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Peel AJ, Terzopoulos A, Jethwa RB, Choudhury D, Niu HC, Bond AD, Slaughter J, Wright DS. A chiral phosphazane reagent strategy for the determination of enantiomeric excess of amines. Chem Sci 2022; 13:5398-5412. [PMID: 35655560 PMCID: PMC9093139 DOI: 10.1039/d2sc01692c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2022] [Accepted: 04/12/2022] [Indexed: 11/21/2022] Open
Abstract
Methods for measuring enantiomeric excess (ee) of organic molecules by NMR spectroscopy provide rapid analysis using a standard technique that is readily available. Commonly this is accomplished by chiral derivatisation of the detector molecule (producing a chiral derivatisation agent, CDA), which is reacted with the mixture of enantiomers under investigation. However, these CDAs have almost exclusively been based on carbon frameworks, which are generally costly and/or difficult to prepare. In this work, a methodology based on the readily prepared inorganic cyclodiphosph(iii)azane CDA ClP(μ-NtBu)2POBorn (Born = endo-(1S)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-yl) is shown to be highly effective in the measurement of ee’s of chiral amines, involving in situ reaction of the chiral amines (R*NH2) with the P–Cl bond of the CDA followed by quaternization of the phosphorus framework with methyl iodide. This results in sharp 31P NMR signals with distinct chemical shift differences between the diastereomers that are formed, which can be used to obtain the ee directly by integration. Spectroscopic, X-ray structural and DFT studies suggest that the NMR chemical shift differences between diastereomers is steric in origin, with the sharpness of these signals resulting from conformational locking of the bornyl group relative to the P2N2 ring induced by the presence of the P(v)-bonded amino group (R*NH). This study showcases cheap inorganic phosphazane CDAs as simple alternatives to organic variants for the rapid determination of ee. The simple inorganic cyclodiphosph(iii)azane chiral derivatisation agent ClP(μ-tBuN)2POBorn (Born = endo-(1S)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-yl) is shown to be effective in the measurement of ee’s of chiral amines using 31P NMR spectroscopy.![]()
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Affiliation(s)
- Andrew J. Peel
- Yusuf Hamied Department of Chemistry, Cambridge University, Lensfield Road, Cambridge, CB2 1EW, UK
| | - Alexandros Terzopoulos
- Yusuf Hamied Department of Chemistry, Cambridge University, Lensfield Road, Cambridge, CB2 1EW, UK
| | - Rajesh B. Jethwa
- Yusuf Hamied Department of Chemistry, Cambridge University, Lensfield Road, Cambridge, CB2 1EW, UK
| | - Dipanjana Choudhury
- Yusuf Hamied Department of Chemistry, Cambridge University, Lensfield Road, Cambridge, CB2 1EW, UK
| | - Hao-Che Niu
- Yusuf Hamied Department of Chemistry, Cambridge University, Lensfield Road, Cambridge, CB2 1EW, UK
| | - Andrew D. Bond
- Yusuf Hamied Department of Chemistry, Cambridge University, Lensfield Road, Cambridge, CB2 1EW, UK
| | - Jonathan Slaughter
- Yusuf Hamied Department of Chemistry, Cambridge University, Lensfield Road, Cambridge, CB2 1EW, UK
- The Faraday Institution Quad One, Harwell Science and Innovation Campus, Didcot, UK
| | - Dominic S. Wright
- Yusuf Hamied Department of Chemistry, Cambridge University, Lensfield Road, Cambridge, CB2 1EW, UK
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Abstract
This short review describes the transition metal chemistry of cyclodiphosphazanes.
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Roth T, Wadepohl H, Wright DS, Gade LH. Chiral ditopic cyclophosphazane (CycloP) ligands: synthesis, coordination chemistry, and application in asymmetric catalysis. Chemistry 2013; 19:13823-37. [PMID: 24038171 DOI: 10.1002/chem.201302327] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2013] [Indexed: 11/10/2022]
Abstract
A series of dichlorocyclophosphazanes [{ClP(μ-NR)}2 ] containing chiral and achiral R groups was obtained from simple commercially available amines and PCl3 . Their condensation reactions with axially chiral biaryl diols yielded ansa-bridged chiral cyclophosphazane (CycloP) ligands. This highly modular methodology allows extensive elaboration of the ligand set, in which the chirality can be introduced at the diol bridge and/or the amido R group. This provides the possibility to observe match and mismatch effects in catalysis. A series of twenty CycloP ligands was synthesized and characterized by multinuclear NMR spectroscopy, HRMS, elemental analysis, and in selected cases, single-crystal X-ray diffraction. These studies show that all of the ditopic CycloP ligands are C2 symmetric, rendering their metal coordination sites symmetry equivalent. Two well-established enantioselective reactions were explored by using late-transition metal CycloP complexes as catalysts; the gold-catalyzed hydroamination of γ-allenyl sulfonamides and the asymmetric nickel-catalyzed three-component coupling of a diene and an aldehyde. The steric demands of the CycloP ligands have a subtle influence on the reactivity and selectivity observed in both reactions. Good enantiomeric ratios (e.r.) as high as 89:11 in the gold-catalyzed reaction and 92:8 in the nickel-catalyzed bis-homoallylation reaction were observed.
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Affiliation(s)
- Torsten Roth
- Anorganisch Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg (Germany), Fax: (+49) 6221-54-5609
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Mono-, di- and tetranuclear rhodium(I) complexes of morpholine and N-methylpiperazine functionalized cyclodiphosph(III)azanes, cis-[( t BuN-μ)2(PNC4H8X)2] (X = O, NMe). J CHEM SCI 2011. [DOI: 10.1007/s12039-011-0153-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
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Balakrishna MS, Suresh D, Mague JT. Cyclodiphosphazane appended with thioether functionality: Synthesis, transition metal chemistry and catalytic application in Suzuki–Miyaura cross-coupling reactions. Inorganica Chim Acta 2011. [DOI: 10.1016/j.ica.2011.02.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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Balakrishna MS, Venkateswaran R, Mague JT. Transition metal chemistry of cyclodiphosphanes containing phosphine and amide-phosphine functionalities: Formation of a stable dipalladium(II) complex containing a Pd–P σ-bond. Dalton Trans 2010; 39:11149-62. [PMID: 20936211 DOI: 10.1039/c0dt00614a] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Affiliation(s)
- Maravanji S Balakrishna
- Phosphorus Laboratory, Department of Chemistry, Indian Institute of Technology Bombay, Mumbai, 400 076, India, 3480.
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