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Steven P. Nolan - One of the best experts on this subject based on the ideXlab platform.
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What can NMR spectroscopy of selenoureas and phosphinidenes teach us about the π-accepting abilities of N-heterocyclic carbenes?
Chemical Science, 2015Co-Authors: Sai V. C. Vummaleti, Steven P. Nolan, David B. Cordes, Alexandra M. Z. Slawin, David J. Nelson, Albert Poater, Adrián Gómez‐suárez, Luigi CavalloAbstract:selenoureas derived from a range of Imidazol-2-Ylidenes, 4,5-dihydroImidazol-2-Ylidenes and triazol-2ylidenes are documented. Computational studies are used to explore the link between the shielding of the selenium centre and the electronic properties of the NHCs. Results show that dSe is correlated to the energy gap between a filled lone pair orbital on Se and the empty p* orbital corresponding to the Se–NHC bond. Bond energy decomposition analysis indicated no correlation between the orbital s-contribution to bonding and the chemical shielding, while a good correlation was found between the p-contribution to bonding and the chemical shielding, confirming that this technique is indeed able to quantify the ability of NHCs to accept p-electron density. Calculations conducted on phosphinidene adducts yielded similar results. With the link between dSe and dP and p-back bonding ability clearly established, these compounds represent useful ways in which to fully understand and quantify this aspect of the electronic properties of NHCs.
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hydrofluorination of alkynes catalysed by gold bifluorides
Chemcatchem, 2015Co-Authors: Fady Nahra, Davide Bello, Marcel Brill, Alan Obled, Scott R. Patrick, David Ohagan, David B. Cordes, Alexandra M. Z. Slawin, Steven P. NolanAbstract:We report the synthesis of nine new N-heterocyclic carbene gold bifluoride complexes starting from the corresponding N-heterocyclic carbene gold hydroxides. A new methodology to access N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene gold(I) fluoride starting from N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene gold(I) hydroxide and readily available potassium bifluoride is also reported. These gold bifluorides were shown to be efficient catalysts in the hydrofluorination of symmetrical and unsymmetrical alkynes, thus affording fluorinated stilbene analogues and fluorovinyl thioethers in good to excellent yields with high stereo- and regioselectivity. The method is exploited further to access a fluorinated combretastatin analogue selectively in two steps starting from commercially available reagents.
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large yet flexible n heterocyclic carbene ligands for palladium catalysis
Chemistry: A European Journal, 2013Co-Authors: Sebastien Meiries, Alexandra M. Z. Slawin, Gaetan Le Duc, Anthony Chartoire, Alba Collado, Klaus Speck, Kasun Athukorala S Arachchige, Steven P. NolanAbstract:A straightforward and scalable eight-step synthesis of new N-heterocyclic carbenes (NHCs) has been developed from inexpensive and readily available 2-nitro-m-xylene. This process allows for the preparation of a novel class of NHCs coined ITent ("Tent" for "tentacular") of which the well-known IMes (N,N′-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), IPr (N,N′-bis(2,6-di(2-propyl)phenyl)imidazol-2-ylidene) and IPent (N,N′-bis(2,6-di(3-pentyl)phenyl)imidazol-2-ylidene) NHCs are the simplest and already known congeners. The synthetic route was successfully used for the preparation of three members of the ITent family: IPent (N,N′-bis(2,6- di(3-pentyl)phenyl)imidazol-2-ylidene), IHept (N,N′-bis(2,6-di(4-heptyl) phenyl)imidazol-2-ylidene) and INon (N,N′-bis(2,6-di(5-nonyl)phenyl) imidazol-2-ylidene). The electronic and steric properties of each NHC were studied through the preparation of both nickel and palladium complexes. Finally the effect of these new ITent ligands in Pd-catalyzed Suzuki-Miyaura and Buchwald-Hartwig cross-couplings was investigated. Tentacular NHCs: A straightforward, scalable eight-step synthesis of N-heterocyclic carbenes (NHCs) has been developed using inexpensive and readily available 2-nitro-m-xylene, allowing the preparation of a class of NHCs designated ITent ("Tent" for "tentacular"). The electronic and steric properties of each NHC were studied through the preparation of both nickel and palladium complexes, and the effect of these new ITent ligands in Pd-catalyzed Suzuki-Miyaura and Buchwald-Hartwig cross-couplings was investigated.
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[Pd(IPr*OMe)(acac)Cl] : tuning the N-heterocyclic carbene in catalytic C-N bond formation
Organometallics, 2012Co-Authors: Sebastien Meiries, Alexandra M. Z. Slawin, David B. Cordes, Klaus Speck, Steven P. NolanAbstract:A new N-heterocyclic ligand IPr*OMe [N,N′-bis(2,6-bis(diphenylmethyl)-4-methoxyphenyl)imidazol-2-ylidene] has been synthesized and compared with its earlier methyl-substituted congener IPr* [N,N′-bis(2,6-bis(diphenylmethyl)-4-methylphenyl)imidazol-2-ylidene]. IPr*OMe was successfully bound to palladium, and the catalytic activity of the resulting complex [Pd(IPr*OMe)(acac)Cl] was investigated in Buchwald–Hartwig arylamination. Catalytic activity was compared to that of [Pd(IPr*)(acac)Cl].
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Synthesis and characterization of IPrMe-containing silver(I), gold(I) and gold(III) complexes
Dalton transactions (Cambridge England : 2003), 2009Co-Authors: Sylvain Gaillard, Alexandra M. Z. Slawin, Xavier Bantreil, Steven P. NolanAbstract:The compounds 4,5-dimethyl-N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene silver chloride [AgCl(IPrMe)] 3 and 4,5-dimethyl-N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene gold(I) chloride [AuCl(IPrMe)] 4 have been synthesized. The attempted synthesis of the corresponding 4,5-dimethyl-N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene gold(III) chloride by oxidative addition of chlorine gas on 4 allowed for the formation of the expected complex, concomitantly with 6, resulting from a chlorination of a methyl group situated in the backbone of the NHC (N-heterocyclic carbene). Additionally, the buried volume %Vbur of the IPrMe ligand in [AgCl(IPrMe)] 3 and [AuCl(IPrMe)] 4 complexes was calculated and compared to %Vbur of more classical NHCs. This quantification of the steric hinderance of the IPrMe ligand reveals the influence of the substituent modulation in the backbone of NHCs.
N. Lugan - One of the best experts on this subject based on the ideXlab platform.
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Oxidative Coupling of Anionic Abnormal N-Heterocyclic Carbenes: Efficient Access to Janus-Type 4,4'-Bis(2H-imidazol-2-ylidene)s.
Angewandte Chemie (International ed. in English), 2018Co-Authors: Alina A. Grineva, Dmitry A. Valyaev, V. Cesar, O. A. Filippov, Victor N. Khrustalev, Sergei. E. Nefedov, N. LuganAbstract:Abstract The oxidative coupling of anionic imidazol-4-ylidenes protected at the C2 position with [MnCp(CO)2] or BH3 led to the corresponding 4,4′-bis(2H-imidazol-2-ylidene) complexes or adducts, in which the two carbene moieties are connected through a single C−C bond. Subsequent acidic treatment of the later species led to the corresponding 4,4′-bis(imidazolium) salts in good yields. The overall procedure offers practical access to a novel class of Janus-type bis(NHC)s. Strikingly, the coplanarity of the two NHC rings within the mesityl derivative 4,4′-bis(IMes), favored by steric hindrance along with stabilizing intramolecular C−H⋅⋅⋅π aryl interactions, allows the alignment of the π-systems and, as a direct consequence, significant electron communication through the bis(carbene) scaffold.
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Oxidative coupling of anionic abnormal N-Heterocyclic carbenes: Efficient access to Janus-type 4,4′-bis(2H-imidazol-2-ylidene)s
Angewandte Chemie International Edition, 2018Co-Authors: Alina A. Grineva, Dmitry A. Valyaev, V. Cesar, O. A. Filippov, Victor N. Khrustalev, Sergei. E. Nefedov, N. LuganAbstract:The oxidative coupling of anionic imidazol-4-ylidenes protected at the C2 position with [MnCp(CO)2] or BH3 led to the corresponding 4,4′-bis(2H-imidazol-2-ylidene) complexes or adducts, in which the two carbene moieties are connected through a single C−C bond. Subsequent acidic treatment of the later species led to the corresponding 4,4′-bis(imidazolium) salts in good yields. The overall procedure offers practical access to a novel class of Janus-type bis(NHC)s. Strikingly, the coplanarity of the two NHC rings within the mesityl derivative 4,4′-bis(IMes), favored by steric hindrance along with stabilizing intramolecular C−H⋅⋅⋅π aryl interactions, allows the alignment of the π-systems and, as a direct consequence, significant electron communication through the bis(carbene) scaffold.
Panayiotis A. Koutentis - One of the best experts on this subject based on the ideXlab platform.
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Reactions of Tetracyanoethylene with N′‑Arylbenzamidines: A Route to 2‑Phenyl‑3H‑imidazo[4,5‑b]quinoline-9-carbonitriles
2016Co-Authors: Styliana I. Mirallai, Maria Manoli, Panayiotis A. KoutentisAbstract:Eight 2-phenyl-3H-imidazo[4,5-b]quinoline-9-carbonitriles 15 are prepared in four steps from N′-arylbenzamidines 11 and tetracyanoethylene (TCNE) in ∼70–90% yields. The transformation involves the initial formation of N-aryl-N′-(1,2,2-tricyanovinyl)benzamidines 12 in 87–99% yields, which in MeCN undergo a 5-exodig cyclization to give the 2-[1-aryl-5-imino-2-phenyl-1H-imidazol-4(5H)-ylidene]malononitriles 13 in 84–92% yields, while in MeOH the (Z)-2-[2-phenyl-4-(arylimino)-1H-imidazol-5(4H)-ylidene]malononitriles 14 are formed in 85–94% yields. The imidazoles 14 can also be prepared directly from imidazoles 13 via a Dimroth rearrangement in either neat MeOH or in DCM with DBU. Subsequent thermolysis of imidazoles 14 in diphenyl ether affords 2-phenyl-3H-imidazo[4,5-b]quinoline-9-carbonitriles 15 in near quantitative yields. Mechanistic rationale is provided for all transformations
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reactions of tetracyanoethylene with n arylbenzamidines a route to 2 phenyl 3h imidazo 4 5 b quinoline 9 carbonitriles
Journal of Organic Chemistry, 2013Co-Authors: Styliana I. Mirallai, Maria Manoli, Panayiotis A. KoutentisAbstract:Eight 2-phenyl-3H-imidazo[4,5-b]quinoline-9-carbonitriles 15 are prepared in four steps from N′-arylbenzamidines 11 and tetracyanoethylene (TCNE) in ∼70–90% yields. The transformation involves the initial formation of N-aryl-N′-(1,2,2-tricyanovinyl)benzamidines 12 in 87–99% yields, which in MeCN undergo a 5-exodig cyclization to give the 2-[1-aryl-5-imino-2-phenyl-1H-imidazol-4(5H)-ylidene]malononitriles 13 in 84–92% yields, while in MeOH the (Z)-2-[2-phenyl-4-(arylimino)-1H-imidazol-5(4H)-ylidene]malononitriles 14 are formed in 85–94% yields. The imidazoles 14 can also be prepared directly from imidazoles 13 via a Dimroth rearrangement in either neat MeOH or in DCM with DBU. Subsequent thermolysis of imidazoles 14 in diphenyl ether affords 2-phenyl-3H-imidazo[4,5-b]quinoline-9-carbonitriles 15 in near quantitative yields. Mechanistic rationale is provided for all transformations.
Edwin D. Stevens - One of the best experts on this subject based on the ideXlab platform.
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Cationic Iridium Complexes Bearing Imidazol-2-ylidene Ligands as Transfer Hydrogenation Catalysts
Organometallics, 2001Co-Authors: Anna C. Hillier, Edwin D. Stevens, Man Lee, Steven P. NolanAbstract:The synthesis and characterization by X-ray crystallography of the complexes [Ir(cod)(py)(L)]PF6 (L = IMes, 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (2); L = IPr, 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (3); L = ICy, 1,3-bis(cyclohexyl)imidazol-2-ylidene (4)) are reported. Complexes 2−4 have been employed as catalysts for transfer hydrogenation reactions from 2-propanol to a number of unsaturated substrates and their activity compared with that of the related cationic iridium(I) species [Ir(cod)(py)(SIMes)]PF6 (1), [Ir(cod)(py)(PCy3)]PF6 (5), and complexes formed in situ from [Ir(cod)(py)2]PF6 and diazabutadienes (RNCHCHNR, DAB-R; R = cyclohexyl, DAB-Cy; R = 2,4,6-trimethylphenyl, DAB-Mes; R = adamantyl, DAB-Ad; R = 2,4,6-trimethoxyphenyl, DAB-trimethoxyphenyl). All complexes tested were found to be active catalysts for transfer hydrogenation of ketones, with complex 4 displaying the highest activity. Complex 4 also exhibits moderate activity toward simple olefins and an aromatic nitro co...
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influence of sterically demanding carbene ligation on catalytic behavior and thermal stability of ruthenium olefin metathesis catalysts
Organometallics, 1999Co-Authors: Jinkun Huang, Hans-joerg Schanz, Edwin D. Stevens, Steven P. NolanAbstract:The exchange reaction of one phosphine ligand in Cl2(PCy3)2RuCHPh (1; Cy = cyclohexyl, C6H11) with the sterically demanding carbene ligands 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes), 1,3-bis(4-methylphenyl)imidazol-2-ylidene (ITol), and 1,3-bis(4-chlorophenyl)imidazol-2-ylidene (IpCl) leads to the isolation of the new complexes (PCy3)(IMes)Cl2RuCHPh (2), (PCy3)(ITol)Cl2RuCHPh (3), and (PCy3)(IpCl)Cl2RuCHPh (4). Similarly, one IMes ligand can be substituted for one PCyp3 ligand in Cl2(PCyp3)2RuCHCHC(CH3)2 (5; Cyp = cyclopentyl, C5H9) to produce (PCyp3)(IMes)Cl2RuCHPh (6) in high yield. X-ray structure analysis of 6 confirmed a near-square-pyramidal coordination sphere around the metal center. Improved catalytic properties and thermal stability are observed for 2 and 6 in comparison to the parent 1 and 5.
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(p-cymene)RuLCl2 (L = 1,3-Bis(2,4,6-trimethylphenyl)imidazol-2-ylidene and 1,3-Bis(2,6-diisopropylphenyl)imidazol-2-ylidene) and Related Complexes as Ring Closing Metathesis Catalysts
Organometallics, 1999Co-Authors: Laleh Jafarpour, Jinkun Huang, Edwin D. Stevens, Steven P. NolanAbstract:Complexes of (η6-arene)ruthenium bearing the carbene ligand 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) and 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) Ru(IMes)(Cl)2(η6-arene), Ru(IPr)(Cl)2(η6-arene), and [RuCCCPh2(IMes)(Cl)(η6-arene)]PF6 were prepared and found to be efficient catalyst precursors for ring closing olefin metathesis.
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Indenylidene−Imidazolylidene Complexes of Ruthenium as Ring-Closing Metathesis Catalysts
Organometallics, 1999Co-Authors: Laleh Jafarpour, Hans-joerg Schanz, Edwin D. Stevens, Steven P. NolanAbstract:The indenylidene−imidazolylidene complexes of ruthenium (IMes)(PR3)Cl2Ru(3-phenylindenylid-1-ene) and (IPr)(PR3)Cl2Ru(3-phenylindenylid-1-ene) (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, and R= Ph, Cy) were prepared and found to be efficient catalyst precursors for ring-closing metathesis.
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Stereoelectronic Effects Characterizing Nucleophilic Carbene Ligands Bound to the Cp*RuCl (Cp* = η5-C5Me5) Moiety: A Structural and Thermochemical Investigation
Organometallics, 1999Co-Authors: Jinkun Huang, Hans-joerg Schanz, Edwin D. Stevens, Steven P. NolanAbstract:The reaction of [Cp*RuCl]4 (1) with carbene ligands affords unsaturated Cp*Ru(L)Cl [Cp* = η5-C5Me5; L = 1,3-R2-imidazol-2-ylidene [R = cyclohexyl (ICy, 2); 4-methylphenyl (ITol, 3); 4-chlorophenyl (IpCl, 4); adamantyl (IAd, 5)] and 4,5-dichloro-1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMesCl, 6)] complexes 2−6 in high yield. Solution calorimetric investigations of this series provides a measure of the electron donor properties of all ligands, and comparisons are made with IMes [1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] and the widely used PCy3. Structural information from single X-ray studies for complexes 2, 3, 5, 6, Cp*Ru(IMes)Cl (7), Cp*Ru(PCy3)Cl (8), and Cp*Ru(PiPr3)Cl (9) permits a quantitative treatment of steric parameters associated with these ligands.
Pedro Valerga - One of the best experts on this subject based on the ideXlab platform.
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Ruthenium(II) Picolyl-NHC Complexes: Synthesis, Characterization, and Catalytic Activity in Amine N-alkylation and Transfer Hydrogenation Reactions
Organometallics, 2012Co-Authors: Francys E. Fernández, M. Carmen Puerta, Pedro ValergaAbstract:Ruthenium(II) p-cymene complexes with picolyl-functionalized N-heterocyclic carbenes [(η6-p-cymene)Ru(L)(Cl)][PF6] (L = 3-methyl-1-(2-picolyl)imidazol-2-ylidene (1a), 3-isopropyl-1-(2-picolyl)imidazol-2-ylidene (1b), 3,4,5-trimethyl-1-(2-picolyl)imidazol-2-ylidene (1c), 3-mesityl-1-(2-picolyl)imidazol-2-ylidene (1d), 3-methyl-1-(2-picolyl)benzoimidazol-2-ylidene (1e), 3-methyl-1-(2-picolyl)-4,5-dichloroimidazol-2-ylidene (1f), 3-phenyl-1-(2-picolyl)imidazol-2-ylidene (1g)) have been synthesized and characterized. Compounds 1a–g were recrystallized, and X-ray crystal structures are reported for 1a,f. Furthermore, compounds 1a–f show catalytic activity in transfer hydrogenation of ketones and N-alkylation of amines. Notably, complexes 1a,c,f were found to be very efficient and versatile catalysts toward transfer hydrogenation of a wide range of ketones and imines in addition to N-alkylation of several amines.
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Half-Sandwich Ruthenium(II) Picolyl-NHC Complexes: Synthesis, Characterization, and Catalytic Activity in Transfer Hydrogenation Reactions
Organometallics, 2011Co-Authors: Francys E. Fernández, M. Carmen Puerta, Pedro ValergaAbstract:Pentamethylcyclopentadienyl ruthenium(II) complexes with picolyl-functionalized N-heterocyclic carbenes [(η5-C5Me5)Ru(L)(CH3CN)][PF6] (L = 3-methyl-1-(2-picolyl)imidazol-2-ylidene (1a), 3-isopropyl-1-(2-picolyl)imidazol-2-ylidene (1b), 3-phenyl-1-(2-picolyl)imidazol-2-ylidene (1c), 3-mesityl-1-(2-picolyl)imidazol-2-ylidene (1d), 3-methyl-1-(2-picolyl)benzoimidazol-2-ylidene (1e), 3-methyl-1-(2-picolyl)-4,5-dichloroimidazol-2-ylidene (1f)) have been synthesized and characterized. Compounds 1a,b were recrystallized as BAr4F salts (anion BAr4F– = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate), giving 2a,b. X-ray crystal structures of the acetonitrile adduct 2a and the dioxygen compound 2b are also reported. Furthermore, carbonyl derivatives 3a–f have been prepared, characterized, and used to study the donor properties of the picolylcarbene ligands (L) via infrared spectroscopy. Compounds 1a–f show catalytic activity in transfer hydrogenation of ketones. Notably, complex 1a was found to be a very efficient a...
