Ruthenium complexes with an N-heterocyclic carbene NNC-pincer ligand: preparation and catalytic properties (original) (raw)
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Synthesis and catalytic properties of novel ruthenium N-heterocyclic-carbene complexes
Journal of Organometallic Chemistry, 2009
The reaction of [RuCl 2 (p-cymene)] 2 with 1,3-dialkylimidazolinium salts 1a-f in the presence of a small excess of cesium carbonate yields chelated g 6 -arene, g 1 -carbene ruthenium complexes 2a-f. All synthesised compounds were characterized by elemental analysis, NMR spectroscopy. The catalytic activity of RuCl 2 (g 6 -arene, g 1 -imidazolinylidene) complexes 2a-f was evaluated in the direct arylation of 2-phenylpyridine with chlorobenzene derivatives.
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
European Journal of Inorganic Chemistry, 2009
The reaction of RuCl2(PPh3)3 with tBuOK-deprotonated ortho-xylyl-bis(N-imidazolinium) salts 1a–d yields RuCl2(PPh3)[bis(imidazolidin-2-ylidene)] complexes (2a–d). Under similar conditions, [RuCl2(p-cymene)]2 leads to the ruthenium complex 3 containing a tridentate η6-arene-dicarbene ligand. All synthesized compounds were characterized byelemental analysis and NMR spectroscopy, and the molecular structures of 2a, 2b and 3 were determined by X-ray crystallography. The catalytic activity of RuCl2(PPh3)[bis(imidazolidin-2-ylidene)] complexes 2a–b was evaluated in the direct arylation of 2-phenylpyridine with chlorobenzene derivatives. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
New Ruthenium(II) Complexes Bearing N - Heterocyclic Carbenes
Organometallics, 2002
N-heterocyclic carbene complexes of ruthenium(II), [CpRu(L*) 2 Cl] (2) and [CpRu(CO)(L*)-Cl] (3) (Cp ) η 5 -C 5 H 5 ; L* ) 1,3-dicyclohexyl-imidazolin-2-ylidene), have been obtained in high yields by reaction of [CpRu(PR 2 R′) 2 Cl] (R ) R′ ) Ph, 1a; R ) Ph, R′ ) 2-MeC 6 H 4 , 1b) and [CpRu(CO){PPh 2 (2-MeC 6 H 4 )}Cl] (1c), respectively, with the free carbene L*. The mixed dicarbene complex [CpRu(dCPh 2 )(L*)Cl] (4) is prepared from [CpRu(dCPh 2 ){PPh 2 (2-MeC 6 H 4 )}Cl] (1d) and an equimolar amount of L*, whereas subsequent reaction of 1d with L* leads to formation of 2, along with tetraphenylethene. The reaction of [Cp*Ru(PPh 3 ) 2 Cl] (1e) with L* gives the pentamethylcyclopentadienyl derivative [Cp*Ru(PPh 3 )(L*)Cl] (5) (Cp* ) η 5 -C 5 Me 5 ) by displacement of 1 equiv of PPh 3 . Complex 5 reacts in toluene with CO, pyridine (Py), and N 2 CHCO 2 Et, affording [Cp*Ru(CO)(L*)Cl] (6), [Cp*Ru(Py)(L*)Cl] , and the mixed dicarbene [Cp*Ru(dCHCO 2 Et)(L*)Cl] (8), which were isolated in high yields. The molecular structure of complex 6 has been determined by an X-ray investigation, and the carbene-ruthenium distance clearly indicates a single bond (2.0951(18) Å). The Nheterocyclic carbene does not undergo substitution by other two-electron ligands.
Organometallics, 2008
The synthesis of Ru-based catalysts, presenting saturated chiral C 2 symmetric (3, 5) and C 1 symmetric (4) N-heterocyclic carbene (NHC) ligands bearing N-(S)-phenylethyl groups, was carried out. Variabletemperature NMR studies were conducted to investigate the interconversion of atropisomers in solution. The complex behaviors were rationalized evaluating the rotation barrier of alkylidene and NHC groups around the C-Ru bonds, by DFT calculations. Comparison between NMR data and DFT calculations suggested that interconversion between different atropisomers, which occurs at room temperature, is due to the free rotation of the benzylidene group around the RudC bond. The activity and stereoselectivity of 3-5 were investigated in ring-closing metathesis (RCM), asymmetric ring-closing metathesis (ARCM), cross-metathesis (CM), and ring-opening metathesis polymerization (ROMP). 4 showed the highest activity in all reactions and gave a significantly low E:Z ratio in the CM reaction. Modest enantioselectivity in the ARCM of an achiral triene was observed in the presence of C 2 symmetric catalyst 5.
Synthesis, characterization, and transfer hydrogenation of Ru(II)-N-heterocyclic carbene complexes
Journal of Coordination Chemistry, 2014
A series of ruthenium(II) complexes with N-heterocyclic carbene ligands were successfully synthesized by transmetalation reactions between silver(I) N-heterocyclic carbene complexes and [RuCl 2 (p-cymene)] 2 in dichloromethane under Ar conditions. All new compounds were characterized by spectroscopic and analytical methods. These ruthenium(II)-NHC complexes were found to be efficient precatalysts for the transfer hydrogenation of ketones by using 2-propanol as the hydrogen source in the presence of KOH as a co-catalyst. The antibacterial activity of ruthenium N-heterocyclic carbene complexes 3a-f was measured by disc diffusion method against Gram positive and Gram-negative bacteria. Compounds 3d exhibited potential antibacterial activity against five bacterial species among the six used as indicator cells. The product 3e inhibits the growth of all the six tested microorganisms. Moreover, the antioxidant activity determination of these complexes 3a-f, using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2 0azinobis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS) as reagent, showed that compounds 3b and 3d possess DPPH and ABTS antiradical activities. From a concentration of 1 mg ml À1 , these two complexes presented a similar scavenging activity to that of the two used controls gallic acid (GA) and butylated hydroxytoluene (BHT). From a concentration of 10 mg ml À1 , the percentage inhibition of complexes 3b and 3d was respectively 70% and 90%. In addition, these two Ru-NHC complexes exhibited antifungal activity against Candida albicans. Investigation of the anti-acetylcholinesterase activity of the studied complexes showed that compounds 3a, 3b, 3d and 3e exhibited good activity at 100 mg ml À1 and product 3d is the most active. In a cytotoxicity study the complexes 3 were evaluated against two human cancer cell lines MDA-MB-231 and MCF-7. Both 3d and 3e complexes were found to be active against the tested cell lines showing comparable activity with examples in the literature.