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Analysis with the linear free energy relationship log\u2009<jats:italic>K<\/jats:italic><jats:sub>B<\/jats:sub>=<jats:italic>LA<\/jats:italic><jats:sub>B<\/jats:sub>+<jats:italic>LB<\/jats:italic><jats:sub>B<\/jats:sub> allows equilibrium constants, <jats:italic>K<\/jats:italic><jats:sub>B<\/jats:sub>, to be calculated for any type of borane\/Lewis base combination through the sum of two descriptors, one for Lewis acidity (<jats:italic>LA<\/jats:italic><jats:sub>B<\/jats:sub>) and one for Lewis basicity (<jats:italic>LB<\/jats:italic><jats:sub>B<\/jats:sub>). The resulting Lewis acidity\/basicity scale is independent of fixed reference acids\/bases and valid for various types of trivalent boron\u2010centered Lewis acids. It is demonstrated that the newly developed Lewis acidity\/basicity scale is easily extendable through linear relationships with quantum\u2010chemically calculated or common physical\u2013organic descriptors and known thermodynamic data (\u0394<jats:italic>H<\/jats:italic><jats:inline-graphic xmlns:xlink=\"http:\/\/www.w3.org\/1999\/xlink\" xlink:href=\"graphic\/chem202003916-math-0001.png\" xlink:title=\"urn:x-wiley:09476539:media:chem202003916:chem202003916-math-0001\"\/>\n). Furthermore, this experimental platform can be utilized for the rational development of borane\u2010catalyzed reactions.<\/jats:p>","DOI":"10.1002\/chem.202003916","type":"journal-article","created":{"date-parts":[[2020,11,20]],"date-time":"2020-11-20T16:10:09Z","timestamp":1605888609000},"page":"4070-4080","update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":74,"title":["Lewis Acidic Boranes, Lewis Bases, and Equilibrium Constants: A Reliable Scaffold for a Quantitative Lewis Acidity\/Basicity Scale"],"prefix":"10.1002","volume":"27","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-9864-7042","authenticated-orcid":false,"given":"Robert J.","family":"Mayer","sequence":"first","affiliation":[{"name":"Department Chemie Ludwig-Maximilians-Universit\u00e4t M\u00fcnchen  Butenandtstr. 5\u201313 81377 M\u00fcnchen Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Nathalie","family":"Hampel","sequence":"additional","affiliation":[{"name":"Department Chemie Ludwig-Maximilians-Universit\u00e4t M\u00fcnchen  Butenandtstr. 5\u201313 81377 M\u00fcnchen Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9600-2793","authenticated-orcid":false,"given":"Armin R.","family":"Ofial","sequence":"additional","affiliation":[{"name":"Department Chemie Ludwig-Maximilians-Universit\u00e4t M\u00fcnchen  Butenandtstr. 5\u201313 81377 M\u00fcnchen Germany"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2021,1,26]]},"reference":[{"key":"e_1_2_6_1_1","unstructured":"\u00a0"},{"key":"e_1_2_6_2_2","doi-asserted-by":"publisher","DOI":"10.1002\/(SICI)1099-0690(199903)1999:3<527::AID-EJOC527>3.0.CO;2-R"},{"key":"e_1_2_6_3_2","doi-asserted-by":"publisher","DOI":"10.1002\/9783527618309.ch4"},{"key":"e_1_2_6_4_2","doi-asserted-by":"publisher","DOI":"10.1002\/9783527618309.ch5"},{"key":"e_1_2_6_5_2","first-page":"187","volume-title":"Acid Catalysis in Modern Organic Synthesis","author":"Rauniyar V.","year":"2008"},{"key":"e_1_2_6_6_2","first-page":"27","volume-title":"Boron Reagents in Synthesis (ACS Symposium Series, Vol. 1236)","author":"Hatano M.","year":"2016"},{"key":"e_1_2_6_7_2","doi-asserted-by":"publisher","DOI":"10.1021\/acs.inorgchem.6b02911"},{"key":"e_1_2_6_8_2","doi-asserted-by":"publisher","DOI":"10.1039\/C9CS00769E"},{"key":"e_1_2_6_9_2","doi-asserted-by":"publisher","DOI":"10.1016\/j.chempr.2020.06.035"},{"key":"e_1_2_6_10_1","unstructured":"\u00a0"},{"key":"e_1_2_6_11_2","doi-asserted-by":"publisher","DOI":"10.1021\/ja005607u"},{"key":"e_1_2_6_12_2","doi-asserted-by":"publisher","DOI":"10.1021\/ja205037t"},{"key":"e_1_2_6_13_2","doi-asserted-by":"publisher","DOI":"10.1039\/C3CC48796B"},{"key":"e_1_2_6_14_2","doi-asserted-by":"publisher","DOI":"10.1002\/anie.201704097"},{"key":"e_1_2_6_14_3","doi-asserted-by":"publisher","DOI":"10.1002\/ange.201704097"},{"key":"e_1_2_6_15_2","doi-asserted-by":"publisher","DOI":"10.1002\/anie.201910908"},{"key":"e_1_2_6_15_3","doi-asserted-by":"publisher","DOI":"10.1002\/ange.201910908"},{"key":"e_1_2_6_16_2","doi-asserted-by":"publisher","DOI":"10.1002\/anie.202003119"},{"key":"e_1_2_6_16_3","doi-asserted-by":"publisher","DOI":"10.1002\/ange.202003119"},{"key":"e_1_2_6_17_1","unstructured":"Concepts of semiquantitative Lewis acidity rankings were used for a rational reaction design for example in:"},{"key":"e_1_2_6_18_2","doi-asserted-by":"publisher","DOI":"10.1002\/chem.201301158"},{"key":"e_1_2_6_19_2","doi-asserted-by":"publisher","DOI":"10.1021\/om501284a"},{"key":"e_1_2_6_20_2","doi-asserted-by":"publisher","DOI":"10.1021\/jacs.7b01982"},{"key":"e_1_2_6_21_1","doi-asserted-by":"publisher","DOI":"10.1002\/chem.201802698"},{"key":"e_1_2_6_22_1","volume-title":"Lewis Basicity and Affinity Scales: Data and Measurement","author":"Laurence C.","year":"2010"},{"key":"e_1_2_6_23_1","doi-asserted-by":"publisher","DOI":"10.1351\/pac199466051077"},{"key":"e_1_2_6_24_1","unstructured":"\u00a0"},{"key":"e_1_2_6_25_2","doi-asserted-by":"publisher","DOI":"10.1021\/ja961536g"},{"key":"e_1_2_6_26_2","doi-asserted-by":"publisher","DOI":"10.1021\/om9710327"},{"key":"e_1_2_6_27_2","doi-asserted-by":"publisher","DOI":"10.1021\/om3011195"},{"key":"e_1_2_6_28_1","doi-asserted-by":"publisher","DOI":"10.1021\/ja4119169"},{"key":"e_1_2_6_29_1","unstructured":"\u00a0"},{"key":"e_1_2_6_30_2","doi-asserted-by":"publisher","DOI":"10.1021\/ja900572x"},{"key":"e_1_2_6_31_2","doi-asserted-by":"publisher","DOI":"10.1021\/ic901726b"},{"key":"e_1_2_6_32_1","unstructured":"\u00a0"},{"key":"e_1_2_6_33_2","doi-asserted-by":"publisher","DOI":"10.1016\/j.ccr.2013.10.017"},{"key":"e_1_2_6_34_2","doi-asserted-by":"publisher","DOI":"10.1021\/om9709953"},{"key":"e_1_2_6_35_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0022-328X(00)80358-7"},{"key":"e_1_2_6_36_2","first-page":"83","volume":"6","author":"Cohen S. 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Attractive aryl\u2013aryl interactions have been observed however in the Lewis adduct1\u2009i\/ethyl benzoate. For selected examples of X-ray structures for Lewis adducts of1\u2009iwith"},{"key":"e_1_2_6_53_2","unstructured":"benzaldehyde (7\u2009b) acetophenone and ethyl benzoate: refs.\u2005[7a b];"},{"key":"e_1_2_6_54_2","unstructured":"pyridines: ref.\u2005[9b];"},{"key":"e_1_2_6_55_2","doi-asserted-by":"publisher","DOI":"10.1021\/om981033e"},{"key":"e_1_2_6_56_2","doi-asserted-by":"publisher","DOI":"10.1016\/S1387-7003(00)00129-5"},{"key":"e_1_2_6_57_1","doi-asserted-by":"publisher","DOI":"10.1021\/ol000164k"},{"key":"e_1_2_6_58_1","unstructured":"\u00a0"},{"key":"e_1_2_6_59_2","doi-asserted-by":"publisher","DOI":"10.1016\/j.trechm.2020.02.005"},{"key":"e_1_2_6_60_2","doi-asserted-by":"publisher","DOI":"10.1039\/C6SC00705H"},{"key":"e_1_2_6_61_2","unstructured":"for full details of the computational methods and references see the Supporting Information."},{"key":"e_1_2_6_62_1","doi-asserted-by":"publisher","DOI":"10.1039\/C4DT02822H"},{"key":"e_1_2_6_63_1","doi-asserted-by":"publisher","DOI":"10.1021\/om980229b"},{"key":"e_1_2_6_64_1","unstructured":"Analogously the Lewis acidities for B(o-HC6F4)3(LAB=6.7) and B(p-HC6F4)3(LAB=6.9) can be derived from equilibrium constants reported in ref.\u2005[7c]."},{"key":"e_1_2_6_65_1","unstructured":"\u00a0"},{"key":"e_1_2_6_66_2","doi-asserted-by":"publisher","DOI":"10.1039\/C8DT01699B"},{"key":"e_1_2_6_67_2","doi-asserted-by":"publisher","DOI":"10.1021\/acs.inorgchem.8b02517"},{"key":"e_1_2_6_68_1","unstructured":"\u00a0"},{"key":"e_1_2_6_69_2","volume-title":"Exploring QSAR\u2014Hydrophobic, Electronic, and Steric Constants (ACS Professional Reference Book)","author":"Hansch C.","year":"1995"},{"key":"e_1_2_6_70_2","doi-asserted-by":"publisher","DOI":"10.1039\/j29700000053"},{"key":"e_1_2_6_71_2","doi-asserted-by":"publisher","DOI":"10.1039\/jr9640003591"},{"key":"e_1_2_6_72_2","doi-asserted-by":"publisher","DOI":"10.1021\/ja00759a062"},{"key":"e_1_2_6_73_2","doi-asserted-by":"publisher","DOI":"10.1039\/tf9545000918"},{"key":"e_1_2_6_74_1","doi-asserted-by":"publisher","DOI":"10.1201\/9781420007282"},{"key":"e_1_2_6_75_1","unstructured":"\u00a0"},{"key":"e_1_2_6_76_2","doi-asserted-by":"publisher","DOI":"10.1002\/anie.201103615"},{"key":"e_1_2_6_76_3","doi-asserted-by":"publisher","DOI":"10.1002\/ange.201103615"},{"key":"e_1_2_6_77_2","doi-asserted-by":"publisher","DOI":"10.1039\/C6SC02727J"},{"key":"e_1_2_6_78_1","doi-asserted-by":"publisher","DOI":"10.1002\/chem.201701080"},{"key":"e_1_2_6_79_1","unstructured":"Attractive interactions through C\u2212H\u22c5\u22c5\u22c5F bonds of the triarylboranes\u2019ortho-fluorine atoms in Lewis adducts with aldehydes were discussed in ref.\u2005[7b]."},{"key":"e_1_2_6_80_1","unstructured":"\u00a0"},{"key":"e_1_2_6_81_2","unstructured":"A binding constant ofK=3.0\u00d7104\u2009m\u22121(in CH2Cl2) was determined for the Lewis acid\/base couple B(C6Cl5)3\/2\u2009a(ref.\u2005[30b]). 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