CC Multiple Bonds Research Articles

The first example of a “click” reaction with a carboranyl azide and an olefin

While typical organic azides have long been known to undergo 1–3 dipolar cycloadditions with strained CC multiple bonds, such chemistry has never been reported between organomimetic carboranyl azides and alkenes. Here we show that the carborane o-PhCN3CB10H10 readily undergoes cycloaddition with norbornene at ambient temperature to afford the corresponding triazole adduct with perfect exo-selectivity. The structure of the ensuing heterocycle was unambiguously determined by multinuclear NMR, correlation NMR, and single crystal X-ray diffraction experiments. This first example of such reactivity demonstrates a method to easily introduce carborane clusters directly to scaffolds of interest, without having an organic spacer between the azide functionality and cluster.

Infrared Photodissociation Spectroscopy of C4 N- , C6 N- and C8 N.

The gas-phase vibrational spectroscopy of cold C2n N- (n=2-4) anions is investigated in the CC and CN multiple bond stretching region (1700-2250 cm-1 ) by means of infrared photodissociation (IRPD) spectroscopy in a cryogenically cooled ion trap of the corresponding messenger-tagged complexes. The IRPD spectra are assigned to N-terminated linear structures with triplet ground states (3 Σ- ) based on a comparison with harmonic vibrational frequencies and intensities from density functional theory computations. In contrast to the polyacetylenic C2n+1 N- anions, the linear C-C chains investigated here exhibit cumulenic character, which is most pronounced in C4 N- and decreases with chain length. Additional intense transitions are observed for C6 N- above 3000 cm-1 and are attributed to overtone and combination bands involving the CC stretching modes, based on anharmonic computations. The influence of a D2 tag on the vibrational features of C2n N- anions is shown to be small.

ChemInform Abstract: Theoretical and Experimental Insights into the Origin of the Catalytic Activity of Subnanometric Gold Clusters: Attempts to Predict Reactivity with Clusters and Nanoparticles of Gold

AbstractReview: 46 refs.

Solid supported rhodium(0) nanoparticles: an efficient catalyst for chemo- and regio-selective transfer hydrogenation of nitroarenes to anilines under microwave irradiation

A Solid-supported rhodium(0) (SS-Rh) catalyst has been developed and applied for the chemo- and regio-selective reduction of nitroarenes functionalized with CC multiple bonds and dinitroarenes to their corresponding amines respectively using hydrazine hydrate (N2H4·H2O) as a reducing source under mild microwave irradiation (MWI) conditions. The present methodology also shows excellent compatibility with a broad range of structurally diverse reducible functional groups. The catalyst can be recovered by simple filtration and reused for 13 cycles with consistent activity hence reduces the cost of the catalyst assertively.

Activation of a σ-SnSn Bond at Copper, Followed by Double Addition to an Alkyne

Many synthetically useful copper-catalyzed transformations involve the activation of apolar or weakly polar σ-bonds (E-H and E-E' bonds, with E = C, B, Si, Sn, etc.). Yet, little is known so far about the associated elementary steps, and it is highly desirable to gain better knowledge regarding the way σ-bonds can be activated by copper to help further development in this area. To this end, we became interested in investigating the coordination and activation of apolar or weakly polar σ-bonds at copper using chelating assistance. Here we report investigations of gold and copper complexes deriving from the diphosphine-stannane [Ph2P(o-C6H4)Me2Sn-SnMe2(o-C6H4)PPh2] 1. The σ-SnSn bond of 1 readily undergoes oxidative addition at both gold and copper, giving bis(stannyl) Au(+) and Cu(+) complexes 2 and 3. Coordination of 1 to CuBr leads to the neutral complex 4 which features more σ-SnSn complex character. The ability of complex 3 to undergo insertion reactions with alkynes was then examined. With methyl propiolate, a clean reaction occurred, and the bis-stannylated alkene copper complex 5 was isolated. The structures of ligand 1 and complexes 2-5 have been unambiguously determined by multinuclear NMR spectroscopy and crystallography. These results substantiate the ability of copper to promote the addition of apolar σ-bonds to CC multiple bonds via a 2e redox sequence and draw thereby an unprecedented parallel with the group 10 metals.

Theoretical and Experimental Insights into the Origin of the Catalytic Activity of Subnanometric Gold Clusters: Attempts to Predict Reactivity with Clusters and Nanoparticles of Gold

Particle size is one of the key parameters determining the unexpected catalytic activity of gold, with reactivity improving as the particle gets smaller. While this is valid in the 1-5 nm range, chemists are now investigating the influence of particle size in the subnanometer regime. This is due to recent advances in both characterization techniques and synthetic routes capable of stabilizing these size-controlled gold clusters. Researchers reported in early studies that small clusters or aggregates of a few atoms can be extremely active in some reactions, while 1-2 nm nanoparticles are catalytically more efficient for other reactions. Furthermore, the possibility that small gold clusters generated in situ from gold salts or complexes could be the real active species in homogeneous gold-catalyzed organic reactions should be considered. In this Account, we address two questions. First, what is the origin of the enhanced reactivity of gold clusters on the subnanometer scale? And second, how can we predict the reactions where small clusters should work better than larger nanoparticles? Both geometric factors and electronic or quantum size effects become important in the subnanometer regime. Geometric reasons play a key role in hydrogenation reactions, where only accessible low coordinated neutral Au atoms are needed to dissociate H2. The quantum size effects of gold clusters are important as well, as clusters formed by only a few atoms have discrete molecule-like electronic states and their chemical reactivity is related to interactions between the cluster's frontier molecular orbitals and those of the reactant molecules. From first principles calculations, we predict an enhanced reactivity of small planar clusters for reactions involving activation of CC multiple bonds in alkenes and alkynes through Lewis acid-base interactions, and a better catalytic performance of 3D gold nanoparticles in redox reactions involving bond dissociation by oxidative addition and new bond formation by reductive elimination. In oxidation reactions with molecular O2, initial dissociation of O2 into basic oxygen atoms would be more effectively catalyzed by gold nanoparticles of ∼1 nm diameter. In contrast, small planar clusters should be more active for reactions following a radical pathway involving peroxo or hydroperoxo intermediates. We have experimentally confirmed these predictions for a series of Lewis acid and oxidation reactions catalyzed by gold clusters and nanoparticles either in solution or supported on solid carriers.

C═C, C≡C, and C═O Bond Activation by Coinage Metal Cations in ZSM-5 Zeolites: Quantitative Charge Transfer Resolution

Adsorption and activation of ethene, ethyne, and formaldehyde by copper and silver sites in ZSM-5 are reinspected by quantitative assessment of the donation and backdonation processes between the three molecules and either models comprising bare cations (M+) or the cations embedded in zeolite framework (M(I)). ETS-NOCV analysis (decoupling the deformation density upon substrate bonding into independent components) reveals two predominant channels for electron transfer between adsorbed molecule and a cation or a cationic site, namely π*-backdonation from metal d orbitals to π* antibonding orbital of a substrate and σ-donation from π bonding or lone pair orbitals of the substrate to the cation. Alternative fragmentation of a complex modeling the cation embedded in zeolitic framework, treated as a three-part entity, allows for extracting predominant electron transfer channels from framework oxygens to the cation with bound substrate, namely, opposing σ-donation and supporting π*-backdonation. Critical analysis of charge flows between various parts of a complex system shows that effective activity of the cationic site comes from two contradictory processes and must be viewed as resulting from the framework effect on the sensitive balance between opposing electron transfer channels. Juxtaposition of density transfer channels between the substrate with CC and CO multiple bonds and either a bare metal cation or the cation embedded in a zeolite framework shows that σ-donation prevails over π*-backdonation for free cations, while for zeolitic sites their order is reversed. Quantitative analysis reveals that for title systems, activation decrease due to the reduction of σ-donation becomes outweighed by the increase in π*-backdonation for Cu(I) but not for Ag(I). Thus zeolitic framework, regarded as an electron reservoir, may either support (Cu+) or impair (Ag+) electronic processes underlying catalytic activation of multiple bonds.

A UB3LYP and UMP2 theoretical investigation on unusual cation–π interaction between the triplet state HB=BH ( $$ {}^3\Sigma_g^{-} $$ ) and H+, Li+, Na+, Be2+ or Mg2+

The nature of the unusual cation-pi interactions between cations (H(+), Li(+), Na(+), Be(2+) and Mg(2+)) and the electron-deficient B=B bond of the triplet state HB=BH (3 Sigma g-) was investigated using UMP2(full) and UB3LYP methods at 6-311++G(2df,2p) and aug-cc-pVTZ levels, accompanied by a comparison with 1:1 and 2:1 sigma-binding complexes between BH and the cations. The binding energies follow the order HB=BH...H(+) > HB=BH...Be(2+) > HB=BH...Mg(2+) >> HB=BH...Li(+) > HB=BH...Na(+) and HB=BH ((1)Delta(g))...M(+)/M(2+) > H(2)C=CH(2)...M(+)/M(2+) > HC identical with CH...M(+)/M(2+) > HB=BH (3 Sigma g-)...M(+)/M(2+). Furthermore, except for HB...H(+), the sigma-binding interaction energy of the 1:1 complex HB...M(+)/M(2+) is stronger than the cation-pi interaction energy of the C(2)H(2)...M(+)/M(2+), C(2)H(4)...M(+)/M(2+), B(2)H(2) ((1)Delta(g))...M(+)/M(2+) or B(2)H(2) (3 Sigma g-)...M(+)/M(2+) complex, and, for the 2:1 sigma-binding complexes, except for HBBe(2+)...BH, they are less stable than the cation-pi complexes of B(2)H(2) ((1)Delta(g)) or B(2)H(2) (3 Sigma g-). The atoms in molecules (AIM) theory was also applied to verify covalent interactions in the H(+) complexes and confirm that HB=BH (3 Sigma 3-) can be a weaker pi-electron donor than HB=BH ((1)Delta(g)), H(2)C=CH(2) or HC identical with CH in the cation-pi interaction. Analyses of natural bond orbital (NBO) and electron density shifts revealed that the origin of the cation-pi interaction is mainly that many of the lost densities from the pi-orbital of B=B and CC multiple bonds are shifted toward the cations.

Can the BB multiple bonds be as the stronger hydrogen-bond proton acceptors than the CC multiple bonds: A comparative theoretical investigation on unusual intermolecular T-shaped X [sbnd]H…π interaction between HF and HB [dbnd]BH ( [formula omitted]), HB [dbnd]BH ( 1Δ g), OCB [tbnd]BCO, H 2C [dbnd]CH 2 or HC [tbnd]CH

The unusual T-shaped X H…π hydrogen bonds between HF and BB or CC multiple bonds are compared using the (U)MP2 and DFT ((U)B3LYP functional) methods with the 6-311++G(2df,2p) and aug-cc-pVTZ basis sets. The binding energies follow the order of HB BH ( 1Δ g)…HF > H 2C CH 2…HF > HC CH…HF > OCB BCO…HF > HB BH ( 3 Σ g - )…HF. NBO analysis and the results of the AIM charge density and electron density shifts confirm that, although BB multiple bonds are more electron-deficient than CC multiple bonds, HB BH ( 1Δ g) can be as the stronger T-shaped X H…π hydrogen-bond proton acceptor than the CC multiple-bond monomers.

Two or More CH Bond(s) Formed by Addition to CC Multiple Bonds

AbstractFor Abstract see ChemInform Abstract in Full Text.

One or More CC Bond(s) Formed by Addition: Addition of Carbon Radicals and Electrocyclic Additions to CC Multiple Bonds

AbstractFor Abstract see ChemInform Abstract in Full Text.

One or More CC Bonds Formed by Addition: Addition of Carbon Electrophiles and Nucleophiles to CC Multiple Bonds

AbstractFor Abstract see ChemInform Abstract in Full Text.

Copper(II) ion-exchanged montmorillonite as catalyst for the direct addition of N [sbnd]H bond to CC triple bond

An efficient synthesis of phenyl-(1-phenylethylidene)amine using copper-exchanged montmorillonite clay (Cu K-10) is demonstrated. The catalyst was characterized using UV–vis, XRD, BET surface area measurements, pyridine adsorption etc. The XRD and surface area measurement show that the structural characteristics of the support montmorillonite K-10 (K-10) are preserved after Cu exchange. The hydroamination of phenyl acetylene with aniline was carried out in toluene under reflux condition in N 2 atmosphere at 393 K. The reaction is highly regio-selective for only Markovnikoff's addition of amine to CC multiple bond and proceeded smoothly to completion. The reaction conditions were optimized to obtain complete conversion with respect to phenyl acetylene. Reaction data showed that the activity of the catalyst in hydroamination reaction is greater at higher reaction temperatures and nonpolar solvents and N 2 pressure promotes the reaction drastically.

Reactivity of Ar'GeGeAr' (Ar' = C6H3-2,6-Dipp2, Dipp = C6H3-2,6-iPr2) toward alkynes: isolation of a stable digermacyclobutadiene.

The first reactions of the "digermyne" Ar'GeGeAr' (1, Ar' = C6H3-2,6-Dipp2, Dipp = C6H3-2,6-iPr2) with alkynes are reported. 1 reacts with 1 equiv of H5C6CCC6H5 to afford the 1,2-digermacyclobutadiene 2 in high yield, while it reacts with 2 equiv of the less hindered alkyne Me3SiCCH to yield an unexpected bicyclic compound 3. Molecular structures of 2 and 3 were determined by X-ray crystallography. A possible mechanism for the formation of 3 is discussed. The high reactivity of 1, even at room temperature, emphasizes the fundamental differences between the GeGe and CC multiple bonds.

Addition to CC Multiple Bonds (Except for CC Bond Formation)

AbstractFor Abstract see ChemInform Abstract in Full Text.

Hydroamination on homogeneous and heterogeneous catalysts: Kinetic study

AbstractThis kinetic analysis compares homogeneous and heterogeneous catalysts for the cyclization of 6‐aminohex‐1‐yne. The reaction was studied as a model for the direct addition of amine NH bonds to CC multiple bonds (hydroamination). Kinetic modeling showed that the metal‐catalyzed hydroamination reaction is followed by a proton‐catalyzed isomerization of the primary reaction product, 2‐methylene‐piperidine, to the thermodynamically more stable 2‐methyl‐1,2‐dehydropiperidine.

Continuous hydroamination in a liquid-liquid two-phase system.

The direct addition of NH across a CC multiple bond (hydroamination) was efficiently catalysed in a liquid-liquid two-phase system. The latter comprised a polar catalyst phase of Zn(CF3SO3)2 in the ionic liquid 1-ethyl-3-methylimidazolium trifuoromethanesulfonate and a substrate mixture in heptane. The possibility of catalysing different hydroamination reactions continuously was demonstrated.

Palladium-Catalyzed Insertion of Alkynes into the Sn−B Bond of a 2-Stannyl-2,3-dihydro-1H-1,3,2-diazaborole and X-ray Structure Analyses of 1,3-Di-tert-butyl-2[(Z)-2-phenyl-2-trimethylstannylethenyl]- 2,3-dihydro-1H-1,3,2-diazaborole and 1,3-Di-tert-butyl-2[(Z)-1-ethyl-2-phenyl-2- trimethylstannylethenyl]-2,3-dihydro-1H-1,3,2-diazaborole

Reaction of equimolar amounts of 1,3-di-tert-butyl-2-trimethylstannyl-2,3-dihydro-1H-1,3,2-diazaborole (1) with a series of alkynes R1−C⋮C−R2 (2) (a: R1 = H, R2 = Ph; b: H, 4-ClC6H4; c: H, 4-BrC6H4; d: Ph, Ph; e: Me, Ph; f: Et, Ph; g: H, n-C4H9; h: Et, Et; i: H, n-C6H13) in the presence of a catalytic amount of [Pd(PPh3)4] (2 mol %) regioselectively afforded high yields of the alkenes (Z)-R1[B]CC(R2)SnMe3 (3a−h) ([B] = as the result of a cis-addition of the BSn bond of 1 to the acetylenic triple bond of 2. Spectroscopic evidence and X-ray structural analyses of 3a and 3f revealed that the bulky borolyl unit was added to the least sterically hindered end of the CC multiple bond.

1,3‐Dipolar Cycloadditions, 96. – Cycloadditions of Alicyclic Thione S‐Oxides with Alicyclic Thiones

AbstractThione S‐oxides (sulfines) harbor the allyl anion MO of 1,3‐dipoles, but fail to undergo 1,3‐cycloadditions to the usual dipolarophiles with a CC multiple bond. Thioketones stand the test as superdipolarophiles. The thione S‐oxides 3 and 9 combined with the thioketones 5 and 7 at 80–100°C, furnishing spiro‐1,2,4‐oxadithiolanes in high yields despite steric hindrance. The structures of the cycloadducts were clarified by their spectra and an X‐ray analysis of 11. Becke3LYP/6‐31G* calculations of transition structures and products for the cycloadditions of thioformaldehyde S‐oxide to thioformaldehyde support the observed regiochemistry. The activation energy amounts to 3.9 kcal mol−1, in contrast to EA = 17.4 kcal mol−1 for the corresponding addition to ethylene. The transition structures are in accordance with concerted cycloadditions.

ChemInform Abstract: One or More CC Bond(s) Formed by Addition: Addition of Carbon Radicals and Electrocyclic Additions to CC Multiple Bonds

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