In chemistry, the Gutmann–Beckett method is an experimental procedure used by chemists to assess the Lewis acidity of molecular species. Triethylphosphine oxide (Et3PO, TEPO) is used as a probe molecule and systems are evaluated by 31P-NMR spectroscopy. In 1975, Viktor Gutmann [de] used 31P-NMR spectroscopy to parameterize Lewis acidity of solvents by acceptor numbers (AN).[1] In 1996, Michael A. Beckett recognised its more generally utility and adapted the procedure so that it could be easily applied to molecular species, when dissolved in weakly Lewis acidic solvents.[2] The term Gutmann–Beckett method was first used in chemical literature in 2007.[3]
The 31P chemical shift (δ) of Et3PO is sensitive to chemical environment but can usually be found between +40 and +100 ppm. The O atom in Et3PO is a Lewis base, and its interaction with Lewis acid sites causes deshielding of the adjacent P atom. Gutmann, a chemist renowned for his work on non-aqueous solvents, described an acceptor-number scale for solvent Lewis acidity [4] with two reference points relating to the 31P NMR chemical shift of Et3PO in the weakly Lewis acidic solvent hexane (δ = 41.0 ppm, AN 0) and in the strongly Lewis acidic solvent SbCl5 (δ = 86.1 ppm, AN 100). Acceptor numbers can be calculated from AN = 2.21 x (δsample – 41.0) and higher AN values indicate greater Lewis acidity. It is generally known that there is no one universal order of Lewis acid strengths (or Lewis base strengths) and that two parameters (or two properties) are needed (see HSAB theory and ECW model) to define acid and base strengths[5][6] and that single parameter or property scales are limited to a smaller range of acids (or bases). The Gutmann-Beckett method is based on a single parameter NMR chemical shift scale but is in commonly used due to its experimental convenience.
Application to boranes
Interaction of triethylphosphine oxide with a Lewis acid
Boron trihalides are archetypal Lewis acids and have AN values between 89 (BF3) and 115 (BI3).[2] The Gutmann–Beckett method has been applied to fluoroarylboranes [7][8] such as B(C6F5)3 (AN 82), and borenium cations, and its application to these and various other boron compounds has been reviewed.[9]
Application to other compounds
The Gutmann–Beckett method has been successfully applied to alkaline earth metal complexes,[10][11]p-block main group compounds [7][12][13][14][15] (e.g. AlCl3, AN 87; silylium cations; [E(bipy)2]3+ (E = P, As, Sb, Bi) cations; cationic 4 coordinate Pv and Sbv derivatives) and transition-metal compounds [7][16] (e.g. TiCl4, AN 70).
References
^U. Mayer, V. Gutmann, and W. Gerger, "The acceptor number – a quantitative empirical parameter for the electrophilic properties of solvents", Monatshefte fur Chemie, 1975, 106, 1235–1257. doi: 10.1007/BF00913599
^ abM.A. Beckett, G.C. Strickland, J.R. Holland, and K.S. Varma, "A convenient NMR method for the measurement of Lewis acidity at boron centres: correlation of reaction rates of Lewis acid initiated epoxide polymerizations with Lewis acidity", Polymer, 1996, 37, 4629–4631. doi: 10.1016/0032-3861(96)00323-0
^G.C. Welch, L.Cabrera, P.A. Chase, E. Hollink, J.M. Masuda, P. Wei, and D.W. Stephan,"Tuning Lewis acidity using the reactivity of "frustrated Lewis pairs": facile formation of phosphine-boranes and cationic phosphonium-boranes", Dalton Trans., 2007, 3407–3414. doi: 10.1039/b704417h
^V. Gutmann, "Solvent effects on reactivities of organometallic compounds", Coord. Chem. Rev., 1976, 18, 225–255. doi: 10.1016/S0010-8545(00)82045-7
^Laurence, C. and Gal, J-F. Lewis Basicity and Affinity Scales, Data and Measurement, (Wiley 2010) pp 50-51 ISBN 978-0-470-74957-9
^Cramer, R. E.; Bopp, T. T. (1977). "Graphical display of the enthalpies of adduct formation for Lewis acids and bases". Journal of Chemical Education. 54: 612–613. doi:10.1021/ed054p612. The plots shown in this paper used older parameters. Improved E&C parameters are listed in ECW model.
^ abcM.A. Beckett, D.S. Brassington, S.J. Coles, and M.B. Hursthouse, "Lewis acidity of tris(pentafluorophenyl)borane: crystal and molecular structure of B(C6F5)3.OPEt3", Inorg. Chem. Commun., 2000, 3, 530–533. doi: 10.1016/S1387-7003(00)00129-5
^S.C. Binding, H. Zaher, F.M. Chadwick, and D. O'Hare, "Heterolytic activation of hydrogen using frustrated Lewis pairs containing tris(2,2',2'-perfluorobiphenyl)borane", Dalton Trans., 2012, 41, 9061–9066. doi: 10.1039/c2dt30334e
^S. Brand, J. Pahl, H. Elsen, and S. Harder, "Frustrated Lewis pair chemistry with magnesium Lewis acids", European J. Inorg. Chem., 2017, 4187-4195. doi: 10.1002/ejic.201700787
^J. Pahl, S. Brand, H. Elsen, and S. Harder,"Highly Lewis acidic cationic alkaline earth metal complexes", Chem. Commun., 2018, 54, 8685-8688. doi: 10.1039/C8CC04083D
^H. Grossekappenberg, M. Reissmann, M. Schmidtmann, and T. Mueller, “Quantitative assessment of the Lewis acidity of silylium ions”, Organometallics, 2015, 34, 4952-4958. doi: 10.1021/acs.organomet.5b00556
^S.S. Chitnis, A.P.M. Robertson, N. Burford, B.O. Patrick, R. McDonald, and M.J. Ferguson, “Bipyridine complexes of E3+ (E = P, As, Sb, Bi): strong Lewis acids, sources of E(OTf)3 and synthons for EI and Ev cations”, Chemical Sciences, 2015, 6, 6545-6555. doi: 10.1039/C5SC02423D
^J.M. Bayne and D.W. Stephan, “Phosphorus Lewis acids: emerging reactivity and applications in catalysis”, Chem. Soc. Rev., 2015, 45, 765-774. doi:10.1039/c5cs00516g
^B. Pan and F. Gabbai, “[Sb(C6H5)4][B(C6F5)4]: an air stable Lewis acidic stibonium salt that activates strong element-fluorine bonds”, J. Am. Chem. Soc., 2014, 136, 9564-9567. doi: 10.1021/ja505214m
^C.-Y. Wu, T. Horibe, C.B. Jacobsen, and D. Toste, “Stable gold(III) catalysts by oxidative addition of a carbon-carbon bond”, Nature, 2015, 517, 449-454. doi: 10.1038/nature14104
January 06, 2023
gutmann, beckett, method, chemistry, experimental, procedure, used, chemists, assess, lewis, acidity, molecular, species, triethylphosphine, oxide, et3po, tepo, used, probe, molecule, systems, evaluated, spectroscopy, 1975, viktor, gutmann, used, spectroscopy,. In chemistry the Gutmann Beckett method is an experimental procedure used by chemists to assess the Lewis acidity of molecular species Triethylphosphine oxide Et3PO TEPO is used as a probe molecule and systems are evaluated by 31P NMR spectroscopy In 1975 Viktor Gutmann de used 31P NMR spectroscopy to parameterize Lewis acidity of solvents by acceptor numbers AN 1 In 1996 Michael A Beckett recognised its more generally utility and adapted the procedure so that it could be easily applied to molecular species when dissolved in weakly Lewis acidic solvents 2 The term Gutmann Beckett method was first used in chemical literature in 2007 3 Contents 1 Background 2 Application to boranes 3 Application to other compounds 4 ReferencesBackground EditThe 31P chemical shift d of Et3PO is sensitive to chemical environment but can usually be found between 40 and 100 ppm The O atom in Et3PO is a Lewis base and its interaction with Lewis acid sites causes deshielding of the adjacent P atom Gutmann a chemist renowned for his work on non aqueous solvents described an acceptor number scale for solvent Lewis acidity 4 with two reference points relating to the 31P NMR chemical shift of Et3PO in the weakly Lewis acidic solvent hexane d 41 0 ppm AN 0 and in the strongly Lewis acidic solvent SbCl5 d 86 1 ppm AN 100 Acceptor numbers can be calculated from AN 2 21 x dsample 41 0 and higher AN values indicate greater Lewis acidity It is generally known that there is no one universal order of Lewis acid strengths or Lewis base strengths and that two parameters or two properties are needed see HSAB theory and ECW model to define acid and base strengths 5 6 and that single parameter or property scales are limited to a smaller range of acids or bases The Gutmann Beckett method is based on a single parameter NMR chemical shift scale but is in commonly used due to its experimental convenience Application to boranes Edit Interaction of triethylphosphine oxide with a Lewis acidBoron trihalides are archetypal Lewis acids and have AN values between 89 BF3 and 115 BI3 2 The Gutmann Beckett method has been applied to fluoroarylboranes 7 8 such as B C6F5 3 AN 82 and borenium cations and its application to these and various other boron compounds has been reviewed 9 Application to other compounds EditThe Gutmann Beckett method has been successfully applied to alkaline earth metal complexes 10 11 p block main group compounds 7 12 13 14 15 e g AlCl3 AN 87 silylium cations E bipy 2 3 E P As Sb Bi cations cationic 4 coordinate Pv and Sbv derivatives and transition metal compounds 7 16 e g TiCl4 AN 70 References Edit U Mayer V Gutmann and W Gerger The acceptor number a quantitative empirical parameter for the electrophilic properties of solvents Monatshefte fur Chemie 1975 106 1235 1257 doi 10 1007 BF00913599 a b M A Beckett G C Strickland J R Holland and K S Varma A convenient NMR method for the measurement of Lewis acidity at boron centres correlation of reaction rates of Lewis acid initiated epoxide polymerizations with Lewis acidity Polymer 1996 37 4629 4631 doi 10 1016 0032 3861 96 00323 0 G C Welch L Cabrera P A Chase E Hollink J M Masuda P Wei and D W Stephan Tuning Lewis acidity using the reactivity of frustrated Lewis pairs facile formation of phosphine boranes and cationic phosphonium boranes Dalton Trans 2007 3407 3414 doi 10 1039 b704417h V Gutmann Solvent effects on reactivities of organometallic compounds Coord Chem Rev 1976 18 225 255 doi 10 1016 S0010 8545 00 82045 7 Laurence C and Gal J F Lewis Basicity and Affinity Scales Data and Measurement Wiley 2010 pp 50 51 ISBN 978 0 470 74957 9 Cramer R E Bopp T T 1977 Graphical display of the enthalpies of adduct formation for Lewis acids and bases Journal of Chemical Education 54 612 613 doi 10 1021 ed054p612 The plots shown in this paper used older parameters Improved E amp C parameters are listed in ECW model a b c M A Beckett D S Brassington S J Coles and M B Hursthouse Lewis acidity of tris pentafluorophenyl borane crystal and molecular structure of B C6F5 3 OPEt3 Inorg Chem Commun 2000 3 530 533 doi 10 1016 S1387 7003 00 00129 5 S C Binding H Zaher F M Chadwick and D O Hare Heterolytic activation of hydrogen using frustrated Lewis pairs containing tris 2 2 2 perfluorobiphenyl borane Dalton Trans 2012 41 9061 9066 doi 10 1039 c2dt30334e I B Sivaev V L Bregadze Lewis acidity of boron compounds Coord Chem Rev 2014 270 271 75 88 doi 10 1016 j ccr 2013 10 017 S Brand J Pahl H Elsen and S Harder Frustrated Lewis pair chemistry with magnesium Lewis acids European J Inorg Chem 2017 4187 4195 doi 10 1002 ejic 201700787 J Pahl S Brand H Elsen and S Harder Highly Lewis acidic cationic alkaline earth metal complexes Chem Commun 2018 54 8685 8688 doi 10 1039 C8CC04083D H Grossekappenberg M Reissmann M Schmidtmann and T Mueller Quantitative assessment of the Lewis acidity of silylium ions Organometallics 2015 34 4952 4958 doi 10 1021 acs organomet 5b00556 S S Chitnis A P M Robertson N Burford B O Patrick R McDonald and M J Ferguson Bipyridine complexes of E3 E P As Sb Bi strong Lewis acids sources of E OTf 3 and synthons for EI and Ev cations Chemical Sciences 2015 6 6545 6555 doi 10 1039 C5SC02423D J M Bayne and D W Stephan Phosphorus Lewis acids emerging reactivity and applications in catalysis Chem Soc Rev 2015 45 765 774 doi 10 1039 c5cs00516g B Pan and F Gabbai Sb C6H5 4 B C6F5 4 an air stable Lewis acidic stibonium salt that activates strong element fluorine bonds J Am Chem Soc 2014 136 9564 9567 doi 10 1021 ja505214m C Y Wu T Horibe C B Jacobsen and D Toste Stable gold III catalysts by oxidative addition of a carbon carbon bond Nature 2015 517 449 454 doi 10 1038 nature14104 Retrieved from https en wikipedia org w index php title Gutmann Beckett method amp oldid 1111014823, wikipedia, wiki, book, books, library,
