Reactions of acetylene ketones in superacids

Vinyl type cations ArC⁺=CHCOR generated from acetylene ketones ArC≡CCOR in superacids HSO₃F and CF₃SO₃H react with diverse benzene derivatives to form alkenylation products, E-/Z-isomers of diarylpropenone structures Ar(Ar’)C=CHCOR. The alkenylation of aromatic compounds with acetylene ketones in superacids occurs with the primary syn-addition of a hydrogen and an aryl residue to the acetylene bond followed by transformation of the product into anti-isomer under the conditions of the reaction.     

Trifluoromethylated allyl alcohols: acid-promoted reactions with arenes and unusual ‘dimerization’

An unusual ‘dimerization’ of CF₃-allyl alcohols [ArCHCHCH(OH)CF₃] under the action of anhydrous FeCl₃ was found to give fluorinated indanes in 62–90% yields via the formation of intermediate allyl cations. Reactions of CF₃-allyl alcohols with arenes (Ar′H) led to CF₃-alkenes [Ar(Ar′)CHCHCHCF₃] in 48–75% yields. The mechanisms of the transformations are discussed.     

A Widely Applicable Synthetic Approach to Alk‐1‐yn‐1‐yl(polyfluoroorganyl)‐iodonium Salts [(RC≡C)(R′)I][BF4]

The reaction of alkynyldifluoroboranes RC≡CBF₂ (R = (CH₃)₃C, CF₃, (CF₃)₂CF) with organyliodine difluoride R′IF₂ bearing electron‐withdrawing polyfluoroorganyl groups R′ = C₆F₅, (CF₃)₂CFCF=CF, C₄F₉, and CF₃CH₂ leads to the corresponding alkynyl(organyl)iodonium salts [(RC≡C)(R′)I][BF₄]. This approach uses a widely applicable method as demonstrated for a representative series of polyfluorinated aryl‐, alkenyl‐, and alkyliodine difluorides. Generally, these syntheses proceed with good yields and deliver pure iodonium salts. The distinct electrophilic nature of their [(RC≡C)(R′)I]⁺ cations is deduced from multinuclear magnetic resonance data. Within the series of new iodonium salts [CF₃C≡C(C₄F₉)I][BF₄] is an intrinsic unstable one and decomposed forming CF₃C≡CI and C₄F₁₀.     

Protonation of 3-Arylpropynoic Acid Derivatives in Superacids

According to the ¹H and ¹³C NMR data, 3-arylpropynoic acids and their esters XC₆H _n -C≡C-CO₂R (R = H, Me, Et) having electron-withdrawing substituents in the benzene ring (X = NO₂, CN, COMe, CO₂Me) exist in HSO₃F at ?80 to 0°C as XC₆H _n -C≡C-C⁺(OH)OR ions. Derivatives with other substituents (X = H, F, Me, MeO) in HSO₃F or CF₃SO₃H above ?40°C undergo protonation at the acetylenic carbon atom neighboring to the acid group to give unstable vinyl-type XC₆H _n -C⁺=CH-CO₂R cations which are then transformed into mixtures of stereoisomeric (Z and E) fluorosulfonates or triflluoromethanesulfonates XC₆H _n -CY=CH-CO₂R (Y = OSO₂F, OSO₂CF₃), the E isomer prevailing.     

<Emphasis Type="Italic">N</Emphasis>-allyl and <Emphasis Type="Italic">N</Emphasis>-propargyl trifluoromethanesulfonimides. Theoretical analysis

Tautomers of N-allyl- and N-propargyl-substituted trifluoromethanesulfonimides (CF₃SO₂)₂NR (R = CH₂CH=CH₂, Z/E-CH=CHMe, CH₂C≡CH, CH=CH=CH₂, C≡CCH₂) were calculated by the DFT (B3LYP, wB97XD, PBE1PBE), MP2, and CBS-QB3 methods. The results were compared with the theoretical data for the corresponding amines and amides NHRR¹ (R¹ = H, CF₃SO₂). It was shown that there is no conjugation between the nitrogen atom and C=C bond and that conjugation exists with the C≡C bond with electron density displacement toward the nitrogen atom. The calculations of anions derived from N-allyl- and N-propargyl-trifluoromethanesulfonimides revealed the possibility of their rearrangement with elimination of trifluoromethanesulfinate anion and formation of its H-complex with N-(prop-2-en-1-ylidene)trifluoromethanesulfonamide or N-(prop-2-yn-1-ylidene)trifluoromethanesulfonamide.     

Copper(I) π-complexes with 2-butyne-1,4-diol. Synthesis and crystal structure of (2-AmpH)[CuCl<Subscript>2</Subscript>(HOCH<Subscript>2</Subscript>C≡CCH<Subscript>2</Subscript>OH)] (2-AmpH<Superscript>+</Superscript> is 2-aminopyridinium cation)

Crystals of the π-complex (2-AmpH)[CuCl₂(HOCH₂C≡CCH₂OH)] (2-AmpH⁺ is the 2-aminopyridinium cation) were obtained by the reaction of 2-butyne-1,4-diol with CuCl in aqueous 2-aminopyridinium chloride solution and studied by X-ray diffraction: space group P \(\overline 1 \), a= 7.172(4), b= 7.796(3), c = 11.60(9) Å, α = 99.75(6)°, β = 96.53(7)°, γ = 101.03(3)°, Z = 2. The crystals consist of individual anions [CuCl₂(HOCH₂C≡CCH₂OH)]^? and cations [2-AmpH]⁺. The π-coordinated Cu(I) atoms of the complex anion have trigonal-planar surrounding of two chlorine atoms and C≡C bond of the 2-butyne-1,4-diol molecule. The alcohol groups form stable hydrogen bonds N-H?O (1.89 Å) and O-H?Cl (2.20 Å).     

From As‐Zincoarsasilene (LZn‐As=SiL′) to Arsaethynolato (As≡C−O) and Arsaketenylido (O=C=As) Zinc Complexes

The reactivity of the As‐zincosilaarsene LZn?As=SiL′ A (L=[CH(CMeNDipp)₂]^?, Dipp=2,6‐ⁱPr₂C₆H₃, L′=[{C(H)N(2,6‐ⁱPr₂‐C₆H₃)}₂]^2?) towards small molecules was investigated. Due to the pronounced zwitterionic character of the Si=As bond of A , it undergoes addition reactions with H₂O and NH₃, forming LZnAs(H)SiOH(L′) 1 and LZnAs(H)SiNH₂(L′) 2 . Oxygenation of A with N₂O at ?60 °C furnishes the deep blue 1,2‐disiloxydiarsene, [LZnOSi(L′)As]₂ 4 , presumably via dimerization of the arsinidene intermediate LZnOSi(L′)As 3 . Oxygenation of A with CO₂ leads to the monomeric arsaethynolato siloxido zinc complex LZnOSi(L′)(OC≡As) 5 , essentially trapping the intermediary arsinidene 3 with liberated CO following initial oxidation of the Si=As bond. DFT calculations confirm the ambident coordination mode of the anionic [AsCO] ligand in solution, with the O‐arsaethynolato [As≡C?O]^.? in 5 , and the As‐arsaketenylido ligand mode [O=C=As]^? present in LZnO?Si(L′)(?As=C=O) 5′ akin to the analogous phosphorus system, [PCO]^?.     

Versatile Reaction Pathways of 1,1,3,3,3-Pentafluoropropene at Rh(I) Complexes [Rh(E)(PEt3)3] (E=H,GePh3, Si(OEt)3, F,Cl): C-F versus C-H Bond Activation Steps

The reaction of the rhodium(I) complexes [Rh(E)(PEt₃)₃] (E=GePh₃ ( 1 ), H ( 6 ), F ( 7 )) with 1,1,3,3,3-pentafluoropropene afforded the defluorinative germylation products Z/E-2-(triphenylgermyl)-1,3,3,3-tetrafluoropropene and the fluorido complex [Rh(F)(CF₃CHCF₂)(PEt₃)₂] ( 2 ) together with the fluorophosphorane E-(CF₃)CH=CF(PFEt₃). For [Rh(Si(OEt)₃)(PEt₃)₃] ( 4 ) the coordination of the fluoroolefin was found to give [Rh{Si(OEt)₃}(CF₃CHCF₂)(PEt₃)₂] ( 5 ). Two equivalents of complex 2 reacted further by C−F bond oxidative addition to yield [Rh(CF=CHCF₃)(PEt₃)₂(μ-F)₃Rh(CF₃CHCF₂)(PEt₃)] ( 9 ). The role of the fluorido ligand on the reactivity of complex 2 was assessed by comparison with the analogous chlorido complex. The use of complexes 1 , 4 and 6 as catalysts for the derivatization of 1,1,3,3,3-pentafluoropropene provided products, which were generated by hydrodefluorination, hydrometallation and germylation reactions.     

π-Complexes of Cu(I) with Alkynes. Synthesis and Crystal Structure of Cs[CuCl<Subscript>2</Subscript>(HOCH<Subscript>2</Subscript>C≡CCH<Subscript>2</Subscript>OH)] ⋅ H<Subscript>2</Subscript>O

Crystals of anionic π-complex Cs[CuCl₂(HOCH₂C≡CCH₂OH)] ? H₂O were synthesized by reaction of 2-butyne-1,4-diol with CuCl in a saturated aqueous solution of CsCl at 90°C and studied by X-ray diffraction analysis. The crystals are triclinic (space group \(P\bar 1\) ; a = 10.155(4) Å, b = 7.828(4) Å, c = 7.115(3) Å, α = 102.62(4)°, β = 100.77(3)°, γ = 106.71(4)°, V = 509(1) ų, Z = 2) and consist of stacks of individual anions [CuCl₂(HOCH₂C≡CCH₂OH)]^? and hydrated [Cs ? H₂O]⁺ cations between the stacks. The Cu(I) atom has trigonal surrounding of two Cl atoms and the C≡C bond of 2-butyne-1,4-diol molecule. The Cu-(C≡C) distance in the π-core is 1.905(8) Å; the C≡C bond is elongated to 1.223(11) Å. In addition to hydrogen bonds O-H?Cl, crystals of the complex also contain O(w)?H-O and O(w)?Cl bonds stabilizing their structure.     

Oxydifluoromethylation of Alkenes by Photoredox Catalysis: Simple Synthesis of CF2H‐Containing Alcohols

We have developed a novel and simple protocol for the direct incorporation of a difluoromethyl (CF₂H) group into alkenes by visible‐light‐driven photoredox catalysis. The use of fac‐[Ir(ppy)₃] (ppy=2‐pyridylphenyl) photocatalyst and shelf‐stable Hu's reagent, N‐tosyl‐S‐difluoromethyl‐S‐phenylsulfoximine, as a CF₂H source is the key to success. The well‐designed photoredox system achieves synthesis of not only β‐CF₂H‐substituted alcohols but also ethers and an ester from alkenes through solvolytic processes. The present method allows a single‐step and regioselective formation of C(sp³)–CF₂H and C(sp³)?O bonds from C=C moiety in alkenes, such as hydroxydifluoromethylation, regardless of terminal or internal alkenes. Moreover, this methodology tolerates a variety of functional groups.     

Reactions of alkyl 4-hydroxybut-2-ynoates with arenes under superelectrophilic activation with triflic acid or HUSY zeolite: Alternative propargylation or allenylation of arenes,and synthesis of furan-2-ones

Reactions of alkyl 4-aryl(or 4,4-diaryl)-4-hydroxybut-2-ynoates [Ar(H or Ar')(OH)C⁴–C³≡C²–CO₂Alk] with arenes under the action of triflic acid TfOH or HUSY zeolite result in the formation of two main compounds, aryl substituted furan-2-ones or products of propargylation of electron rich arenes. Key reactive intermediates in these transformations are the corresponding O,O-diprotonated forms of starting butynoates, Ar(H or Ar')(⁺OH₂)C⁴–C³≡C²– C(=O⁺H)(OAlk), dehydration of which gives rise to mesomeric propargyl-allenyl cations Ar(H or Ar')(OH)⁴C⁺–C³≡C²–C(=O⁺H)(OAlk) ? Ar(H or Ar')(OH)⁴C = C³ = ²C⁺–C(=O⁺H)(OAlk), having two electrophilic centers on the carbons C4 and C2 respectively. Reactions of these species with arenes at C4 lead to products of arene propargylation, alternatively, reactions at C2 result in allenylation of arenes, followed by further transformation into furan-2-ones. Using quantum chemical calculations by the DFT method, it has been shown that the reactivity of such propargyl-allenyl cations is mainly explained by orbital factors. Plausible reaction mechanism is discussed.     

Fragmentation of some 4<Emphasis Type="Italic">H</Emphasis>-pyran-4-one and pyridin-4-one derivatives under electron impact

Fragmentation of 13 compounds of the 4H-pyran-4-one and pyridin-4-one series under electron impact involves formation of rearrangement ions stabilized by multiple bonds and oxygen atoms (mostly [RC≡O]⁺ and RCH=OR′]⁺), as well of neutral molecules with low enthalpies of formation (CO, H₂O, CH₂O, CO₂, CH₂=C=O, C₃O₂, and RCOOH; R = H, Me, HC≡C, HOC≡C).     

Weak hydrogen and halogen bonding in 4‐[(2,2‐difluoroethoxy)methyl]pyridinium iodide and 4‐[(3‐chloro‐2,2,3,3‐tetrafluoropropoxy)methyl]pyridinium iodide

To enable a comparison between a C—H…X hydrogen bond and a halogen bond, the structures of two fluorous‐substituted pyridinium iodide salts have been determined. 4‐[(2,2‐Difluoroethoxy)methyl]pyridinium iodide, C₈H₁₀F₂NO⁺·I⁻, (1), has a –CH₂OCH₂CF₂H substituent at the para position of the pyridinium ring and 4‐[(3‐chloro‐2,2,3,3‐tetrafluoropropoxy)methyl]pyridinium iodide, C₉H₉ClF₄NO⁺·I⁻, (2), has a –CH₂OCH₂CF₂CF₂Cl substituent at the para position of the pyridinium ring. In salt (1), the iodide anion is involved in one N—H…I and three C—H…I hydrogen bonds, which, together with C—H…F hydrogen bonds, link the cations and anions into a three‐dimensional network. For salt (2), the iodide anion is involved in one N—H…I hydrogen bond, two C—H…I hydrogen bonds and one C—Cl…I halogen bond; additional C—H…F and C—F…F interactions link the cations and anions into a three‐dimensional arrangement.     

Protonation of (μ-H)3Ru3(μ3-CR)(CO)9. Evidence for the formation of an agostic metalhydrogencarbon bond

Protonation of (μ-H)₃M₃(μ₃-CR)(CO)₉ (M = Ru, R = Et or M = Os, R = Me) by dissolution in HSO₃CF₃ yields H₃M₃(HCR)(CO)₉⁺, containing a MHC bridge. The products were characterized by ¹H and ¹³C NMR spectroscopy. Decompositions of other protonated methylidyne clusters from CH₃R and a variety of metal-containing products.     

The Use of Bridging Ligand Substituents to Bias the Population of Localized and Delocalized Mixed-Valence Conformers in Solution

The electronic structure and associated spectroscopic properties of ligand-bridged, bimetallic ‘mixed-valence’ complexes of the general form {M}(μ-B){M⁺} are dictated by the electronic couplings, and hence orbital overlaps, between the metal centers mediated by the bridge. In the case of complexes such as [{Cp*(dppe)Ru}(μ-C≡CC₆H₄C≡C){Ru(dppe)Cp*}]⁺, the low barrier to rotation of the half-sandwich metal fragments and the arylene bridge around the acetylene moieties results in population of many energy minima across the conformational energy landscape. Since orbital overlap is also sensitive to the particular mutual orientations of the metal fragment(s) and arylene bridge through a Karplus-like relationship, the different members of the population range exemplify electronic structures ranging from strongly localized (weakly coupled Robin-Day Class II) to completely delocalized (Robin-Day Class III). Here, we use electronic structure calculations with the hybrid density functional BLYP35-D3 and a continuum solvent model in combination with UV-vis-NIR and IR spectroelectrochemical studies to show that the conformational population in complexes [{Cp*(dppe)Ru}(μ-C≡CArC≡C){Ru(dppe)Cp*]⁺, and hence the dominant electronic structure, can be biased through the steric and electronic properties of the diethynylarylene (Ar) moiety (Ar=1,4-C₆H₄, 1,4-C₆F₄, 1,4-C₆H₂-2,5-Me₂, 1,4-C₆H₂-2,5-(CF₃)₂, 1,4-C₆H₂-2,5-ⁱPr₂).     

Nucleophilic Reactions of Osmanaphthalynes with PMe3 and H2O

Members of a new class of complexes, 2 (CF₃), 2 (H), 2 (Br), 2 (I), and 2 (OCH₃), have been synthesized in a one-pot method involving the treatment of osmanaphthalynes bearing corresponding substituents ( 1 (CF₃), 1 (H), 1 (Br), 1 (I), and 1 (OCH₃)) with trimethylphosphine (PMe₃) and water. The main reaction process involves two steps, namely a ligand-exchange with trimethylphosphine and nucleophilic addition of water to the Os≡C bond of the osmanaphthalyne. The substituents have a significant influence on the rate of the reaction, as befits a nucleophilic addition. Fortunately, the key intermediate [ 1 (OCH₃)]′ could be successfully captured, and the detailed reaction mechanism has been explored with the aid of density functional theory (DFT) calculations, which were in excellent agreement with the experimental findings. All of the target complexes have been fully characterized by ¹H, ³¹P{¹H}, and ¹³C{¹H} NMR spectroscopy, high-resolution mass spectrometry, and elemental analysis.     

Reductive Elimination and Oxidative Addition of Hydrogen at Organostannylium and Organogermylium Cations

Bulkily substituted organodihydrogermylium and -stannylium cations [Ar*EH₂]⁺ (E=Ge, Sn; Ar*=2,6-Trip₂C₆H₃, Trip=2,4,6-triisopropylphenyl) were characterized as salts of the weakly coordinating perfluorinated alkoxyaluminate anion [Al{OC(CF₃)₃}₄]⁻. At room temperature, the stannylium cation liberates hydrogen to generate the low valent organotin cation [Ar*Sn]⁺. In contrast, the dihydrogermylium cation transfers the hydrogen atoms to an aryl moiety of the terphenyl ligand and oxidatively adds either hydrogen under an atmosphere of hydrogen or a sp² CH unit of the 1,2-difluorobenzene solvent.     

Theoretical study on the reaction of (Z)‐CF3CHCHCF3 with OH radicals

The mechanism on the OH‐initiated atmospheric oxidation reaction of (Z)‐CF₃CH?CHCF₃ with and without O₂/NO has been investigated theoretically. The electronic structure information of the potential energy surface was obtained at the M06‐2X/aug‐cc‐pVDZ level, and the single‐point energies were refined by MCG3/3 method. The calculations show that the (Z)‐CF₃CH?CHCF₃ + OH reaction occurs via addition‐elimination mechanism, leading to products CF₃ and CF₃CH?CH(OH), rather than H‐abstraction mechanism at low temperature. Under atmospheric condition, the OH‐addition intermediate is likely to react rapidly with O₂/NO, and the likely products are CF₃C(O)H, CF₂(O), CF₃CH(OH)CH(O), FNO, and HO₂, as is proposed by experiment. © 2013 Wiley Periodicals, Inc.     

Copper(I) complexes with 2-butyne-1,4-diol: Synthesis and crystal structure of the anionic π-complex (ImH)[CuCl2(HOCH2C≡CCH2OH)] (ImH[CuCl2(HOCH2C≡CCH2OH)] (ImH+ is imidazolium cation)

The crystalline complex ImH[CuCl₂(HOCH₂C≡CCH₂OH)] has been synthesized by the direct interaction of 2-butyne-1,4-diol with CuCl in concentrated aqueous solution of (ImH)Cl (ImH⁺ is imidazolium cation) and studied by X-ray crystallography. The crystals are triclinic, space group P $\overline 1 $ , a = 7.08(2) Å, b = 7.49(1) Å, c = 10.962(8) Å, α = 101.76(8)°, β = 95.85(8)°, γ = 99.57(8)°, Z = 2. The structure consists of stacks of discrete anions [CuCl₂(HOCH₂C≡CCH₂OH)]^? arranged along the [100] axis and [ImH]⁺ cations occupying the free space. The environment of π-coordinated Cu(I) atoms is trigonal and consists of two chlorine atoms and the C≡C bond of 2-butyne-1,4-diol molecule. The alcohol groups do not participate in the coordination, but they form strong hydrogen bonds N-H···O (H···O, 1.76(6) Å) and O-H···Cl(H···Cl, 2.29(5) Å).     

5,5,5-Trichloropent-3-en-one as a Precursor of 1,3-Bi-centered Electrophile in Reactions with Arenes in Brønsted Superacid CF3SO3H. Synthesis of 3-Methyl-1-trichloromethylindenes

Reactions of 5,5,5-trichloropent-3-en-2-one Cl₃CCH=CHC(=O)Me with arenes in Brønsted superacid CF₃SO₃H at room temperature for 2 h–5 days afford 3-methyl-1-trichloromethylindenes, a novel class of indene derivatives. The key reactive intermediate, O-protonated form of starting compound Cl₃CCH=CHC(=OH⁺)Me, has been studied experimentally by NMR in CF₃SO₃H and theoretically by DFT calculations. The reaction proceeds through initial hydroarylation of the carbon-carbon double bond of starting CCl₃-enone, followed by cyclization onto the O-protonated carbonyl group, leading to target indenes. In general, 5,5,5-trichloropent-3-en-2-one in CF₃SO₃H acts as a 1,3-bi-centered electrophile.