Chiral Metal Complexes. 27. Stereoselectivity in the synthesis and reaction of coordinated aminomalonic acid derivatives |
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| Institution: | 1. Research Chair of Exploitation of Renewable Energy Applications in Saudi Arabia, Physics & Astronomy Department, College of Science, King Saud University, P.O. Box 2455, Riyadh, 11451, Saudi Arabia;2. Physics Department, Faculty of Science, Ain Shams University, Cairo, Egypt;3. Physics & Astronomy Department, College of Science, King Saud University, P.O. Box 2455, 11451, Riyadh, Saudi Arabia;4. Intelligent Construction Automation Center, Kyungpook National University, 80, Daehak-ro, Buk-gu, Daegu, 41566, Republic of Korea;1. Department of Radiochemistry, China Institute of Atomic Energy, Beijing 102413, PR China;2. School of Nuclear Science and Technology, University of South China, 28 Changsheng West Road, Hengyang 421001, PR China;3. Guangxi Key Laboratory of Processing for Non-ferrous Metals and Featured Materials, MOE Key Laboratory of New Processing Technology for Non-ferrous Metals and Materials, School of Resources, Environment and Materials, Guangxi University, Nanning 530004, PR China;4. Institute of Nuclear Energy Safety Technology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, PR China;5. University of Science and Technology of China, Hefei 230026, PR China;1. Faculty of Materials Science and Engineering, Hubei University, Ministry of Education Key Laboratory for the Green Preparation and Application of Functional Materials, and Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Hubei University, Wuhan 430062, PR China;2. The Institute of Technological Sciences, Wuhan University, Wuhan 430072, PR China |
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| Abstract: | The synthesis is reported of a series of ternary cationic complexes of general form Co(R,Rpicchxn)(ARMA)+ (where picchxn is the N4 tetradentate N,N′-di(2-picolyl)-1,2-diaminocyclohexane and ARMA is a bidentate α-substituted-α-aminomalonate dianion). The aminomalonic acid (NH2· C(COOH)2·R) derivatives investigated have R = -CH3 (AMMAH2), -CH2·CH3 (AEMAH2), -CH2· CH2·CH3 (APMAH2), -CH2·(CH2)2·CH3 (ABuTMAH2, -CH2·C6H5 (ABMAH2), -CH2·(p-C6H4)· C(CH3)3 (ABuBMAH2) and -CH2·C10H7 (ANMAH2). The isomeric species in the complex products have been separated using cation exchange chromatography and each isomer has been characterized using NMR and circular dichroism techniques. In each synthesis the major isomeric product obtained has a Λ-β1 topology. However, where ARMAH2 possesses a lengthy alkyl sidechain trace amounts of Δ-α-Co(R,R-picchxn)(ARMA)]+ isomers have been observed during the synthetic reactions. This unusual isomeric form readily undergoes inversion of its absolute configuration in DMSO solution to yield the more thermodynamically stable Λ-β1-Co(R,R-picchxn()R-ARMA)]+ species stereospecifically.In the case of Λ-β1-Co(R,R,-pichxn)(S-APMA)]ClO4·2NaClO4·5H2O the crystal structure has been determined. The compound crystallises in the orthorhombic space group P212121, with a = 10.056(3),b = 16.475(7),c = 23.370(7)Å and Z = 4. The structure was refined to R = 0.079 for 4460 non-zero reflexions, and confirms the absolute configuration of each chiral centre to be consistent with the NMR and circular dichroism interpretations.The decar☐ylation of these chelate ARMAH2 derivatives under acid conditions leads to corresponding complexes containing mixtures of coordinated R-andS-α-aminoacids in various ratios. This ratio has been determined in each case, and factors which may influence the degree of chiral induction observed are discussed. |
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