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Sharbatdaran M, Farzaneh F, Larijani MM, Salimi A, Ghiasi M, Ghandi M. Synthesis, characterization, DFT studies, and immobilization of cobalt(II) complex with N,N′,N″-tris(2-pyrimidinyl)dimethylentriamine on modified iron oxide as oxidation catalyst. Polyhedron 2016. [DOI: 10.1016/j.poly.2016.05.023] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Karukurichi KR, Fei X, Swyka RA, Broussy S, Shen W, Dey S, Roy SK, Berkowitz DB. Mini-ISES identifies promising carbafructopyranose-based salens for asymmetric catalysis: Tuning ligand shape via the anomeric effect. SCIENCE ADVANCES 2015; 1:e1500066. [PMID: 26501130 PMCID: PMC4613784 DOI: 10.1126/sciadv.1500066] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2015] [Accepted: 05/11/2015] [Indexed: 05/24/2023]
Abstract
This study introduces new methods of screening for and tuning chiral space and in so doing identifies a promising set of chiral ligands for asymmetric synthesis. The carbafructopyranosyl-1,2-diamine(s) and salens constructed therefrom are particularly compelling. It is shown that by removing the native anomeric effect in this ligand family, one can tune chiral ligand shape and improve chiral bias. This concept is demonstrated by a combination of (i) x-ray crystallographic structure determination, (ii) assessment of catalytic performance, and (iii) consideration of the anomeric effect and its underlying dipolar basis. The title ligands were identified by a new mini version of the in situ enzymatic screening (ISES) procedure through which catalyst-ligand combinations are screened in parallel, and information on relative rate and enantioselectivity is obtained in real time, without the need to quench reactions or draw aliquots. Mini-ISES brings the technique into the nanomole regime (200 to 350 nmol catalyst/20 μml organic volume) commensurate with emerging trends in reaction development/process chemistry. The best-performing β-d-carbafructopyranosyl-1,2-diamine-derived salen ligand discovered here outperforms the best known organometallic and enzymatic catalysts for the hydrolytic kinetic resolution of 3-phenylpropylene oxide, one of several substrates examined for which the ligand is "matched." This ligand scaffold defines a new swath of chiral space, and anomeric effect tunability defines a new concept in shaping that chiral space. Both this ligand set and the anomeric shape-tuning concept are expected to find broad application, given the value of chiral 1,2-diamines and salens constructed from these in asymmetric catalysis.
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Ford DD, Nielsen LPC, Zuend SJ, Musgrave CB, Jacobsen EN. Mechanistic basis for high stereoselectivity and broad substrate scope in the (salen)Co(III)-catalyzed hydrolytic kinetic resolution. J Am Chem Soc 2013; 135:15595-608. [PMID: 24041239 PMCID: PMC3875305 DOI: 10.1021/ja408027p] [Citation(s) in RCA: 104] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
In the (salen)Co(III)-catalyzed hydrolytic kinetic resolution (HKR) of terminal epoxides, the rate- and stereoselectivity-determining epoxide ring-opening step occurs by a cooperative bimetallic mechanism with one Co(III) complex acting as a Lewis acid and another serving to deliver the hydroxide nucleophile. In this paper, we analyze the basis for the extraordinarily high stereoselectivity and broad substrate scope observed in the HKR. We demonstrate that the stereochemistry of each of the two (salen)Co(III) complexes in the rate-determining transition structure is important for productive catalysis: a measurable rate of hydrolysis occurs only if the absolute stereochemistry of each of these (salen)Co(III) complexes is the same. Experimental and computational studies provide strong evidence that stereochemical communication in the HKR is mediated by the stepped conformation of the salen ligand, and not the shape of the chiral diamine backbone of the ligand. A detailed computational analysis reveals that the epoxide binds the Lewis acidic Co(III) complex in a well-defined geometry imposed by stereoelectronic rather than steric effects. This insight serves as the basis of a complete stereochemical and transition structure model that sheds light on the reasons for the broad substrate generality of the HKR.
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Affiliation(s)
- David D Ford
- Department of Chemistry and Chemical Biology, Harvard University , Cambridge, Massachusetts 02138, United States
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Xie HQ, Xiong Y, Dang YL. Zinc(II) complexes with the tetradentate schiff base ligand N,N′-bis(1-pyridin-2-yl-ethylidene)propane-1,3-diamine: Synthesis and crystal structures. J STRUCT CHEM+ 2013. [DOI: 10.1134/s0022476613030189] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Hamidipour L, Farzaneh F. Cobalt metal organic framework as an efficient heterogeneous catalyst for the oxidation of alkanes and alkenes. REACTION KINETICS MECHANISMS AND CATALYSIS 2013. [DOI: 10.1007/s11144-012-0533-2] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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So SM, Kim H, Mui L, Chin J. Mimicking Nature to Make Unnatural Amino Acids and Chiral Diamines. European J Org Chem 2011. [DOI: 10.1002/ejoc.201101073] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Soon Mog So
- Diaminopharm Inc., 880 Grandview Way, Unit 706, Toronto, Ontario, M2N 7B2, Canada
| | - Hyunwoo Kim
- Department of Chemistry, KAIST, Daejon, 305‐701, Korea
| | - Leo Mui
- Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, Canada, Fax: +1‐416‐946‐7335
| | - Jik Chin
- Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, Canada, Fax: +1‐416‐946‐7335
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Xie HQ, Zhang QA, Yan JW. Synthesis and crystal structures of the zinc(II) complexes with a tridentate Schiff base (1-pyridin-2-ylethylidene)pyridin-2-ylmethylamine. RUSS J COORD CHEM+ 2011. [DOI: 10.1134/s1070328411060108] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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8
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Wang Y, Wang M, Wang Y, Chen Y, Sun L. Synthesis of New Chiral Schiff Bases Containing Bromo- and Iodo-Functionalized Hydroxynaphthalene Frameworks. SYNTHETIC COMMUN 2011. [DOI: 10.1080/00397911.2010.486505] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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9
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Dong Z, Bai S, Yap GPA, Fox JM. Interplay between the diamine structure and absolute helicity in Ni-salen metallofoldamers. Chem Commun (Camb) 2011; 47:3781-3. [PMID: 21298140 DOI: 10.1039/c0cc04794e] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The nature of internal chiral diamines can greatly influence the ratio of helical diastereomers for Ni-salen based metallofoldamers. The diastereomer ratio is small for metallofoldamers derived from (1R, 2R)-cyclohexanediamine, (11R, 12R)-9,10-dihydro-9,10-ethanoanthracene-11,12-diamine, or (1R, 2R)-cyclopentanediamine. By contrast, the foldamer from (1S, 2S)-1,2-diphenylethylenediamine provides a relatively large bias (6 : 1) for the P-helical diastereomer as evidenced by NMR studies, chiroptical data, and X-ray studies. A model is proposed to explain the origin of the helical bias. These findings underscore the need to consider helical diastereomers in models for asymmetric induction in metal-salen catalyzed reactions.
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Affiliation(s)
- Zhenzhen Dong
- Brown Laboratories, Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19803, USA
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Carter E, Fallis IA, Kariuki BM, Morgan IR, Murphy DM, Tatchell T, Van Doorslaer S, Vinck E. Structure and pulsed EPR characterization of N,N′-bis(5-tert-butylsalicylidene)-1,2-cyclohexanediamino-vanadium(iv) oxide and its adducts with propylene oxide. Dalton Trans 2011; 40:7454-62. [DOI: 10.1039/c1dt10378d] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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11
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Fisher LA, Zhang F, Yap GP, Fox JM. Weak absolute helicity direction in Ni–salen by trans-cyclohexane-(1R,2R)-diamine. Inorganica Chim Acta 2010. [DOI: 10.1016/j.ica.2010.07.044] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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12
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Bobka R, Roedel JN, Wirth S, Lorenz IP. Reactions of Cu(I)Br with aziridine derivatives. Synthesis, characterization and crystal structures of monomeric, dimeric and hexameric aziridine (= az) complexes of the formal type [CuBr(az)2]n (n = 1, 2) and [CuBr(az)]6. Dalton Trans 2010; 39:10142-7. [PMID: 20877890 DOI: 10.1039/c0dt00320d] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The first syntheses of monomeric and oligomeric aziridine complexes of copper(I) are described. Cu(I)Br (1) reacts with a series of different aziridine derivatives (C(2)H(3)PhNH (2), C(2)H(2)Me(2)NH (3), C(2)H(2)Me(2)NC(2)H(2)Me(2)NH(2) (4)) to give the neutral dimeric complex [CuBr(C(2)H(3)PhNH)(2)](2) (5) and the ionic hexameric complex [Cu(6)Br(5)(C(2)H(2)Me(2)NH)(6)]Br (6) with terminal bound aziridine ligands as well as the neutral monomeric complex [CuBr(C(2)H(2)Me(2)NC(2)H(2)Me(2)NH(2))] (7) where the dimerized aziridine acts as a N,N'-chelating ligand. After purification, all of the complexes were fully characterized and their IR, (1)H and (13)C NMR spectra are reported and discussed. The single crystal structure analysis revealed distorted tetrahedral geometry for the copper(I) centres in the complexes 5 and 6 and a trigonal planar structure for complex 7. In the oligomers the copper centres are bridged by two μ(2)- (5) or two μ(3)- and three μ(4)-bromido ligands (6), respectively.
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Affiliation(s)
- Roman Bobka
- Department Chemistry and Biochemistry, Ludwig-Maximilians-University Munich, Butenandtstraße 5-13 (House D), D-81377, Munich, Germany
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Kurahashi T, Hada M, Fujii H. Critical role of external axial ligands in chirality amplification of trans-cyclohexane-1,2-diamine in salen complexes. J Am Chem Soc 2009; 131:12394-405. [PMID: 19705918 DOI: 10.1021/ja904635n] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A series of Mn(IV)(salen)(L)(2) complexes bearing different external axial ligands (L = Cl, NO(3), N(3), and OCH(2)CF(3)) from chiral salen ligands with trans-cyclohexane-1,2-diamine as a chiral scaffold are synthesized, to gain insight into conformational properties of metal salen complexes. X-ray crystal structures show that Mn(IV)(salen)(OCH(2)CF(3))(2) and Mn(IV)(salen)(N(3))(2) adopt a stepped conformation with one of two salicylidene rings pointing upward and the other pointing downward due to the bias from the trans-cyclohexane-1,2-diamine moiety, which is in clear contrast to a relatively planar solid-state conformation for Mn(IV)(salen)(Cl)(2). The CH(2)Cl(2) solution of Mn(IV)(salen)(L)(2) shows circular dichroism of increasing intensity in the order L = Cl < NO(3) << N(3) < OCH(2)CF(3), which indicates Mn(IV)(salen)(L)(2) adopts a solution conformation of an increasing chiral distortion in this order. Quantum-chemical calculations with a symmetry adapted cluster-configuration interaction method indicate that a stepped conformation exhibits more intense circular dichroism than a planar conformation. The present study clarifies an unexpected new finding that the external axial ligands (L) play a critical role in amplifying the chirality in trans-cyclohexane-1,2-diamine in Mn(IV)(salen)(L)(2) to facilitate the formation of a chirally distorted conformation, possibly a stepped conformation.
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Affiliation(s)
- Takuya Kurahashi
- Institute for Molecular Science, National Institutes of Natural Sciences, Myodaiji, Okazaki, Aichi 444-8787, Japan
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Kemper S, Hrobárik P, Kaupp M, Schlörer NE. Jacobsen's catalyst for hydrolytic kinetic resolution: structure elucidation of paramagnetic Co(III) salen complexes in solution via combined NMR and quantum chemical studies. J Am Chem Soc 2009; 131:4172-3. [PMID: 19275230 DOI: 10.1021/ja806151g] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
NMR investigation of chiral Co(III) salen catalysts, important for enantioselective hydrolytic kinetic resolution (HKR), revealed the presence of a paramagnetic high-spin Co(III) species, which is in solvent- and temperature-dependent equilibrium with the known diamagnetic low-spin Co(III) complex. Combined with quantum chemical DFT calculations, the para- and diamagnetic chemical shifts were used to study the salen ligand conformation of the para- and diamagnetic complexes, resulting in a mechanistic proposal for the enantioselective step in catalysis.
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Affiliation(s)
- Sebastian Kemper
- Department für Chemie, Universität zu Köln, Greinstrasse 4, 50939 Köln, Germany
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Lee DN, Kim H, Mui L, Myung SW, Chin J, Kim HJ. Electronic Effect on the Kinetics of the Diaza-Cope Rearrangement. J Org Chem 2009; 74:3330-4. [DOI: 10.1021/jo900133g] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Dong-Nam Lee
- Department of Chemistry, College of Natural Sciences, Kyonggi University, Suwon 443-760, Korea, and Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, ON M5S 3H6, Canada
| | - Hyunwoo Kim
- Department of Chemistry, College of Natural Sciences, Kyonggi University, Suwon 443-760, Korea, and Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, ON M5S 3H6, Canada
| | - Leo Mui
- Department of Chemistry, College of Natural Sciences, Kyonggi University, Suwon 443-760, Korea, and Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, ON M5S 3H6, Canada
| | - Seung-Woon Myung
- Department of Chemistry, College of Natural Sciences, Kyonggi University, Suwon 443-760, Korea, and Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, ON M5S 3H6, Canada
| | - Jik Chin
- Department of Chemistry, College of Natural Sciences, Kyonggi University, Suwon 443-760, Korea, and Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, ON M5S 3H6, Canada
| | - Hae-Jo Kim
- Department of Chemistry, College of Natural Sciences, Kyonggi University, Suwon 443-760, Korea, and Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, ON M5S 3H6, Canada
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16
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Murphy DM, Fallis IA, Carter E, Willock DJ, Landon J, Van Doorslaer S, Vinck E. Enantioselective binding of structural epoxide isomers by a chiral vanadyl salen complex: a pulsed EPR, cw-ENDOR and DFT investigation. Phys Chem Chem Phys 2009; 11:6757-69. [DOI: 10.1039/b907807j] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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17
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Garnovskii AD, Vasilchenko IS, Garnovskii DA, Kharisov BI. Molecular design of mononuclear complexes of acyclic Schiff-base ligands. J COORD CHEM 2008. [DOI: 10.1080/00958970802398178] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Affiliation(s)
- A. D. Garnovskii
- a Institute of Physical and Organic Chemistry , Southern Federal University , 344090, Stachki. av., 104/2, Rostov-on-Don, Russian Federation
| | - I. S. Vasilchenko
- b Southern Scientific Center of Russian Academy of Sciences , 344006, Chekhova av., 41, Rostov-on-Don, Russian Federation
| | - D. A. Garnovskii
- a Institute of Physical and Organic Chemistry , Southern Federal University , 344090, Stachki. av., 104/2, Rostov-on-Don, Russian Federation
| | - B. I. Kharisov
- c CIIDIT-Facultad de Ciencias Quimicas , Universidad Autonoma de Nuevo Leon , San Nicolas de los Garza, N.L., A.P.18-F, C.P. 66450, Mexico
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Bobka R, Roedel JN, Neumann B, Nigst T, Lorenz IP. Spectroscopic and structural characterization of cationic N-(2-aminoethyl)aziridine-N,N′ chelate complexes of the d6-metals Rh(III) and Ir(III). Polyhedron 2008. [DOI: 10.1016/j.poly.2007.11.023] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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19
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Liu H, Wang M, Wang Y, Gu Q, Sun L. Synthesis of 3‐Aryl‐5‐t‐butylsalicylaldehydes and their Chiral Schiff Base Compounds. SYNTHETIC COMMUN 2007. [DOI: 10.1080/00397910701572423] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Affiliation(s)
- Hai‐bin Liu
- a State Key Laboratory of Fine Chemicals, DUT‐KTH Joint Education and Research Center on Molecular Devices , Dalian University of Technology (DUT) , Dalian, China
| | - Mei Wang
- a State Key Laboratory of Fine Chemicals, DUT‐KTH Joint Education and Research Center on Molecular Devices , Dalian University of Technology (DUT) , Dalian, China
| | - Ying Wang
- a State Key Laboratory of Fine Chemicals, DUT‐KTH Joint Education and Research Center on Molecular Devices , Dalian University of Technology (DUT) , Dalian, China
| | - Qiang Gu
- a State Key Laboratory of Fine Chemicals, DUT‐KTH Joint Education and Research Center on Molecular Devices , Dalian University of Technology (DUT) , Dalian, China
| | - Li‐cheng Sun
- a State Key Laboratory of Fine Chemicals, DUT‐KTH Joint Education and Research Center on Molecular Devices , Dalian University of Technology (DUT) , Dalian, China
- b Department of Chemistry , Royal Institute of Technology (KTH) , Stockholm, Sweden
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Bobka R, Roedel JN, Neumann B, Krinninger C, Mayer P, Wunderlich S, Penger A, Lorenz IP. NeutralMono- and CationicBis-Aziridine d6-Metal Complexes of the Type [(π-arene)M(Az)Cl2] and [(π-arene)M(Az)2Cl]Cl (π-arene/M = η6-C6Me6/Ru; η5-C5Me5/Rh, Ir). Z Anorg Allg Chem 2007. [DOI: 10.1002/zaac.200700276] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Electronic and Steric Effects in Diamine Recognition with a Highly Rigid Zn(II) Complex. B KOREAN CHEM SOC 2007. [DOI: 10.5012/bkcs.2007.28.1.133] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Chin J, Chong YS, Bobb R, Studnicki L, Hong JI. Imprinting and locking chiral memory for stereoselective catalysis. Chem Commun (Camb) 2007:120-2. [PMID: 17180219 DOI: 10.1039/b611709k] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A salen ligand based Co(III) complex +/- with imprintable chiral memory was locked-in and used for stereoselective catalysis.
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Affiliation(s)
- Jik Chin
- Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, M5S 3H6, Canada.
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Kim HJ, Kim H, Alhakimi G, Jeong EJ, Thavarajah N, Studnicki L, Koprianiuk A, Lough AJ, Suh J, Chin J. Preorganization in Highly Enantioselective Diaza-Cope Rearrangement Reaction. J Am Chem Soc 2005; 127:16370-1. [PMID: 16305204 DOI: 10.1021/ja055776k] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Crystal structure and activation entropy data indicate that H-bond directed diaza-Cope rearrangement of chiral diimines takes place with a high degree of preorganization. CD spectroscopy and HPLC data show that there is inversion of stereochemistry for the reaction with excellent enantioselectivity.
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Affiliation(s)
- Hae-Jo Kim
- Department of Chemistry, University of Toronto, 80 St. George Street, Toronto M5S 3H6, Canada
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Kim HJ, Kim W, Lough AJ, Kim BM, Chin J. A Cobalt(III)−Salen Complex with an Axial Substituent in the Diamine Backbone: Stereoselective Recognition of Amino Alcohols. J Am Chem Soc 2005; 127:16776-7. [PMID: 16316210 DOI: 10.1021/ja0557785] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A cobalt(III)-salen complex (3) with an axial substituent on the diamine backbone has been synthesized. Crystal structure reveals that the axial substituent (p-nitrophenyl group) is positioned in close proximity to the metal binding site. The stereoselectivity of the cobalt complex for binding amino alcohols increases with increasing steric bulk of the amino alcohol from alaninol (2.9) to valinol (6.2) and t-leucinol (36.0).
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Affiliation(s)
- Hae-Jo Kim
- Department of Chemistry, University of Toronto, Canada
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Fallis IA, Murphy DM, Willock DJ, Tucker RJ, Farley RD, Jenkins R, Strevens RR. Direct observation of enantiomer discrimination of epoxides by chiral salen complexes using ENDOR. J Am Chem Soc 2005; 126:15660-1. [PMID: 15571385 DOI: 10.1021/ja045491s] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Electron nuclear double resonance (ENDOR) spectroscopy was used to investigate the weak enantioselective binding between chiral salen complexes [VO(1)] ((R,R)- and (S,S)-vanadyl N,N'-bis(3,5-di-tert-butylsalcylidene)-1,2-cyclohexanediamine) and chiral epoxides (e.g., (R)-/(S)-propylene epoxide, 5) in frozen (10 K) solution. Differences in epoxide binding by enatiomers of [VO(1)] was evidenced by changes to the 1H epoxide derived peaks in the ENDOR spectra, such that (R,R)-[VO(1)] + (R)-5 and (R,R)-[VO(1)] + (S)-5 yield noticeably different spectra. These changes were assigned to the small structural differences between the diastereomeric metal-epoxide adducts. Simulation of the spectra revealed differences in the VO...1Hepoxide distances for the diastereomeric pairs, which was confirmed by a complementary set of density functional theory (DFT) calculations. While the epoxide molecule is very weakly coordinated, ENDOR measurements of the racemic complex in racemic epoxide nevertheless indicated the preferential coordination of the (R)-5 to (R,R)-[VO(1)] (likewise (S)-(5) to (S,S)-[VO(1)]), which is favored over the binding of (S)-5 epoxide to (R,R)-[VO(1)] (and likewise (R)-5 epoxide to (S,S)-[VO(1)]). This demonstrates the unique power of the ENDOR technique to resolve weak chiral interactions for which EPR spectroscopy alone lacks sufficient resolution.
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Affiliation(s)
- Ian A Fallis
- School of Chemistry, Cardiff University, P.O. Box 912 Cardiff, CF10 3TB, UK.
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