RC CH Research Articles

Synthesis of Deuterated Enaminones with High Isotopic Fidelity.

The unexpected oxidation of nitrogenous heterocycles by aldehyde oxidase (AO) may be addressed by the substitution of deuterium for hydrogen adjacent to the heterocycle nitrogen atom. Enaminones are versatile intermediates in the synthesis of nitrogenous heterocycles. We report that heretofore inaccessible monodeuterated enaminones of the general structure RC(=O)CH=CDNMe2 may be synthesized from methyl ketones and DCO2Me with high isotopic fidelity and efficient utilization of deuterium.

A [C1 + C2] route to propargylidyne complexes.

The reactions of [W([triple bond, length as m-dash]CBr)(CO)2(Tp*)] (Tp* = hydrotris(dimethylpyrazolyl)borate) with a range of terminal alkynes (RC[triple bond, length as m-dash]CH), mediated by [Pd(PPh3)4] and CuI, afford new proparylidynes [W([triple bond, length as m-dash]C-C[triple bond, length as m-dash]CR)(CO)2(Tp*)] [R = tBu, C6H4X (X = H, NH2, NO2), ferrocenyl, APh3 (A = C, Si, Ge), B(O2CCH2)2NMe]. Similar treatment of [W([triple bond, length as m-dash]CBr)(CO)2(Tp*)] with Ph2Si(C[triple bond, length as m-dash]CH)2 affords the ditungstaoctatetrayne [W2(μ-C6)(CO)4(Tp*)2] while the bimetallic complex [W2{μ-([triple bond, length as m-dash]CC[triple bond, length as m-dash]C)2SiPh2}(CO)4(Tp*)2], which is obtained from [W([triple bond, length as m-dash]CBr)(CO)2(Tp*)] and Ph2Si(C[triple bond, length as m-dash]CSnPh3)2, reacts with [AuCl(THT)] (THT = tetrahydrothiophene) to provide the tetrametallic complex [W2Au2{μ-([triple bond, length as m-dash]CC[triple bond, length as m-dash]C)2SiPh2}Cl2(CO)4(Tp*)2].

Deep eutectic solvent mediated synthesis of thiomethyltriazolo[1,5-a]pyrimidines

Molecular solvents, ionic liquids, and choline chloride-based DES were evaluated for the synthesis of a methylthiotriazolo[1,5-a]pyrimidines series via the cyclocondensation reaction between 4-dimethylamino-1-aryl-3-alken-2-ones (RC(O)CH=CHNMe2, in which R=C6H5, 4-Me-C6H4, 4-OMe-C6H4, 4-F-C6H4, 4-Br-C6H4, 4-I-C6H4, Fur-2-yl, and Thien-2-yl) and 3-amino-5-methylthio-1H-1,2,4-triazole. The best result was obtained using ChCl with TsOH at a ratio of 1:2, and it drastically reduced the reaction time from 1.5h to 5min, with high regioselectivity and good yields (82–98%). Quantum chemical calculations helped to show the mechanism for high regioselectivity of the reaction. Up until now, ChCl:TsOH (1:2) has not been completely characterized and used as a catalyst in organic synthesis. Thus, it was fully characterized by NMR, DSC, TGA, and ICP-AES. The results showed that ChCl:TsOH (1:2) presents two forms that can act as catalyst: acid form (17%) and its conjugate base (83%).

Reactions of a Tungsten–Germylyne Complex with α,β-Unsaturated Ketones: Complete Cleavage of the W≡Ge Bond and Formation of Two Types of η3-Germoxyallyl Tungsten Complexes

Germylyne complex Cp*(CO)2W≡Ge{C(SiMe3)3} (1) reacted with two molecules of RC(O)CH═CH2 (R = Me, Et) to give η(3)-allyl complexes, in which an oxagermacyclopentene framework was bound to an η(3)-allyl ligand through an oxygen atom. In the reaction with α-Me-substituted MeC(O)C(Me)═CH2, 1 reacted with only one molecule of the substrate to give another type of η(3)-allyl complex, in which a five-membered oxagermacyclopentenyl ring was coordinated to the W center in an η(3) fashion. Both reactions resulted in unprecedented complete cleavage of a W≡Ge triple bond.

A theoretical study of the structure and conductivity of polycytosineacetylene

Inspired by the helical structure as well as the conductivity of DNA and substituted polyphenylacetylenes, a new kind of substituted polyacetylene is introduced. More specifically, polycytosineacetylene ((RC CH) n , R = cytosine) with a trans-polyacetylene backbone is investigated theoretically. The neutral and cationic geometries are optimized as single helical chains with n = 20. It is found that when an electron is removed the polymer stretches from 19.80 Å to 28.41 Å. The polyacetylene backbone in the optimized cationic polymer exhibits the formation of a soliton. It is predicted that a doped polycytosineacetylene would have good conductivity, and would also behave as a nanomechanical spring and as a piezoelectric material.

Kinetico-mechanistic studies of the acidolysis of Rh–C bonds in monocyclometallated dirhodium(ii) acetato complexes; influence of electronic and steric effects

The protonation/demetallation reaction, in CD(3)COOD, of phosphine monometallated triacetato-bridged dirhodium(ii) complexes of general formulae [Rh(2)(μ-OOCCH(3))(3){(RC(5)CH(3))P(RC(6)H(4))(2)}(2)] has been studied from a kinetico-mechanistic perspective. The process has been monitored via the disappearance of the nuclear magnetic resonance signals of the protons present in the non-metallated ortho positions of the phosphine ligand and taking advantage of the relatively fast back metallation process that follows the acidolysis reaction, the sequence behaving as an overall equilibrium reaction. The process has a high associative character with important entropy demands, increasing both for the larger and the more electron withdrawing phosphine ligands. For the complexes with electron withdrawing CF(3) substituents on the cyclometallated phenyl ring, this demand is compensated by very low activation enthalpies. The data agree with an intimate mechanism that corresponds to the reverse of the electrophilic C-H bond activation, which has already been studied for this type of system, and requires the presence of a protonated acetato ligand in the axial position, close to the metallated Rh-C(aromatic) bond. The involvement of external solvent molecules, interacting via hydrogen bonds with the system, is also evident for systems which include CF(3) groups with the correct geometric arrangement.

Synthesis and characterisation of aluminium(iii) and tin(ii) complexes bearing quinoline-based N,N,O-tridentate ligands and their catalysis in the ring-opening polymerisation of ε-caprolactone

The synthesis and catalysis in the ring-opening polymerisation (ROP) of ε-caprolactone (ε-CL) of aluminium(iii) and tin(ii) complexes supported by quinoline-based N,N,O-tridentate ligands are reported. Reaction of 8-{RC(O)CH(2)P(Ph(2)) = N}C(9)H(6)N (R = Bu(t), 2; R = Ph, 3) with AlMe(3) gave [Al(Me(2)){OCR = CHP(Ph(2)) = N(8-C(9)H(6)N)}] (R = Bu(t), 4; R = Ph, 5). Treatment of 2 and 3 with Sn[N(SiMe(3))(2)](2) generated tin(ii) complexes [Sn{OC(R) = CHP(Ph(2)) = N(8-C(9)H(6)N)}{N(SiMe(3))(2)}] (R = Bu(t), 6; R = Ph, 7). A similar reaction of AlMe(3) with 8-{MeC(O)CH(2)C(Me) = N}C(9)H(6)N gave [Al(Me(2)){OC(Me) = CHC(Me) = NC(9)H(6)N}] (9). Compounds 2-9 were characterised by NMR spectroscopy and elemental analysis. The molecular structures of complexes 4, 6 and 9 were determined by single crystal X-ray diffraction techniques. Investigation of catalysis of complexes 4-7 and 9 in the ROP of ε-CL revealed that the aluminium complexes, 4, 5 and 9, are much more active than the tin(ii) complexes. The kinetic studies for the polymerisation of ε-CL catalysed by complexes 4, 5 and 9 in the presence of benzyl alcohol (BnOH) indicated that the polymerisations proceed with the first-order dependence on monomer concentration. The polymerisation was well controlled and gave a polymer with narrow molecular weight distribution.

Efficient preparation of novel N-propargylic β-enaminones from the reaction of β-alkoxyvinyltrihalomethyl[carboxy]ketones and propargylamines

Fifteen N-propargylic β-enaminones were synthesized from the reaction of propargyl amines [4X-PhNHCH2C≡CH, where X = H, Me] and 4-alkoxy-1,1,1-trihalo[ethoxy]-3-alken-2-ones [RC(O)CH=C(R)OMe, where R = CF3, CCl3, CO2Et and R = Me, Et, Pr, Bu, i-Pent, CH2CH2CO2Me]. The methodology described herein proceeded smoothly and furnished the products in good to high yields (70-95%).

Evaluation of heterocumulenic ferrocene derivatives for “click” chemistry type reactions

Azidoferrocene ( 1), 1,1′-diazidoferrocene ( 2) and 1,1′-diisothiocyanatoferrocene ( 3) were subjected to reactions from the repertoire of “click” chemistry, with a view to applications in the post-functionalisation of self-assembled monolayers. The copper-catalysed 1,3-dipolar cycloaddition of 1 and FcC CH (Fc = ferrocenyl) afforded the expected 1,2,3-triazole derivative under anhydrous and anaerobic conditions. Analogous reactions also succeeded with 2 and RC CH (R = Ph, Fc). The Staudinger reaction of 2 with 1,1′-bis(diphenylphosphanyl)ferrocene (dppf) gave the expected bis(iminophosphoranyl)ferrocene in high yield. The nucleophilic addition of 2 equiv. of NHR 2 (R = Et, iPr) to 3 afforded the corresponding thiourea derivative in quantitative yield.

An ionic liquid as reaction medium for the synthesis of halo-containing β-enaminones at room temperature

A series of twenty halomethylated β-enaminones [RC(O)CH=C(R1)NR3R4, where R = CF3,CCl3, CHCl2; R1 = H, Me, Ph; R3 = H, Me, Bu, Et; R4 = Me, Et, Bu, allyl, tert-amyl, CH2CH2OH, Bn, Ph] were synthesized using the ionic liquid [bmim]BF4 at room temperature. It is demonstrated that this ionic liquid is a reaction medium suitable for the amination of β-alkoxyvinyl halomethyl ketones. The advantages of this method are the absence of solvents, short reaction times, and good yields.

Synthesis of β-enaminones by ionic liquid catalysis: A one-pot condensation under solvent-free conditions

The synthesis of a series of 12 β-dimethylaminovinylketones [RC(O)CH CHN(Me) 2 , where X = Ph, Me-4-Ph, F-4-Ph, Cl-4-Ph, Br-4-Ph, NO 2 -4-Ph, fur-2-yl, thien-2-yl, pirrol-2-yl, pyrid-2-yl, CH(OMe) 2 and hexyl] from the condensation reaction of methyl ketones with dimethylformamide dimethylacetal in the presence of equimolar amounts of imidazolium based ionic liquids [BMIM] · BF 4 and [OMIM] · BF 4 is reported. The reaction time and the yields were investigated and this method showed advantages over the methods described in the literature.

Synthesis and some properties of binuclear ruthenocene derivatives bridged by both ethene and thiophene derivatives

Binuclear ruthenocenes bridged by ethenes and thiophene derivatives, Rc–CH CH–Z–Rc and Rc ∗–CH CH–Z–CH CH–Rc ∗ (Z = thiophene, thieno[3,2- b]thiophene, and 2,2′-bithiophene; Rc = ruthenocenyl, R ∗ = 1′,2′,3′,4′,5′-pentamethylruthenocenyl) were prepared. These complexes showed a one-step two-electron redox wave in the cyclic voltammograms, in contrast to the benzenoid-bridged dinuclear ruthenocenes. The chemical oxidation of the Rc–CH CH–Z–Rc complexes gave no stable oxidized species. The two-electron oxidized species of the Rc ∗–CH CH–Z–CH CH–Rc ∗ complexes were comparably stable and contained a fulvene-complex type structure.

Hydrogen and Trimethylsilyl Transfers During EI Mass Spectral Fragmentation of Hydroxycarboxylic and Oxocarboxylic Acid Trimethylsilyl Derivatives

This paper, describing electron ionization mass spectral fragmentation of some hydroxycarboxylic and oxocarboxylic acid trimethylsilyl derivatives, focuses on the formation of fragment ions resulting from the interactions between the two functionalities of these compounds. These interactions result in the formation of fragment ions at [CH2=C(OTMS)2]+., [CH2=CHC(OTMS)=OTMS]+, [M-31]+, [M-105]+, and [M-RCHO]+. in the case of hydroxycarboxylic acid trimethylsilyl derivatives of formula RCHOTMS(CH2)nCOOTMS and at [RC(OTMS)=CH2]+., [RC(=OTMS)CH=CH2]+, and [M-RC(=O)CH2]+ in the case of oxocarboxylic acid trimethylsilyl esters of formula RC(=O)(CH2)nCOOTMS. Some of these fragmentations appeared to be sufficiently specific to be used to characterize these compounds. Several fragmentation pathways involving trimethylsilyl and hydrogen transfers were proposed to explain the formation of these different fragment ions and were substantiated by deuterium labeling.

Mechanism of alkyne conversion to carbyne by 14- or 16-electron Os(H) 2ClL 2X (L = P iPr 3; X = OTf or B(C 6H 3(CF 3) 2) 4)

The mechanism of conversion of terminal alkynes RC CH to coordinated carbyne Os CCH 2R by Os(H) 2ClXL 2 (L = P i Pr 3) has been studied for X = OTf and BAr F 4 (Ar F = 3,5-di(CF 3) 2(C 6H 3). Ready loss of these X makes possible detection of η 2-RCCH (4-electron donor) and CH(CH 2R) intermediates, and D-labeling (RCCD) gives OsDClX(CCH 2R)L 2. The energy of various intermediates, including the only experimentally unobserved one, η 2-vinyl, was evaluated with DFT(PBE) calculations.

Preparation and Isolation of Dithiolene Thiophosphoryl Molecules as Stable, Protected Forms of Dithiolene Ligands

The reaction of P4S10 with acyloins, RC(O)CH(OH)R, in refluxing dioxane, followed by the addition of alkylating agents, forms dithiolene thiophosphoryl thiolate compounds, (R2C2S2)P(S)(SR'), which are readily isolated and purified. The compounds that have been prepared and identified spectroscopically are those with R = p-anisyl, R' = Me (1); R = p-anisyl, R' = Bz (2); R = Ph, R' = Me (4); R = Et, R' = Bz (5). Compounds 1, 2, and 4 were structurally characterized by X-ray crystallography and found to possess a tetrahedral coordination geometry about the phosphorus atom, with overall Cs symmetry. In each case, the mirror plane bisects the dithiolene S-P-S chelate and contains the thiophosphoryl bond, which ranges in length from 1.9241(8) to 1.9361(7) A. The use of 2-(bromomethyl)naphthalene as organic electrophile in the P4S10/acyloin reaction produced bis(2-methylnaphthalenyl) disulfide as the only identifiable product. The substitution of Lawesson's reagent for P4S10 in reactions with acyloins produced deoxy acyloin rather than products resulting from chalcogen exchange. Compounds 1-2 and 4-5 are Group 5 analogues of 1,3-dithiol-2-ones, (R2C2S2)C=O, and undergo a similar hydrolysis in aqueous base to liberate ene-1,2-dithiolate dianions from which corresponding metal dithiolene complexes may be prepared. Deprotection of 1 in MeO-/MeOH, followed by the addition of NiCl2.6H2O and then I2, produces square planar [Ni(S2C2(C6H4-p-OCH3)2)2] (8) in 93% yield. A high-resolution structure of 8 (P) reveals dithiolene C-C and C-S bond lengths that are clearly indicative of the thionyl radical monoanionic nature of the ligand. The use of isolated (R2C2S2)P(S)(SR') compounds as a dithiolene ligand source for the preparation of metal dithiolene complexes offers the advantages of clean reactivity and high yield.

Iridium-catalyzed addition of methanol to terminal alkynes

The 18-crown-6 (18C6) ether adduct of sodium hexachloroiridate [Na(18C6)] 2[IrCl 6]· xH 2O ( 1) was found to catalyze an addition of methanol to a variety of nonfunctionalized alkynes RC CH (R = H, n Pr, n Bu, n Pen, Ph, HC C(CH 2) 4) yielding the corresponding Markovnikov addition products (ketals) and in the cases of hex-1-yne and hept-1-yne also anti-Markovnikov ones (acetals, <10%). Furthermore, the reaction of methanol with octa-1,7-diyne resulted in a double Markovnikov addition to only one triple bond, yielding 7,7-dimethoxyoct-1-yne with 80% degree of conversion. On the other hand, the regioselectivity in an addition of methanol to functionalized terminal alkynes of the type RC(O)C CH (R = OMe, Me) was found to be towards anti-Markovnikov products (70–93%). In these two cases vinyl ether intermediates were observed NMR spectroscopically in the course of the reactions.

Neutral (bis-β-diketonato) iron(iii), cobalt(ii), nickel(ii), copper(ii) and zinc(ii) metallocycles: structural, electrochemical and solvent extraction studies

Neutral dimeric metallocyclic complexes of type [M(2)(L(1))(2)B(n)] (where M = cobalt(II), nickel(II) and zinc(II), L(1) is the doubly deprotonated form of a 1,3-aryl linked bis-beta-diketone ligand of type 1,3-bis(RC(O)CH(2)C(O))C(6)H(4) (R=Me, n-Pr, t-Bu) and B is pyridine (Py) or 4-ethylpyridine (EtPy)) have been synthesised, adding to similar complexes already reported for copper(II). New lipophilic ligand derivatives with R = octyl or nonyl were also prepared for use in solvent extraction experiments. Structural, electrochemical and solvent extraction investigations of selected metal complex systems from the above series are reported, with the X-ray structures of [Co(2)(L(1))(2)(Py)(4)] x 2.25CHCl(3) x 0.5H(2)O (R=Pr), [Co(2)(L(1))(2)(EtPy)(4)] (R=t-Bu), [Ni(2)(L(1))(2)(EtPy)(4)] (R=t-Bu), [Zn(2)(L(1))(2)(EtPy)(2)] (R=Me) and [Zn(2)(L(1))(2)(EtPy)(4)] (R=t-Bu) being presented. The electrochemistry of H(2)L(1) (R=t-Bu) and of [Fe(2)(L(1))(3)], [Co(2)(L(1))(2)(Py)(4)], [Ni(2)(L(1))(2)(Py)(4)], [Cu(2)(L(1))(2)] and [Zn(2)(L(1))(2)(Py)(2)] has been examined. Oxidative processes for the complexes are dominantly irreversible, but several examples of quasireversible behaviour were observed and support the assignment of an anodic process, seen between +1.0 and +1.6 V, as a metal-centred oxidation. The reduction processes for the respective metal complexes are not simple, and irreversible in most cases. Solvent extraction studies (water/chloroform) involving variable concentrations of metal, bis-beta-diketone and heterocyclic base have been performed for cobalt(II) and zinc(II) using a radiotracer technique to probe the stoichiometries of the extracted species in each case. Synergism was observed when 4-ethylpyridine was added to the bis-beta-diketone ligand in the chloroform phase. Competitive extraction studies show a clear uptake preference for copper(II) over cobalt(II), nickel(II), zinc(II) and cadmium(II).

Cyclic acetals from catalytic addition of diols to terminal alkynes with a cationic iridium complex containing two labile ligands

Cationic iridium complex [Ir(CH 3)(OTf)(CO)(OH 2)(PPh 3) 2](OTf) ( 1) catalyzes addition of diols (HO (CH 2) n OH ( n = 2–6)) to terminal alkynes (RC CH: R H, CH 2(CH 2) 2CH 3, C 6H 5, p-CH 3C 6H 4) to produce cyclic acetals ▪ exclusively in the absence of H 2O at room temperature. While complex 1 does not catalyze the hydration of alkynes to produce the carbonyl compounds (RCOCH 3), the cyclic acetals rapidly undergo hydrolysis to give RCOCH 3 and regenerate diols in the presence of 1. A deuterium-labeling study (MeO D + n-BuC CH → CH D 2C(OMe) 2( n-Bu)) suggests a reaction pathway involving a π-alkyne complex, η 2-(RC CH)Ir which is attacked by alcohol (R′O D ) to give a β-alkoxy-alkenyl complex, Ir CH CRO + D R′. Proton transfer and attack by another alcohol molecule on the intermediate, Ir CH D C +R(OR′) to produce Ir CH D CR(OR′) O + D R′ that finally yields the acetal CH D 2CR(OR′) 2. It has been found that bulky substituents R on RC CH cause a decrease in the rate of diol addition, and that the production of six- and seven-membered acetals is faster than that of five- and eight-membered ones.

Addition of benzenethiol to terminal alkynes catalyzed by hydrotris(3,5-dimethylpyrazolyl)borate–Rh(III) bis(thiolate) complex: Mechanistic studies with characterization of the key intermediate

The Rh(III)–thiolate complex [Tp ∗Rh(SPh) 2(MeCN)] ( 2; Tp ∗ = hydrotris(3,5-dimethylpyrazolyl)borate) readily undergoes substitution of MeCN by XyNC (Xy = 2,6-dimethylphenyl) to give the isocyanide complex [Tp ∗Rh(SPh) 2(XyNC)] ( 3), whereas reaction of 2 with terminal alkynes results in the formation of the rhodathiacyclobutene complex [Tp ∗Rh(SPh){η 2-CH CR(SPh)}] ( 4; R = aryl, alkyl). Molecular structures of 3 and 4 (R = CH 2Ph) have been determined by single crystal X-ray diffraction. Complex 2 as well as [Tp ∗Rh(cyclooctene)(MeCN)] have been found to catalyze regioselective addition of benzenethiol to terminal alkynes RC CH at 50 °C to give R(PhS)C CH 2 in moderate to high yields. The above products are selectively formed when R = CH 2Ph and n-C 6H 13, while cis-RCH CHSPh and RC(SPh) 2CH 3 are also obtained as by-products when R = p-MeOC 6H 4. Catalytic cycle involving 2 and 4 is proposed based on the mechanistic studies using NMR measurement.

Formation of pyridine from acetylenes and nitriles catalyzed by RuCpCl, CoCp, and RhCp derivatives – A computational mechanistic study

The mechanism of the catalytic formation of pyridines from the coupling of two alkynes and the nitriles N CR (R = H, Me, Cl, COOMe) with the fragments CpRuCl, CpCo, and CpRh has been investigated by means of DFT/B3LYP calculations. According to the proposed mechanism, the key reaction step is the oxidative coupling of two alkyne ligands to give metallacyclopentatriene (Ru, Rh) and metallacyclopentadiene (Co) intermediates. In the case of ruthenium, this process is thermodynamically clearly favored over the oxidative coupling between one alkyne and one nitrile ligand to afford an azametallacycle. This alternative pathway however cannot be dismissed in the case of Co and Rh. The rate determining step of the overall catalytic cycle is the addition of a nitrile molecule to the metallacyclopentatriene and metallacyclopentadiene intermediates, respectively, which has to take place in a side-on fashion. Competitive alkyne addition leads to benzene formation. Thus, also the chemoselectivity of this reaction is determined at this stage of the catalytic cycle. In the case of the RuCpCl fragment, the addition of nitriles R–C N and acetylenes RC CH has been studied in more detail. For R = H, Cl, and COOMe the side-on addition of nitriles is kinetically more favored than alkyne addition and, in accordance with experimental results, pyridine formation takes place. In the case of R = Me nitrile addition could not be achieved and the addition of alkynes to give benzene derivatives seems to be kinetically more favored. Once the nitrile is coordinated facile C–C bond coupling takes place to afford an unusual five- and four-membered bicyclic ring system. This intermediate eventually rearranges to a very unsymmetrical azametallaheptatriene complex which in turn provides CpRuCl(κ 1-pyridine) via a reductive elimination step. Completion of the catalytic cycle is achieved by an exergonic displacement of the respective pyridine product by two acetylene molecules regenerating the bisacetylene complex.