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Friedrich A, Pahl J, Eyselein J, Langer J, van Eikema Hommes N, Görling A, Harder S. Magnesium-halobenzene bonding: mapping the halogen sigma-hole with a Lewis-acidic complex. Chem Sci 2020; 12:2410-2418. [PMID: 34164006 PMCID: PMC8179342 DOI: 10.1039/d0sc06321e] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Complexes of the Lewis base-free cations (MeBDI)Mg+ and ( tBuBDI)Mg+ with Ph-X ligands (X = F, Cl, Br, I) have been studied (MeBDI = HC[C(Me)N-DIPP]2 and tBuBDI = HC[C(tBu)N-DIPP]2; DIPP = 2,6-diisopropylphenyl). For the smaller β-diketiminate ligand (MeBDI) only complexes with PhF could be isolated. Heavier Ph-X ligands could not compete with bonding of Mg to the weakly coordinating anion B(C6F5)4 -. For the cations with the bulkier tBuBDI ligand, the full series of halobenzene complexes was structurally characterized. Crystal structures show that the Mg⋯X-Ph angle strongly decreases with the size of X: F 139.1°, Cl 101.4°, Br 97.7°, I 95.1°. This trend, which is supported by DFT calculations, can be explained with the σ-hole which increases from F to I. Charge calculation and Atoms-In-Molecules analyses show that Mg⋯F-Ph bonding originates from electrostatic attraction between Mg2+ and the very polar C δ+-F δ- bond. For the heavier halobenzenes, polarization of the halogen atom becomes increasingly important (Cl < Br < I). Complexation with Mg leads in all cases to significant Ph-X bond activation and elongation. This unusual coordination of halogenated species to early main group metals is therefore relevant to C-X bond breaking.
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Affiliation(s)
- Alexander Friedrich
- Inorganic and Organometallic Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg Egerlandstraße 1 91058 Erlangen Germany
| | - Jürgen Pahl
- Inorganic and Organometallic Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg Egerlandstraße 1 91058 Erlangen Germany
| | - Jonathan Eyselein
- Inorganic and Organometallic Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg Egerlandstraße 1 91058 Erlangen Germany
| | - Jens Langer
- Inorganic and Organometallic Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg Egerlandstraße 1 91058 Erlangen Germany
| | - Nico van Eikema Hommes
- Computer Chemistry Center, Friedrich-Alexander-Universität Erlangen-Nürnberg Nägelsbachstraße 25 91052 Erlangen Germany.,Theoretical Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg Egerlandstraße 3 91058 Erlangen Germany
| | - Andreas Görling
- Theoretical Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg Egerlandstraße 3 91058 Erlangen Germany
| | - Sjoerd Harder
- Inorganic and Organometallic Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg Egerlandstraße 1 91058 Erlangen Germany
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Friedrich A, Pahl J, Elsen H, Harder S. Bulky cationic β-diketiminate magnesium complexes. Dalton Trans 2019; 48:5560-5568. [PMID: 30566138 DOI: 10.1039/c8dt03576h] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Cationic β-diketiminate Mg complexes with the bulky tBuBDI ligand and the weakly coordinating anion B(C6F5)4- have been prepared by the reaction of (tBuBDI)MgnBu with [Ph3C]+[B(C6F5)4]-; tBuBDI = CH[C(tBu)N-Dipp]2 and Dipp = 2,6-diisopropylphenyl. Their structures are compared to the previously reported cationic (MeBDI)Mg+ complexes; MeBDI = CH[C(Me)N-Dipp]2. Crystallization of [(tBuBDI)Mg]+[B(C6F5)4]- from chlorobenzene gave a unique (tBuBDI)Mg+·ClC6H5 cation with a rather short MgCl and consequently long C-Cl bond. Crystallization from chlorobenzene/arene solvent mixtures gave (tBuBDI)Mg+·arene complexes (arene = benzene, toluene, m-xylene) but in the presence of mesitylene the chlorobenzene complex was formed. Due to the greater shielding of the metal, none of these complexes display Mg(F5C6)4B- interactions. Crystal structures of the arene complexes show in all cases η2-coordination of the arene ligands. Ring slippage from a more favorable η2-coordination can be explained by the steric bulk of the tBuBDI ligand. The smaller arenes, benzene and toluene, also bind to (tBuBDI)Mg+ in bromobenzene solution. The Lewis acidity of these cationic Mg complexes was determined by the Gutmann-Beckett test. The acceptor number for (tBuBDI)Mg+ (AN = 76.0) is substantially higher than that estimated for (MeBDI)Mg+ (AN = 70.3). Calculation of the atomic NPA charges by DFT shows that the Mg2+ ion in (tBuBDI)Mg+ is slightly more positively charged than the metal in (MeBDI)Mg+, confirming its higher Lewis acidity. The lower benzene complexation energy calculated for (tBuBDI)Mg+versus (MeBDI)Mg+ is due to steric congestion of the metal in the (tBuBDI)Mg+ cation which allows only for Mg(η1)C6H6 instead of Mg(η6)C6H6 bonding. This ring slippage, however, results in a significant polarization of the electron density in the benzene ring, making it susceptible for nucleophilic attack.
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Affiliation(s)
- Alexander Friedrich
- Inorganic and Organometallic Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstraße 1, 91058 Erlangen, Germany.
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Ligand acidity constants as calculated by density functional theory for PF3 and N-Heterocyclic carbene ligands in hydride complexes of Iron(II). J Organomet Chem 2019. [DOI: 10.1016/j.jorganchem.2018.10.024] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Morris RH. Mechanisms of the H2- and transfer hydrogenation of polar bonds catalyzed by iron group hydrides. Dalton Trans 2018; 47:10809-10826. [DOI: 10.1039/c8dt01804a] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
This Perspective describes the mechanism-based development of iron-group catalysts for the asymmetric hydrogenation of ketones and imines.
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Abstract
Transition metal hydride complexes are usually amphoteric, not only acting as hydride donors, but also as Brønsted-Lowry acids. A simple additive ligand acidity constant equation (LAC for short) allows the estimation of the acid dissociation constant Ka(LAC) of diamagnetic transition metal hydride and dihydrogen complexes. It is remarkably successful in systematizing diverse reports of over 450 reactions of acids with metal complexes and bases with metal hydrides and dihydrogen complexes, including catalytic cycles where these reactions are proposed or observed. There are links between pKa(LAC) and pKa(THF), pKa(DCM), pKa(MeCN) for neutral and cationic acids. For the groups from chromium to nickel, tables are provided that order the acidity of metal hydride and dihydrogen complexes from most acidic (pKa(LAC) -18) to least acidic (pKa(LAC) 50). Figures are constructed showing metal acids above the solvent pKa scales and organic acids below to summarize a large amount of information. Acid-base features are analyzed for catalysts from chromium to gold for ionic hydrogenations, bifunctional catalysts for hydrogen oxidation and evolution electrocatalysis, H/D exchange, olefin hydrogenation and isomerization, hydrogenation of ketones, aldehydes, imines, and carbon dioxide, hydrogenases and their model complexes, and palladium catalysts with hydride intermediates.
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Affiliation(s)
- Robert H Morris
- Department of Chemistry, University of Toronto , 80 Saint George Street, Toronto, Ontario M5S 3H6, Canada
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Ren P, Pike SD, Pernik I, Weller AS, Willis MC. Rh–POP Pincer Xantphos Complexes for C–S and C–H Activation. Implications for Carbothiolation Catalysis. Organometallics 2015. [DOI: 10.1021/om500984y] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- Peng Ren
- Department of Chemistry,
Chemistry Research Laboratories, Mansfield Road, University of Oxford, Oxford, OX1 3TA, U.K
| | - Sebastian D. Pike
- Department of Chemistry,
Chemistry Research Laboratories, Mansfield Road, University of Oxford, Oxford, OX1 3TA, U.K
| | - Indrek Pernik
- Department of Chemistry,
Chemistry Research Laboratories, Mansfield Road, University of Oxford, Oxford, OX1 3TA, U.K
| | - Andrew S. Weller
- Department of Chemistry,
Chemistry Research Laboratories, Mansfield Road, University of Oxford, Oxford, OX1 3TA, U.K
| | - Michael C. Willis
- Department of Chemistry,
Chemistry Research Laboratories, Mansfield Road, University of Oxford, Oxford, OX1 3TA, U.K
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Chakraborty S, Blacque O, Fox T, Berke H. Hydrogenation of Imines Catalyzed by Trisphosphine-Substituted Molybdenum and Tungsten Nitrosyl Hydrides and Co-Catalytic Acid. Chem Asian J 2014; 9:2896-907. [DOI: 10.1002/asia.201402280] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2014] [Indexed: 11/10/2022]
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Hopmann KH, Bayer A. Enantioselective imine hydrogenation with iridium-catalysts: Reactions, mechanisms and stereocontrol. Coord Chem Rev 2014. [DOI: 10.1016/j.ccr.2014.01.023] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Landwehr A, Dudle B, Fox T, Blacque O, Berke H. Bifunctional Rhenium Complexes for the Catalytic Transfer-Hydrogenation Reactions of Ketones and Imines. Chemistry 2012; 18:5701-14. [DOI: 10.1002/chem.201103685] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2011] [Indexed: 12/20/2022]
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Mejía E, Togni A. Rhenium Complexes Containing the Chiral Tridentate Ferrocenyl Ligand Pigiphos. Organometallics 2011. [DOI: 10.1021/om200621y] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Esteban Mejía
- Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Antonio Togni
- Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, ETH Zürich, CH-8093 Zürich, Switzerland
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Xu BH, Kehr G, Fröhlich R, Grimme S, Erker G. Reaction of Aminodihydropentalenes with HB(C6F5)2: The Crucial Role of Dihydrogen Elimination. J Am Chem Soc 2011; 133:3480-91. [DOI: 10.1021/ja1092369] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Bao-Hua Xu
- Organisch-Chemisches Institut der Universität Münster, Corrensstrasse 40, 48149 Münster, Germany
| | - Gerald Kehr
- Organisch-Chemisches Institut der Universität Münster, Corrensstrasse 40, 48149 Münster, Germany
| | - Roland Fröhlich
- Organisch-Chemisches Institut der Universität Münster, Corrensstrasse 40, 48149 Münster, Germany
| | - Stefan Grimme
- Organisch-Chemisches Institut der Universität Münster, Corrensstrasse 40, 48149 Münster, Germany
| | - Gerhard Erker
- Organisch-Chemisches Institut der Universität Münster, Corrensstrasse 40, 48149 Münster, Germany
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Kuninobu Y, Nakahara T, Yu P, Takai K. Rhenium-catalyzed insertion of terminal alkenes into a C(sp2)–H bond and successive transfer hydrogenation. J Organomet Chem 2011. [DOI: 10.1016/j.jorganchem.2010.09.064] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Dybov A, Blacque O, Berke H. Molybdenum Nitrosyl Complexes and Their Application in Catalytic Imine Hydrogenation Reactions. Eur J Inorg Chem 2010. [DOI: 10.1002/ejic.201000973] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Bolaño S, Bravo J, Castro J, García-Fontán S, Marín MC. Synthesis and Characterization of New Chlorocarbonylrhenium(I) Complexes with P-Donor Chelate Ligands. Z Anorg Allg Chem 2010. [DOI: 10.1002/zaac.200900390] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Tao J, Li S. Theoretical study on the mechanism of H2activation mediated by two transition metal thiolate complexes: Homolytic for Ir, heterolytic for Rh. Dalton Trans 2010; 39:857-63. [DOI: 10.1039/b910589a] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Liu L, Bi S, Sun M, Yuan X, Zheng N, Li P. Mechanistic investigation on hydrogenation and hydrosilylation of ethylene catalyzed by rhenium nitrosyl complex. J Organomet Chem 2009. [DOI: 10.1016/j.jorganchem.2009.05.038] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Jiang Y, Blacque O, Fox T, Frech CM, Berke H. From Alkynes to Carbenes Mediated by [Re(Br)(H)(NO)(PR3)2] (R = Cy, iPr) Complexes. Organometallics 2009. [DOI: 10.1021/om900459x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Yanfeng Jiang
- Anorganisch-Chemisches Institut, Universität Zürich, Winterthurerstrasse 190, CH-8037, Zürich, Switzerland
| | - Olivier Blacque
- Anorganisch-Chemisches Institut, Universität Zürich, Winterthurerstrasse 190, CH-8037, Zürich, Switzerland
| | - Thomas Fox
- Anorganisch-Chemisches Institut, Universität Zürich, Winterthurerstrasse 190, CH-8037, Zürich, Switzerland
| | - Christian M. Frech
- Anorganisch-Chemisches Institut, Universität Zürich, Winterthurerstrasse 190, CH-8037, Zürich, Switzerland
| | - Heinz Berke
- Anorganisch-Chemisches Institut, Universität Zürich, Winterthurerstrasse 190, CH-8037, Zürich, Switzerland
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Bolaño S, Bravo J, Castro J, García-Fontán S, Marín MC. Synthesis, characterization and crystal structure of fac-[Re(H2O)(CO)3{Ph2PO(CH2)3OPPh2}]BArF. INORG CHEM COMMUN 2008. [DOI: 10.1016/j.inoche.2008.05.032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Choualeb A, Maccaroni E, Blacque O, Schmalle HW, Berke H. Rhenium Nitrosyl Complexes for Hydrogenations and Hydrosilylations. Organometallics 2008. [DOI: 10.1021/om7011024] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- A. Choualeb
- Anorganisch-Chemisches Institut Universität Zürich, Winterthurerstrasse 190, CH-8057, Switzerland
| | - E. Maccaroni
- Anorganisch-Chemisches Institut Universität Zürich, Winterthurerstrasse 190, CH-8057, Switzerland
| | - O. Blacque
- Anorganisch-Chemisches Institut Universität Zürich, Winterthurerstrasse 190, CH-8057, Switzerland
| | - H. W. Schmalle
- Anorganisch-Chemisches Institut Universität Zürich, Winterthurerstrasse 190, CH-8057, Switzerland
| | - H. Berke
- Anorganisch-Chemisches Institut Universität Zürich, Winterthurerstrasse 190, CH-8057, Switzerland
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Wu JY, Thanasekaran P, Cheng YW, Lee CC, Manimaran B, Rajendran T, Liao RT, Lee GH, Peng SM, Lu KL. Unprecedented Reduction of 2,2′-Bipyrimidine in a One-Pot Synthesis of Neutral Rhenium(I)-Based Molecular Rectangles. Organometallics 2008. [DOI: 10.1021/om700873x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- Jing-Yun Wu
- Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan, and Department of Chemistry, National Taiwan University, Taipei 106, Taiwan
| | - P. Thanasekaran
- Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan, and Department of Chemistry, National Taiwan University, Taipei 106, Taiwan
| | - Yi-Wei Cheng
- Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan, and Department of Chemistry, National Taiwan University, Taipei 106, Taiwan
| | - Chung-Chou Lee
- Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan, and Department of Chemistry, National Taiwan University, Taipei 106, Taiwan
| | - B. Manimaran
- Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan, and Department of Chemistry, National Taiwan University, Taipei 106, Taiwan
| | - T. Rajendran
- Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan, and Department of Chemistry, National Taiwan University, Taipei 106, Taiwan
| | - Rong-Tang Liao
- Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan, and Department of Chemistry, National Taiwan University, Taipei 106, Taiwan
| | - Gene-Hsiang Lee
- Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan, and Department of Chemistry, National Taiwan University, Taipei 106, Taiwan
| | - Shie-Ming Peng
- Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan, and Department of Chemistry, National Taiwan University, Taipei 106, Taiwan
| | - Kuang-Lieh Lu
- Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan, and Department of Chemistry, National Taiwan University, Taipei 106, Taiwan
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Martín M, Sola E, Tejero S, Andrés JL, Oro LA. Mechanistic Investigations of Imine Hydrogenation Catalyzed by Cationic Iridium Complexes. Chemistry 2006; 12:4043-56. [PMID: 16534823 DOI: 10.1002/chem.200501230] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Complexes [IrH2(eta6-C6H6)(PiPr3)]BF4 (1) and [IrH2(NCMe)3(PiPr3)]BF4 (2) are catalyst precursors for homogeneous hydrogenation of N-benzylideneaniline under mild conditions. Precursor 1 generates the resting state [IrH2{eta5-(C6H5)NHCH2Ph}(PiPr3)]BF4 (3), while 2 gives rise to a mixture of [IrH{PhN=CH(C6H4)-kappaN,C}(NCMe)2(PiPr3)]BF4 (4) and [IrH{PhN=CH(C6H4)-kappaN,C}(NCMe)(NH2Ph)(PiPr3)]BF4 (5), in which the aniline ligand is derived from hydrolysis of the imine. The less hindered benzophenone imine forms the catalytically inactive, doubly cyclometalated compound [Ir{HN=CPh(C6H4)-kappaN,C}2(NH2CHPh2)(PiPr3)]BF4 (6). Hydrogenations with precursor 1 are fast and their reaction profiles are strongly dependent on solvent, concentrations, and temperature. Significant induction periods, minimized by addition of the amine hydrogenation product, are commonly observed. The catalytic rate law (THF) is rate = k[1][PhN=CHPh]p(H2). The results of selected stoichiometric reactions of potential catalytic intermediates exclude participation of the cyclometalated compounds [IrH{PhN=CH(C6H4)-kappaN,C}(S)2(PiPr3)]BF4 [S = acetonitrile (4), [D6]acetone (7), [D4]methanol (8)] in catalysis. Reactions between resting state 3 and D2 reveal a selective sequence of deuterium incorporation into the complex which is accelerated by the amine product. Hydrogen bonding among the components of the catalytic reaction was examined by MP2 calculations on model compounds. The calculations allow formulation of an ionic, outer-sphere, bifunctional hydrogenation mechanism comprising 1) amine-assisted oxidative addition of H2 to 3, the result of which is equivalent to heterolytic splitting of dihydrogen, 2) replacement of a hydrogen-bonded amine by imine, and 3) simultaneous H delta+/H delta- transfer to the imine substrate from the NH moiety of an arene-coordinated amine ligand and the metal, respectively.
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Affiliation(s)
- Marta Martín
- Departamento de Compuestos de Coordinación y Catálisis Homogénea, Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-CSIC and Instituto Universitario de Catálisis Homogénea, Universidad de Zaragoza, 50009 Zaragoza, Spain
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Martín M, Sola E, Tejero S, López JA, Oro LA. Mechanistic Investigations of Imine Hydrogenation Catalyzed by Dinuclear Iridium Complexes. Chemistry 2006; 12:4057-68. [PMID: 16534824 DOI: 10.1002/chem.200501231] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Treatment of [Ir2(mu-H)(mu-Pz)2H3(NCMe)(PiPr3)2] (1) with one equivalent of HBF4 or [PhNH=CHPh]BF4 affords efficient catalysts for the homogeneous hydrogenation of N-benzylideneaniline. The reaction of 1 with HBF4 leads to the trihydride-dihydrogen complex [Ir2(mu-H)(mu-Pz)2H2(eta2-H2)(NCMe)(PiPr3)2]BF4 (2), which has been characterized by NMR spectroscopy and DFT calculations on a model complex. Complex 2 reacts with imines such as tBuN=CHPh or PhN=CHPh to afford amine complexes [Ir2(mu-H)(mu-Pz)2H2(NCMe){L}(PiPr3)2]BF4 (L = NH(tBu)CH2Ph, 3; NH(Ph)CH2Ph, 4) through a sequence of proton- and hydride-transfer steps. Dihydrogen partially displaces the amine ligand of 4 to form 2; this complements a possible catalytic cycle for the N-benzylideneaniline hydrogenation in which the amine-by-dihydrogen substitution is the turnover-determining step. The rates of ligand substitution in 4 and its analogues with labile ligands other than amine are dependent upon the nature of the leaving ligand and independent on the incoming ligand concentration, in agreement with dissociative substitutions. Water complex [Ir2(mu-H)(mu-Pz)2H2(NCMe)(OH2)(PiPr3)2]BF4 (7) hydrolyzes N-benzylideneaniline, which eventually affords the poor hydrogenation catalyst [Ir2(mu-H)(mu-Pz)2H2(NCMe)(NH2Ph)(PiPr3)2]BF4 (11). The rate law for the catalytic hydrogenation in 1,2-dichloroethane with complex [Ir2(mu-H)(mu-Pz)2H2(OSO2CF3)(NCMe)(PiPr3)2] (8) as catalyst precursor is rate = k[8]{p(H2)}; this is in agreement with the catalytic cycle deduced from the stochiometric experiments. The hydrogenation reaction takes place at a single iridium center of the dinuclear catalyst, although ligand modifications at the neighboring iridium center provoke changes in the hydrogenation rate. Even though this catalyst system is also capable of effectively hydrogenating alkenes, N-benzylideneaniline can be selectively hydrogenated in the presence of simple alkenes.
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Affiliation(s)
- Marta Martín
- Departamento de Compuestos de Coordinación y Catálisis Homogénea, Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-CSIC and Instituto Universitario de Catálisis Homogénea, Universidad de Zaragoza, 50009 Zaragoza, Spain
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Babushkin DE, Naundorf C, Brintzinger HH. Distinct methylalumoxane(MAO)-derived Me–MAO−anions in contact with a zirconocenium cation—a13C-NMR study. Dalton Trans 2006:4539-44. [PMID: 17016564 DOI: 10.1039/b611028m] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Zirconocenium cations of the type [(MeC5H4)2ZrMe]+, formed by excess methylalumoxane (MAO) from (MeC5H4)2ZrCl2 or (MeC5H4)2ZrMe2 with 13C-labelled ring ligands, are found to form ion pairs with two types of anions, Me-MAO(A)- and Me-MAO(B)-, which differ in their coordinative strengths: More strongly coherent ion pairs [(MeC5H4)2ZrMe+...Me-MAO(B)-] are converted to more easily separable ion pairs [(MeC5H4)2ZrMe+...Me-MAO(A)-] by a sufficient excess of MAO. These react with Al2Me6 to form outer-sphere ion pairs containing the cationic AlMe3 adduct [(MeC5H4)2Zr(mu-Me)2AlMe2]+; formation of the more easily separable ion pairs might be required also for polymerisation catalysis.
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Affiliation(s)
- Dmitrii E Babushkin
- Boreskov Institute of Catalysis, Russian Academy of Science, RU-630090, Novosibirsk, Russia.
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