Olefin metathesis on nanostructures

Alkene metathesis processes on nanostructures can proceed via radial or lateral pathways. Radial metathesis installs new functionalities on the surface of a nanostructure through outward growth from its core. Lateral metathesis involves successive crosslinking of neighboring alkenes on the nanostructure and creates a polymer shell around the particle.     

Olefin metathesis of alkenyltrimethylsilanes

WCl₆ has been used as a catalyst for the metathesis of various alkenylsilanes and the degree of conversion found to be dependent on the distance between the olefinic bond and the silyl group. The first observation of metathetical conversion of allyltrimethylsilane in the absence of a co-catalyst is reported     

Olefin metathesis in ionic liquids

This tutorial review covers the use of ionic liquids as (co)solvents for the olefin metathesis reaction. Olefin metathesis is a simple and effective synthetic tool used to create many compounds which otherwise would require complex multistep syntheses. It is expected that the application of ionic liquids (IL) as well as the development of IL-enabled catalysts and separation techniques will create a green aspect to this important methodology.     

Olefin metathesis in supercritical carbon dioxide

Liquid or supercritical carbon dioxide (scCO(2)) is a versatile reaction medium for ring-opening metathesis polymerization (ROMP) and ring-closing olefin metathesis (RCM) reactions using well-defined metal catalysts. The molybdenum alkylidene complex 1 and ruthenium carbenes 2 and 3 bearing PCy(3) or N-heterocyclic carbene ligands, respectively, can be used and are found to exhibit efficiency similar to that in chlorinated organic solvents. While compound 1 is readily soluble in scCO(2), complexes 2 and 3 behave like heterogeneous catalysts in this reaction medium. Importantly, however, the unique properties of scCO(2) provide significant advantages beyond simple solvent replacement. This pertains to highly convenient workup procedures both for polymeric and low molecular weight products, to catalyst immobilization, to reaction tuning by density control (RCM versus acyclic diene metathesis polymerization), and to applications of scCO(2) as a protective medium for basic amine functions. The latter phenomenon is explained by the reversible formation of the corresponding carbamic acid as evidenced by (1)H NMR data obtained in compressed CO(2). Together with its environmentally and toxicologically benign character, these unique physicochemical features sum up to a very attractive solvent profile of carbon dioxide for sustainable synthesis and production.     

Olefin metathesis: what have we learned about homogeneous and heterogeneous catalysts from surface organometallic chemistry?

Since its early days, olefin metathesis has been in the focus of scientific discussions and technology development. While heterogeneous olefin metathesis catalysts based on supported group 6 metal oxides have been used for decades in the petrochemical industry, detailed mechanistic studies and the development of molecular organometallic chemistry have led to the development of robust and widely used homogeneous catalysts based on well-defined alkylidenes that have found applications for the synthesis of fine and bulk chemicals and are also used in the polymer industry. The development of the chemistry of high-oxidation group 5–7 alkylidenes and the use of surface organometallic chemistry (SOMC) principles unlocked the preparation of so-called well-defined supported olefin metathesis catalysts. The high activity and stability (often superior to their molecular analogues) and molecular-level characterisation of these systems, that were first reported in 2001, opened the possibility for the first direct structure–activity relationships for supported metathesis catalysts. This review describes first the history of SOMC in the field of olefin metathesis, and then focuses on what has happened since 2007, the date of our last comprehensive reviews in this field.

Surface organometallic chemistry bridges the gap between homogeneous and heterogeneous olefin metathesis catalysts.     

Olefin metathesis catalyst bearing a chelating phosphine ligand

An improved synthetic procedure for the complex (SPY-5-34)-dichloro-(κ²(C,P)-diphenyl-(2-benzylidene)-phosphine)-(1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydro-imidazol-2-ylidene)-ruthenium (2) was elaborated and the title compound was tested as latent initiator in Ring Opening Metathesis Polymerization (ROMP) and as catalyst for Ring-Closing Metathesis (RCM) at elevated temperatures. While not particularly suited as latent initiator for ROMP, exhibiting a switching temperature of only 42 °C in the polymerization of a typical norbornene derivative, 2 shows an appealing performance in RCM of α,ω-dienes at higher temperatures.     

Olefin metathesis as an inorganic synthetic tool: cross and ring closing metathesis reactions of diruthenium-bound omega-alkene-alpha-carboxylates

Diruthenium compounds containing one omega-alkene-alpha-carboxylate ligand, Ru2Cl(D(3,5-Cl2Ph)F)3(O2C(CH2)nCH=CH2) (n=1 (1a) and 2 (1b)), were prepared from the reaction between Ru2Cl(D(3,5-Cl2Ph)F)3(O2CCH3) (D(3,5-Cl2Ph)F=N,N'-bis(3,5-dicholorophenyl)formamidinate) and the corresponding omega-alkene-alpha-carboxylic acid. Compounds 1a and 1b both underwent olefin cross metathesis reactions catalyzed by (Cy3P)2Cl2Ru(=CHPh) to afford the dimerized compounds [Ru2Cl(D(3,5-Cl2Ph)F)3]2(mu-O2C(CH2)nCH=CH(CH2)nCO2) (n=1 (2a) and 2 (2b)). Similarly, diruthenium compounds containing two omega-alkene-alpha-carboxylate ligands, cis-Ru2Cl(D(3,5-Cl2Ph)F)2(O2C(CH2)nCH=CH2)2 (n=1 (3a), 2 (3b), and 3 (3c)), were prepared by substituting the acetate ligands in cis-Ru2Cl(D(3,5-Cl2Ph)F)2(O2CCH3)2 with the corresponding omega-alkene-alpha-carboxylate ligands. Compounds 3 exhibited different reactivity under olefin metathesis conditions: both 3b and 3c underwent the intramolecular ring closing reaction quantitatively to afford compounds cis-Ru2(D(3,5-Cl2Ph)F)2(mu-O2C(CH2)nCH=CH2(CH2)nCO2)Cl with n=2 (4b) and 3 (4c), respectively, but 3a displayed no metathesis reactivity. Molecular structures of compounds 1a/1b, 2a/2b, 3a/3b, and 4b were established via X-ray diffraction studies, confirming the formation of cross and ring closing metathesis products. Voltammograms of compounds 2 are nearly identical to those of compounds 1, indicating the absence of electronic interactions mediated by the tether derived from olefin metathesis.     

Olefin metathesis in homogeneous aqueous media catalyzed by conventional ruthenium catalysts

Olefin metathesis in aqueous solvents is sought for applications in green chemistry and with the hydrophilic substrates of chemical biology, such as proteins and polysaccharides. Most demonstrations of metathesis in water, however, utilize exotic complexes. We have examined the performance of conventional catalysts in homogeneous water/organic mixtures, finding that the second-generation Hoveyda-Grubbs catalyst has extraordinary efficiency in aqueous dimethoxyethane and aqueous acetone. High (71-95%) conversions are achieved for ring-closing and cross metathesis of a variety of substrates in these solvent systems.     

Olefin metathesis in room temperature ionic liquids using imidazolium-tagged ruthenium complexes

New recyclable imidazolium-tagged ruthenium catalysts have been developed to perform olefin metathesis in room temperature ionic liquids (RTILs). High level of recyclability combined with a high reactivity were obtained in the ring-closing metathesis (RCM) of a variety of di- or tri-substituted and/or oxygen-containing dienes. Extremely low residual ruthenium levels were detected in the RCM products (average of 7.3 ppm per run). Several examples of olefin cross-metathesis (CM) have been also studied.     

Olefin metathesis for metal incorporation: Preparation of conjugated ruthenium-containing complexes and polymers

Olefin Metathesis for Metal Incorporation (OMMI) was used for the stoichiometric attachment of ruthenium to both small and large polyenes. The dinuclear complexes (PCy₃)₂C1₂RuCH(CHCH)_nCHRu(PCy₃)₂Cl₂ (n = 1, 2), were prepared by reacting 2 equiv. of the Grubbs first-generation catalyst (PCy₃)₂C1₂Ru(CHPh)) with 1 equiv. of the appropriate polyene (1,3,5-hexatriene for n = 1 and 1,3,5,7-octatetraene for n = 2). Use of excess hexatriene led to the formation of the monoruthenium complex (PCy₃)₂C1₂RuCHCH CHCHCH₂. The mono- and di-ruthenium complexes exhibited marked differences in their spectroscopic and electrochemical properties, in addition to their Z–E isomerization rates. Nucleophilic attack of PCy₃ on the end CH₂ of the mono complex was observed, leading to both isomerization and phosphonium products. Extending the OMMI strategy to the second-generation catalyst was also done, despite the reduced initiation rate. The more reactive catalyst (H₂IMes)RuCl₂(CHPh)(3-bromopyridine)₂ allowed for ruthenium incorporation into polyacetylene, leading to the formation of polymers and oligomers with high ruthenium content.     

Molden 2.0: quantum chemistry meets proteins

Since the first distribution of Molden in 1995 and the publication of the first article about this software in 2000 work on Molden has continued relentlessly. A few of the many improved or fully novel features such as improved and broadened support for quantum chemistry calculations, preparation of ligands for use in drug design related softwares, and working with proteins for the purpose of ligand docking.     

Immobilized boron-centered heteroscorpionates: heterocycle metathesis and coordination chemistry

The preparation of a resin-supported boron-scorpionate ligand and its nickel(II) coordination complexes are reported. The supported ligand is prepared as its potassium salt, making it a general reagent suitable for chelation of any transition metal ion. Resin-immobilized benzotriazole (Bead-btz) reacted cleanly with KTp* (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate) by heterocycle metathesis in warm dimethylformamide (DMF) to yield bead-Tp'K, {resin-btz(H)B(pz*)(2)}K. Significantly, bead-Tp'K readily bound nickel(II) from simple salts with minimal leaching of the nickel ion. Bead-Tp'NiNO(3) reacts further with cysteine thiolate (ethyl ester), imparting the deep green color to the beads characteristic of a Tp(R)NiCysEt coordination sphere. Bead-Tp'NiCysEt exhibited an oxygen sensitivity similar to Tp*NiCysEt in solution (Inorg. Chem. 1999, p 5690) and also independently verified for a selenocystamine analogue, Tp*NiSeCysAm. Addition of fresh cysteine thiolate ethyl ester to oxidized bead-Tp'NiCysEt reproduced the original green color. Heterocycle metathesis was also used to prepare KTp' as a white solid. Reaction with nickel(II) gave (Tp')(2)Ni, separable into two different isomers. The air-sensitive molybdenum(0) complex, [PPh(4)][Tp'Mo(CO)(3)], was also prepared and the C(s) complex symmetry demonstrated by infrared and (13)C NMR spectroscopies. Immobilized TpmMo(CO)(3) was prepared from the previously reported resin-supported tris(pyrazolyl)methane. In contrast to its weak coordination of nickel(II) (Inorg. Chem. 2009, p 3535), bead-Tpm proved a strong chelate toward this second row metal. The supported scorpionates described here should find use in studies of selective metal-protein binding, metalloprotein modeling, and heterogeneous catalysis, and render such scorpionate applications amenable to combinatorial methods.     

Olefin metathesis: remote substituents governing the stereoselectivity of 11-membered-ring formation

[reaction: see text] Stereospecific RCM reaction of 7 (R1 = Me) results in the formation of (Z)-11-membered macrocycle 9c. Cascade RCM/ROM/RCM transformation of 7 (R1 = H) affords the thermodynamically more stable spirocycle product 12.     

Olefin metathesis catalyst: stabilization effect of backbone substitutions of N-heterocyclic carbene

Ruthenium olefin metathesis catalysts bearing an N-phenyl-substituted N-heterocyclic carbene (NHC) ligand that are resistant to decomposition through C-H activation have been prepared and tested in ring closing metathesis (RCM), cross metathesis (CM), and ROMP reactions. The N, N'-diphenyl-substituted NHC complex proved to be one of the most efficient catalysts in RCM to form tetrasubstituted olefins.     

Olefin metathesis featuring ruthenium indenylidene complexes with a sterically demanding NHC ligand

The synthesis and characterization of two new ruthenium indenylidene complexes [RuCl(2)(SIPr)(Py)(Ind)] 6 and [RuCl(2)(SIPr)(3-BrPy)(Ind)] 7 featuring the sterically demanding N-heterocyclic carbene 1,3-bis(2,6-di isopropylphenyl)-4,5-dihydroimidazol-2-ylidene (SIPr) are reported. Remarkable activity was observed with these complexes in ring closing, enyne, and cross metathesis of olefins at low catalyst loadings. The performance of SIPr-bearing complexes 6 and 7 as well as [RuCl(2)(SIPr)(PCy(3))(Ind)] 5 in ring opening metathesis polymerization is also disclosed. This work highlights the enormous influence of the neutral "spectator" ligands on catalyst activity and stability.     

Complex surface engineering meets simple and beautiful surface chemistry

Surface chemistry of solids is the fundamental for processes on solid surfaces and properties of solid surfaces,such as heterogeneous catalysis,electrochemistry,corrosion,thin film growth,sensing,friction and lubrication[1].Understanding surface chemistry of solids is not only of great scientific interest,but also of important technological value for optimizing surface properties and processes.Due to the complexity of solid surface structures,it is challenging to unambiguously elucidate the surface chemistry of surface properties and processes at a molecular level.