Synthesis,structure, and activity of enhanced initiators for olefin metathesis

A series of ruthenium olefin metathesis catalysts of the general structure (H(2)IMes)(PR(3))(Cl)(2)Ru=CHPh (H(2)IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) have been prepared; these complexes are readily accessible in two steps from commercially available (H(2)IMes)(PCy(3))(Cl)(2)Ru=CHPh. Their phosphine dissociation rate constants (k(1)), relative rates of phosphine reassociation, and relative reaction rates in ring-opening metathesis polymerization (ROMP) and ring-closing metathesis (RCM) have been investigated. The rates of phosphine dissociation (initiation) from these complexes increase with decreasing phosphine donor strength. Complexes containing a triarylphosphine exhibit dramatically improved initiation relative to (H(2)IMes)(PCy(3))(Cl)(2)Ru=CHPh. Conversely, phosphine reassociation shows no direct correlation with phosphine electronics. In general, increased phosphine dissociation leads to faster olefin metathesis reaction rates, which is of direct significance to both organic and polymer metathesis processes.     

Model compounds of ruthenium-alkene intermediates in olefin metathesis reactions

The development of a model system to study ruthenium-olefin complexes relevant to the mechanism of olefin metathesis is reported. Upon addition of 1,2-divinylbenzene to (H2IMes)(py2)(Cl)2Ru=CHPh (H2IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene), two ruthenium-olefin adducts are formed. On the basis of 1H NMR spectroscopy experiments and X-ray crystallographic analysis, these complexes are assigned as side-bound isomers in which the olefin and H2IMes ligands are coordinated cis to each other. The dynamic interconversion of these two ruthenium complexes was determined to have a barrier of 19.1 +/- 0.1 kcal/mol.     

Ruthenium-based olefin metathesis catalysts coordinated with unsymmetrical N-heterocyclic carbene ligands: synthesis, structure, and catalytic activity

A series of ruthenium-based olefin metathesis catalysts coordinated with unsymmetrical N-heterocyclic carbene (NHC) ligands has been prepared and fully characterized. These complexes are readily accessible in one or two steps from commercially available [(PCy(3))(2)Cl(2)Ru==CHPh]. All of the complexes reported herein promote the ring-closing of diethyldiallyl and diethylallylmethallyl malonate, the ring-opening metathesis polymerization of 1,5-cyclooctadiene, and the cross metathesis of allyl benzene with cis-1,4-diacetoxy-2-butene, in some cases surpassing in efficiency the existing second-generation catalysts. Especially in the cross metathesis of allyl benzene with cis-1,4-diacetoxy-2-butene, all new catalysts demonstrate similar or higher activity than the second-generation ruthenium catalysts and, most importantly, afford improved E/Z ratios of the desired cross-product at conversion above 60 %. The influence of the unsymmetrical NHC ligands on the initiation rate and the activation parameters for the irreversible reaction of these ruthenium complexes with butyl vinyl ether were also studied. Finally, the synthesis of the related chlorodicarbonyl(carbene) rhodium(I) complexes allowed for the study of the electronic properties of the new unsymmetrical NHC ligands that are discussed in detail.     

Ruthenium-olefin complexes: effect of ligand variation upon geometry

The development of a model system to study ruthenium-olefin complexes relevant to the mechanism of olefin metathesis has been reported recently. Upon addition of the ligand precursor 1,2-divinylbenzene to [RuCl(2)(Py)(2)(H(2)IMes)(==CHPh)] (H(2)IMes=1,3-dimesityl-4,5-dihydroimidazol-2-ylidene), two ruthenium-olefin adducts are formed. Based on (1)H NMR spectroscopy experiments and X-ray crystallographic analysis, these complexes are assigned as side-bound isomers in which the olefin and H(2)IMes ligands are coordinated cis to each other. Herein is reported an investigation of the generality of these observations through variation of the N-heterocyclic carbene ligand and the ligand precursor.     

Decomposition of ruthenium olefin metathesis catalysts

The decomposition of a series of ruthenium metathesis catalysts has been examined using methylidene species as model complexes. All of the phosphine-containing methylidene complexes decomposed to generate methylphosphonium salts, and their decomposition routes followed first-order kinetics. The formation of these salts in high conversion, coupled with the observed kinetic behavior for this reaction, suggests that the major decomposition pathway involves nucleophilic attack of a dissociated phosphine on the methylidene carbon. This mechanism also is consistent with decomposition observed in the presence of ethylene as a model olefin substrate. The decomposition of phosphine-free catalyst (H2IMes)(Cl)2Ru=CH(2-C6H4-O-i-Pr) (H2IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) with ethylene was found to generate unidentified ruthenium hydride species. The novel ruthenium complex (H2IMes)(pyridine)3(Cl)2Ru, which was generated during the synthetic attempts to prepare the highly unstable pyridine-based methylidene complex (H2IMes)(pyridine)2(Cl)2Ru=CH2, is also reported.     

Dithiocarboxylate complexes of ruthenium(II) and osmium(II)

The ruthenium(II) complexes [Ru(R)(κ(2)-S(2)C·IPr)(CO)(PPh(3))(2)](+) (R = CH=CHBu(t), CH=CHC(6)H(4)Me-4, C(C≡CPh)=CHPh) are formed on reaction of IPr·CS(2) with [Ru(R)Cl(CO)(BTD)(PPh(3))(2)] (BTD = 2,1,3-benzothiadiazole) or [Ru(C(C≡CPh)=CHPh)Cl(CO)(PPh(3))(2)] in the presence of ammonium hexafluorophosphate. Similarly, the complexes [Ru(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·ICy)(CO)(PPh(3))(2)](+) and [Ru(C(C≡CPh)=CHPh)(κ(2)-S(2)C·ICy)(CO)(PPh(3))(2)](+) are formed in the same manner when ICy·CS(2) is employed. The ligand IMes·CS(2) reacts with [Ru(R)Cl(CO)(BTD)(PPh(3))(2)] to form the compounds [Ru(R)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+) (R = CH=CHBu(t), CH=CHC(6)H(4)Me-4, C(C≡CPh)=CHPh). Two osmium analogues, [Os(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+) and [Os(C(C≡CPh)=CHPh)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+) were also prepared. When the more bulky diisopropylphenyl derivative IDip·CS(2) is used, an unusual product, [Ru(κ(2)-SC(H)S(CH=CHC(6)H(4)Me-4)·IDip)Cl(CO)(PPh(3))(2)](+), with a migrated vinyl group, is obtained. Over extended reaction times, [Ru(CH=CHC(6)H(4)Me-4)Cl(BTD)(CO)(PPh(3))(2)] also reacts with IMes·CS(2) and NH(4)PF(6) to yield the analogous product [Ru{κ(2)-SC(H)S(CH=CHC(6)H(4)Me-4)·IMes}Cl(CO)(PPh(3))(2)](+)via the intermediate [Ru(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+). Structural studies are reported for [Ru(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·IPr)(CO)(PPh(3))(2)]PF(6) and [Ru(C(C≡CPh)=CHPh)(κ(2)-S(2)C·ICy)(CO)(PPh(3))(2)]PF(6).     

[(NHC)(NHCewg)RuCl2(CHPh)] Complexes with Modified NHCewg Ligands for Efficient Ring‐Closing Metathesis Leading to Tetrasubstituted Olefins

Imidazolium salts (NHC_ewg ? HCl) with electronically variable substituents in the 4,5‐position (H,H or Cl,Cl or H,NO₂ or CN,CN) and sterically variable substituents in the 1,3‐position (Me,Me or Et,Et or iPr,iPr or Me,iPr) were synthesized and converted into the respective [AgI(NHC)_ewg] complexes. The reactions of [(NHC)RuCl₂(CHPh)(py)₂] with the [AgI(NHC_ewg)] complexes provide the respective [(NHC)(NHC_ewg)RuCl₂(CHPh)] complexes in excellent yields. The catalytic activity of such complexes in ring‐closing metathesis (RCM) reactions leading to tetrasubstituted olefins was studied. To obtain quantitative substrate conversion, catalyst loadings of 0.2–0.5 mol % at 80 °C in toluene are sufficient. The complex with the best catalytic activity in such RCM reactions and the fastest initiation rate has an NHC_ewg group with 1,3‐Me,iPr and 4,5‐Cl,Cl substituents and can be synthesized in 95 % isolated yield from the ruthenium precursor. To learn which one of the two NHC ligands acts as the leaving group in olefin metathesis reactions two complexes, [(FL‐NHC)(NHC_ewg)RuCl₂(CHPh)] and [(FL‐NHC_ewg)(NHC)RuCl₂(CHPh)], with a dansyl fluorophore (FL)‐tagged electron‐rich NHC ligand (FL‐NHC) and an electron‐deficient NHC ligand (FL‐NHC_ewg) were prepared. The fluorescence of the dansyl fluorophore is quenched as long as it is in close vicinity to ruthenium, but increases strongly upon dissociation of the respective fluorophore‐tagged ligand. In this manner, it was shown for ring‐opening metathesis ploymerization (ROMP) reactions at room temperature that the NHC_ewg ligand normally acts as the leaving group, whereas the other NHC ligand remains ligated to ruthenium.     

Ruthenium carbene complexes bearing an anionic carboxylate chelated to a hemilabile ligand

A series of bidentate ruthenium-based NHC complexes with the general formula [(H(2)IMes)(kappa(2)-L-COO)ClRu=CHPh)], where L is either PAr(3), HNR(2), or ROR, were prepared from commercially available [(H(2)IMes)(PCy(3))Cl(2)Ru(CHPh)] (2) and the appropriate ligand. The catalytic activities of the complexes were evaluated in ring-closing metathesis reactions. The type of donor ligand has a major impact on both the initiation behavior and also the stability of the complexes. Upon addition of CuCl to the reaction mixture the initiation is improved for the phosphine or amine containing chelates. For the P,O-chelate, the fast initiation was followed by decomposition. In the case of the N,O-containing chelate, a stable catalytic system was achieved. Trapping experiments support that the nitrogen lone-pair reversibly coordinates CuCl during the reaction.     

Fluorous phase-transfer activation of catalysts: application of a new rate-enhancement strategy to alkene metathesis

Reactions of the bis(pyridine) complex (H2IMes)(Py)2(Cl)2Ru(=CHPh) and fluorous phosphines P(CH2CH2R(fn))3 (n = a, 6; b, 8; c, 10; R(fn) = (CF2)(n-1)CF3) give (H2IMes)(P(CH2CH2R(fn))3)(Cl)2Ru(=CHPh) (2a-c, 64-73%), which are analogs of Grubbs' second generation catalyst and effective alkene metathesis catalysts under organic monophasic and fluorous/organic biphasic conditions. The latter give rate accelerations, which are believed to arise from phase transfer of the dissociated fluorous phosphine.     

A general method for preparation of metal carbenes via solution- and polymer-based approaches

A new general, synthetically simple, and safe method for the preparation of metal carbene complexes, which is based on diphenyl sulfonium salts as carbenoid precursors, has been developed, and its scope and applications were studied. In general, deprotonation of a sulfonium salt with a base results in a sulfur ylide, which, in turn, reacts with an appropriate metal precursor to give the corresponding metal carbene complex. Thus, starting from benzyldiphenylsulfonium salt, the complexes (PCX)Rh=CHPh (X = P, N) were prepared in quantitative yield. Syntheses of Grubbs' catalyst, (PCy(3))(2)Cl(2)Ru=CHPh, and of Werner's carbene, [Os(=CHPh)HCl(CO)(P(i)Pr(3))(2)], were achieved by this method. Novel trans-bisphosphine Rh and Ir carbenes, ((i)Pr(3)P)(2)(Cl)M=CHPh, which could not be prepared by other known methods, were synthesized by the sulfur ylide approach. The method is not limited to metal benzylidenes, as demonstrated by the preparation of the Ru vinyl-alkylidene, (PCy(3))(2)Cl(2)Ru=CH-CH=CH(2), methoxycarbonyl-alkylidene, (PCy(3))(2)Cl(2)Ru=CH(CO(2)Me), and alkylidene (PCy(3))(2)Cl(2)Ru=CH(CH(3)), (PCy(3))(2)Cl(2)Ru=CH(2) compounds. The problem of recycling of starting materials as well as the issue of facile purification of the product metal carbene complex were addressed by the synthesis of a polymer-supported diarylsulfide, the carrier of the carbenoid unit in the process. Based on the sulfur ylide route, a methodology for the synthesis of metallocarbenes anchored to a polymer via the carbene ligand, using a commercial Merrifield resin, was developed.     

Stoichiometric and catalytic reactivity of the N-heterocyclic carbene ruthenium hydride complexes [Ru(NHC)(L)(CO)HCl] and [Ru(NHC)(L)(CO)H(eta2-BH4)] (L=NHC, PPh3)

Thermolysis of [Ru(AsPh3)3(CO)H2] with the N-aryl heterocyclic carbenes (NHCs) IMes (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), IPr (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) or the adduct SIPr.(C6F5)H (SIPr=1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene), followed by addition of CH2Cl2, affords the coordinatively unsaturated ruthenium hydride chloride complexes [Ru(NHC)2(CO)HCl] (NHC=IMes , IPr , SIPr ). These react with CO at room temperature to yield the corresponding 18-electron dicarbonyl complexes . Reduction of and [Ru(IMes)(PPh3)(CO)HCl] () with NaBH4 yields the isolable borohydride complexes [Ru(NHC)(L)(CO)H(eta2-BH4)] (, L=NHC, PPh3). Both the bis-IMes complex and the IMes-PPh3 species react with CO at low temperature to give the eta1-borohydride species [Ru(IMes)(L)(CO)2H(eta1-BH4)] (L=IMes , PPh3), which can be spectroscopically characterised. Upon warming to room temperature, further reaction with CO takes place to afford initially [Ru(IMes)(L)(CO)2H2] (L=IMes, L=PPh3) and, ultimately, [Ru(IMes)(L)(CO)3] (L=IMes , L=PPh3). Both and lose BH3 on addition of PMe2Ph to give [Ru(IMes)(L)(L')(CO)H2](L=L'=PMe2Ph; L=PPh3, L'=PMe2Ph). Compounds and have been tested as catalysts for the hydrogenation of aromatic ketones in the presence of (i)PrOH and H2. For the reduction of acetophenone, catalytic activity varies with the NHC present, decreasing in the order IPr>IMes>SIMes.     

Synthesis and characterization of half-sandwich N-heterocyclic carbene complexes of cobalt and rhodium

A series of novel half-sandwich M(I) and M(III) complexes (M = Co, Rh) bearing the N-heterocyclic carbene ligand 1,3-dimesitylimidazol-2-ylidene (IMes) have been prepared and characterized. Thus, (eta5-C(5)R(5))M(IMes)(C(2)H(4))(M = Co, Rh; R = H, Me) were obtained from the corresponding bis(ethene) complexes (eta5-C(5)R(5))M(C(2)H(4))(2), except for CpRh(IMes)(C(2)H(4)) which was prepared via the novel 16-electron Rh(I) compound Rh(IMes)(C(2)H(4))(2)Cl. The carbonyl compounds (eta5-C(5)R(5))Co(IMes)(CO)(R = H, Me) were synthesized by thermal CO substitution of (eta5-C(5)R(5))Co(CO)(2). A diamagnetic, apparently 16-electron Co(III) compound [CpCo(IMes)I](+)[I(3)(-)] was obtained from CpCo(IMes)(CO) and I(2). Finally, Co(III) and Rh(III) complexes CpCo(IMes)Me(2) and Cp*Rh(IMes)Me(2) were prepared by methylation of [CpCo(IMes)I](+)[I(3)(-)], and ligand exchange at Cp*Rh(Me(2)SO)Me(2), respectively. The molecular structures of CpCo(IMes)(CO), CpRh(IMes)(C(2)H(4)), Cp*Rh(IMes)(C(2)H(4)), and Cp*Rh(IMes)Me(2) were determined by single crystal X-ray diffraction. Steric and electronic factors imposed by the strongly donating and sterically demanding IMes ligand are discussed on the basis of X-ray crystallographic, NMR, and IR spectroscopic analyses. Very poor correlations are found between values for (1)J(Rh-C(carbene)) and dRh-C(carbene) data for Rh(i) N,N-heterocyclic carbene complexes including literature data and this work.     

Steric and electronic properties of N-heterocyclic carbenes (NHC): a detailed study on their interaction with Ni(CO)4

N-heterocyclic carbene ligands IMes (1), SIMes (2), IPr (3), SIPr (4), and ICy (5) react with Ni(CO)(4) to give the saturated tricarbonyl complexes Ni(CO)(3)(IMes) (8), Ni(CO)(3)(SIMes) (9), Ni(CO)(3)(IPr) (10), Ni(CO)(3)(SIPr) (11), and Ni(CO)(3)(ICy) (12), respectively. The electronic properties of these complexes have been compared to their phosphine analogues of general formula Ni(CO)(3)(PR(3)) by recording their nu(CO) stretching frequencies. While all of these NHCs are better donors than tertiary phosphines, the differences in donor properties between ligands 1-5 are surprisingly small. Novel, unsaturated Ni(CO)(2)(IAd) (13) and Ni(CO)(2)(I(t)()Bu) (14) compounds are obtained from the reaction of Ni(CO)(4) with IAd (6) and I(t)()Bu (7). Complexes 13 and 14 are highly active toward substitution of the NHC as well as the carbonyl ligands. This has allowed the determination of Ni-C(NHC) bond dissociation energies and the synthesis of various unsaturated Ni(0) and Ni(II) complexes. Computational studies on compounds 8-14 are in line with the experimental findings and show that IAd (6) and I(t)()Bu (7) are more bulky than IMes (1), SIMes (2), IPr (3), SIPr (4), and ICy (5). Furthermore, a method based on %V(bur) values has been developed for the direct comparison of steric requirements of NHCs and tertiary phosphines. Complexes 8-14, as well as NiCl(C(3)H(5))(I(t)()Bu) (16) and NiBr(C(3)H(5))(I(t)()Bu) (17), have been characterized by X-ray crystallography.     

Mechanism of ruthenium-catalyzed olefin metathesis reactions from a theoretical perspective

This paper presents a density functional theory study of the ruthenium-catalyzed olefin metathesis reactions. The ligand binding energy has been calculated in the first generation of Grubbs-type (PCy3)2Cl2Ru=CHPh (pre)catalyst, as well as in the heteroleptic (pre)catalytic systems in which a N-heterocyclic carbene, NHC, ligand substitutes a single phosphine. In agreement with experiments PCy3 coordinates more strongly to Ru in the heteroleptic (pre)catalysts than in the Grubbs-type (pre)catalyst. Moreover, ethene coordination and insertion into the Ru-alkylidene bond in the above-mentioned systems, as well as in the Hofmann type catalytic system with a cis-coordinated phosphane ligand, has been studied. The calculated insertion barrier for the NHC systems are lower than that of the (PCy3)2Cl2Ru=CHPh system. This is consistent with the higher activity experimentally observed for the NHC-based system.     

Characterization and dynamics of substituted ruthenacyclobutanes relevant to the olefin cross-metathesis reaction

The reaction of the phosphonium alkylidene [(H(2)IMes)RuCl(2)=CHP(Cy)(3))](+) BF(4)(-) with propene, 1-butene, and 1-hexene at -45 °C affords various substituted, metathesis-active ruthenacycles. These metallacycles were found to equilibrate over extended reaction times in response to decreases in ethylene concentrations, which favored increased populations of α-monosubstituted and α,α'-disubstituted (both cis and trans) ruthenacycles. On an NMR time scale, rapid chemical exchange was found to preferentially occur between the β-hydrogens of the cis and trans stereoisomers prior to olefin exchange. Exchange on an NMR time scale was also observed between the α- and β-methylene groups of the monosubstituted ruthenacycle (H(2)IMes)Cl(2)Ru(CHRCH(2)CH(2)) (R = CH(3), CH(2)CH(3), (CH(2))(3)CH(3)). EXSY NMR experiments at -87 °C were used to determine the activation energies for both of these exchange processes. In addition, new methods have been developed for the direct preparation of metathesis-active ruthenacyclobutanes via the protonolysis of dichloro(1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene)(benzylidene) bis(pyridine)ruthenium(II) and its 3-bromopyridine analogue. Using either trifluoroacetic acid or silica-bound toluenesulfonic acid as the proton source, the ethylene-derived ruthenacyclobutane (H(2)IMes)Cl(2)Ru(CH(2)CH(2)CH(2)) was observed in up to 98% yield via NMR at -40 °C. On the basis of these studies, mechanisms accounting for the positional and stereochemical exchange within ruthenacyclobutanes are proposed, as well as the implications of these dynamics toward olefin metathesis catalyst and reaction design are described.     

Mechanism and activity of ruthenium olefin metathesis catalysts: the role of ligands and substrates from a theoretical perspective

The reaction mechanism of olefin metathesis by ruthenium carbene catalysts is studied by gradient-corrected density functional calculations (BP86). Alternative reaction mechanisms for the reaction of the "first-generation" Grubbs-type catalyst (PCy(3))(2)Cl(2)Ru=CH(2) (1) for the reaction with ethylene are studied. The most likely dissociative mechanism with trans olefin coordination is investigated for the metathesis reaction between the "first-" and the "second-generation" Grubbs-type catalysts 1 and (H(2)IMes)(PCy(3))Cl(2)Ru=CH(2) (2) with different substrates, ethylene, ethyl vinyl ether, and norbornene, and a profound influence of the substrate is found. In contrast to the degenerate reaction with ethylene, the reactions with ethyl vinyl ether and norbornene are strongly exergonic by 8-15 kcal/mol, and this excess energy is released after passing through the metallacyclobutane structure. While the metallacyclobutane is in a deep potential minimum for degenerate metathesis reactions, the energy barrier for the [2+2] cycloreversion vanishes for the most exergonic reactions. On the free energy surface under typical experimental conditions, the rate-limiting steps for the overall reactions are then either metallacyclobutane formation for 1 or phosphane ligand dissociation for 2.     

Experimental and computational investigation of C-N bond activation in ruthenium N-heterocyclic carbene complexes

A combination of experimental studies and density functional theory calculations is used to study C-N bond activation in a series of ruthenium N-alkyl-substituted heterocyclic carbene (NHC) complexes. These show that prior C-H activation of the NHC ligand renders the system susceptible to irreversible C-N activation. In the presence of a source of HCl, C-H activated Ru(I(i)Pr(2)Me(2))'(PPh(3))(2)(CO)H (1, I(i)Pr(2)Me(2) = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) reacts to give Ru(I(i)PrHMe(2))(PPh(3))(2)(CO)HCl (2, I(i)PrHMe(2) = 1-isopropyl-4,5-dimethylimidazol-2-ylidene) and propene. The mechanism involves (i) isomerization to a trans-phosphine isomer, 1c, in which hydride is trans to the metalated alkyl arm, (ii) C-N cleavage to give an intermediate propene complex with a C2-metalated imidazole ligand, and (iii) N-protonation and propene/Cl(-) substitution to give 2. The overall computed activation barrier (ΔE(++)(calcd)) corresponds to the isomerization/C-N cleavage process and has a value of +24.4 kcal/mol. C-N activation in 1c is promoted by the relief of electronic strain arising from the trans disposition of the high-trans-influence hydride and alkyl ligands. Experimental studies on analogues of 1 with different C4/C5 carbene backbone substituents (Ru(I(i)Pr(2)Ph(2))'(PPh(3))(2)(CO)H, Ru(I(i)Pr(2))'(PPh(3))(2)(CO)H) or different N-substituents (Ru(IEt(2)Me(2))'(PPh(3))(2)(CO)H) reveal that Ph substituents promote C-N activation. Calculations confirm that Ru(I(i)Pr(2)Ph(2))'(PPh(3))(2)(CO)H undergoes isomerization/C-N bond cleavage with a low barrier of only +21.4 kcal/mol. Larger N-alkyl groups also facilitate C-N bond activation (Ru(I(t)Bu(2)Me(2))'(PPh(3))(2)(CO)H, ΔE(++)(calcd) = +21.3 kcal/mol), and in this case the reaction is promoted by the formation of the more highly substituted 2-methylpropene.     

1,3-二(2,6-二甲基苯基)-2-四氢咪唑基-苯亚甲基-二吡啶基-二氯合钌化合物的合成

设计了由1,3-二(2,6-二甲基苯基)-2-四氢咪唑基-苯亚甲基-三苯基膦-二氯合钌(7)和吡啶反应生成无膦型金属钌卡宾化合物1,3-二(2,6-二甲苯基)-2-四氢咪唑基-苯亚甲基-2-吡啶基-二氯合钌(8),8作为高效催化剂用于丙烯腈和烯丙基苯的交叉交互置换反应.新化合物7,8经核磁共振氢谱、碳谱和高分辨率质谱予以证实.     

1,3-二(2,6-二甲基苯基)-2-四氢咪唑基-苯亚甲基-二吡啶基-二氯合钌 化合物的合成

设计了由1,3-二(2,6-二甲基苯基)-2-四氢咪唑基-苯亚甲基-三苯基膦-二氯合钌(7)和吡啶反应生成无膦型金属钌卡宾化合物1,3-二(2,6-二甲苯基)-2-四氢咪唑基-苯亚甲基-2-吡啶基-二氯合钌(8), 8作为高效催化剂用于丙烯腈和烯丙基苯的交叉交互置换反应. 新化合物7, 8经核磁共振氢谱、碳谱和高分辨率质谱予以证实.     

Non-metathetic behavior patterns of Grubbs' carbene

Grubbs' carbene complex [Cl(2)(Cy(3)P)(2)Ru=CHPh] and its second-generation counterpart [Cl(2)(Im)(Cy(3)P)Ru=CHPh] have demonstrated remarkable efficiency metathesizing olefins. Furthermore, a growing number of newly discovered catalytic processes mediated by this complex broaden its synthetic utility beyond olefin metathesis. In addition, the ready availability of these stable ruthenium-based catalysts coupled with their tolerance toward a wide variety of common functional groups make Grubbs' catalysts very convenient synthetic tools. This paper presents recent advances in the non-metathetic behavior patterns of Grubbs' carbene.