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The syntheses of the neutral molybdenum imido alkylidene N‐heterocyclic carbene (NHC) complexes of the general formula [Mo(NAr)(CHCMe2Ph)(NHC)XY] (Ar=2‐tBu‐C6H4, 2‐CF3‐C6H4, 2,6‐Me2‐C6H3, 2,6‐Cl2‐C6H3, adamantyl; X, Y=OTf, OC(CF3)3, OCH(CF3)2, OC6F5, SC6F5, 2,5‐bis(pentafluorophenyl)phen‐1‐yl) bearing electron‐withdrawing NHCs (1,3‐dimethyl‐4,5‐dichloroimidazol‐2‐ylidene (IMeCl2), 1,3,4‐triphenyl‐1,2,4‐triazol‐5‐ylidene (TPT)) are reported. Complementary, the corresponding cationic molybdenum imido alkylidene NHC complexes of the general formula [Mo(NAr)(CHCMe2R)(NHC)X+][B(ArF)4−/Al(OC(CF3)3)4−] (R=Me, Ph; B(ArF)4−=tetrakis (3,5‐bis(trifluoromethyl)phenyl)borate) have been prepared. Aiming at tungsten oxo complexes, reaction of [W(O)Cl2(CHCMe2Ph)(PMe2Ph)2] with [1,3‐dimethyl‐4,5‐dichloroimidazol‐2‐ylidene⋅AgI] (IMeCl2⋅AgI) followed by the addition of lithium terphenoxide yields [W(O)(CHCMe2Ph)(IMeCl2)(DPPO)2]. For comparison, [W(O)Cl(CHCMe2Ph)(IMes)(OSi(OtBu)3)] was prepared via reaction of [W(O)Cl2(CHCMe2Ph)(PMe2Ph)(IMes)] with KOSi(OtBu)3. [W(O)(CHCMe2Ph)(IMeCl2)(DPPO)(Et2O)+][B(ArF)4−] (DPPO=2,6‐diphenylphenoxide) became accessible via reaction of [W(O)(DPPO)2(CHCMe2Ph)(IMeCl2)] with anilinium B(ArF)4−. The structural peculiarities of selected complexes are reported. Benchmark ring‐closing metathesis and homometathesis reactions revealed that the neutral complexes bearing weakly coordinating NHCs such as IMeCl2 and TPT possessed only moderate activity, which could, however, be improved by preparing the corresponding cationic metal alkylidene complexes. [ABSTRACT FROM AUTHOR]

Despite their excellent selectivities and activities, Mo‐and W‐based catalysts for olefin metathesis have not gained the same widespread use as Ru‐based systems, mainly due to their inherent air sensitivity. Herein, we describe the synthesis of air‐stable cationic‐at‐metal molybdenum and tungsten imido alkylidene NHC nitrile complexes. They catalyze olefin metathesis reactions of substrates containing functional groups such as (thio‐) esters, (thio‐) ethers and alcohols without the need for prior activation, for example, by a Lewis acid. The presence of a nitrile ligand was found to be essential for their stability towards air, while no decrease in activity and productivity could be observed upon coordination of a nitrile. Variations of the imido and anionic ligand revealed that alkoxide complexes with electron‐withdrawing imido ligands offer the highest reactivities and excellent stability compared to analogous triflate and halide complexes. [ABSTRACT FROM AUTHOR]

Isolable cationic PtII and PtIV alkylidenes, proposed intermediates in catalytic organic transformations, are reported. The bonding in these species was probed by experimental, structural, spectroscopic, electrochemical and computational methods, providing direct evidence for π‐bonding, the often‐theorized relativistic stabilization of these species, and the influence of oxidation state. It's all relative: A homologous series of Group 10 PCcarbeneP complexes were prepared and the bonding in the M=C moiety probed by experimental and computational techniques to show that relativistic stabilization is significant in the platinum carbene. [ABSTRACT FROM AUTHOR]

Facile α‐H elimination from tetrakis(trimethylsilylmethyl)titanium precursors to give adducts of (alkylidene)bis(alkyl)titanium complexes is induced by light alkali metal amides of the NNNN‐type macrocyclic anionic ligand Me3TACD [(Me3TACD)H=1,4,7‐trimethyl‐1,4,7,10‐tetraazacyclododecane]. In the crystal, the alkali metal interacts with the carbene carbon atom or with the CH2 group of the trimethylsilymethyl ligand. The nucleophilic character of the carbene carbon atom was shown by the reaction with benzophenone and terminal acetylenes. Facile α‐H elimination from tetrakis(trimethylsilylmethyl)titanium is induced by alkali metal amides to give adducts of (alkylidene)bis(alkyl)titanium complexes. In the crystal, the alkali metal interacts with the carbene carbon atom or with the CH2 group of the trimethylsilymethyl ligand. The nucleophilic character of the carbene carbon atom was shown by reactions with benzophenone and terminal acetylenes. [ABSTRACT FROM AUTHOR]

Silica‐supported cationic Mo‐imido alkylidene N‐heterocyclic carbene catalysts, prepared by surface organometallic chemistry, display contrasting olefin metathesis activity for terminal and internal olefins. The high metathesis activity towards terminal alkenes is attributed to the strong σ‐donating property of the NHC ancillary ligand, which disfavors the formation of the parent square‐planar metallacyclobutane, an off‐cycle reaction intermediate resulting from the reaction with ethylene, one of the metathesis products. This tailored ligand environment also allowed the first trigonal bipyramidal (TBP) metallacyclobutane reaction intermediate for supported Mo metathesis catalysts to be identified. [ABSTRACT FROM AUTHOR]

Abstract: This article outlines the fundamental concept to molybdenum imido, tungsten imido and tungsten oxo alkylidene N‐heterocyclic carbene (NHC) catalysts for olefin metathesis. Starting from Mo(NR)(CHCMe2R′)(OTf)2⋅DME (R=alkyl, aryl; R′=CH3, Ph; OTf=CF3SO3; DME=1,2‐dimethoxyethane), W(NR)(CHCMe2Ph)X2 (X=pyrrolide, OR′′, SiPh3) and W(O)Cl2(CHCMe2Ph)(PMe2Ph)2, respectively, the neutral, pentacoordinated 16‐valence electron (VE) complexes became accessible. These serve as precursors for the corresponding cationic, tetracoordinated 14‐VE catalysts. This class of olefin metathesis catalysts based on group 6 metal alkylidene NHCs is characterized by a broad structural variability, high activity, high productivity and, in tailored systems, high functional group tolerance even vs. protic groups including alcohols and carboxylic acids. Also, high regio‐ and stereoselectivity is achieved, both in ring‐opening metathesis polymerization (ROMP) and in the cyclopolymerization of α,ω‐diynes. Fundamentals concerning the influence of the imido/oxo ligand, the different NHCs and the anionic ligands on catalyst performance and stability as well as reaction pathways are summarized. Also, the concepts for catalyst immobilization, whether via the NHC or by substitution of an alkoxide, are presented. Finally, special features such as the use of betaine‐type anionic ligands (alkoxides and sulfonates), which offer access to ionic catalysts for use biphasic reaction setups, are briefly outlined. [ABSTRACT FROM AUTHOR]

Although generally the ruthenium based homogeneous catalysts are used to initiate metathesis reactions, immobilization of homogeneous ruthenium metathesis catalysts on various solid supports has attracted a lot of interest from the scientific community in recent years. In this article, the synthesis and applications of highly active polyHIPE-supported N-heterocyclic carbene ligand (NHC)-bearing ruthenium alkylidene metathesis catalysts were described. Open-celled porous polyHIPE foams having surface area of 575 m2/g were synthesized by polymerization of the continuous phase of w/o high internal phase emulsions. Then RuCl2(PCy3)(H2IMes)(=CHPh) complex was attached to porous polyHIPE solid supports via alkylidene exchange reactions to obtain new olefin metathesis catalysts. The amount of initiator loadings was determined by ruthenium analysis via ICP-OES and found to be 0.0336-0.0514 mmol/g. Subsequently, the activity of new catalysts was tested in ring opening metathesis polymerization of norbornene and a series of its derivatives.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Abstract: Unprecedented silyl‐phosphino‐carbene complexes of uranium(IV) are presented, where before all covalent actinide–carbon double bonds were stabilised by phosphorus(V) substituents or restricted to matrix isolation experiments. Conversion of [U(BIPMTMS)(Cl)(μ‐Cl)2Li(THF)2] (1, BIPMTMS=C(PPh2NSiMe3)2) into [U(BIPMTMS)(Cl){CH(Ph)(SiMe3)}] (2), and addition of [Li{CH(SiMe3)(PPh2)}(THF)]/Me2NCH2CH2NMe2 (TMEDA) gave [U{C(SiMe3)(PPh2)}(BIPMTMS)(μ‐Cl)Li(TMEDA)(μ‐TMEDA)0.5]2 (3) by α‐hydrogen abstraction. Addition of 2,2,2‐cryptand or two equivalents of 4‐N,N‐dimethylaminopyridine (DMAP) to 3 gave [U{C(SiMe3)(PPh2)}(BIPMTMS)(Cl)][Li(2,2,2‐cryptand)] (4) or [U{C(SiMe3)(PPh2)}(BIPMTMS)(DMAP)2] (5). The characterisation data for 3–5 suggest that whilst there is evidence for 3‐centre P−C−U π‐bonding character, the U=C double bond component is dominant in each case. These U=C bonds are the closest to a true uranium alkylidene yet outside of matrix isolation experiments. [ABSTRACT FROM AUTHOR]

We report an unexpected rearrangement of a deprotonated picolyl-functionalized N-heterocyclic carbene (NHC) ligand from N,C-chelate to N,N-chelate in three-legged piano-stool Fe(II) and Ru(II) complexes. The reaction mechanism has been explored for one of the Fe(II) complexes. Experimental and computational studies suggest an unusual intermediate featuring a four-membered chelate ring, where the NHC and the α-carbon of one of the N-substituents coordinate to the Fe(II) center. A possible Fe-alkylidene intermediate has also been predicted by computations. [ABSTRACT FROM AUTHOR]

This review aims to offer a detailed summary of the discoveries regarding non-heteroatom-substituted alkylidenes of group 10 and 11 metals that have appeared in the literature since the first isolable representative of this class was reported in 2002. Special attention is focused on synthetic and bonding aspects of well-defined species. The importance of this family of compounds in catalytic organic transformations is often mentioned and a number of references are provided. We stress, however, that it is not the main issue of this review, as this topic has received considerable attention in the current literature. [ABSTRACT FROM AUTHOR]

The synthesis of W(NAr′)(NHC)(=CHR)(2,5-Me2pyr)2 ( 1; Ar′: 2,6- iPr2C6H3; NHC: 1,3-diisopropylimidazol-2-ylidene; 2,5-Me2pyr: 2,5-dimethylpyrrolide; R: CMe2Ph), W(NAr′)(NHC)(=CHR)(2,5-Me2pyr)(OC6F5) ( 2), W(NAr′)(NHC)(=CHR)(OSiPh3)2 ( 3), [W(NAr′)(NHC)(=CHR)(OSiPh3))(MeCN)+][B(ArF)4−] ( 4; B(ArF)4−: B(3,5-(CF3)2C6H3)4−), [W(NAr′)(NHC)(=CHR)(2,5-Me2pyr))+][B(ArF)4−] ( 5), [W(NAr′)(NHC)(=CHR)(OC6F5))( tBuCN)+][B(ArF)4−] ( 6), W(NAr′)(NHC)(=CHR)(O tBu)2 ( 7), [W(NAr′)(NHC)(=CHR)(O tBu)+][B(ArF)4−] ( 8), and W(NAr′)(NHC)(=CHR)(OCMe(CF3)2)2 ( 9) is described, and the reactivity of the complexes in olefin metathesis and cyclopolymerization is reported. The cationic complexes 4, 5, and 6 showed high productivity and activity in olefin metathesis reactions, with turnover numbers of up to 40 000 and turnover frequencies (TOF5min) of up to 31 s−1, and also substantial functional group tolerance toward esters, nitriles, alcohols, and sulfides, particularly in the cyclopolymerization of α,ω-diynes. [ABSTRACT FROM AUTHOR]

Ionic Mo- and W-imido alkylidene N-heterocyclic carbene (NHC) olefin metathesis catalysts, [Mo{ N-2,6-(Me2)C6H3}(CHCMe2Ph)(IMesH2)(OTf)(PPS)]OTf ( 3), [Mo( N-2,6-(Me2)C6H3)(CHCMe2Ph)(IMesH2)(OC6F5)(PPS)][B(ArF)4] ( 5), [Mo(N tBu)(CHCMe2Ph)(4,5-dichloro-1,3-dimethylimidazol-2-ylidene)(OTf)(2,6-Ph-4-{2,4,6-Ph-pyridinium}phenolate)][OTf] ( 9), [Mo(N tBu)(CHCMe2Ph)(4,5-dichloro-1,3-dimethylimidazol-2-ylidene)(2,6-Ph-4-{2,4,6-Ph-pyridinium}phenolate)][B(ArF)4]2 ( 10, PPS=pyridiniumpropanesulfonate, IMesH2=1,3-dimesitylimidazolin-2-ylidene, OTf=CF3SO3, B(ArF)4=tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) were prepared from betaine-type ligands. Also, the first bis-NHC and a nitron-based bis(amido) bistriflate imido alkylidene complex, [Mo(N tBu)(CHCMe2Ph)(4,5-dichloro-1,3-dimethylimidazol-2-ylidene)2(THF)(2,6-Ph-4-{2,4,6-Ph-pyridinium}phenolate)][OTf]2 ( 11) and [Mo( N-2,6-Me2-C6H3)(CHCMe2Ph)( N-{1,4-diphenyl-1,3,4-triazol-2-ylium}- N-phenyl-amido)2][OTf]2 ( 14) along with ionic [W( N-2,6- iPr2-C6H3)(CHCMe2Ph)( N-2,5-Me2C4H2)(I iPr)(2,6- tBu-4-PPh3-phenolate)] (17, I iPr=1,3-diisopropylimidazol-2-ylidene) are reported. With these new catalysts, the first biphasic reaction setup with Group 6 metal alkylidene NHC complexes was successfully established using a pyrrole/heptane mixture as a liquid phase. Productivities under biphasic conditions were comparable to those of reactions in 1,2-dichloroethane or toluene. Metal concentrations of <2 ppm migrated into the nonpolar heptane phase as measured by inductively coupled plasma-optical emission spectroscopy. [ABSTRACT FROM AUTHOR]

Graphical abstract New monothiolate ruthenium alkylidene complexes bearing bulky tricyclic N-heterocyclic carbene ligands decorated with two geminal trifluoromethyl groups were synthesized. Their catalytic activity in representative olefin metathesis reactions, such as ring closing metathesis of diallyltosylamine and selfmetathesis of allylbenzene, has been evaluated. [ABSTRACT FROM AUTHOR]

Thermal treatment of the dinuclear compound [{Ti(η5-C5Me5)(CH2SiMe3)2}2(μ-O)] (1) provides the formation of the metallacycle derivatives [Ti2(η5-C5Me5)2(μ-CH2SiMe2CH2)(CH2SiMe3)2(μ-O)] (2) and [Ti2(η5-C5Me5)2(μ-CH2SiMe2CH2)2(μ-O)] (3) and the μ-alkylidene complex [Ti2(η5-C5Me5)2(μ-CH2SiMe2CH2)(μ-CHSiMe3)(μ-O)] (4) by sequential carbon-hydrogen activation processes. The reaction of 3 with tert-butylisocyanide, in 1:1 and 1:2 ratios, leads to the η²-iminoacyl complexes [Ti2(η5-C5Me5)2(μ-tBuNCCH2SiMe2CH2)(μ-CH2SiMe2CH2)(μ-O)] (5) and [Ti2(η5-C5Me5)2(μ-tBuNCCH2SiMe2CH2)2(μ-O)] (6), respectively. The molecular structures of complexes 3, 4, 5, and 6 have been determined by single-crystal X-ray diffraction analyses. [ABSTRACT FROM AUTHOR]

The Kinugasa reaction applied to alkynes bearing a nucleofuge in propargylic position affords directly, and in fair yields, α-methylene- or α-alkylidene-β-lactams. [ABSTRACT FROM AUTHOR]

A method based on in situ alkylidene carbene generation-C-H insertion reaction of 5-(3-oxobutyl)pyrrolidin-2-ones and 6-(3-oxobutyl)piperidin-2-ones is developed for the enantioselective synthesis of 1-azaspiro[4,4]non-6-ene-2-ones and 6-azaspiro[4,5]dec-1-ene-7-ones. The required 5-(3-oxobutyl)pyrrolidin-2-ones and 6-(3-oxobutyl)piperidin-2-ones are prepared from the Wacker oxidation of internal alkenes typified by 5-(but-2-enyl)pyrrolidin-2-ones and 6-(but-2-enyl)piperidin-2-ones, respectively. Excellent regioselectivity (=92:8) is realized for the Wacker oxidation, and high yields (78-89%) of the desired lactam ketones are obtained. The results from further investigations into the Wacker oxidation suggested that the high regioselectivity of the oxidation in these lactam alkenes might be due to the participation of the lactam nitrogen via intramolecular coordination to Pd(II) during the reaction. Studies on alkylidene carbene generation-C-H insertion reaction of the lactam ketones revealed that the reaction efficiency is sensitive to the reaction temperature and the amount of lithio(trimethylsilyl)diazomethane employed, which led to the development of optimal reaction conditions for effecting alkylidene carbene generation-C-H insertion. Using the optimal reaction conditions, good to high yields (53-76%) of both γ- and δ-lactam spirocycles were obtained. The synthetic utility of the spirolactams was demonstrated by the synthesis of (-)-adalinine. [ABSTRACT FROM AUTHOR]

Mostpalladium-catalyzed reactions involving insertion of alkylideneswith α-hydrogens undergo β-hydride elimination from alkylpalladium(II)intermediates to form alkenes. Vinyl iodides were shown to generateη3-allylpalladium intermediates that resist β-hydrideelimination, preserving the sp3center adjacent to thecarbene moiety. Acyclic stereocontrol (syn/anti) for carbenylative amination and alkylation reactionswas low, suggesting a lack of control in the migratory insertion step.Highly hindered carbene precursors inexplicably led to formation of Z-alkenes with high levels of stereocontrol. [ABSTRACT FROM AUTHOR]

The article presents a comprehensive review of the use of N-heterocyclic carbene (NHC) and other carbenes as ligands for surfaces. It discusses NHC stabilization of molecular elemental allotrope species. It describes examples of NHC ligands bound to nanoparticles (NP) and the formation of NHC monolayers on planar surfaces. Topics include metal(loid) nanoparticles stabilized by NHC, planar surfaces stabilized by NHC, and surfaces stabilized by alkylidenes.

The synthesis and single-crystal X-ray structures of the novel molybdenum imido alkylidene N-heterocyclic carbene complexes [Mo(N-2,6-Me2C6H3)(IMesH2)(CHCMe2Ph)(OTf)2] ( 3), [Mo(N-2,6-Me2C6H3)(IMes)(CHCMe2Ph)(OTf)2] ( 4), [Mo(N-2,6-Me2C6H3)(IMesH2)(CHCMe2Ph)(OTf){OCH(CF3)2}] ( 5), [Mo(N-2,6-Me2C6H3)(CH3CN)(IMesH2)(CHCMe2Ph)(OTf)]+ BArF− ( 6), [Mo(N-2,6-Cl2C6H3)(IMesH2)(CHCMe3)(OTf)2] ( 7) and [Mo(N-2,6-Cl2C6H3)(IMes)(CHCMe3)(OTf)2] ( 8) are reported (IMesH2=1,3-dimesitylimidazolidin-2-ylidene, IMes=1,3-dimesitylimidazolin-2-ylidene, BArF−=tetrakis-[3,5-bis(trifluoromethyl)phenyl] borate, OTf=CF3SO3−). Also, silica-immobilized versions I1 and I2 were prepared. Catalysts 3- 8, I1 and I2 were used in homo-, cross-, and ring-closing metathesis (RCM) reactions and in the cyclopolymerization of α,ω-diynes. In the RCM of α,ω-dienes, in the homometathesis of 1-alkenes, and in the ethenolysis of cyclooctene, turnover numbers (TONs) up to 100 000, 210 000 and 30 000, respectively, were achieved. With I1 and I2, virtually Mo-free products were obtained (<3 ppm Mo). With 1,6-hepta- and 1,7-octadiynes, catalysts 3, 4, and 5 allowed for the regioselective cyclopolymerization of 4,4-bis(ethoxycarbonyl)-1,6-heptadiyne, 4,4-bis(hydroxymethyl)-1,6-heptadiyne, 4,4-bis[(3,5-diethoxybenzoyloxy)methyl]-1,6-heptadiyne, 4,4,5,5-tetrakis(ethoxycarbonyl)-1,7-octadiyne, and 1,6-heptadiyne-4-carboxylic acid, underlining the high functional-group tolerance of these novel Group 6 metal alkylidenes. [ABSTRACT FROM AUTHOR]

After seminal reports of covalent uranium carbene U˭C complexes in the 1980s by Gilje, the area fell dormant for around 30 years. However, in the past five years, there has been a resurgence of interest in the area. Despite recent advances, the classification of these U˭C complexes as either methanediides, carbenes, or alkylidenes has remained a contentious issue. Herein, we review U˭C complexes reported to date, along with reactivity and computational studies, and conclude that although U˭C complexes sit midway on the continuum between rare-earth methanediides and Schrock-type alkylidenes, they can be justifiably described as carbenes. [ABSTRACT FROM AUTHOR]

Ruthenium carbene catalysts are able to catalyze cross [2 + 2 + 2] cyclotrimerizations of 1,6-diynes with cyclic and acyclic double bonds. A plausible mechanistic competition is described in which electron-deficient alkenes follow similar pathways as those of other ruthenium catalysts previously utilized and produce mixtures of trienes and cyclohexadienes. On the contrary, allylethers give different isomers of the same final products, suggesting that a metathetic cascade pathway operates in these cases. [ABSTRACT FROM AUTHOR]

We synthesized the first N-heterocyclic carbene (NHC) complexes of Schrock's molybdenum imido alkylidene bis(triflate) complexes. Unlike existing bis(triflate) complexes, the novel 16-electron complexes represent metathesis active, functional-group-tolerant catalysts. Single-crystal X-ray structures of two representatives of this novel class of Schrock catalysts are presented and reactivity is discussed in view of their structural peculiarities. In the presence of monomer (substrate), these catalysts form cationic species and can be employed in ring-closing metathesis (RCM), ring-opening metathesis polymerization (ROMP), as well as in the cyclopolymerization of α,ω-diynes. Monomers containing functional groups, which are not tolerated by the existing variations of Schrock's catalyst, e.g., sec-amine, hydroxy, and carboxylic acid moieties, can be used. These catalysts therefore hold great promise in both organic and polymer chemistry, where they allow for the use of protic monomers. [ABSTRACT FROM AUTHOR]

There have been numerous significant advances in catalytic olefin metathesis (OM) during the past two decades. Such progress has transformed this important set of reactions to strategically pivotal processes that generate stereochemical identity while delivering molecules that cannot be easily prepared by alternative routes. In this Perspective, an analysis of the origin of the inception of bidentate benzylidene ligands for Ru-based OM catalysts is first presented. This is followed by an overview of the intellectual basis that culminated in the development of Mo-based diolates and stereogenic-at-Ru complexes for enantioselective OM. The principles accrued from the study of the latter Ru carbenes and Mo alkylidenes and utilized in the design of stereogenic-at-Mo, -W, and -Ru species applicable to enantioselective and Z-selective OM are then discussed. The influence of the recently introduced catalytic OM protocols on the design of synthesis routes leading to complex organic molecules is probed. The impact of a better understanding of the mechanistic nuances of OM toward the discovery of stereoselective catalysts is reviewed as well. [ABSTRACT FROM AUTHOR]

Abstract: The synthesis of a bis-silylated Hoveyda–Grubbs ruthenium alkylidene complex is described, as well as the preparation via the sol–gel process and the characterization of an organosilica by co-gelification with tetraethyl orthosilicate (TEOS). This material is an active supported catalyst for various metathesis reactions. The recyclability has been proven even for the formation of a trisubstituted olefin. This is the first example of an immobilized Hoveyda–Grubbs’ type complex prepared by sol–gel co-gelification from a well-defined ruthenium alkylidene precursor bearing a silylated NHC moiety. [Copyright &y& Elsevier]

Comparative quantum chemical calculations on the reaction pathways for the formation of ruthena(IV)cyclobutanes from both 1st- and 2nd-generation Grubbs catalysts of the general formula RuX2(L)(L′)(&dbond;CH2) (L = PCy3 or 1,3-dimesityl-4,5-dihydroimidazolin-2-ylidene, L′ = PCy3) and norborn-2-ene (NBE) were carried out on the B3LYP/LACVP** level in dependence on the ligand X = I, Br, Cl, and F. The mechanism proposed by Straub for the formation of (one) active and (three) inactive NBE–Ru–carbene complexes for non-cyclic alkenes was applied to the cyclic alkene NBE. In RuX2(PCy3)2(&dbond;CH2), the inactive NBE–Ru–carbene complex is energetically more stable than the active one; however, in RuX2(IMesH2)(PCy3)(&dbond;CH2), the active NBE–Ru–carbene complex is more stable than the inactive one. In due consequence, the possible rate limiting barrier for the conversion of the NBE–Ru–carbene complex into the corresponding metallocyclobutane (MCB) is systematically larger in the case of 1st-generation Grubbs catalysts than of 2nd-generation Grubbs catalysts due to an additional re-arrangement for the formation of an active π-complex from the more stable (inactive) conformer. This correlates with the observed reactivity of both types of initiators. There is a strong influence of the ligands L and X on the conformational properties and relative stabilities of the 14-electron intermediates, which has a direct effect on the distribution of the inactive and active conformations of the corresponding Ru–carbene–NBE complexes. A direct correlation between the conformational properties of the 14-electron intermediates and the relative stabilities of the active Ru–carbene–NBE complexes was observed. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The adsorption and dissociation of cyclobutanone on a β-Mo2C foil was studied using RAIRS, XPS and TPD. Adsorption at 105K populates η1 and η2 states in a 5:1 ratio. Heating to 170–300K causes scission of the carbonyl bond and the development of RAIRS spectra characteristic of a cyclobutylidene–oxo surface complex. This dissociation chemistry is compared to literature data for the interaction of ketones with a single-metal atom tungsten complex. [Copyright &y& Elsevier]

The concepts of functional precision polymers and the latest accomplishments in their synthesis are summarized. Synthetic concepts based on chain growth polymerization are compared to iterative synthetic approaches. Here, the term "functional precision polymers" refers to polymers that are not solely hydrocarbon‐based but contain functional groups and are characterized by a highly ordered primary structure. If insertion polymerization is used for their synthesis, olefin metathesis‐based polymerization techniques, that is, ring‐opening metathesis polymerization (ROMP), acyclic diene metathesis (ADMET) polymerization, and the regio‐ and stereoselective cyclopolymerization of α,ω‐diynes are almost exclusively applied. Particularly with regio‐ and stereospecific ROMP and with cyclopolymerization, the synthesis of tactic polymers and copolymers with high regio‐, stereo‐, and sequence control can be accomplished; however, it requires carefully tailored transition metal catalysts. The fundamental synthetic concepts and strategies are outlined. The state‐of‐the‐art in functional precision polymers is outlined. Synthetic concepts based on chain growth polymerization are compared to iterative synthetic approaches. If insertion polymerization such as regio‐ and stereospecific ring‐opening metathesis polymerization or the regio‐ and stereoselective cyclopolymerization of α,ω‐diynes is used, tactic polymers and copolymers are accessible with high regio‐, stereo‐, and sequence control. [ABSTRACT FROM AUTHOR]

The application of the Kinugasa reaction to alkynes bearing a nucleofuge in propargylic position gives a very direct entry to α-methylene- and α-alkylidene-β-lactams. [ABSTRACT FROM AUTHOR]

Review: [134 refs. [ABSTRACT FROM AUTHOR]

Review: 48 refs. [ABSTRACT FROM AUTHOR]