Selective C-C bond formation between alkynes mediated by the [RuCp(PR)(3)](+) fragment leading to allyl,butadienyl, and allenyl carbene complexes--an experimental and theoretical study

The reaction of alkynes with [RuCp(PR(3))(CH(3)CN)(2)]PF(6) (R=Me, Ph, Cy) affords, depending on the structure of the alkyne and the substituent of the phosphine ligand, allyl carbene or butadienyl carbene complexes. These reactions involve the migration of the phosphine ligand or a facile 1,2 hydrogen shift. Both reactions proceed via a metallacyclopentatriene complex. If no alpha C[bond]H bonds are accessible, allyl carbenes are formed, while in the presence of alpha C[bond]H bonds butadienyl carbenes are typically obtained. With diphenylacetylene, on the other hand, a cyclobutadiene complex is formed. A different reaction pathway is encountered with HC[triple bond]CSiMe(3), ethynylferrocene (HC[triple bond]CFc), and ethynylruthenocene (HC[triple bond]CRc). Whereas the reaction of [RuCp(PR(3))(CH(3)CN)(2)]PF(6) (R=Ph and Cy) with HC[triple bond]CSiMe(3) affords a vinylidene complex, with HC[triple bond]CFc and HC[triple bond]CRc this reaction does not stop at the vinylidene stage but subsequent cycloaddition yields allenyl carbene complexes. This latter C[bond]C bond formation is effected by strong electronic coupling of the metallocene moiety with the conjugated allenyl carbene unit, which facilitates transient vinylidene formation with subsequent alkyne insertion into the Ru[double bond]C bond. The vinylidene intermediate appears only in the presence of bulky substituents of the phosphine coligand. For the small R=Me, head-to-tail coupling between two alkyne molecules involving phosphine migration is preferred, giving the more usual allyl carbene complexes. X-ray structures of representative complexes are presented. A reasonable mechanism for the formation of both allyl and allenyl carbenes has been established by means of DFT calculations. During the formation of allyl and allenyl carbenes, metallacyclopentatriene and vinylidene complexes, respectively, are crucial intermediates.     

Highly efficient catalytic routes to spiroketal motifs

The versatile and efficient synthesis of a variety of spiroketal motifs via the double intramolecular hydroalkoxylation of aliphatic and aromatic alkyne diols was achieved using simple and readily accessible Ir(I) and Rh(I) cyclooctadiene complexes as catalysts.     

Recent Mechanistic and Synthetic Developments in the Chemistry of Transition‐Metal Vinylidene Complexes

Transition‐metal vinylidene complexes are intermediates in a number of synthetically important transformations of alkynes. Underpinning these applications is the ability of various electron‐rich transition‐metal complexes to effectively facilitate the conversion of alkynes into their vinylidene tautomers. Recent experimental and theoretical studies have provided considerable insight into the mechanisms by which this process occurs and they are detailed herein. In particular, it has been demonstrated that different substituents on both the metal and the alkyne may have profound effects on both the kinetic and thermodynamic profiles of the alkyne/vinylidene tautomerisation. An important finding is that internal alkynes may be employed to prepare disubstituted vinylidene complexes under easily accessible conditions. This discovery brings to light a new facet of the potential synthetic applications of transition metal vinylidene complexes.     

Transition metal vinylidene complexes as supramolecular building blocks: nucleobase-mediated self-assembly of crystals with hexagonal symmetry

Reaction of the ruthenium half sandwich compound RuCl(eta(5)-C(5)H(5))(PPh(3))(2) with the uracil (Ur) substituted alkyne HC[triple bond, length as m-dash]CUr in the presence of halide scavengers NH(4)X (X = PF(6), BF(4), OTf) results in the formation of the vinylidene complexes [Ru([double bond, length as m-dash]C[double bond, length as m-dash]CHUr)(eta(5)-C(5)H(5))(PPh(3))(2)][X] which crystallize in the hexagonal space group P6(3)/m. The hexagonal symmetry inherent to the system is due to the formation of a hydrogen bonded array mediated by the two sets of donor-acceptor units on the uracil, resulting in the formation of a cyclic "rosette" containing six ruthenium cations. In solution the (1)H and (31)P{(1)H} NMR spectra of the vinylidene complexes are both concentration and temperature dependent, in accord with the presence of monomer-dimer equilibria in which the rate of rotation of the vinylidene group is fast on the NMR timescale in the monomeric species, but slow in the dimers. The isoelectronic molybdenum-containing vinylidene complex [Mo(eta(7)-C(7)H(7))(dppe)([double bond, length as m-dash]C[double bond, length as m-dash]CHUr)][BF(4)] (dppe = 1,2-bis(diphenylphosphino)ethane) has also been prepared, but forms symmetric dimers in the solid state.     

Ruthenium-Induced Cyclization of Heteroatom-Functionalized Alkynes: Progress,Challenges and Perspectives

Metal-induced cyclization of functionalized alkynes represents one of the most general approaches to prepare organic heterocycles. Although Ru^II centers are well-established to promote alkyne to vinylidene rearrangements and many Ru^II-mediated alkyne cyclizations have been rationalized to be the results of post-vinylidene transformations, recent discoveries indicate that Ru^II centers can serve as electrophiles and induce alkyne cyclizations without vinylidene intermediacy. In this Minireview, an overview of the Ru^II-induced cyclization of heteroatom-functionalized alkynes in the last decade is provided, with an emphasis on the discoveries and validations of the unconventional “non-vinylidene-involving” pathways.     

Unexpected direct formation of a bridging 4-cyanobuta-1,3-dienylidene group from reaction of [(C5H5)Fe(CO)]2(μ-CCH2) with HCCCN

The ethenylidenediiron complex [C₅H₅Fe(CO)]₂ (μ-CO)(μ-CCh₂) reacts with the nitrile substituted alkyne HCCCn to give high yield of [(C₅H₅)Fe(CO)]₂ (μ-CO)(μ-CCHCHC(CN)H). It is suggested that this bridging 4-cyanobuta-1,3-dien-ylidenediiron complex is formed by attack of the electron rich double bond of the ethenylidenediiron complex on the electrophilic protonated carbon of the alkyne. An IR study has indicated that hydride reduction of the complex occurs selectively at the bridging vinylidene carbon atom to give am anionic bridging cyanovinylalkylidenediiron complex.     

Rhodium-catalyzed arylative and alkenylative cyclization of 1,5-enynes induced by geminal carbometalation of alkynes

A rhodium(I)-catalyzed addition-cyclization of 1,5-enynes with aryl- and alkenylboronic acids has been developed. The reaction allows for efficient C-C coupling of multiple reactive components while accomplishing a net R,H-addition in a single step under mild conditions. In the presence of [Rh(OH)(COD)]2 catalyst and triethylamine base in methanol solvent, a range of 1,5-enynes undergo an intermolecular addition with a wide variety of aryl- and alkenylboronic acids and concomitant endo-selective cyclization to yield 1-aryl and alkenyl-substituted cyclopentene derivatives as the products. Deuterium labeling studies suggest that the reaction involves formation of a rhodium vinylidene complex with the terminal alkyne of the enyne substrate. The subsequent migration of the aryl or alkenyl group from the rhodium center to the alpha-carbon of the vinylidene ligand gives a vinyl rhodium complex, a formal 1,1-carbometalation process of the alkyne. This vinyl rhodium then adds to the pendent alkene, and the protodemetalation of the resulting rhodium enolate affords the product.     

Cyclopropenylmethyl Cation: A Concealed Intermediate in Gold(I)‐Catalyzed Reactions

The last years have witnessed many gold‐catalyzed reactions of alkynes. One of the most prominent species in the reaction of two alkyne units is the vinyl‐substituted gold vinylidene intermediate. Here, we were able to show that the reaction of a haloacetylene and an alkyne proceeds via a hitherto overlooked intermediate, namely the cyclopropenylmethyl cation. The existence and relative stability of this concealed intermediate is verified by quantum chemical calculations and ¹³C‐labeling experiments. A comparison between the cyclopropenylmethyl cation and the well‐known vinylidene intermediate reveals that the latter is more stable only for smaller cycles. However, this stability reverses in larger cycles. In the case of the smallest representative of both species, the vinylidene cation is the transition state en route to the cyclopropenylmethyl cation. The discovery of this intermediate should help to get a deeper understanding for gold‐catalyzed carbon–carbon bond‐forming reactions of alkynes. Furthermore, since enynes can be formed from the cyclopropenylmethyl cation, the inclusion of this intermediate should enable the development of new synthetic methods for the construction of larger cyclic halogenated and non‐halogenated conjugated enyne systems.     

Heterograft copolymers via double click reactions using one‐pot technique

The double click reactions (Cu catalyzed Huisgen and Diels–Alder reactions) were used as a new strategy for the preparation of well‐defined heterograft copolymers in one‐pot technique. The synthetic strategy to the various stages of this work is outlined: (i) preparing random copolymers of styrene (St) and p‐chloromethylstyrene (CMS) (which is a functionalizable monomer) via nitroxide mediated radical polymerization (NMP); (ii) attachment of anthracene functionality to the preformed copolymer by the o‐etherification procedure and then conversion of the remaining ? CH₂Cl into azide functionality; (iii) by using double click reactions in one‐pot technique, maleimide end‐functionalized poly(methyl methacrylate) (PMMA‐MI) via atom transfer radical polymerization (ATRP) of MMA and alkyne end‐functionalized poly (ethylene glycol) (PEG‐alkyne) were introduced onto the copolymer bearing pendant anthryl and azide moieties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6969–6977, 2008     

Efficient synthesis of tetrasubstituted alkenes by allylsilane-terminated domino-Heck double cyclisation

The domino-Heck double cyclisation of the arylbromides 1, which contain an allylsilane and an alkyne moiety and are easily accessible by an addition of the corresponding lithiated alkynes 5 to the aldehydes 4, leads to the tetrasubstituted alkenes 2 and 3 in good yield. The reaction produces exclusively compounds with an E double bond and additionally proceeds with good to excellent induced diastereoselectivity in the case of 1e and 1f. Irradiation of 2e leads to a steady state equilibrium of the E and Z compounds in a 1:1 ratio.     

Hydrogen Migration in Transition Metal Alkyne and Related Complexes

The electronic and structural characteristics of the reaction interconverting a l-alkyne complex into a vinylidene via a 1,2 hydrogen shift are examined. In a mononuclear system, initial slippage of the alkyne to an η¹ geometry is indicated. The subsequent step is shown to be analogous to the isomerization of a methylvinyl cation. We conclude that an alternative route involving a hydrido-acetylide species will be of much higher energy. A concerted shift in binuclear and trinuclear systems is ruled out, based on the loss of a strong bonding interaction between the alkyne and the metallic piece, in the transition state. In trinuclear systems, a mechanism for the isomerization is suggested involving prior oxidative addition of the C? H bond across a metal-metal bond. The metallic piece in this case assists the transformation. The discussion is extended to other reactions featuring hydrogen shifts; these include the intramolecular formation of a binuclear vinylidene from a 1,2-hydrido-acetylide complex, the isomerization of a binuclear μ-alkylidyne into a μ-vinyl geometry and the transfer of a bridging hydrogen onto a capping hydrocarbon fragment in trinuclear cluster complexes.     

Palladium-catalyzed cyclization of 1-alkynyl-8-iodonaphthalene and double isocyanides for the synthesis of acenaphtho[1,2-b]pyrroles

A palladium-catalyzed formal [2 + 2 + 1] cyclization of 1-alkynyl-8-iodonaphthalene with double isocyanides is developed herein. The transformation worked well to produce a series of 7H-acenaphtho[1,2-b]pyrrole with a broad reaction scope. Isocyanides play a dual role in the reaction. One is a C1 building block, and another is used as C1N1 component. In the process, the [2 + 2 + 1] cyclization involves imidoylation, regioselective addition of imidoylpalladium species into alkyne, double imidoylation, and another addition of the resulting imidoylpalladium species into imine bonds.     

Catalytic non-conventional trans-hydroboration: a theoretical and experimental perspective

We have studied the non-conventional trans-hydroboration reaction of alkynes both experimentally and theoretically. A catalytic system based on the in situ mixture of [{Rh(cod)Cl}(2)]/PCy(3) (cod=1,5-cyclooctadiene, Cy=cyclohexyl) has been able to activate pinacolborane and catecholborane and transfer boryl and hydride groups onto the same unhindered carbon atom of the terminal alkynes. The presence of a base (Et(3)N) favored the non-conventional trans-hydroboration over the traditional cis-hydroboration. Varying the substrate had a significant influence on the reaction, with up to 99% conversion and 94% regioselectivity observed for para-methyl-phenylacetylene. Both DFT and quantum mechanical/molecular mechanical ONIOM calculations were carried out on the [RhCl(PR(3))(2)] system. To explain the selectivity towards the (Z)-alkenylboronate we explored several alternative mechanisms to the traditional cis-hydroboration, using propyne as a model alkyne. The proposed mechanism can be divided into four stages: 1) isomerization of the alkyne into the vinylidene, 2) oxidative addition of the borane reagent, 3) vinylidene insertion into the Rh-H bond, and finally 4) reductive elimination of the C-B bond to yield the 1-alkenylboronate. Calculations indicated that the vinylidene insertion is the selectivity-determining step. This result was consistent with the observed Z selectivity when the sterically demanding phosphine groups, such as PCy(3) and PiPr(3), were introduced. Finally, we theoretically analyzed the effect of the substrate on the selectivity; we identified several factors that contribute to the preference for aryl alkynes over aliphatic alkynes for the Z isomer. The intrinsic electronic properties of aryl substituents favored the Z-pathway over the E-pathway, and the aryl groups containing electron donating substituents favored the occurrence of the vinylidene reaction channel.     

Reductive activation of carbon-fluorine bonds in perfluoroalkyl ligands: an unexpected route to the only known tetrafluorobutatriene transition metal complex: Ir(eta 5-C5Me5)(PMe3)(2,3-eta 2 -CF2[double bond]C[double bond]C[double bond]CF2)

Six-electron reduction of the perfluoro-sec-butyl ligand in Cp*Ir(PMe3)I(C4F9) with sodium naphthalenide affords the first known example of a transition metal complex of tetrafluorobutatriene, Cp*Ir(PMe3)(C4F4). The free ligand is a highly unstable compound. The compound has been completely characterized by a single-crystal X-ray diffraction study; the center coordinated double bond shows significant elongation, and the flanking fluoroalkenes show significant shortening, as compared to the dimensions in the free ligand.     

亚乙烯基(vinylidene)钌络合物中间体在有机合成中 的应用

综述了近几年钌亚乙烯基络合物中间体α-碳的亲核反应。亲核试剂包括烯烃、炔烃、醇、酸、胺水等。     

亚乙烯基(vinylidene)钌络合物中间体在有机合成中的应用

综述了近几年钌亚乙烯基络合物中间体α-碳的亲核反应。亲核试剂包括烯烃、炔烃、醇、酸、胺、水等。     

Ruthenium catalyzed regioselective hydrophosphination of propargyl alcohols

Catalytic hydrophosphination of propargyl alcohols by ruthenium complexes RuCl(cod)(C5Me5) and RuCl(PPh3)2(C5Me5) leads to the formation of functionalized vinylphosphines, with linkage of the phosphorus atom to the terminal alkyne carbon, via a ruthenium vinylidene intermediate.     

Iridium-catalyzed [2+2+2] cycloaddition of α,ω-diynes with isocyanates

[Ir(cod)Cl](2)/BINAP was found to be an efficient catalyst for the [2+2+2] cycloaddition of α,ω-diynes with isocyanates to give 2-pyridones. A wide range of isocyanates can be used for this reaction. Both aliphatic and aromatic isocyanates smoothly reacted with α,ω-diynes to give 2-pyridones in high yields. Aliphatic isocyanates were more reactive than aromatic isocyanates. For aromatic isocyanates, the electronic properties of the substituents affected the reactivity: electron-donating substituents enhanced the reaction. The reaction of unsymmetrical α,ω-diynes possessing two different internal alkyne moieties with isocyanates was regiospecific and gave a single product. This regioselectivity could be explained by the reaction of iridacyclopentadiene with a nitrogen-carbon double bond. The regioselectivity of the reaction of malonate-derived diyne was controlled by a steric effect, while that of the reaction of ester-tethered diyne was controlled by an electronic effect. [Ir(cod)Cl](2)/chiral diphosphine catalyst could be used for the enantioselective synthesis of C-N axially chiral 2-pyridone. The reaction of diyne 1a with o-methoxyphenyl isocyanate (7a) gave C-N axially chiral 2-pyridone (R)-8aa in 78% yield with 94% ee.     

非催化瞬态铱脱溶一筛选铱基钙钛矿析氧催化剂时不可忽视的实验现象

传统化石燃料的过度开采、消耗在推动各国工业化进程的同时,也导致了能源枯竭、环境污染和气候恶化等问题2为应对全球环境治理等难题,推进能源变革,构建脱碳化的能源体系势在必行2质子交换膜电解槽(PEMWE)能够在高电流密度下运行,其体积小,效率高,具有更高的灵活性,更有利于反应进行,能够克服可再生能源(太阳能、风能和水电等)...     

Ruthenium-catalyzed hydrative cyclization of 1,5-enynes

A ruthenium-catalyzed hydrative cyclization of enynes has been developed. The reaction converts a range of 1,5-enynes bearing terminal alkyne and Michael acceptor moieties into cyclopentanone derivatives. From extensive catalyst screening experiments, a trinuclear ruthenium complex, [Ru3(dppm)3Cl5]PF6, has been identified to be an effective catalyst in mediating the 1,1-difunctionalization of alkynes. It is proposed that this novel umpolung reaction proceeds through the formation of a ruthenium vinylidene, anti-Markovnikov hydration, and intramolecular Michael addition of an acyl ruthenium to the alkene.