Allenylidene-to-Indenylidene Rearrangement in Arene−Ruthenium Complexes: A Key Step to Highly Active Catalysts for Olefin Metathesis Reactions

Conrad J.C., Parnas H.H., Snelgrove J.L., Fogg D.E.

Ruthenium alkylidene complexes containing one aryloxide "pseudohalide" ligand catalyze ring-closing metathesis of diene and ene-yne substrates with exceptionally high efficiency. Chromatographic removal of Ru residues is unexpectedly facile, offering a convenient means of isolating pure organic products in high yields.

Castarlenas R., Esteruelas M.A., Oñate E.

The complexes [(η6-p-cymene)OsCl(CHPh)(IPr)]OTf (4a; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolylidene) and [(η6-p-cymene)OsCl(CHPh)(IMes)]OTf (4b; IMes = 1,3-bis(2,4,6-trimethylphenyl)imida-zolylidene) have been prepared by reaction of the corresponding 16-electron compounds [(η6-p-cymene)OsCl(NHC)]OTf (NHC = IPr (3a), IMes (3b)) with phenyldiazomethane, and their potential as initiators for olefin CM, RCM, and ROMP reactions has been explored.

Nicolaou K.C., Bulger P.G., Sarlah D.

With the exception of palladium-catalyzed cross-couplings, no other group of reactions has had such a profound impact on the formation of carbon-carbon bonds and the art of total synthesis in the last quarter of a century than the metathesis reactions of olefins, enynes, and alkynes. Herein, we highlight a number of selected examples of total syntheses in which such processes played a crucial role and which imparted to these endeavors certain elements of novelty, elegance, and efficiency. Judging from their short but impressive history, the influence of these reactions in chemical synthesis is destined to increase.

Cadierno V., Díez J., García-Garrido S.E., Gimeno J.

Alkenyl-carbyne complexes fac-[RuX3{⋮CC(H)CR2}(dppf)] (X = Cl, Br; R = Ph, iPr or CR2 = C13H8) (2a−c, 3a−c) have been prepared by reaction of the bis(allyl)-ruthenium(II) derivative [Ru(η3-2-C3H4Me)2(dppf)] (1) with the appropriate propargylic alcohol HC⋮CCR2(OH) in the presence of 3.5 equiv of the corresponding hydrogen halide HX. The structure of compounds fac-[RuCl3{⋮CC(H)CR2}(dppf)] (R = Ph (2a) and iPr (2c)) has been confirmed by X-ray crystallography. Structural parameters within the alkenyl-carbyne chain in 2a,c suggest an important contribution of the zwitterionic vinylidene canonical form fac-[RuCl3{CC(H)-CR2}(dppf)]. Formation of complexes 2,3a−c involves the 1,3-addition of HX to the corresponding dinuclear allenylidene intermediates [{RuX(μ-X)(CCCR2)(dppf)}2]. Such allenylidene complexes, i.e., [{RuX(μ-X)(CCCR2)(dppf)}2] (X = Cl, Br; R = Ph or CR2 = C13H8) (4a,b, 5a,b), have been prepared and characterized by treatment of fac-[RuX3{⋮CC(H)CR2}(dppf)] (X = Cl, Br; R = Ph or CR2 = C13H8) (2a,b, 3...

Li J.Y., Ziegler A., Wegner G.

A group of fluorene-based polymers, PF-1SOR and PF-2SOR, were synthesized and characterized as blue light-emitting materials. PF-1SOR and PF-2SOR displayed nematic liquid crystalline mesophase in films cast from solution. Compared with conventional polyfluorene, PF-1SOR and PF-2SOR display blue-shifted UV absorption and structureless blue fluorescence. The photoluminescence spectra of PF-1SOR and PF-2SOR were found insensitive against thermal treatment in air up to 200 degrees C and the blue electroluminescence in their light-emitting devices was independent of the driving voltage. Compared to the conventional polyfluorenes, the improved spectral stability of these polymers is attributed to the anti-oxidization effect of (3,5-di(tert-butyl)phenoxy)sulfonyl side groups attached to the backbone.

Halbach T.S., Mix S., Fischer D., Maechling S., Krause J.O., Sievers C., Blechert S., Nuyken O., Buchmeiser M.R.

The syntheses and reactivity of seven different ruthenium-based metathesis catalysts are described. Ru(CF3COO)2(PCy3)(=CH-2-(2-PrO)C6H4) (1), Ru(CF3COO)2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (2), and Ru(CF3COO)2(PCy(3))(1,3-dimesityldihydroimidazolin-2-ylidene)(=CHC6H5) (3) were prepared via chlorine exchange by reacting RuCl2(PCy3)2(=CH-2-(2-PrO)C6H4), RuCl2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4), and RuCl2(PCy3)(1,3-dimesityldihydroimidazolin-2-ylidene)(=CHC6H5), respectively, with silver trifluoroacetate (Cy =cyclohexyl). In analogy, Ru(CF3CF2COO)2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (4) and Ru(CF3CF2CF2COO)2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (5) were prepared from RuCl2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) via reaction with CF3CF2COOAg and CF3CF2CF2COOAg, respectively. Ru(C6F5COO)2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (6) and Ru(C6F5O)2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (7) were prepared from RuCl2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) via reaction with C6F5COOTl and C6F5OTl, respectively. Supported catalysts Ru(PS-DVB-CH2OOCCF2CF2CF2COO)(CF3COO)(PCy3)(1,3-dimesityldihydroimidazolin-2-ylidene)(=CHC6H5) (8), Ru(PS-DVB-CH2OOCCF2CF2CF2COO)(CF3COO)(PCy3)(=CH-2-(2-PrO)C6H4) (9), and Ru(PS-DVB-CH2OOCCF2CF2CF2COO)(CF3COO)(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (10) were synthesized by reaction of RuCl2(PCy3)(1,3-dimesityldihydroimidazolin-2-ylidene)(=CHC6H5), RuCl2(PCy3)(=CH-2-(2-PrO)C6H4), and RuCl2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4), respectively, with a perfluoroglutaric acid-derivatized poly(styrene-co-divinylbenzene) (PS-DVB) support (silver form). Halogen exchange in PCy3-containing systems had to be carried out in dichloromethane in order to suppress precipitation of AgCl.PCy3. The reactivity of all new catalysts in ring-closing metathesis (RCM) of hindered electron-rich and -poor substrates, respectively, at elevated temperature (45 degrees C) was compared with that of existing systems. Diethyl diallylmalonate (DEDAM, 11), diethyl allyl(2-methylallyl)malonate (12), N,N-diallyl-p-toluenesulfonamide (13), N-benzyl-N-but-1-en-4-ylbut-2-enecarboxylic amide (14), and N-allyl-N-(1-carboxymethyl)but-3-en-1-yl-p-toluenesulfonamide (15) were used as educts. Supported catalysts were prepared with high loadings (2.4, 22.1, and 160 mg of catalyst/g PS-DVB for 8, 9, and 10, respectively). Catalyst 8 showed higher and catalysts 9 and 10 sowed significantly reduced activities in RCM compared to their homogeneous analogues. Thus, with 8, turnover numbers (TONs) up to 4200 were realized in stirred-batch (carousel) RCM experiments. To elucidate the nature of the bound species, catalysts 8-10 were subjected to 13C- and 31P-MAS NMR spectroscopy. These investigations provided evidence for the proposed structures. Leaching of ruthenium into the reaction mixture was low, resulting in ruthenium contents

Wong W.

This review covers recent developments in the molecular design and synthesis of metal-based functional materials of fluorenes and their derivatives. Conjugated organic compounds containing metal centers constitute an important class of molecular materials nowadays because of the combined good features of the chemical, electrochemical, electronic and optical properties of the metal groups to those of the organic chromophores. Recently, substituted fluorene derivatives have been extensively explored in the field of optoelectronics and molecular electronics. They are synthetically easily accessible and possess high thermal and chemical stability as well as high emission quantum yields. Such rapidly emerging chemistry of organic-based fluorene derivatives leads us to believe that a related chemistry involving metal centers should present a fascinating subclass and pose potential for the development of new types of novel materials. While there is great scope for chemical modifications of the metal units and structure of the fluorene ring and its substituents in a systematic fashion, these classes of metal–organics can exhibit rich photophysical, redox and structural properties. An understanding of the structure–property relationships of these molecules allows us to establish good model systems in the development of optoelectronic devices, molecular electronics and chemical sensing applications. In this article, homo- and heterometallic systems containing fluorene chromophores and their structural analogues such as carbazoles and diazafluorenes are discussed, and particular attention is paid to chemical reactivities, electronic absorption spectroscopy, photoluminescence and redox behavior, and structural aspects of these metal–organic compounds. The applications that these materials have found in various domains are also highlighted.

Castarlenas R., Eckert M., Dixneuf P.H.

Wallace D.J.

Yang X., Gong B.

Trimmel G., Riegler S., Fuchs G., Slugovc C., Stelzer F.

Liquid crystalline polymers (LCPs) have gained attention as materials with interesting optical, mechanical and rheological properties. This review summarizes research on thermotropic liquid crystalline polymers synthesized by metathesis polymerization techniques. Ring opening metathesis polymerization (ROMP) is a versatile tool for preparing side chain liquid crystalline polymers (SCLCPs) with different mesogenic units. The living character of ROMP allows us to design well-defined polymers and copolymers with controlled molecular weight and molecular weight distributions. The mesophase type and the thermal transition temperatures are influenced not only by the attached mesogenic moiety but also by the stiffness of the polymer backbone, the spacer lengths between the main chain and the liquid crystalline entity, the Z/E isomerism, the tacticity, and so on. In addition, the use of acyclic diene metathesis polymerization (ADMET) or alternating diene metathesis polycondensation (ALTMET) offer new possibilities for creating new main chain liquid crystalline polymers (MCLCPs). A short discussion of new trends and potential applications for these polymers concludes the review.

Baughman T.W., Wagener K.B.

Acyclic diene metathesis (ADMET) polymerization techniques and methodologies developed over the past five years are reviewed. Through constant catalyst development and further understanding of catalytic activity and side reactions, metathesis has solved a number of synthetic problems through the mild carbon-carbon bond-forming reaction. Polymerization of functionalized α,ω-dienes has afforded strictly linear copolymers of ethylene and various polar monomers that are unattainable through chain polymerization methodology. Telechelic preparation via ADMET allows the synthesis of reactive polymers as starting points for block and segmented copolymers. Application of ADMET to materials synthesis has yielded novel amino acid and peptide polymers as well as silicon-based materials.

Dragutan B.V., Dragutan I., Verpoort F.

Hercouet A., Baudet C., Carboni B.

Ruthenium catalyzed ring-closing metathesis has been used as a key step for the synthesis of cyclic α-aminoboronic esters as, for example, boron-containing mimics of pipecolic, 2-azepanecarboxylic acid or baikiain.

Asensio A., Buil M.L., Esteruelas M.A., Oñate E.

Financial support from the MCYT of Spain (Proyects BQU2002-00606 and PPQ2000-0488-P4-02) is acknowledged. M.L.B. thanks the Spanish MCYT and the Universidad de Zaragoza for funding through the “ Ramon y Cajal” Program.

Hu J.R., Zhao S.Q., Wang J.H., Sun S.Q., Miao C.P.

A novel complex (p-cymene)Ru(S2C2B10H9)(PhCH=CCH2OCH(Ph)C≡CH)·CH2Cl2 based on the ortho-carborane-1,2-dithiolate ligand and 1-phenyl-2-propyn-1-ol has been synthesized successfully and characterized by IR, NMR, MS, elemental analysis and single-crystal X-ray diffraction. The complex crystallizes in monoclinic system, space group P21/n with: a = 10.221(4) Å, b = 14.912(6) Å, c = 24.182(10) Å, α = 90.00°, β = 99.096(6)°, γ = 90.00°, C31H40B10Cl2ORuS2, Mr = 772.82, V = 3639(3) Å3, Dc = 1.410 g/cm3, Z = 4, F(000) = 1576, μ(MoKα) = 0.719 mm–1, R = 0.0600 and wR = 0.1561 for 5463 observed reflections (I > 2σ(I)). Structural analysis shows that there are the coordination of C=C bond, the formation of C–S bod, and metal-induced B–H activation with the formation of Ru–B bond.

Saha S., Averkiev B., Sues P.E.

Wei W., Jia G.

The coordination chemistry of ruthenium, osmium, technetium and rhenium with carbon-based ligands covering the literature from 2003 to 2018 is discussed. These metals form a vast number of coordination compounds with carbon-based ligands ranging from a single carbon atom (a carbido ligand) to polydentate hydrocarbon chains, and from monodentate organometallic ligands such as carbenes to multidentate ligands such as pincers and macrocycles. Particular focus of this review is given to syntheses, properties and applications of complexes with popular carbon-based ligands such as monodentate N-heterocyclic carbenes (NHCs), cyclometallated bidentate ligands, tridentate pincers and porphyrin-like macrocycles.

Soulé J., Bruneau C., Darcel C.

Dong Y., Wrobel A.T., Porter G.J., Kim J.J., Essman J.Z., Zheng S., Betley T.A.

Intramolecular alkoxylation of C-H bonds can rapidly introduce structural and functional group complexities into seemingly simple or inert precursors. The transformation is particularly important due to the ubiquitous presence of tetrahydrofuran (THF) motifs as fundamental building blocks in a wide range of pharmaceuticals, agrochemicals, and natural products. Despite the various synthetic methodologies known for generating functionalized THFs, most show limited functional group tolerance and lack demonstration for the preparation of spiro or fused bi- and tricyclic ether units prevalent in molecules for pharmacological purposes. Herein we report an intramolecular C-H alkoxylation to furnish oxacycles from easily prepared α-diazo-β-ketoesters using commercially available iron acetylacetonate (Fe(acac)2) as a catalyst. The reaction is proposed to proceed through the formation of a vinylic carboradical arising from N2 extrusion, which mediates a proximal H-atom abstraction followed by a rapid C-O bond forming radical recombination step. The radical mechanism is probed using an isotopic labeling study (vinyl C-D incorporation), ring opening of a radical clock substrate, and Hammett analysis and is further corroborated by density functional theory (DFT) calculations. Heightened reactivity is observed for electron-rich C-H bonds (tertiary, ethereal), while greater catalyst loadings or elevated reaction temperatures are required to fully convert substrates with benzylic, secondary, and primary C-H bonds. The transformation is highly functional group tolerant and operates under mild reaction conditions to provide rapid access to complex structures such as spiro and fused bi-/tricyclic O-heterocycles from readily available precursors.

Zachmann R.J., Fürstner A.

Cui M., Guo X., Sung H.H., Williams I.D., Lin Z., Jia G.

[(η6-p-cymene)OsI2]2 was found to be a good catalyst for the cyclopropanation reaction of isobutyl vinyl ether with 3-tert-butyldiazoindene. In contrast, the complexes [(η6-p-cymene)OsX2]2 (X = Cl,...

Matveevskaya V.V., Pavlov D.I., Sukhikh T.S., Gushchin A.L., Ivanov A.Y., Tennikova T.B., Sharoyko V.V., Baykov S.V., Benassi E., Potapov A.S.

A series of novel mono- and binuclear arene–ruthenium(II) complexes [(p-cym)Ru(L)Cl] containing 11H-indeno[1,2-b]quinoxalin-11-one derivatives or tryptanthrin-6-oxime were synthesized and characterized by X-ray crystallography, IR, NMR spectroscopy, cyclic voltammetry, and elemental analysis. Theoretical calculations invoking singlet state geometry optimization, solvation effects, and noncovalent interactions were done using density functional theory (DFT). DFT calculations were also applied to evaluate the electronic properties, and time-dependent DFT was applied to clarify experimental UV–vis results. Cytotoxicity for cancerous and noncancerous human cell lines was evaluated with cell viability MTT assay. Complexes demonstrated a moderate cytotoxic effect toward cancerous human cell line PANC-1. The catalytic activity of the complexes was evaluated in transfer hydrogenation of aryl ketones. All complexes exhibited good catalytic activity and functional group tolerance.

Samzadeh‐Kermani A., Poorhabibi‐Zarandi M.

Smit W., Ekeli J.B., Occhipinti G., Woźniak B., Törnroos K.W., Jensen V.R.

Ru-alkylidenes bearing sterically demanding arylthiolate ligands (SAr) constitute one of only two classes of catalyst that are Z-selective in metathesis of 1-alkenes. Of particular interest are com...

Kaur N., Ahlawat N., Verma Y., Grewal P., Bhardwaj P.

The field of heterocyclic chemistry has been revolutionized using transition metal catalysts in recent years. Various research groups have focused on the development of general protocols to achieve better functional group compatibilities and greater levels of molecular complexity under mild reaction conditions, using easily available starting substrates. The methodologies used earlier for their synthesis were less approachable to organic chemists because of their high cost, highly specified instrumentation and inconvenient methods. For both stereoselective and regioselective synthesis of five-membered nitrogen- containing heterocycles, cyclic reactions that are Ru-catalyzed have known to be very efficient. These methods have many advantages as compared to alternative pathways involved in the synthesis of heterocyclic compounds. In this review article, we concentrated on the synthesis of nitrogen-containing five-membered heterocycles in the presence of a ruthenium catalyst. This review mostly covers the literature published during the period from 1977-2019.

Liu R., Yang D., Chang F., Giordano L., Liu G., Tenaglia A.

It was there all along! A ruthenium(II)-catalyzed cycloisomerization of 1,6-enynes to access azabicyclo[4.1.0]heptenes was achieved. A series of 1,6-enynes bearing an internal/terminal alkyne/alkenes motif proved to be good candidates for substrates, giving their corresponding bicyclic products in good to excellent yields.

Nandhini R., Venkatachalam G.

The ruthenium(II) complexes of the general formula [Ru(η6‒p‒cymene)(Cl)(L1‒5)] (L = O, N-donors of biphenylazo derivatives), formed by reacting 2‒(biphenylazo)phenol (HL1 ‒ HL4) and 1‒(biphenylazo)naphthol ligands (HL5) with [{η6‒p‒cymene)RuCl}2(μ‒Cl)2] have been synthesized. The compositions of the complexes have been established by IR, UV–Vis, 1H NMR spectral methods and X-ray crystallography. The synthesized complex could act as an efficient, reusable homogeneous catalyst for transformation of aldehydes to the corresponding primary amides in the presence of NH2OH·HCl, thus resulting an expansion of Beckmann rearrangement. The effect of solvent, base, temperature, time, catalyst loading and recyclability was also investigated. They also effectively catalyze the transfer hydrogenation reaction of various ketones with 2-propanol.

Di Bussolo V., Princiotto S., Bordoni V., Martinelli E., Favero L., Crotti S., Uccello Barretta G., Balzano F., Pineschi M., Crotti P.

Upon treatment with the metal enolates of methylene active compounds (dimethyl malonate and dibenzoylmethane) (C-nucleophiles) and benzyl carbamate (N-nucleophile), d -allal- and d -galactal-derived vinyl epoxides are stereoselectively transformed, in a single step, into diastereoisomeric, highly functionalized, enantiopure cis- and trans-2,5-disubstituted-2,5-dihydrofurans.

Roh S.W., Choi K., Lee C.

With their mechanistic novelty and various modalities of reactivity, transition metal unsaturated carbene (alkenylidene) complexes have emerged as versatile intermediates for new reaction discovery. In particular, the past decade has witnessed remarkable advances in the chemistry of metal vinylidenes and allenylidenes, leading to the evolution of a diverse array of new catalytic transformations that are mechanistically distinct from those developed in the previous two decades. This review aims to provide a survey of the recent achievements in the development of organic reactions that make use of transition metal alkenylidenes as catalytic intermediates and their applications to organic synthesis.