Reactions involving alkynes and tungsten-tungsten triple bonds supported by alkoxide ligands

W₂(OR)₆L_n compounds [R = Bu^t n = 0; R = Prⁱ or Np (Np = neopentyl), L = py (py = pyridine) or HNMe₂, n = 2] react with alkynes (R′C-CR′) under mild conditions (hexane solutions, room temperature or below) to yield a variety of products depending upon the nature of the alkoxide, the alkyne and the mole ratio of the reactants. The products include alkylidyne complexes L_n(RO)₃W CR′ (n = 1 or 0) (Schrock et al., Organometallics 1985, 4, 74), alkyne adducts, W₂(OR)₆(py)_n(μ-C₂R′₂), alkylidyne-capped tritungsten complexes, W₃(μ₃-CR′)(OR)₉, and W₂(OR)₆(L)(μ-C₄R′₄) or W₂(OR)₆(μ-C₄R′₄) (μ²-C₂R′₂) compounds. Evidence for equilibria involving alkyne adducts and alkylidyne species is found for certain combinations of R and R′. (1) The alkylidyne complexes (Bu^tO)₃ WCMe and (py)₂(Pr_iO)₃ W CNMe₂ react with CO (1 atm 22°C, in hexane) to yield alkyne adducts W₂(OBu^t)₆(μ-C₂Me₂)(CO) and W₂[(OPrⁱ)₆(CO)₂(η²-C₂(NMe₂)₂], respectively. (2) The alkylidyne complexes [Pr_iO)₂(HNMe₂)(R′C)W(μ-OPr_i)]₂ react with alkynes R′CCR′ (> 2 equiv, hexane, 22°C) to give W₂(OPr_i)₆(μ-C₄R′₄)(η²-C₂R′₂) compound (R′ = Me or Et). (3) The alkyne adducts W₂(ONp)₆(py)_n(μ-C₂R′₂) (R′ = Et or Ph, n = 1; R′ = Me, n = 2) react with W₂(ONp)₆(py)₂ in a 1:2 mole ratio at 22°C in hexane to yield W₃(μ₃-CR′)(ONp)(₉ compounds. In related reactions involving 1,2-bishydrocarbyl-tetraalkoxides, W₂(CH₂R″)₂(OR)₄, and alkynes (R′CCR′) (2 equiv), alkyne adducts of formula W₂(CH₂R″)₂(η²-C₂R′₂)₂(OPrⁱ)₄ and W₂(CH₃)₂(μ-C₂R′₂)(OBu^t)₄(py), alkylidyne-bridged complexes HW₂(μ-CR″)(μ-C₄R′₄)(OPr_i)₄ and products of WW and CC metathesis have been isolated for various combinations of R, R′ and R″.     

The Varied Frustrated Lewis Pair Reactivity of the Germylene Phosphaketene (CH{(CMe)(2,6-iPr2C6H3N)}2)GePCO

The germylene species (CH{(CMe)(2,6-iPr₂C₆H₃N)}₂)GePCO 1 is shown to react with the Lewis acids (E(C₆F₅)₃ E=B, Al). Nonetheless, 1 participates in FLP chemistry with electron deficient alkynes or olefins, acting as an intramolecular FLP. In contrast, in the presence of B(C₆F₅)₃ and an electron rich alkyne, 1 behaves as Ge-based nucleophile to effect intermolecular FLP addition to the alkyne. This reactivity demonstrates that the reaction pathway is controlled by the nature of the electrophile and nucleophile generated in solution, as revealed by extensive DFT calculations.     

Triazolyl C-nucleosides via the intermediacy of β-1′-ethynyl-2′-deoxyribose derived from a Nicholas reaction: Synthesis,photophysical properties and interaction with BSA

We report the design and synthesis of triazolyl donor/acceptor unnatural C-nucleosides via alkyne (sugar)—azide (aromatic) 1, 3-dipolar cyclo-addition reaction as a key step and studies on their photophysical properties. We have chosen β-1′-ethynyl-2′-deoxyribose as a precursor to synthesize triazolyl-C-nucleosides. Overcoming the difficulties, we obtain β-1′-ethynyl-2′-deoxyribose as a major product following a Co₂(CO)₈ catalyzed intramolecular Nicholas reaction. The 1,3-diaxial interaction is the driving force for the α to β-anomeric conversion while performing cobalt complexation followed by oxidation to afford β-1′- ethynyl-2′-deoxyribose as the major product. A Cu(I)-catalyzed click reaction between different aromatic donor/acceptor azides and β-1′- ethynyl-2′-deoxyribose generates the desired unnatural triazolyl donor-acceptor aromatic C-nucleosides (^cTB_Do/Ac) within 30 min. Single crystal X-ray structure shows the puckered conformation of sugar as C3′-exo. Studies on the photophysical properties suggests good fluorophoric as well as solvatochromic characteristics of these nucleosides. Two of the synthesised nucleosides, ^cTAnthB_Do and ^cTPyB_Do, are found to interact with BSA as the only tested protein with quenching of fluorescence signal. The designed bases, thus, might find applications in stabilizing a DNA and in the biophysical study thereof, if a pair of such donor acceptor C-nucleosides could be incorporated into a DNA sequence.     

Montmorillonite K-10 as a mild acid for the Nicholas reaction

The use of Montmorillonite K-10 as a convenient acid component in the Nicholas reaction is described. Its use permits functional selectivity, inter- and intramolecular reactions and convenience in the experimental conditions. A four-step one-pot [Co₂(CO)₆-acetylene complex formation, THP-removal, cyclization and complex cleavage] process permits the direct synthesis of 2-ethynyl-tetrahydrofuran from 6-(tetrahydro-2H-pyran-2-yloxy)hex-1-yn-3-ol.     

Probing the reactivity of microhydrated α‐nucleophile in the anionic gas‐phase SN2 reaction

To probe the kinetic performance of microsolvated α‐nucleophile, the G2(+)_M calculations were carried out for the gas‐phase S_N2 reactions of monohydrated and dihydrated α‐oxy‐nucleophiles XO^?(H₂O)_{n = 1,2} (X = HO, CH₃O, F, Cl, Br), and α‐sulfur‐nucleophile, HSS^?(H₂O)_{n = 1,2}, toward CH₃Cl. We compared the reactivities of hydrated α‐nucleophiles to those of hydrated normal nucleophiles. Our calculations show that the α‐effect of monohydrated and dihydrated α‐oxy‐nucleophiles will become weaker than those of unhydrated ones if we apply a plot of activation barrier as a function of anion basicity. Whereas the enhanced reactivity of monohydrated and dihydrated ROO^? (R = H, Me) could be observed if compared them with the specific normal nucleophiles, RO^? (R = H, Me). This phenomena can not be seen in the comparisons of XO^?(H₂O)_{n = 1,2} (X = F, Cl, Br) with ClC₂H₄O^?(H₂O)_{n = 1,2}, a normal nucleophile with similar gas basicity to XO^?(H₂O)_{n = 1,2}. These results have been carefully analyzed by natural bond orbital theory and activation strain model. Meanwhile, the relationships between activation barriers with reaction energies and the ionization energies of α‐nucleophile are also discussed. © 2015 Wiley Periodicals, Inc.     

Transition metal complexes of azo compounds : VI. Cycloaddition of alkynes to the complexed cis-azo group. Stepwise cyclodimerisation of diphenylacetylene to tetraphenylcyclobutadiene tricarbonyliron

The μ-(cis-azo) complexes LFe₂(CO)₆ (L  4-phenyl-3,3-bis(methoxycarbonyl)-1-pyrazoline, 4-isopropyl-3,3-bis(methoxycarbonyl)-1-pyrazoline, 2,3-diazanorbornene, and benzo[c]cinnoline) each contain an activated NN bond which reacts thermally and/or photochemically with the alkynes RC₂R (R  H, CH₃, Ph, COOCH₃) by insertion into the FeN bond to give the novel cycloaduct L(RC₂R)Fe₂(CO)₆. The pyrazoline and diazanorbornene complexes are transformed smoothly into the 1,2,3-diazaferrole derivatives L(RC₂R)Fe(CO)₄. These compounds react with a further molecule of the alkyne to give the “double-addition” products L(RC₂R)₂COFe(CO)₂, which can be converted into the cyclobutadiene derivative π-(RC₂R)₂Fe)CO)₃ if R  Ph; this complex can be synthesized very conveniently in yields of 70% by reaction of diphenylacetylene and the pyrazoline compound LFe₂(CO)₆ at 150°C. It is shown that the cyclodimerisation of the alkyne occurs stepwise.     

Functional sulfur-containing compounds

The Thorpe-Ziegler intramolecular cyclization of 2-RCH₂S-, 2-RCH₂S(O)-, and 2-RCH₂SO₂-substituted nicotinic acid esters and nitriles (R is alkyl, aryl, and 2-thienyl) upon the action of potassium tert-butoxide has been studied. The reaction results in the formation of the corresponding 2-R-substituted 3-aminothieno[2,3-b]pyridines, 3-aminothieno[2,3-b]pyridine 1-oxides, and 3-aminothieno[2,3-b]pyridine 1,1-dioxides with the reaction taking place only in the case if R is aryl or 2-thienyl. Methyl esters of 2-RCH₂S-, 2-RCH₂S(O)-, and 2-RCH₂SO₂-substituted nicotinic acids also undergo the intramolecular cyclization of the Dieckmann type to form the corresponding 2-R-substituted 3-hydroxythieno[2,3-b]pyridines, thieno[2,3-b]pyridin-3(2H)-one 1-oxides, and thieno[2,3-b]pyridin-3(2H)-one 1,1-dioxides. Such a reaction takes place for all the R groups except when R = AlkCH₂S and AlkCH₂S(O).     

The addition of small molecules to (η-C5H5)2Rh2(CO)(CF3C2CF3): IV. The sunlight assisted making and breaking of alkene CH bonds on the dirhodium centre; the crystal and molecular structures of (η-C5H5)2Rh2(CHCHCN){C(CF3)CF3)H} · H2O and (η-C5H5)2Rh2(CHCF2){C(CF3)C(CF3)H}

Bis-alkenyl complexes of the type (η-C₅H₅)₂RH₂(alkene − H)(alkyne + H) are obtained when the alkyne complex (η-C₅H₅)₂Rh₂(CO)(CF₃C₂CF₃) is treated with the following alkenes: H₂CCH₂, H₂CCHR (R = Me, Bu^t, Ph, CN), H₂CCF₂, RHCCHR′ (R = R′ = Me, Ph, Cl; R = Me, R′ = Et), cyclooctene and norbornene. An approximately equimolar amount of (η-C₅H₅)₂Rh₂(CO)₂(CF₃C₂CF₃) is also formed. The reactions are greatly accelerated when the reaction mixtures are exposed to sunlight. There is some regioselectivity in the reactions with H₂CCHR and MeHCCHet, with a preference for CH bond cleavage at the least crowded alkene-carbon. When the reaction with acrylonitrile is performed in the absence of sunlight, the complex (η-C₅H₅)₂(CO){(H₂CCHCN)(CF₃C₂CF₃)} can be isolated; upon exposure to sunlight, there is loss of CO and H-transfer to form two isomers of the appropriate bis-alkenyl complex.The molecular geometries of (η-C₅H₅)₂Rh₂(CHCHCN){C(CF₃)C(CF₃)H} and (η-C₅H₅)₂Rh₂(CHCF₂){C(CF₃)C(CF₃)H} have been ascertained by X-ray structure determination. Each molecule has two bridging alkenyl units spanning a RhRh single bond; the dihedral angle between the two RhRhCC planes is just above 90°. There is a cyclopentadienyl ring η⁵-attached to each metal. Crystal data: C₁₇H₁₃F₆NRh₂·H₂O, M 569.1, monoclinic, P2₁/n, a 15.014(7), b 14.882(7), c 8.590(5) Å, β 94.57(9)°, Z = 4, final R 0.056 for 2493 observed reflections; C₁₆H₁₂F₈Rh₂, M 562.1, monoclinic, P2₁/c, a 13.037(6), b 8.765(2), c 14.873(3) Å, β 103.16(3)°, Z = 4, final R 0.062 for 1820 observed reflections.     

Coordination complexes of acetylenic phosphines and diphosphines : V. Acetylene bridged derivatives of dicobalt octacarbonyl

Reactions of the phosphinoacetylenes RR′PCCR″ (R  R′  Ph, R″  H, CF₃, Ph, Me, t-Bu; R  R′  C₆F₅, R″  Ph, Me; R  Ph, R′  Me, R″  Me) with Co₂(CO)₈ have been studied. Complexes of four types have been characterised: (A)(RR′PC₂R″)CO₂(CO)₆ (R  R′  C₆F₅, R″  Ph, Me; R  R′  Ph, R″  t-Bu), (B) (RR′PC₂R″)₂Co₄(CO)₁₀ (R  R′  Ph, R″  H, CF₃, Ph, Me; R  R′  C₆F₅, R″  Me; R  Ph, R′  Me, R″  Me), (C) (RR′PC₂R″)₂Co₂(CO)₆ (R  R′  Ph, R″  t-Bu), (D) (RR′P(O)C₂R″)Co₂(CO)₆ (R  R′  Ph, R″  t-Bu; R  R′  C₆F₅, R  Ph). The complexes were characterised by microanalysis, IR, NMR and where possible mass spectra. Substitution reactions of the complexes with tertiary phosphites are described. In complexes of type (A) only the alkyne function is utilised whereas the tetranuclear compounds (B) have structures in which both alkyne and phosphorus moieties are coordinated. Compounds of type (C) are simple disubstituted phosphine complexes of Co₂(CO)₈ and those of type (D) are μ-alkyne derivatives of acetylenic phosphine oxides. The mechanism of formation of complexes of type (B) is discussed in the light of IR data.     

Synthesis and properties of alkylruthenium complexes bearing primary and secondary amine ligands

A series of 18-electron alkylruthenium complexes, RuR[κ²(N,N′)-(S,S)-R′SO₂NCHPhCHPhNH₂](η⁶-arene) (Ph = C₆H₅, R′ = p-CH₃C₆H₄ and CH₃), bearing a N-sulfonylated diamine ligand was synthesized from the reaction of RuCl[κ²(N, N′)-(S,S)-R′SO₂NCHPhCHPhNH₂](η⁶-arene) with alkylzinc reagents, in which transmetalation proceeded smoothly to give the desired alkyl complexes in good yield and selectivity. Although the isolable amine Ru complexes bearing functionalized alkyl ligands were thermally stable, the simple methyl and ethyl Ru complexes underwent intramolecular deprotonation from NH protons to give the amido Ru complexes with release of the alkanes. The reactivity of the alkyl Ru complexes is highly affected by the structures of the arene ligands.     

Diiron models for active site of FeFe-hydrogenase with aromatic thiolate bridges: Structures and electrochemistry

Complexes of type Fe₂(CO)₆(μ-SC₆H₄–R)₂, [R = p-H (1); o-CH₃O (2); p-CH₃O (3); p-Cl (4)] were synthesized by reaction of triiron dodecacarbonyl with the corresponding aromatic thiols. In the presence of an excess of PMe₃, 2 was transformed to compound Fe₂(CO)₄(μ-SC₆H₄–o-CH₃O)₂(PMe₃)₂ (5). The structures and biochemical properties of these complexes, especially electrochemistry, have been studied.     

Cumulated double bond systems as ligands : IV. 1H and 13C NMR studies of the intra- and inter-molecular exchange processes of cationic dialkylsulfurdiimine compounds of RhI,IrI and PtII

The preparation and properties are described of trans-[(Ph₃P)₂(CO)M(RNSNR)] [ClO₄] (M  Rh^I, Ir^I; R  Me, Et, i-Pr, t-Bu) and of cis- or trans-[L₂Pt(RNSNR)X] [ClO₄] (X  Cl^?, L  Et₂S, PhMe₂As, PhMe₂P, R  Me, t-Bu; X  CH₃, L  PhMe₂P, R  Me).¹H and ¹³C NMR data show the existence of various isomers in solution which may interconvert via intra- and inter-molecular exchange processes. A general reaction scheme for the intramolecular exchange processes is discussed.     

Thermal properties and reactions towards nucleophiles of an iron complex displaying an acetyl and a pyruvoyl ligands

Thermal evolution at 4 °C of the structurally characterized cis(CO)₄Fe[C(O)C(O)CH₃][C(O)CH₃] (1(2)) gives rise to the cis(CO)₄Fe[C(O)CH₃]₂ (1(3)) which, probably owing to synthetic problems, has never been described in the literature. By reaction with anionic nucleophiles (Nu⁻), 1(2) affords anionic trifunctionalized metallalactones {(CO)₃Fe[C(O)CH₃][C(O)C(CH₃)(Nu)OC⁷(O);(Fe-C⁷)]}⁻ (3) formed by addition of the nucleophile reagent on the β carbon of the pyruvoyl moiety followed by the cyclization of this ligand on a terminal carbonyl of the complex. Anions 3 are characterized by ¹H and ¹³C NMR and by X-ray diffraction for the complex with Nu = C(H)(CO₂C₂H₅)₂. Complexes 3 are also prepared by reaction of CH₃Li with the neutral metallalactones (CO)₄Fe[C(O)C(CH₃)(Nu)OC⁷(O);Fe-⁷C] (2). The results of this study shed light on the reaction of cyclization of a pyruvoyl ligand as they clearly show that the presence of a second ligand (for example CO₂R) with a labile OR group is not required to perform the formation of the metallalactone ring and then that the observed reaction has no connection with organic chain-ring transformations.     

Equilibria in complexes ofN-heterocyclic molecules,Part XV+. Intermediates in the reaction of cyanide with transition metal tris complexes of 1,10-phenanthroline, 5-nitro-1,10-phenanthroline and 2,2'-bipyridyl

Summary The Ru(phen)₃(CN)₂ · 6 H₂O, Ru(bipy)₃(CN)₂ · 6H₂O, Fe(phen)₃(CN)₂ · H₂O and Ru(5-NO₂P)₃(CN)₂ · 2 H₂O compounds have been isolated during the reaction of the parent cations with aqueous cyanide solutions. It is evident, that in each case, attack at the ligand has taken placevia the cyanide nucleophile, though the equilibrium constant for the formation of the Reissert-type species are widely different. The implications of the findings with respect to the known reaction kinetics of the parent ions in aqueous cyanide solution are discussed.Part 14: R.D. Gillard and P.A. Williams,Transition Met. Chem., 2, 109(1977)     

Synthesis of pyrrolo-pyrrolo-pyrazines via the Pd/C-catalyzed cyclization of N-propargyl pyrrolinyl-pyrrole derivatives

A novel and efficient synthesis of N-substituted dipyrrolo[1,2-a:2′,1′-c]pyrazine derivatives has been developed. The synthetic strategy relies on the synthesis of 4′,5′-dihydro-1H,3′H-2,2′-bipyrrole, followed by the reaction with propargyl bromide. Various substituents were introduced to the alkyne functionality using the Sonogashira coupling reaction. Aromatization of the dihydropyrrole ring followed by an intramolecular cyclization reaction between the alkyne functionality and the pyrrole nitrogen atom was catalyzed by Pd/C at high temperature to furnish the desired dipyrrolo-pyrazine skeleton.     

A simple organocobalt mediated synthesis of substituted 3-oxabicyclo[3.3.0]oct-6-en-7-ones

A range of substituted propargyl alcohols form ethers with allyl bromide in good yields; conversion of these ethers to the alkyne hexacarbonyl dicobalt complexes using Co₂(CO)₈, followed by intramolecular cyclisation gives substituted 3-oxabicyclo[3.3.0]oct-6-en-7-ones (4a–4e) in fair to moderate yields.     

Synthesis of highly substituted quinolines via heterocyclization of fluorinated acetylenephosphonates with ortho-aminoaryl ketones

A synthetic route to a series of 4-alkyl- or arylquinolines, bearing in 2- and 3-position fluorinated and phosphonate functions at the same time, is reported for the first time. These compounds are synthesized via regioselective heterocyclization of XCF₂-alkynylphosphonates (X=F, Cl, Br, H, CF₃) with ortho-aminoaryl ketones (R=CH₃, CF₃, Ph) in the presence of K₂CO₃ or Li₂CO₃/TMEDA as mediators. 2-Fluoro- and 3-phosphorus-containing 4-Me, 4-CF₃ or 4-Ph quinolines are obtained in good to excellent yields. The influence of substituents in the aromatic ketone, the XCF₂-group in the alkyne as well as mediators and the reaction medium on the reactivity and specificity of the reaction is also investigated.     

Use of the Mitsunobu reaction in the synthesis of orthogonally protected α,β-diaminopropionic acids

Orthogonally protected α,β-diaminopropionic acids have been synthesised in good yields by the reaction of N-trityl l-serine esters with N-substituted sulfonamides under Mitsunobu reaction conditions (DEAD, PPh₃, THF). The best isolated yields were obtained when N-Boc p-toluenesulfonamide was used as the nitrogen nucleophile precursor in the Mitsunobu reaction. Subsequently, the N-trityl group was efficiently replaced with the more stable allyloxycarbonyl (alloc) group.     

Aryl- and acetylene-nickel(I) complexes

Reduction of various pentafluorophenylnickel(II) complexes in the presence of phosphines gives unstable nickel(I) compounds but Ni(C₆F₅)(CO)₂(PPh₃)₂ is isolated in the presence of CO. Similar NiR(CO)₂(PPh₃)₂ (R = C₆F₅,C₆Cl₅, 2,3,5,6-C₆Cl₄H) are obtained by reaction of the halogenonickel(I) complex with MgRBr or LiR. Reduction of NiX₂L₂ in the presence of acetylenes gives [NiXL₂]₂(μ-PhCCR) (R = H, X = Cl and R = Ph, X = Cl, Br) when L = P-n-Bu₃ but only NiX(PPh₃)₃ are recovered when L = PPh₃. No reaction with the alkyne is observed for [NiX(PPh₃)₂]_n but [NiCl(PPh₃)]_n reacts with RCCR′ to give paramagnetic NiCl(PPh₃)(CRCR′) (R = Ph, R′= H, COOEt), diamagnetic [NiCl(PPh₃)]₂(μ-PhCCPh) and cyclotrimerization when R = R′ = COOMe. Chemical and structural behaviour of the new nickel(I) complexes is described.     

A new enzymatic strategy for the preparation of (2R,3S)-3-phenylisoserine: a key intermediate for the Taxol side chain

Burkholderia cepacia lipase PS-IM catalysed the hydrolysis of racemic ethyl 3-amino-3-phenyl-2-hydroxypropionate with excellent enantioselectivity (E >200), when the reaction was performed with added H₂O as a nucleophile, in iPr₂O, at 50 °C. The hydrolysis of the less reactive enantiomeric ethyl 3-amino-3-phenyl-2-hydroxypropionate with 18% HCl afforded the corresponding enantiomerically pure (2R,3S)-3-amino-3-phenyl-2-hydroxypropionic acid hydrochloride, a key intermediate for the Taxol side chain.