Synthesis and Catalytic Activity of a Two-core Ruthenium Carbene Complex: a Unique Catalyst for Ring Closing Metathesis Reaction

The reaction of a ruthenium carbide complex RuCl2(C:)(PCy3)2 with [H(Et2O)x]+[BF4]– at a molar ratio of 1:2 produced a two-core ruthenium carbene complex, {[RuCl(=CHPCy3)(PCy3)]2(μ-Cl)3}+·[BF4]–, in the form of a yellow-green crystalline solid in a yield of 94%. This two-core ruthenium complex is a selective catalyst for ring closing metathesis of unsubstituted terminal dienes. More importantly, no isomerized byproduct was observed for N-substrates when the two-core ruthenium complex was used as the catalyst at an elevated temperature(137 °C), indicating that the complex is a chemo-selective catalyst for ring closing metathesis reactions.     

An ionic liquid-tagged second generation Hoveyda-Grubbs ruthenium carbene complex as highly reactive and recyclable catalyst for ring-closing metathesis of di-, tri- and tetrasubstituted dienes

A second generation Hoveyda-Grubbs ruthenium carbene complex bearing an ionic liquid tag was prepared and shown to be a highly reactive catalyst for the ring-closing metathesis of di-, tri- and tetrasubstituted diene and enyne substrates in minimally ionic solvent systems ([Bmim]PF₆/CH₂Cl₂, 1:9-1:1 v/v). Both the catalyst and the ionic liquid can be conveniently recycled and repeatedly reused (up to 17 cycles) with only a very slight loss of activity. The ionic liquid tag is crucial to the high level of recyclability of the catalyst since the original second generation Grubbs and Hoveyda-Grubbs catalysts rapidly lose their activity when recycled in the ionic liquid layer.     

Protonolysis of a ruthenium-carbene bond and applications in olefin metathesis

The synthesis of a ruthenium complex containing an N-heterocylic carbene (NHC) and a mesoionic carbene (MIC) is described wherein addition of a Br?nsted acid results in protonolysis of the Ru-MIC bond to generate an extremely active metathesis catalyst. Mechanistic studies implicated a rate-determining protonation step in the generation of the metathesis-active species. The activity of the NHC/MIC catalyst was found to exceed those of current commercial ruthenium catalysts.     

梳形接枝共聚物的合成(Ⅱ)——载体化钌卡宾络合物催化降冰片烯基聚苯乙烯的开环岐化聚合

由石油化工副产C₅馏份提取双环戊二烯(DCPD)、以聚合物负载三氟化硼为催化剂进行DCPD与烯丙基氯(AC)的Diels-Alder反应合成5-氯甲基-2-降冰片烯(NBCH₂Cl),经锂代反应后用以引发苯乙烯的活性阴离子聚合合成了降冰片烯(NB)基聚苯乙烯(PS)大分子环烯单体NB-PS,在聚合物负载钌卡宾络合物[RuCl₂(PPh₃)₂(=C=CHtBu)]催化(引发)作用下进行大分子单体NB-PS的开环歧化聚合(ROMP)合成了梳形接枝共聚物PNB-g-PS.实验结果表明所合成聚合物负载硼、钌络合物催化剂的性能均明显优于对应非负载体.讨论了上述催化剂的聚合物载体效应的机理及温度、溶剂等对活性阴离子聚合反应的影响.     

Metathesis of carbonyl containing olefins by 2nd generation Ru alkylidene catalysts: A computational study

The metathesis reaction of cis-1,4-diacetoxy-2-butene (2) mediated by a second generation ruthenium alkylidene catalyst (IMesH₂)Cl₂RuCHPh (1) where IMesH₂ is 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene group has been modeled at PBE0/LACV3P*//PBE0/LACVP* level of theory. The calculations demonstrate that the driving force of the metathesis reaction is the formation of a Ru–O coordination bond in the corresponding Ru acetoxyethylidene complex 8a-II. The free activation energy of metathesis by 8a-II complex is higher than that of the metathesis reaction mediated by the conventional ruthenium alkylidene catalyst (8b), due to the additional stabilization of the Ru center by a carbonyl oxygen revealing lower reactivity of carbonyl containing ruthenium carbene species. It has been shown that conjugation between carbonyl and olefin double bonds decreases the reactivity of olefins due stabilization of nonproductive complex between Ru center and carbonyl group of the olefin.     

Cross enyne metathesis of para-substituted styrenes: a kinetic study of enyne metathesis

[Reaction: see text] The intermolecular enyne metathesis between alkynes and styrene derivatives was developed to study electronic effects in enyne metathesis. A Hammett plot for the overall reaction, catalyst initiation and vinyl carbene turnover was determined with the second generation Grubbs ruthenium carbene catalyst.     

胺基膦钌卡宾化合物的合成及催化烯烃复分解反应

合成并表征了一类含新型胺基膦配体的Grubbs二代型钌卡宾烯烃复分解催化剂[RuCl₂(H₂IMes)·(R¹HNPR²₂)(=CHPh)], 采用核磁共振波谱和单晶X射线衍射确定了催化剂的结构. 在室温条件下, 以N,N-二烯丙基-对甲苯磺酰胺的关环复分解反应(RCM)为模型, 考察了不同胺基膦配体对钌卡宾催化反应速率的影响. 结果表明, G2?1表现出最佳的催化活性. 通过底物研究发现, G2?1催化剂(摩尔分数, 1%)对双端烯及多端烯的RCM反应具有较好的活性和官能团适应性, 产物收率均>95%; G2?1催化剂同样适用于同(异)端烯底物的交叉复分解反应(CM), 其催化苯乙烯与3-苯氧基丙烯的CM反应时产物收率高达92%.     

Synthesis and Evaluation of Ruthenium 2‐Alkyl‐6‐mercaptophenolate Catalysts for Olefin Metathesis

A series of ruthenium carbene catalysts containing 2‐sulfidophenolate bidentate ligand with an ortho‐substituent next to the oxygen atom were synthesized. The molecular structure of ruthenium carbene complex containing 2‐isopropyl‐6‐sulfidophenolate ligand was confirmed through single crystal X‐ray diffraction. An oxygen atom can be found in the opposite position of the N‐heterocyclic carbene (NHC) based on the steric hindrance and strong trans‐effects of the NHC ligand. The ruthenium carbene catalyst can catalyze ring‐opening metathesis polymerization (ROMP) reaction of norbornene with high activity and Z‐selectivity and cross metathesis (CM) reactions of terminal alkenes with (Z)‐but‐2‐ene‐1,4‐diol to give Z‐olefin products (Z/E ratios, 70:30–89:11) in low yields (13%–38%). When AlCl₃ was added into the CM reactions, yields (51%–88%) were considerably improved and process becomes highly selective for E‐olefin products (E/Z ratios, 79:21–96:4). Similar to other ruthenium carbene catalysts, these new complexes can tolerate different functional groups.     

Synthesis and Catalytic Study of Ruthenium Carbene Catalyst Containing a Zn‐Porphyrin Ligand

A ruthenium carbene complex containing a Zn‐porphyrin ligand has been developed. The complex was characterized by ¹H NMR, IR, HRMS and elemental analysis. The catalytic activity of the ruthenium carbene complex for olefin metathesis reactions was also investigated. The complex exhibited excellent performance for both ring‐closing and cross metathesis reactions at 35°C.     

A Thermo‐ and Photo‐Switchable Ruthenium Initiator For Olefin Metathesis

A ruthenium carbene complex bearing azobenzene functionality is reported. The complex exists in the form of two isomers differing by the size of the chelate ring. Both isomers were isolated by applying kinetic or thermodynamic control during the synthesis and characterized by X‐ray diffraction analysis. The isomerization of the complex was studied by UV/Vis spectroscopy. The stable isomer was tested as a catalyst in olefin metathesis. The complex was activated at about 100 °C to promote ring‐closing and ring‐opening polymerization metathesis reactions. The activation took place also at room temperature under middle ultraviolet radiation.     

A new concept for the noncovalent binding of a ruthenium-based olefin metathesis catalyst to polymeric phases: preparation of a catalyst on Raschig rings

A new concept for noncovalent immobilization of a ruthenium olefin metathesis catalyst is presented. The 2-isopropoxybenzylidene ligand of a Hoveyda-Grubbs carbene is further modified by an additional amino group (7) and immobilization is achieved by treatment with sulfonated polystyrene forming the corresponding ammonium salt. In this novel strategy for the immobilization of ruthenium-based metathesis catalysts, the amino group plays a two-fold role, being first an active anchor for immobilization and second, after protonation, activating the catalysts (electron donating to electron withdrawing activity switch). The polymeric support was prepared by precipitation polymerization which led to small bead sizes (0.2-2 microm) and large surface areas. Compared to commercial resins this tailor-made phase showed superior properties in immobilization of complex 7. This concept of immobilization was applied to glass-polymer composite megaporous Raschig rings. Ru catalyst 7 on Raschig rings was used under batch conditions in various metathesis reactions, including ring-closing (RCM), cross- (CM) and enyne metathesis, to give products of high chemical purity with very low ruthenium contamination levels (21-102 ppm). The same ring can be used for up to 6 cycles of metathesis.     

Highly Active Carbene Ruthenium Catalyst for Metathesis of 1-Hexene

A new carbene ruthenium complex, 1,3-bis（2,6-dimethylphenyl）-4,5-dihydroimidazol-2-ylidene）（PPh3）Cl2-Ru=CHPh, was synthesized and used as catalyst for the metathesis of 1-hexene. The resulting complex exhibited very high catalytic activity whose TOF is up to 6680 h^-1. However, at the same time significant olefin isomerization was observed and could be surpressed by changing reaction conditions, such as temperature, time, alkene/Ru molar ratio and solvent.     

Tandem cyclopropanation/ring-closing metathesis of dienynes

Certain dienynes give cyclorearrangement by tandem cyclopropanation/ring-closing alkene metathesis, triggered by either a ruthenium carbene or noncarbene ruthenium(II) precatalyst. The process represents a variation of enyne metathesis where presumed cyclopropyl carbene intermediates undergo a consecutive ring-closing metathesis. A mechanistic proposal is offered, and sequential use of catalysts provided a tandem ring-closing enyne/alkene metathesis product.     

Mechanism of enyne metathesis catalyzed by Grubbs ruthenium-carbene complexes: a DFT study

The complete catalytic cycle of the reaction of alkenes and alkynes to dienes by Grubbs ruthenium carbene complexes has been modeled at the B3LYP/LACV3P**+//B3LYP/LACVP level of theory. The core structures of the substrates and the catalyst were used as models, namely, ethene, ethyne, hept-1-en-6-yne, (Me(3)P)(2)Cl(2)Ru=CH(2), and [C(2)H(4)(NMe)(2)C](Me(3)P)Cl(2)Ru=CH(2). Insight into the electronically most preferred mechanistic pathways was gained for both intermolecular as well as for intramolecular enyne metathesis. Alkene metathesis is predicted to proceed fast and reversible, while the insertion of the alkyne substrate is slower, irreversible, and kinetically regioselectivity determining. Ruthenacyclobut-2-ene structures do not exist as local minima in the catalytic cycle. Instead, vinylcarbene complexes are formed directly. The alkyne insertion step and the cycloreversion of 2-vinyl ruthenacyclobutanes feature comparable predicted overall barriers in intermolecular enyne metathesis. For intramolecular enyne metathesis, a noncyclic alkene fragment of the enyne substrate is first incorporated into the Grubbs catalyst by an alkene metathesis reaction. The subsequent insertion of the alkyne fragment then proceeds intramolecularly. Alkene association, cycloaddition, and cycloreversion to the diene product complex close the catalytic cycle. Rate enhancement by an ethene atmosphere (Mori's conditions) originates from a constantly higher overall alkene concentration that is necessary for the rate-limiting [2 + 2] cycloreversion step to the diene product complex.     

Ring-closing olefin metathesis on ruthenium carbene complexes: model DFT study of stereochemistry

Ring-closing metathesis (RCM) is the key step in a recently reported synthesis of salicylihalamide and related model compounds. Experimentally, the stereochemistry of the resulting cycloolefin (cis/trans) depends strongly on the substituents that are present in the diene substrate. To gain insight into the factors that govern the observed stereochemistry, density functional theory (DFT) calculations have been carried out for a simplified dichloro(2-propylidene)(imidazole-2-ylidene)ruthenium catalyst I, as well as for the real catalyst II with two mesityl substituents on the imidazole ring. Four model substrates are considered, which are closely related to the systems studied experimentally, and in each case, two pathways A and B are possible since the RCM reaction can be initiated by coordination of either of the two diene double bonds to the metal center. The first metathesis yields a carbene intermediate, which can then undergo a second metathesis by ring closure, metallacycle formation, and metallacycle cleavage to give the final cycloolefin complex. According to the DFT calculations, the stereochemistry is always determined in the second metathesis reaction, but the rate-determining step may be different for different catalysts, substrates, and pathways. The ancillary N-heterocyclic carbene ligand lies in the Ru-Cl-Cl plane in the simplified catalyst I, but is perpendicular to it in the real catalyst II, and this affects the relative energies of the relevant intermediates and transition states. Likewise, the introduction of methyl substituents in the diene substrates influences these relative energies appreciably. Good agreement with the experimentally observed stereochemistry is only found when using the real catalyst II and the largest model substrates in the DFT calculations.     

Application of a Grubbs–Hoveyda Metathesis Catalyst Noncovalently Immobilized by Fluorous–Fluorous Interactions

A Grubbs–Hoveyda metathesis catalyst bearing a tris(perfluoroalkyl)silyl tag for efficient noncovalent attachment to fluorous silica gel (FSG) was synthesized and employed in ring‐closing metathesis (RCM) reactions in CH₂Cl₂. After the reaction, a solvent switch to a polar system allowed for recovery of the catalyst by filtration and its reuse. The approach was demonstrated for a number of different substrates. Furthermore, it was shown that the application of this catalytic system yielded products with low ruthenium content.     

Chelating alkylidene ligands as pacifiers for ruthenium catalysed olefin metathesis

Olefin metathesis catalysed by ruthenium has emerged at the frontier of modern synthetic chemistry. The desire to enhance catalyst stability, gain control over the catalytic process and deepen the understanding of the mechanisms of metathesis has yielded a class of latent ruthenium precatalysts of delayed initiation and with switchable activity. One of the main methodologies developed for this purpose has been the introduction of tethered carbene ligands. Herein we track the evolution of ruthenium based metathesis catalysts bearing chelated alkylidenes, from the early oxygen Hoveyda type benzylidenes to the latent sulphur containing complexes.     

SYNTHESIS OF A COMB GRAFT COPOLYMER VIA RING OPENING METATHESIS POLYMERIZATION CATALYZED BY SUPPORTED RHUTHENIUM CARBENE COMPLEX

5－Chloromethyl-2-norbornene was synthesized via Diels-alder reaction of cyclopentadiene and allyl chloride using a polymer supported boron trifluoride as the catalyst,and was then lithiated and used to initiate a livcing anionic polymerization of styrene to prepare a macromonome,5-polystryl-2-norbornene NB-PS,Comb graft copolymer PNB-g-PS was synthesized via ring opening metathesis polymerization of the macromonomer under the catalysis of ruthenium carbene complex RuCl2(PPh3)2(=CCHtBu)and its polymer supported correspondent.Experimetal results showed that the behavior of both the supported boron and supported ruthenium catalysts are superior to their unsupported counterparts.The possible promotion mechanism of the tailor-made supports is discussed.     

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.