- Alkoxydiaminophosphine Ligands as Surrogates of NHCs in Copper Catalysis
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A family of phosphine ligands containing a five-membered ring similar to the popular N-heterocyclic carbene ligands and an alkoxy third substituent has been developed. These alkoxydiaminophosphine ligands (ADAP) can be generated in one pot and reacted with a copper(I) source leading to the high yield isolation of complexes [(ADAP)CuX]2 (X=Cl, Br). The dinuclear nature of these compounds has been established by means of X-ray studies and DOSY experiments. A screening of the catalytic properties of these complexes toward carbene-transfer reactions from diazocompounds to C?H bonds (alkane, arene), olefins or N?H bonds, as well as in CuAAC or nitrene transfer reactions have shown a performance at least similar, if not better, than their (NHC)CuCl analogues, opening a new window in copper catalysis with these readily tunable ADAP ligands.
- Pizarro, Juan Diego,Molina, Francisco,Fructos, Manuel R.,Pérez, Pedro J.
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supporting information
p. 10330 - 10335
(2020/07/24)
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- Mechanism of the Selective Fe-Catalyzed Arene Carbon-Hydrogen Bond Functionalization
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The complete chemoselective functionalization of aromatic C(sp2)-H bonds of benzene and alkyl benzenes by carbene insertion from ethyl diazoacetate was unknown until the recent discovery of an iron-based catalytic system toward such transformation. A Fe(II) complex bearing the pytacn ligand (pytacn = L1 = 1-(2-pyridylmethyl)-4,7-dimethyl-1,4,7-triazacyclononane) transferred the CHCO2Et unit exclusively to the C(sp2)-H bond. The cycloheptatriene compound commonly observed through Buchner reaction or, when employing alkyl benzenes, the corresponding derivatives from C(sp3)-H functionalization are not formed. We herein present a combined experimental and computational mechanistic study to explain this exceptional selectivity. Our computational study reveals that the key step is the formation of an enol-like substrate, which is the precursor of the final insertion products. Experimental evidences based on substrate probes and isotopic labeling experiments in favor of this mechanistic interpretation are provided.
- Postils, Verònica,Rodríguez, Mònica,Sabenya, Gerard,Conde, Ana,Díaz-Requejo, M. Mar,Pérez, Pedro J.,Costas, Miquel,Solà, Miquel,Luis, Josep M.
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p. 4313 - 4322
(2018/05/22)
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- Mechanistic studies on gold-catalyzed direct arene c-h bond functionalization by carbene insertion: The coinage-metal effect
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The catalytic functionalization of the Csp2-H bond of benzene by means of the insertion of the CHCO2Et group from ethyl diazoacetate (N2= CHCO2Et) has been studied with the series of coinage-metal complexes IPrMCl (IPr = 1,3-bis- (diisopropylphenyl)imidazol-2-ylidene) and NaBArF 4 (BArF 4 = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate). For Cu and Ag, these examples constitute the first use of such metals toward this transformation, which also provides ethyl cyclohepta-2,4,6-trienecarboxylate as a byproduct from the so-called Buchner reaction. In the case of methyl-substituted benzenes, the reaction exclusively proceeds onto the aromatic ring, the Csp3-H bond remaining unreacted. A significant coinage-metal effect has been observed, since the gold catalyst favors the formation of the insertion product into the Csp2-H bond whereas copper and silver preferentially induce the formation of the cycloheptatriene derivative. Experimental studies and theoretical calculations have explained the observed selectivity in terms of the formation of a common Wheland intermediate, resembling an electrophilic aromatic substitution, from which the reaction pathway evolves into two separate routes to each product.
- Fructos, Manuel R.,Besora, Maria,Braga, Ataualpa A. C,Díaz-Requejo, M. Mar,Maseras, Feliu,Perez, Pedro J.
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p. 172 - 179
(2017/04/04)
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- Synthesis and catalytic applications of 1,2,3-triazolylidene gold(i) complexes in silver-free oxazoline syntheses and C-H bond activation
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A series of novel 1,2,3-triazolylidene gold(i) chloride complexes have been synthesised and fully characterised. Silver-free methodologies for chloride ion abstraction of these complexes were evaluated for their potential as Au-based catalyst precursors. Using simple potassium salts or MeOTf as chloride scavengers produced metal complexes that catalyse both the regioselective synthesis of oxazolines and the C-H activation of benzene or styrene for carbene transfer from ethyl diazoacetate. These results indicate that Ag-free activation of 1,2,3-triazolylidene gold(i) chloride complexes is feasible for the generation of catalytically active Au triazolylidene species. However, silver-mediated activation imparts substantially higher catalytic activity in oxazoline synthesis.
- Pretorius, René,Fructos, Manuel R.,Müller-Bunz, Helge,Gossage, Robert A.,Pérez, Pedro J.,Albrecht, Martin
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p. 14591 - 14602
(2016/09/28)
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- Iron and manganese catalysts for the selective functionalization of arene C(sp2)-H bonds by carbene insertion
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The first examples of the direct functionalization of non-activated aryl sp2 C-H bonds with ethyl diazoacetate (N2CHCO2Et) catalyzed by Mn- or Fe-based complexes in a completely selective manner are reported, with no formation of the frequently observed cycloheptatriene derivatives through competing Buchner reaction. The best catalysts are FeII or MnII complexes bearing the tetradentate pytacn ligand (pytacn= 1-(2-pyridylmethyl)-4,7-dimethyl-1,4,7-triazacyclononane). When using alkylbenzenes, the alkylic C(sp3)-H bonds of the substituents remained unmodified, thus the reaction being also selective toward functionalization of sp2 C-H bonds. Exclusive catalysis: Iron- and-manganese-based catalysts selectively functionalize the C(sp2)-H bonds of benzene or alkylbenzenes through the formal insertion of the CHCO2Et group from N2CHCO2Et (see scheme). When using alkylbenzenes, the alkylic C(sp3)-H bonds of the substituents remain unmodified.
- Conde, Ana,Sabenya, Gerard,Rodríguez, Mònica,Postils, Verònica,Luis, Josep M.,Díaz-Requejo, M. Mar,Costas, Miquel,Pérez, Pedro J.
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supporting information
p. 6530 - 6534
(2016/06/01)
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- N-Heterocyclic Carbene-Phosphinidene Complexes of the Coinage Metals
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Coinage metal complexes of the N-heterocyclic carbene-phosphinidene adduct IPr·PPh (IPr=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were prepared by its reaction with CuCl, AgCl, and [(Me2S)AuCl], which afforded the monometallic complexes [(IPr·PPh)MCl] (M=Cu, Ag, Au). The reaction with two equivalents of the metal halides gave bimetallic [(IPr·PPh)(MCl)2] (M=Cu, Au); the corresponding disilver complex could not be isolated. [(IPr·PPh)(CuOTf)2] was prepared by reaction with copper(I) trifluoromethanesulfonate. Treatment of [(IPr·PPh)(MCl)2] (M=Cu, Au) with Na(BArF) or AgSbF6 afforded the tetranuclear complexes [(IPr·PPh)2M4Cl2]X2 (X=BArF or SbF6), which contain unusual eight-membered M4Cl2P2 rings with short cuprophilic or aurophilic contacts along the chlorine-bridged M...M axes. Complete chloride abstraction from [(IPr·PPh)(AuCl)2] was achieved with two equivalents of AgSbF6 in the presence of tetrahydrothiophene (THT) to form [(IPr·PPh){Au(THT)}2][SbF6]2. The cationic tetra- and dinuclear complexes were used as catalysts for enyne cyclization and carbene transfer reactions.
- Doddi, Adinarayana,Bockfeld, Dirk,Nasr, Alexandre,Bannenberg, Thomas,Jones, Peter G.,Tamm, Matthias
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p. 16178 - 16189
(2015/11/03)
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- Catalytic hydrocarbon functionalization with gold complexes containing n-heterocyclic carbene ligands with pendant donor groups
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A series of silver and gold complexes bearing N-heterocyclic carbene ligands with a -CH2CO2Et pendant group attached to one N atom of the NHC ligand have been prepared. The catalytic properties of the gold complexes toward the decomposition of ethyl diazoacetate (N2CHCO 2Et) and the transfer of the carbene CHCO2Et group to benzene and hexane have been investigated. A somewhat different reaction outcome has been found for this family of gold catalysts compared with the parent IPrAuCl catalyst. Gold-based catalysts containing NHC ligands with potentially coordinating pendant groups have been tested in the functionalization of Caspa2-H and Caspa3-H bonds by carbene insertion from ethyl diazoacetate, showing moderate catalytic activity.
- Delgado-Rebollo, Manuela,Beltran, Aalvaro,Prieto, Auxiliadora,Mar Diaz-Requejo,Echavarren, Antonio M.,Perez, Pedro J.
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experimental part
p. 1380 - 1386
(2012/05/31)
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- Exclusive aromatic vs aliphatic C-H bond functionalization by carbene insertion with gold-based catalysts
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The direct functionalization of aromatic C-H bonds by carbene insertion from diazo compounds catalyzed by gold complexes with N-heterocyclic ligands is described. The reaction is completely selective toward the C sp2-H bonds, other C sp3-H bonds remaining unreacted. A study with several NHC ligands in Au(I) and Au(III) complexes has been performed. The potential application of this strategy to give profen derivatives has also been explored.
- Rivilla, Ivan,Gomez-Emeterio, B. Pilar,Fructos, Manuel R.,Diaz-Requejo, M. Mar,Perez, Pedro J.
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experimental part
p. 2855 - 2860
(2011/07/08)
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- Intermetallic coinage metal-catalyzed functionalization of alkanes with ethyl diazoacetate: Gold as a ligand
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The complexes [Au2M2(C6F5) 4(NCMe)2]n (M = Cu, 1; M = Ag, 2) have been tested as catalysts for the functionalization of alkanes by the carbene insertion methodology, using ethyl diazoacetate as the carbene source. Moderate to high conversions have been obtained. The observed selectivities seem to favor the proposal that the active metal for catalysis is the Cu/Ag center, the Au(C6F5)2 unit acting as a spectator ligand in both cases.
- Fuentes, M. ángeles,Rodríguez-Castillo, María,Monge, Miguel,Olmos, M. Elena,López-De-Luzuriaga, Jose M.,Caballero, Ana,Pérez, Pedro J.
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experimental part
p. 146 - 149
(2011/06/22)
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- Palladium(II) carboxylates and palladium(I) carbonyl carboxylate complexes as catalysts for olefin cyclopropanation with ethyl diazoacetate
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Palladium(I) carbonyl carboxylate complexes [Pd(μ-CO)(μ-RCO 2)]n (R = Me, n = 4; R = CMe3, n = 6) and the corresponding palladium(II) carboxylates (acetate and pivalate) catalyze the cyclopropanation of olefins with ethyl diazoacetate. The performance of these catalysts is similar in terms of selectivity and cyclopropane yields, regardless of the oxidation state of the metal center. However the rates of the cyclopropanation reactions are significantly higher for the acetate based catalysts than for the pivalate derivatives, which suggests that the main catalytic species are carboxylate containing palladium complexes. Kinetic measurements show that reaction rates are independent of the olefin concentration when these are 1-hexene or styrene, but norbornene exerts an inhibitory effect. In spite of this, competition experiments indicate that the cyclopropanation of styrene is 2.2 times as favorable as that of 1-hexene for any of the four catalysts. These observations indicate that while the rate-determining formation of the intermediate palladium carbenoid species is controlled by the catalyst structure, this is followed by a rapid and less specific cyclopropanation step that is not affected by the nature of the carboxylate groups present in the catalyst. An independent test using a 1:1 benzene/cyclohexane mixture of solvents showed that the transfer of ethoxycarbonylcarbene (:C(CO2Et)H) to these molecules is unselective (relative rate of benzene/cyclohexane functionalization ≈1.8, independent of the catalyst). This result can be interpreted as an indication of the involvement of free ethoxycarbonylcarbene in the carbene transfer step. The Royal Society of Chemistry 2009.
- Shishilov, Oleg N.,Stromnova, Tatiana A.,Campora, Juan,Palma, Pilar,Cartes, M. Angeles,Martinez-Prieto, Luis Miguel
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experimental part
p. 6626 - 6633
(2010/02/16)
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- A gold catalyst for carbene-transfer reactions from ethyl diazoacetate
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(Chemical Equation Presented) Approaching El Dorado: A gold catalyst has been discovered that transfers a carbene unit from ethyl diazoacetate to aromatic substrates (see scheme) as well as olefins, amines, and alcohols. The insertion of carbene units into the C-H bonds of the aromatic ring of benzene, toluene, and styrene is a novel reaction. R = H, CH3, CH=CH 2; IPr = 1,3-bis(diisopropylphenyl)imidazol-2-ylidene.
- Fructos, Manuel R.,Belderrain, Tomas R.,De Fremont, Pierre,Scott, Natalie M.,Nolan, Steven P.,Diaz-Requejo, M Mar,Perez, Pedro J.
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p. 5284 - 5288
(2007/10/03)
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- Cycloheptatrienyl Radicals: An EPR Study of Substituent Effects
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Cycloheptatrienyl radicals with donor and acceptor substituents were generated by hydrogen abstraction from the corresponding cycloheptatrienes and studied by EPR spectroscopy.The barrier to rotation about the C-1-C=O bond in ethoxycarbonylcycloheptatrienyl radicals was found to be ca.7.5 kcal mol-1 (31.4 kJ mol-1).The observed hyperfine splittings of the ring hydrogens were interpreted in terms of a model in which the substituent causes an energy separation ΔE between the frontier orbitals.Populations of the symmetric and antisymmetric orbitals were deduced, and ΔE values were estimated.A similar analysis was carried out from EPR data for substituted benzene radical anions.These energy separations show a linear correlation with Hammett constants.The ρ-values from plots of this type for annulene radicals decrease in magnitude as the size of the ring increases.
- MacCorquodale, Finlay,Walton, John C.
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p. 364 - 369
(2007/10/02)
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