New dmso–ruthenium catalysts bearing N-heterocyclic carbene ligands for the ring-opening metathesis of norbornene (original) (raw)
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Convenient syntheses of novel ruthenium catalysts bearing N-heterocyclic carbenes
Journal of Organometallic Chemistry, 2000
The 16-electron ruthenium(II) complexes Cp*Ru[C(R)N(H)C C(H)Ņ ¹¹¹¹¹¹¹¹¹º (R)]Cl (Cp* = h 5 -C 5 Me 5 ; R=Cy (ICy), 1a; Mes (IMes), 1b) containing N-heterocyclic carbenes are easily accessible in quantitative yields from [Cp*Ru(OMe)] 2 (Me= CH 3 ) and the corresponding 1,3-diorganylimidazolium chloride by methanol elimination. Compounds 1a-b can also be prepared in 75-80% yield by treating the commercially available polymeric ruthenium(III) compound [Cp*RuCl 2 ] n with the free 1,3-diorganylimidazolin-2-ylidenes in 1 to 1.5 molar amounts. 1a reacts with CO, PPh 3 , pyridine and ethyl diazoacetate (EDA) affording the 18-electron derivatives Cp*Ru(ICy)(L)Cl (L = CO, 2; PPh 3 , 3; py, 4; CHCO 2 Et, 5). The mixed dicarbene complex 5 is the first isolable ruthenium cyclopentadienyl species bearing a CHCO 2 Et moiety. Compounds 1a-b catalyze the carbon carbon coupling of terminal alkynes HC CR (R= Ph, SiMe 3 , t Bu, p-Tol) under mild conditions, with the selectivity strongly depending on the substituent R.
Novel Olefin Metathesis Ruthenium Catalysts Bearing Backbone-Substituted Unsymmetrical NHC Ligands
Organometallics, 2014
Stable Ru-based catalysts containing unsymmetrical N-heterocyclic carbene (NHC) ligands with phenyl substituents on the backbone in syn and anti stereochemical relationships have been easily prepared and fully characterized. Preliminary investigation revealed that, depending on the backbone configuration, the new Ru complexes displayed different catalytic behaviors in representative olefin metathesis reactions.
Molecular Catalysis, 2018
Dimethyl sulfoxide ruthenium(II) complexes of N-heterocyclic carbenes derived from cycloalkylamines (cycloalkyl = cyclopentyl (1a), cyclohexyl (1b), cycloheptyl (1c), and cyclooctyl (1d)) were synthesized: [RuCl 2 (Sdmso) 2 (IPent)] (2a), [RuCl 2 (S-dmso) 2 (IHex)] (2b), [RuCl 2 (S-dmso) 2 (IHept)] (2c), and [RuCl 2 (S-dmso) 2 (IOct)] (2d). The imidazolium salts 1a-1d were characterized by FTIR, UV-vis, and 1 H and 13 C NMR spectroscopy, while their respective dimethyl sulfoxide ruthenium(II) complexes (2a-2d) were characterized by elemental analysis, FTIR, UV-vis, 1 H and 13 C NMR, and cyclic voltammetry. The complexes 2a-2d were evaluated as catalytic precursors for ROMP of norbornene (NBE) and for ATRP of methyl methacrylate (MMA). The polynorbornene (polyNBE) syntheses via ROMP using the complexes 2a-2d as pre-catalysts were evaluated under reaction conditions of [EDA]/[Ru] = 28 (5 μL), [NBE]/[Ru] = 5000 at 50°C as a function of time. The polymerization of MMA via ATRP was conducted using the complexes 2a-2d in the presence of ethyl 2-bromoisobutyrate (EBiB) as the initiator. All tests were using the molar ratio [MMA]/[EBiB]/[Ru] = 1000/2/1 and conducted at 85°C. The linear correlation of ln([MMA] 0 /[MMA]) and time clearly indicates that the concentration of radicals remains constant during the polymerization and that the ATRP of MMA mediated by 2a-2d proceeds in a controlled manner.
Olefin metathesis ruthenium catalysts bearing unsymmetrical heterocylic carbenes
Coordination Chemistry Reviews
Catalytic olefin metathesis has become a powerful tool for carbon–carbon bond formation in organic and polymer chemistry. The Grubbs’ 1st generation catalyst 1 constitutes a highly efficient metathesis catalyst tolerating a wide variety of functional groups. The introduction of N-heterocyclic carbenes (NHCs) as ligands has afforded the more stable and active 2nd generation ruthenium catalyst 2. Several ruthenium metathesis initiators of the 2nd generation type have been prepared from various NHCs. Altering the steric and electronic properties of the ligand can control the activity and selectivity of the NHC coordinated catalysts. One of the reported modifications for the NHC-containing ruthenium metathesis initiators is the application of unsymmetrical NHC ligands. The unsymmetrical nature of these ligands may lead to the selective catalysts in different metathesis reactions. This survey highlights the developments in ruthenium catalysts coordinated with unsymmetrical NHC ligands an...
Angewandte Chemie, 2022
Ru-based olefin metathesis catalysts containing carbohydrate-derived NHCs from glucose and galactose were synthesized and characterized by NMR spectroscopy. 2D-NMR spectroscopy revealed the presence of Ru-C (benzylidene) rotamers at room temperature, and the rate of rotation was measured using magnetization transfer and VT-NMR spectroscopy. The catalysts were found to be effective at ring-opening metathesis polymerization (ROMP), ring-closing metathesis (RCM), cross-metathesis (CM), and asymmetric ring-opening cross-metathesis (AROCM) and showed surprising selectivity in both CM and AROCM.
Journal of Organometallic Chemistry, 2022
Recent papers in this series (1) illustrated that, besides the highly active and stereoselective tungsten and molybdenum imido alkylidene metathesis catalysts, extensively developed by Schrock and coworkers (2, 3), a large class of ruthenium complexes have been successfully applied in organic and polymer syntheses (4-9). These include arene 1, alkylidene 2, vinylalkylidene 3, vinylidene 4, allenylidene 5 and indenylidene 6 complexes; where R are phenyl (Ph), isopropyl (i-Pr) or cyclohexyl (Cy) and R' are phenyl (Ph) or tert-butyl (t-Bu) groups. This variety of 16-and 18-electron ruthenium complexes, and specifically the 'first generation' catalysts (or pre-catalysts) of diphosphane ruthenium alkylidene type 2 and 3 (5, 6), displayed a set of appealing properties such as good to excellent metathesis activity and high tolerance towards many organic functionalities, various impurities, air and moisture (10). The main inconveniences during their utilisation, however, consist of a limited stability in the course of metathesis reactions and particularly decomposition upon heating, due to a pronounced lability of the phosphane ligands. Type of NHC Ruthenium Complexes, Syntheses and Catalytic Properties A remarkable development in the chemistry of ruthenium alkylidene complexes occurred subsequently when three independent research teams reported the design and synthesis of a novel class of ruthenium pre-catalysts containing alkylidene
Journal of Molecular Catalysis A: Chemical, 2005
The synthesis of monomeric and dendritic ruthenium benzylidene cis-bis-phosphine complexes that catalyze norbornene ROMP previously reported with dicyclohexyl bis-phosphines has now been extended to monomeric and dendritic bis-tertiobutyl phosphines. The reaction of Hoveyda's catalyst [RuCl 2 (=CH-o-O-iPrC 6 H 4 )PPh 3 ] (1) with the diphosphine PhCH 2 N(CH 2 PtBu 2 ) 2 (2) gives the new air-stable green ruthenium carbene complex (3) in which (2) models a dendritic branch of poly(diphosphine) dendrimers DAB-dendr-[N(CH 2 PtBu 2 ) 2 ] n (G 1 , n = 4; G 2 , n = 8; G 3 , n = 16). Metallodendrimers DAB-dendr-[N(CH 2 PtBu 2 ) 2 Ru(=CHAr)(Cl) 2 ] n (4)-(6) derived from the three first generations of DAB polyamines containing, respectively, 4, 8 and 16 ruthenium branches have been synthesized. These dendritic ruthenium-benzylidene complexes initiate the ROMP of norbornene at room temperature to form star-shaped metallodendritic polymers slightly more rapidly than the analogues with bis-cyclohexyl phosphines. Interestingly, the metallodendrimers G 1 (4) initiates the ROMP of norbornene much faster than the model ruthenium complex (3) the overall rate order being G 1 > G 2 > G 3 > model, these positive and negative dendritic effects being comparable with those found for the dicyclohexyl bis-phosphine complexes.