric hydrogenations of cyclic hemiketal 4 and β-keto ester 7. The C25C30 portion of dolabelides was prepared as well by ring opening of chiral epoxy alcohol 12 to set up the C27 stereogenic center.     

Regiocontrol switching in CC bond formation during decomplexation of a tricarbonyl(η4-cyclohexadiene)iron complex

A study has been made of additions of nucleophiles to the tricarbonyl(η⁴-cyclohexadiene)iron complex 1 and subsequently reaction of the resulting anions with several electrophiles in the presence of added ligands. Carbonyl insertion to form a functionalised cyclohexene ring is assisted by the addition of phosphines. Depending on the electrophilic reagent, an unusual phosphine-controlled switch in regiochemistry (PhCH₂Br), and interruption of the process prior to loss of the metal (CH₂=CHCH₂Br), have been observed.