An operationally simple protocol was designed for the enantioselective silane reduction (ESR) of ketones using air- and moisture-stable [Ir(OMe)(cod)] 2 (cod = 1,5-cyclooctadiene) ( 3 ) as a metal catalyst precursor. This reaction was driven by chiral hydroxyamide-functionalized azolium salt 2 . The catalytic ESR reaction could be performed under benchtop conditions at room temperature. Treatment of 2 with 3 in THF yielded the monodentate IrCl(NHC)(cod) (NHC = N -heterocyclic carbene) complex 4 in 93% yield, herein the anionic methoxy ligand of 3 serves as an internal base that deprotonates the azolium ring of 2 . The well-defined Ir complex 4 catalyzed the ESR reaction of propiophenone ( 6 ) with (EtO) 2 MeSiH using the pre-mixing reaction procedure. Based on this success, the catalytic ESR reaction was designed and implemented using an in situ -generated NHC/Ir catalyst derived from 2 and 3 . Thus, a wide variety of aryl ketones could be reduced to the corresponding optically active alcohols in moderate to excellent stereoselectivities at room temperature without temperature control. Since the high catalytic activity of 3 was observed, we next evaluated several other transition metal catalyst precursors for the catalytic ESR reaction under the influence of 2 . This evaluation revealed that Ir(acac)(cod) (acac = acetylacetonate) ( 28 ) and [IrCl(cod)] 2 ( 5 ) can be successfully used as metal catalyst precursors in the ESR reaction.
Wang, H.M.J. and Lin, I.J.B. (1998) Facile Synthesis of Silver(I)-Carbene Complexes. Useful Carbene Transfer Agents. Organometallics, 17, 972-975. https://doi.org/10.1021/om9709704
Garrison, J.C. and Youngs, W.J. (2005) Ag(I) N-Heterocyclic Carbene Complexes: Synthesis, Structure, and Application. Chemical Reviews, 105, 3978-4008. https://doi.org/10.1021/cr050004s
Chianese, A.R., Li, X., Janzen, M.C., Faller, J.W. and Crabtree, R.H. (2003) Rhodium and Iridium Complexes of N-Heterocyclic Carbenes via Transmetalation: Structure and Dynamics. Organometallics, 22, 1663-1667. https://doi.org/10.1021/om021029+
Mas-Marza, E., Poyatos, M., Sanaú, M. and Peris, E. (2004) Carbene Complexes of Rhodium and Iridium from Tripodal N-Heterocyclic Carbene Ligands: Synthesis and Catalytic Properties. Inorganic Chemistry, 43, 2213-2219. https://doi.org/10.1021/ic035317p
Wang, C.-Y., Fu, C.-F., Liu, Y.-H., Peng, S.-M. and Liu, S.-T. (2007) Synthesis of Iridium Pyridinyl N-Heterocyclic Carbene Complexes and Their Catalytic Activities on Reduction of Nitroarenes. Inorganic Chemistry, 46, 5779-5786. https://doi.org/10.1021/ic070330l
Zinner, S.C., Rentzsch, C.F., Herdtweck, E., Herrmann, W.A. and KüHn, F.E. (2009) N-Heterocyclic Carbenes of Iridium(I): Ligand Effects on the Catalytic Activity in Transfer Hydrogenation. Dalton Transactions, 35, 7055-7062. https://doi.org/10.1039/b906855d
Zhao, Q., Meng, G., Nolan, S.P. and Szostak, M. (2020) N-Heterocyclic Carbene Complexes in C-H Activation Reactions. Chemical Reviews, 120, 1981-2048. https://doi.org/10.1021/acs.chemrev.9b00634
Sipos, G. and Dorta, R. (2018) Iridium Complexes with Monodentate N-Heterocyclic Carbene Ligands. Coordination Chemistry Reviews, 375, 13-68. https://doi.org/10.1016/j.ccr.2017.10.019
Van Vuuren, E., Malan, F.P. and Landman, M. (2021) Multidentate NHC Complexes of Group IX Metals Featuring Carbon-Based Tethers: Synthesis and Applications. Coordination Chemistry Reviews, 430, Article ID: 213731. https://doi.org/10.1016/j.ccr.2020.213731
Herrmann, W.A., Baskakov, D., Herdtweck, E., Hoffmann, S.D., Bunlaksananusorn, T., Rampf, F. and Rodefeld, L. (2006) Chiral N-Heterocyclic Carbene Ligands Derived from 2,2’-Bipiperidine and Partially Reduced Biisoquinoline: Rhodium and Iridium Complexes in Asymmetric Catalysis. Organometallics, 25, 2449-2456. https://doi.org/10.1021/om060098b
Yoshida, K., Kamimura, T., Kuwabara, H. and Yanagisawa, A. (2015) Chiral Bicyclic NHC/Ir Complexes for Catalytic Asymmetric Transfer Hydrogenation of Ketones. Chemical Communications, 51, 15442-15445. https://doi.org/10.1039/C5CC05318H
Mukherje, N., Mondal, B., Saha, T.N. and Maity, R. (2022) Palladium, Iridium, and Rhodium Complexes Bearing Chiral N-Heterocyclic Carbene Ligands Applied in Asymmetric Catalysis. Applied Organometallic Chemistry, e6794. https://doi.org/10.1002/aoc.6794
Kawabata, S., Tokura, H., Chiyojima, H., Okamoto, M. and Sakaguchi, S. (2012) Asymmetric Hydrosilane Reduction of Ketones Catalyzed by an Iridium Complex Bearing a Hydroxyamide-Functionalized NHC Ligand. Advanced Synthesis & Catalysis, 354, 807-812. https://doi.org/10.1002/adsc.201100897
Shinohara, K., Kawabata, S., Nakamura, H., Manabe, Y. and Sakaguchi, S. (2014) Enantioselective Hydrosilylation of Ketones Catalyzed by a Readily Accessible N-Heterocyclic Carbene-Ir Complex at Room Temperature. European Journal of Organic Chemistry, 2014, 5532-5539. https://doi.org/10.1002/ejoc.201402279
Teramoto, H. and Sakaguchi, S. (2018) Enantioselective Catalytic Hydrosilylation of Propiophenone with a Simple Combination of a Cationic Iridium Complex and a Chiral Azolium Salt. Journal of Organometallic Chemistry, 875, 52-58. https://doi.org/10.1016/j.jorganchem.2018.09.001
Uson, R., Oro, L.A., Cabeza, J.A., Bryndza, H.E. and Stepro, M.P. (1985) Dinuclear Methoxy, Cyclooctadiene, and Barrelene Complexes of Rhodium(I) and Iridium(I). In: Kirschner, S., Ed., Inorganic Syntheses 23, Wiley-VCH, Weinheim, 126-130. https://doi.org/10.1002/9780470132548.ch25
JiméNez, M.V., FernáNdez-Tornos, J., PéRez-Torrente, J.J., Modrego, F.J., Winterle, S., Cunchillos, C., Lahoz, F.J. and Oro, L.A. (2011) Iridium(I) Complexes with Hemilabile N-Heterocyclic Carbenes: Efficient and Versatile Transfer Hydrogenation Catalysts. Organometallics, 30, 5493-5508. https://doi.org/10.1021/om200747k
Finn, M., Ridenour, J.A., Heltzel, J., Cahill, C. and Voutchkova-Kostal, A. (2018) Next-Generation Water-Soluble Homogeneous Catalysts for Conversion of Glycerol to Lactic Acid. Organometallics, 37, 1400-1409. https://doi.org/10.1021/acs.organomet.8b00081
Karataş, M.O., Alıcı, B., Passarelli, V., Özdemir, I., PÉRez-Torrent, J.J. and Castarlenas, R. (2021) Iridium(I) Complexes Bearing Hemilabile Coumarin Functionalised N-Heterocyclic Carbene Ligands with Application as Alkyne Hydrosilylation Catalysts. Dalton Transactions, 50, 11206-11215. https://doi.org/10.1039/D1DT01946E
Matsuki, T., Teramoto, H., Ichihara, R., Inui, K. and Sakaguchi, S. (2022) Asymmetric Silane Reduction of Ketones and β-Keto Esters Catalyzed by a Chiral Azolium/Iridium System in the Presence of a Base in Methanol at Room Temperature. Results in Chemistry, 4, Article ID: 100364. https://doi.org/10.1016/j.rechem.2022.100364
Enders, D. and Gielen, H. (2001) Synthesis of Chiral Triazolinylidene and Imidazolinylidene Transition Metal Complexes and First Application in Asymmetric Catalysis. Journal of Organometallic Chemistry, 617, 70-80. https://doi.org/10.1016/S0022-328X(00)00600-8
Enders, D., Gielen, H., Runsink, J., Breuer, K., Brode, S. and Boehn, K. (1998) Diastereoselective Synthesis of Chiral (Triazolinylidene)rhodium Complexes Containing an Axis of Chirality. European Journal of Inorganic Chemistry, 1998, 913-919. https://doi.org/10.1002/(SICI)1099-0682(199807)1998:7 3.0.CO;2-1
Zanardi, A., Peris, E. and Mata, J.A. (2008) Alkenyl-Functionalized NHC Iridium-Based Catalysts for Hydrosilylation. New Journal of Chemistry, 32, 120-126. https://doi.org/10.1039/B707280E
GüLcemal, S., Gökçe, A.G. and Çetinkaya, B. (2013) Iridium(I) N-Heterocyclic Carbene Complexes of Benzimidazol-2-Ylidene: Effect of Electron Donating Groups on the Catalytic Transfer Hydrogenation Reaction. Dalton Transactions, 42, 7305-7311. https://doi.org/10.1039/C2DT32482B
Mullick, A.B., Jeletic, A.S., Powers, A.R., Ghiviriga, I., Abboud, I.K.A. and Veige, A.S. (2013) Convenient in Situ Generation of a Chiral Bis-N-Heterocyclic Carbene Palladium Catalyst and Its Application in Enantioselective Synthesis. Polyhedron, 52, 810-819. https://doi.org/10.1016/j.poly.2012.07.046
Riener, K., Bitzer, M.J., PoThig, A., Raba, A., Cokoja, M., Herrmann, W.A. and KuHn, F.E. (2014) On the Concept of Hemilability: Insights into a Donor-Functionalized Iridium(I) NHC Motif and Its Impact on Reactivity. Inorganic Chemistry, 53, 12767-12777. https://doi.org/10.1021/ic5016324
Jeletic, M.S., Jan, M.T., Ghiviriga, I., Abboud, K.A. and Veige, A.S. (2009) New Iridium and Rhodium Chiral Di-N-Heterocyclic Carbene (NHC) Complexes and Their Application in Enantioselective Catalysis. Dalton Transactions, No. 15, 2764-2776. https://doi.org/10.1039/b819524b
Ortega-Lepe, I., Rossin, A., Sánchez, P., Santos, L.L., Rendón, N., Álvarez, E., López-Serrano, J. and Suárez, A. (2021) Ammonia-Borane Dehydrogenation Catalyzed by Dual-Mode Proton-Responsive Ir-CNNH Complexes. Inorganic Chemistry, 60, 18490-18502. https://doi.org/10.1021/acs.inorgchem.1c03056
Olmstead, W.N., Margolin, Z. and Bordwel, F.G. (1980) Acidities of Water and Simple Alcohols in Dimethyl Sulfoxide Solution. Journal of Organic Chemistry, 45, 3295-3299. https://doi.org/10.1021/jo01304a032
Olmstead, W.N. and Bordwel, F.G. (1980) Ion-Pair Association Constants in Dimethyl Sulfoxide. Journal of Organic Chemistry, 45, 3299-3305. https://doi.org/10.1021/jo01304a033
Bordwel, F.G. (1988) Equilibrium Acidities in Dimethyl Sulfoxide Solution. Accounts of Chemical Research, 21, 456-463. https://doi.org/10.1021/ar00156a004
Duan, W.-L., Shi, M. and Rong, G.-B. (2003) Synthesis of Novel Axially Chiral Rh-NHC Complexes Derived from BINAM and Application in the Enantioselective Hydrosilylation of Methyl Ketones. Chemical Communications, No. 23, 2916-2917. https://doi.org/10.1039/B309185F
Xu, Q., Gu, X., Liu, S., Dou, Q. and Shi, M. (2007) The Use of Chiral BINAM NHC-Rh(III) Complexes in Enantioselective Hydrosilylation of 3-Oxo-3-Arylpropionic Acid Methyl or Ethyl Esters. Journal of Organic Chemistry, 72, 2240-2242. https://doi.org/10.1021/jo062453d
Gade, L.H., CéSar, V. and Bellemin-Laponnaz, S. (2004) A Modular Assembly of Chiral Oxazolinylcarbene-Rhodium Complexes: Efficient Phosphane-Free Catalysts for the Asymmetric Hydrosilylation of Dialkyl Ketones. Angewandte Chemie International Edition, 43, 1014-1017. https://doi.org/10.1002/anie.200353133
Albright, A. and Gawley, R.E. (2011) Application of a C2-Symmetric Copper Carbenoid in the Enantioselective Hydrosilylation of Dialkyl and Aryl-Alkyl Ketones. Journal of the American Chemical Society, 133, 19680-19683. https://doi.org/10.1021/ja209187a
Hafedh, N., Favereau, L., Caytan, E., Roisnel, T., Jean, M., Vanthuyne, N., Aloui, F. and Crassous, J. (2019) Synthesis and Chiroptical Properties of Organometallic Complexes of Helicenic N-Heterocyclic Carbenes. Chirality, 31, 1005-1013. https://doi.org/10.1002/chir.23143