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Al-Sulaimi S, Rajendran K, Nikitin K, Gilheany DG. Unexpected rapid P-stereomutation of phosphine oxides catalysed by chlorophosphonium salts. Chem Commun (Camb) 2023; 59:11696-11699. [PMID: 37700722 DOI: 10.1039/d3cc03719c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/14/2023]
Abstract
P-Stereomutation of phosphine oxides is extremely slow. We show that it is catalysed by chlorophosphonium salts (CPS) which can directly be formed in the system in situ. The racemization of phosphine oxides at ambient conditions catalysed by 1 mol% of CPS takes 1-2 hours and can be arrested by additon of a primary alcohol. The process probably proceeds via the development of oxodiphosphonium P-O-P species.
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Affiliation(s)
- Sulaiman Al-Sulaimi
- Department of Biological Science & Chemistry, College of Arts and Sciences, University of Nizwa, Box 33, PC 616, Nizwa, Sultanate of Oman
| | - Kamalraj Rajendran
- School of Chemistry, University College Dublin, Dublin 4, Belfield, Ireland.
| | - Kirill Nikitin
- School of Chemistry, University College Dublin, Dublin 4, Belfield, Ireland.
| | - Declan G Gilheany
- School of Chemistry, University College Dublin, Dublin 4, Belfield, Ireland.
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2
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Bismillah AN, Johnson TG, Hussein BA, Turley AT, Saha PK, Wong HC, Aguilar JA, Yufit DS, McGonigal PR. Control of dynamic sp 3-C stereochemistry. Nat Chem 2023; 15:615-624. [PMID: 36914791 PMCID: PMC10159849 DOI: 10.1038/s41557-023-01156-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2021] [Accepted: 02/09/2023] [Indexed: 03/16/2023]
Abstract
Stereogenic sp3-hybridized carbon centres are fundamental building blocks of chiral molecules. Unlike dynamic stereogenic motifs, such as sp3-nitrogen centres or atropisomeric biaryls, sp3-carbon centres are usually fixed, requiring intermolecular reactions to undergo configurational changes. Here we report the internal enantiomerization of fluxional carbon cages and the consequences of their adaptive configurations for the transmission of stereochemical information. The sp3-carbon stereochemistry of the rigid tricyclic cages is inverted through strain-assisted Cope rearrangements, emulating the low-barrier configurational dynamics typical for sp3-nitrogen inversion or conformational isomerism. This dynamic enantiomerization can be stopped, restarted or slowed by external reagents, while the configuration of the cage is controlled by neighbouring, fixed stereogenic centres. As part of a phosphoramidite-olefin ligand, the fluxional cage acts as a conduit to transmit stereochemical information from the ligand while also transferring its dynamic properties to chiral-at-metal coordination environments, influencing catalysis, ion pairing and ligand exchange energetics.
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Affiliation(s)
| | | | | | | | | | - Ho Chi Wong
- Department of Chemistry, Durham University, Durham, UK
| | | | | | - Paul R McGonigal
- Department of Chemistry, Durham University, Durham, UK. .,Department of Chemistry, University of York, York, UK.
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Stereodynamics of E/ Z isomerization in rotaxanes through mechanical shuttling and covalent bond rotation. Chem 2021; 7:2137-2150. [PMID: 34435161 PMCID: PMC8367298 DOI: 10.1016/j.chempr.2021.04.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2020] [Revised: 01/18/2021] [Accepted: 04/19/2021] [Indexed: 11/20/2022]
Abstract
The mechanical bond has opened a new world for structural and dynamic stereochemistry, which is still largely underexplored and whose significance for various applications is becoming increasingly evident. We demonstrate that designed rearrangements involving both covalent and mechanical bonds can be integrated in [2]rotaxanes, leading to interesting consequences in terms of E/Z isomerization mechanisms. Two entirely distinct and concomitant stereomutations, pertaining to the same stereogenic element but involving different kinds of linkages within the molecule, are observed and are thoroughly characterized. The rate of the two processes is affected in opposite ways upon changing solvent polarity; such a phenomenon can be used to selectively modify the rate of each motion and adjust the relative contribution of the two mechanisms to the isomerization. Although the movements are not synchronized, an analysis of the intriguing fundamental implications for transition state theory, reaction pathway bifurcation, and microscopic reversibility was triggered by our experimental observations. Rotaxanes that display E/Z stereoisomerism depending on the ring position Co-existence of two different stereomutations that yield the same product Mutual influence and opposite solvent dependence of the two dynamic processes Fundamental implications for microscopic reversibility and chemical equilibrium
The concurrence and interplay of different movements of molecular components within the same structure play a key role in providing function to naturally occurring molecular machines. Despite the progress made on artificial counterparts, the construction of molecular systems, where two (or more) motions are integrated together to produce an outcome, is still in its infancy. Molecules called rotaxanes, obtained by interlocking a ring with a dumbbell-shaped axle, are an appealing yet underexplored platform for this purpose. Here, we describe rotaxanes where two coexisting and radically different processes—rotation about a covalent bond and translation of the ring along the axle—lead to the same change in the overall molecular shape. These results are significant not only to improve our fundamental understanding of the way molecular components move but also to develop sophisticated artificial nanomachines capable of transforming or transmitting motion.
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Nikitin K, Ortin Y, McGlinchey MJ. Dynamics of a Molecular Rotor Exhibiting Local Directional Rotational Preference within Each Enantiomer. J Phys Chem A 2021; 125:2061-2068. [PMID: 33666434 PMCID: PMC8154598 DOI: 10.1021/acs.jpca.0c08476] [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] [Indexed: 11/30/2022]
Abstract
Directional internal rotation in molecular systems, generally controlled by chirality, is known to occur in natural and artificial systems driven by light or fueled chemically, but spontaneous directional molecular rotation is believed to be forbidden. We have designed a molecular rotor, whereby ferrocene and triptycene linked by a methylene bridge provide two rotational degrees of freedom. On the basis of experimental observations, in conjunction with computational data, we show that the two different modes of rotation are strongly coupled and the spatial orientation of the bistable ferrocene moiety controls the barrier to its own rotation about the triptycene axis. It is proposed that the barrier to clockwise 120° rotation across each individual triptycene blade is lower in the M-enantiomer and for counterclockwise 120° rotation, it is lower in its P-counterpart. These findings demonstrate the possibility of locally preferred thermal directional intramolecular rotation for each dynamically interconverting enantiomer.
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Affiliation(s)
- Kirill Nikitin
- School of Chemistry, University College Dublin, Belfield, Dublin 4, Ireland
| | - Yannick Ortin
- School of Chemistry, University College Dublin, Belfield, Dublin 4, Ireland
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Yahiaoui O, Patel HD, Chinner KS, Pašteka LF, Fallon T. Stereomutation of Substituted Bullvalenes. Org Lett 2021; 23:1157-1162. [PMID: 33146538 DOI: 10.1021/acs.orglett.0c03470] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The stereomutation of substituted bullvalenes is an inevitable consequence of the valence isomerism that automerizes this unique fluxional hydrocarbon. The introduction of external stereogenicity in the substituents expands the reaction graphs and leads to a wealth of complex diastereochemical relationships. In this communication, we explore these possibilities and prepare a range of stereochemically rich substituted bullvalenes. This includes a series of disubstituted bullvalenes with two external stereocenters as a platform for fluxional, shape-diverse compound libraries. We also prepare a tethered bisbullvalene with central stereogenicity in the tether as an ensemble of 900 unique isomers that are completely stereomutable.
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Affiliation(s)
- Oussama Yahiaoui
- Department of Chemistry, The University of Adelaide, Adelaide, SA 5005, Australia
| | - Harshal D Patel
- Department of Chemistry, The University of Adelaide, Adelaide, SA 5005, Australia
| | - Kylie S Chinner
- Department of Chemistry, The University of Adelaide, Adelaide, SA 5005, Australia
| | - Lukáš F Pašteka
- Department of Physical and Theoretical Chemistry, Faculty of Natural Sciences, Comenius University, 81806 Bratislava, Slovakia
| | - Thomas Fallon
- Department of Chemistry, The University of Adelaide, Adelaide, SA 5005, Australia
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Nikitin K, O'Gara R. Mechanisms and Beyond: Elucidation of Fluxional Dynamics by Exchange NMR Spectroscopy. Chemistry 2019; 25:4551-4589. [PMID: 30421834 DOI: 10.1002/chem.201804123] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2018] [Indexed: 12/31/2022]
Abstract
Detailed mechanistic information is crucial to our understanding of reaction pathways and selectivity. Dynamic exchange NMR techniques, in particular 2D exchange spectroscopy (EXSY) and its modifications, provide indispensable intricate information on the mechanisms of organic and inorganic reactions and other phenomena, for example, the dynamics of interfacial processes. In this Review, key results from exchange NMR studies of small molecules over the last few decades are systemised and discussed. After a brief introduction to the theory, the key types of dynamic processes are identified and fundamental examples given of intra- and intermolecular reactions, which, in turn, could involve, or not, bond-making and bond-breaking events. Following that logic, internal molecular rotation, intramolecular stereomutation and molecular recognition will first be considered because they do not typically involve bond breaking. Then, rearrangements, substitution-type reactions, cyclisations, additions and other processes affecting chemical bonds will be discussed. Finally, interfacial molecular dynamics and unexpected combinations of different types of fluxional processes will also be highlighted. How exchange NMR spectroscopy helps to identify conformational changes, coordination and molecular recognition processes as well as quantify reaction energy barriers and extract detailed mechanistic information by using reaction rate theory in conjunction with computational techniques will be shown.
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Affiliation(s)
- Kirill Nikitin
- School of Chemistry, University College Dublin, Belfield, Dublin, Ireland
| | - Ryan O'Gara
- School of Chemistry, University College Dublin, Belfield, Dublin, Ireland
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McStay N, Reilly AM, Gathergood N, Kellett A. Efficient DNA Condensation by a C3‐Symmetric Codeine Scaffold. Chempluschem 2018; 84:38-42. [DOI: 10.1002/cplu.201800480] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2018] [Revised: 11/12/2018] [Indexed: 12/12/2022]
Affiliation(s)
- Natasha McStay
- School of Chemical Sciencesand National Institute for Cellular BiotechnologyDublin City University Glasnevin Dublin 9 Ireland
| | - Anthony M. Reilly
- School of Chemical SciencesDublin City University Glasnevin Dublin 9 Ireland
- Synthesis and Solid-State Pharmaceutical CentreSchool of Chemical SciencesDublin City University Glasnevin Dublin 9 Ireland
| | - Nicholas Gathergood
- Department of Chemistry and BiotechnologyTallinn University of Technology Akadeemia tee 15 12618 Tallinn Estonia
| | - Andrew Kellett
- School of Chemical Sciencesand National Institute for Cellular BiotechnologyDublin City University Glasnevin Dublin 9 Ireland
- Synthesis and Solid-State Pharmaceutical CentreSchool of Chemical SciencesDublin City University Glasnevin Dublin 9 Ireland
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Nikitin K, Jennings EV, Al Sulaimi S, Ortin Y, Gilheany DG. Dynamic Cross-Exchange in Halophosphonium Species: Direct Observation of Stereochemical Inversion in the Course of an SN2 Process. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201708649] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Kirill Nikitin
- School of Chemistry; University College Dublin; Belfield Dublin Ireland
| | | | | | - Yannick Ortin
- School of Chemistry; University College Dublin; Belfield Dublin Ireland
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Nikitin K, Jennings EV, Al Sulaimi S, Ortin Y, Gilheany DG. Dynamic Cross-Exchange in Halophosphonium Species: Direct Observation of Stereochemical Inversion in the Course of an SN2 Process. Angew Chem Int Ed Engl 2017; 57:1480-1484. [DOI: 10.1002/anie.201708649] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2017] [Revised: 10/17/2017] [Indexed: 11/11/2022]
Affiliation(s)
- Kirill Nikitin
- School of Chemistry; University College Dublin; Belfield Dublin Ireland
| | | | | | - Yannick Ortin
- School of Chemistry; University College Dublin; Belfield Dublin Ireland
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