Tungsten Carbene Complexes Research Articles

Synthesis and reactivity of aziridinocarbene complexes of chromium and tungsten: formation of nitrile and acetiminoester complexes

2-Methylaziridine H NCH 2C HCH 3 reacts with alkyl- and aryl-(alkoxy)carbene complexes of chromium and tungsten to give alkyl- and aryl-aziridinocarbene complexes. The latter undergo a thermal transformation to give olefins and alkyl- or aryl-nitrilechromium pentacarbonyl complexes, e.g. (CO) 5CrNC- o-tolyl (which has been characterized by X-ray crystallography). 2-Phenylaziridine H NCH 2C HPh in turn reacts with the carbene complexes to give directly styrene and the acetiminoester complexes (CO) 5WHNC(CH 3)OCH 2CH 3 and (CO) 5CrHNC(CH 3)OCH 2-CH 3. The latter gives, upon hydrolysis (CO) 5CrNH 3. The structures of (CO) 5WHNC(CH 3)OCH 2CH 3 and (CO) 5CrNH 3 have been determined by X-ray diffraction. The mechanisms of the two reactions are discussed.

Synthesis and properties of (O-acyl imidato)carbene complexes of chromium, molybdenum, and tungsten [Erratum to document cited in CA111(13):115461d

Synthesis and properties of (O-acyl imidato)carbene complexes of chromium, molybdenum, and tungsten [Erratum to document cited in CA111(13):115461d

ChemInform Abstract: Synthesis and Properties of (O‐Acyl imidato)carbene Complexes of Chromium, Molybdenum, and Tungsten.

AbstractThe Mo and W analogues (Vc) of the title complexes are prepared at ‐40 °C in the same way as shown for the Cr compounds.

ChemInform Abstract: Anionic‐Initiated Coupling of Tungsten Carbene Complexes: Synthesis of the First (μ‐Tris(carbene))trimetallic Complex.

AbstractThe sodium alkoxide (I) reacts with the pentacarbonyl carbene complex (II) to yield a mixture of the coupling products (IIIa), (IIIb), (IVa), and (IVb).

Synthesis and properties of (O-acyl imidato)carbene complexes of chromium, molybdenum, and tungsten

Preparation d'une serie de complexes ylidenes d'imides O-acylees du chrome, du molybdene et du tungstene

Bimetallic activation in homogeneous catalysis: Part II. Formation of α-oxo amide by palladium-catalyzed double carbonylation of the tricarbonyl (chlorobenzene) chromium complex

The syntheses of a number of cyclopentadienylcarbene iron half sandwich complexes are described. In addition to their spectroscopic characterization an X-ray crystal structure analysis is provided. The complexes prepared include chromium, molybdenum, and tungsten carbene complexes. The dicarbonyliron unit is substituted by benzyl, butyl or trimethylsilylmethyl groups. In two cases tetrametallic dimeric complexes connected by a propyl chain are presented. The reaction of the formylcyclopentadienyliron complex with a chromium carbene complex provided a vinylogous representative. Cyclic voltammetry was performed, and the data obtained are discussed in comparison to similar ferrocene based complexes.

ChemInform Abstract: Investigations of Polymerization and Metathesis Reactions. Part 15. Heterogeneous, Metathesis‐Active Schrock‐Type Carbene Complexes by Reaction of Carbyne Tungsten(VI) Complexes with Silica Gel.

AbstractReaction of the surface SiOH groups of silica gel (II) with the carbyne complexes (I) affords the heterogeneous carbene tungsten(VI) complexes (III), which serve as storable metathesis catalysts above 100 °C. Their activity is tested by the reaction of 1‐octene in hexane.

Anionic initiated coupling of tungsten carbene complexes: synthesis of the first (μ-tris(carbene))trimetallic complex

Treatment of (CO) 5W[C(OCH 3)C(CH 3CH 2] ( 1) with C 2H 5(CH 3) 2CONa in THF at −78°C followed by HCl produced: (CO) 5W[C(OCH 3)CH(CH 3)CH 2OC(CH 3) 2C 2H 5] ( 3) (1%), C 2H 5(CH 3) 2CO(CO) 5W[C(OCH 3)C(CH 3)CH 2]CH 2C(CH 3)CH(OCH 3) ( 5) (<1%), C 2H 5(CH 3) 2CO (CO) 5W[C(OCH 3)C(CH 3)CH 2] 2H ( 6) (<1%), and the (μ-tris(carbene))trimetallic complex C 2H 5(CH 3) 2CO(CO) 5W[C(OCH 3)C(CH 3)CH 2] 3CH 2C(CH 3)CH(OCH 3) ( 9) (15%) as well as several, as yet, unidentified compounds. Complex 9 was characterized by analytical and spectroscopic methods; moreover, it was converted to the corresponding triester ( 10) upon PDC/DMSO oxidation. Upon standing at 0°C for long periods complex 1 was converted into a new (μ-bis(carbene))ditungsten complex (CO) 5WC(OCH 3)[CH(CH 3)CH 2CH 2C(CH 2)]C(OCH 3)W(CO) 5 ( 11) in low yield.

Third-order susceptibilities of soluble polymers derived from the ring opening metathesis copolymerization of cyclooctatetraene and 1,5-cyclooctadiene

We wish to report some preliminary results on the nonlinear optical properties of a new class of polymers synthesized by the ring-opening metathesis polymerization of highly unsaturated monomers. Mixtures of cyclooctatetraene, 1, and 1,5-cyclooctadiene, 2, have been polymerized by using the tungsten carbene complex 3 as the catalyst (see Figure 1). The solution polymerization of monomers 1 and 2 in tetrahydrofuran leads to an essentially random coploymer. The monomers contain exclusively cis double bonds and no attempt has been made to isomerize the double bonds in the resulting polymer. The general constitution of the copolymers is also shown in Figure 1 (an all-trans geometrical configuration is shown for simplicity).

Synthesis and reactivity of the α-β-unsaturated carbene tungsten complex (CO) 5W[C(OCH) 3)CHCH 2

Treatment of W(CO) 6 with vinyllithium followed by Me 3OBF 4 in the presence of H 2O produced (CO) 5W[C(OCH 3)CHCH 2] ( 1) (25–30%) and (CO) 5W[C(OCH 3)-(η-CHCH 2)]W(CO) 5 ( 2) (20–30%). Complex 1 reacted with (CO) 5W · THF to give W 2(CO) 9[μ-μ 1,η 3-C(OCH 3)CHCH 2] ( 3) (61%). Heating 2 to 45°C in toluene produced 3 (65%) which could be converted back to 2 upon treatment with CO. Complex 1 reacte with D 2O in benzene- d 6 to afford 2 and methyl propionate-2,3- d 2 ( 4). A new route to 1 was developed from C(CO) 6 in an overall yield of 40% using (CO) 5W[C(O)CHCH 2]NME 4 ( 8) as an intermediate.

Detection of diastereoisomers of metallacyclobutane intermediates in the metathesis polymerization of norbornene and its derivatives

Addition of norbornene derivatives to racemic mixtures of chiral tungsten–carbene complexes is shown to lead to the formation of transoid diastereoisomeric tungstacyclobutanes that can be distinguished by 1H n.m.r. spectroscopy; cisoid structures, though formed, are too unstable to be observed.

Ring‐opening polymerization of norbornene and six of its methyl derivatives by well‐defined tungsten‐carbene complex catalysts

AbstractEight tungsten‐carbene complex catalysts of the type W(CHCMe3)L1L2L3L4, where the ligands L are various combinations of OCH2CMe3, SO3CF3, OSiPh3, Br and I, have been used, in the presence and absence of GaBr3, to polymerize norbornene and six of its methyl derivatives by ring opening. The microstructure of the polymers was determined from their 13C NMR spectra; values of cis content, cis‐trans blockiness, ring‐dyad tacticity and head‐tail bias were derived as appropriate to each system. The results are discussed in terms of electronic and steric effects in the propagating carbene complexes.

ChemInform Abstract: Diene‐Dienophile‐Functionalized Carbene Ligands: Synthons for the Intramolecular Diels‐Alder Reaction.

AbstractThe tungsten carbene complex (I) reacts with the furfuryl nucleophiles (II) and (VI) to give the substitution products (III) and (IV) or the adducts (VII).

Kinetics of initiation and propagation of the metathesis polymerization of the exo diels-alder adduct of cyclopentadiene and maleic anhydride initiated by the tungsten-carbene complex W[ H 2](OCH 2CMe 3) 2Br 2

The title reaction was followed by 1H NMR at 277 – 314 K. The initiator (I) adds one molecule of monomer (M) to give a tungsten-carbene species P 1 which then adds further monomer molecules to give P n ( n > 1). P 1 and P n ( n > 1) can be distinguished by their (OCH 2CMe 3) 2 signals at 4.44, 4.39 and 4.46, 4.41 ppm respectively; the two neopentoxy ligands are non-equivalent in each case. [P 1] builds up to a maximum (65% of [I 0]) and then declines. At 294 K the initiator is all consumed after 40 min and [M] then decays according to a first-order law ( t 1 2 = 74 min for [P total] = [I 0] = 5.0 × 10 −2 mol dm −3). The activation energy for the propagation reaction is about 51 kJ mol −1. The initiation rate constant is 3.8 ± 0.2 times as large as the propagation rate constant. The 13C NMR spectrum of the exo, exo-dimethyl ester polymer derived from the polymer of M indicated that the polymer contained 28% cis double bonds. The endo adduct of cyclopentadiene and maleic anhydride was also found capable of adding to the living chain; this is the first report that the endo monomer can undergo metathesis polymerization.

Investigation of polymerisation and metathesis reactions: Part XIII : Heterogeneous bimetallic metathesis catalysts by reactions of differently substituted Fischer-type tungsten carbene complexes with reduced Phillips catalyst

The reactions of reduced Phillips catalyst, a polymerisation catalyst for 1-alkenes, with differently substituted Fischer-type tungsten carbene complexes (CO) 5W = CR 1R 2 (R 1 = Ph, Tol, CH 3; R 2 = Ph, OCH 3), which are metathesis catalysts with poor activity, yield bimetallic heterogeneous compounds by the loss of one CO ligand. Diffuse reflectance FT-IR spectroscopy of the heterogeneous compounds shows a strong shift of the v-CO absorptions to higher wavenumbers, probably caused by a chromium-tungsten bond. The catalytic activity of these surface compounds was tested with 1-octene. All were found to be very active metathesis catalysts, and no polymerisation of 1-octene was observed. These results indicate that the polymerisation activity of the reduced Phillips catalyst was lost, whilst the metathesis activity of the carbene complexes was enhanced by activation with the reduced Phillips catalyst. The surface chromium atoms act as activating species for the carbene complex fragments. The influence of the carbene substituents on the metathesis reaction is not significant, with the exception of the methyl substituent of (CO) 5W = C(OCH 3)CH 3. The acidic protons of this methyl substituent are thought to give rise to further interaction with a Si—O—Cr or Si—O—Si group. The new bimetallic, heterogeneous metathesis catalysts are stable at 20 °C and can be stored without loss of activity for some months.

Novel chelating (N,O) bis(carbene) complexes of chromium and tungsten: synthesis and structure

Novel chelating (N,O) bis(carbene) complexes of chromium and tungsten: synthesis and structure

Crystal and molecular structure of the tungsten-carbene complex [cyclic] W[C(CH2)3CH2](OCH2-tert-Bu)2Br2 and of its gallium tribromide adduct. A structural approach to the mechanism of olefin metathesis

Le premier compose du titre cristallise dans le systeme monoclinique avec le groupe d'espace P2 1 /c. Le second cristallise dans le systeme monoclinique avec le groupe d'espace P2 1 /n. Affinement de la structure jusqu'a 3,5% et 2,9% respectivement

Metathesis polymerisation of norbornene and its derivatives. Relative stability of tungstacyclobutane intermediates and kinetics of their ring opening to form tungsten–carbene complexes

A family of tungstacyclobutane intermediates in the catalytic ring-opening polymerisation of norbornenes have been studied by 1H n.m.r.; their rates of rearrangement into tungsten–carbene complexes are reported and compared.

ChemInform Abstract: Carbene Complexes in Organic Synthesis: A New Tungstacarbene‐Promoted Alkyne Insertion‐Olefin Cyclopropanation Reaction.

AbstractThe tungsten carbene complex (V) is prepared from W(CO)6 (I).

Carbene complexes in organic synthesis: a new tungstacarbene-promoted alkyne insertion–olefin cyclopropanation reaction

Carbene complexes of tungsten, bearing a co-ordinated double bond two carbons away from the carbene function, react with alkynes to give, after insertion of the alkyne, bicyclo[4.1.0]heptane derivatives as a result of cyclopropanation of the double bond by the newly formed carbene complex.