Lewis Acid And Base, Chemistry Of Group 13 Element

Current Organic Chemistry (year of 2017)Lewis Acid and Base, Chemistry of Group 13 ElementMay 30, 2017, #8, Makoto Yamashita (room 1031)makoto@oec.chembio.nagoya-u.ac.jpLewis Acid and BaseLewis acid:Lewis base:vacant orbitalLB LALewis base Lewis acidcoordination bondLB LALewis acid-base adductGilbert Lewis“Octet rule”Lewis, G. N., Valence and the Structure of Atoms and Molecules.Chemical Catalogue Company, Inc.: New York, 1923.

Collecting LiteraturesClassification of literatures and their citation format(1)(2)ex. Tsukahara, N.; Asakawa, H.; Lee, K.-H.; Lin, Z.; Yamashita, M., J. Am. Chem. Soc. 2017, 139, 2593-2596.name of authorsabbreviatedjounal nameyear volumepagesFor full-name of journal, google with a word of “abbreviation” and abbreviated journal name J. Am. Chem. Soc. the Journal of the American Chemical Society (sometimes further abbreviated as JACS)(3)place of publisherex. Pauling, L., The Nature of The Chemical Bond. 3 ed.; Cornell University Press: Ithaca, 1960.name of authortitle of the book (italicized)name of authorstitle of chaptereditionname of publisherpublished yeartitle of the book (italicized)ex. Yamashita, M.; Nozaki, K., Boryl Anions. In Synthesis and Application of Organoboron Compounds,Fernández, E.; Whiting, A., Eds. Springer International Publishing: 2015; pp 1-37.name of editorsname of publisherpublished year page of chapterHow to find the paper(1) go to http://sfx.nul.nagoya-u.ac.jp/nagoya/az/?lang eng on browser of your PC(2) type the journal name into the textbox of “title” and hit “Go”(3) you will find the title of the journal on the bottom, then click it(4) type year, vol, and start page, then hit “go”(5) click PDF in somewhere of the website

Examples of Lewis Acids & BasesLewis acidsmetals possessing vacant orbitalscan also be drawn withO-Mg covalent bond(no formal charge)group 13 element compoundsheavy main group element compoundspossessing a low-energy σ* orbitalLewis basesheteroatoms having lone pair(s)transition metals having a filled d-orbitalOEtFeOC CO ClOEtOEtFeOCOCOrg. Synth. 1988, 66, 95.OEt

Strength of Lewis AcidsDonation of π-electron weakens Lewis acidityLewis acidity of boron compounds(high) BPh3 B(OMe)3 B(NMe2)3 (low)OMeOMeBMeOEnhancement of Lewis acidity by electron-withdrawing groupsLewis acidity of boron compoundsFapplication of strong Lewis acidFMeMeZr(high)FFFB FFF FFFFFFF FBFF FFFFFFF(low)FBZrMe [MeB(C6F5)3]FF FFMe B(C6F5)3MeFFJACS 1998, 120, 1772.Enhancement of Lewis acidity by formal positive chargeHHB H CH2Cl2HHB NEt3 CH2Cl2Hcoordination bondHBH NEt3ClCH2ClBH HH ClCH2ClBH NEt3cationic boron bindsa lone pair of CH2Cl2application of strong Lewis acidFFPC6F5σ*P-FC6F5C6F5 F RC6F5C6F5 RPFC6F5Science 2013, 341, 1374.fluorophosphonium could absorb fluorideeven from alkyl fluoride to form alkyl cationhomework (1):Design your own Lewis acidhaving cationic charge and draw its structure

Lewis Acid Catalyst (1)Basic concept:remind Friedel-Crafts alkylationcoordination of carbonyl to Lewis acidto enhance the reactivityO BF3 OSSHBF3SHSHSHS H2O BF3BF3 is regeneratedto be used as catalysthomework (2):Draw the remaining mechanismwith curved arrows(remind the formation of acetal)AlCl3 is regeneratedto be used as catalystApplication(1) Mukaiyama aldol reactionOrganic Syntheses, 1993, Coll. Vol. 8, 578.BF3 absorbes OEt anion to forman oxonium intermediate(2) CBS (Corey-Bakshi-Shibata) reductionoxazaborolidineJACS 1987, 109, 5551.Double activation:(a) N to BH3, (b) carbonyl to BStoichiometric amount of borane (BH3) catalytic amount of oxazaborolidine

Lewis Acid Catalyst (2)ApplicationChemoselective reductionMAD: ide)Ring-opening alternating co-polymerization ofepoxide and CO2 to produce biodegradable polymerpolymer from CO2recently industrializedMakromol. Chem. 1969, 130, 210.“bulky” Lewis acidJACS 1988, 110, 2650.Ring-opening polymerization of cyclic carbonate estergenerated from CO2 to produce biodegradable polymerOrganometallics 2011, 30, 3217.

Lewis Base CatalystBasic concept:acceleration of nucleophilic acyl substitution by cationic chargeN H 3CMe2NNOCOCOCH3 Me2NOCH 3CN R OHCH3OCH 3CMe2NNR OHO Me2NROHOCOC OH CH3 H3CROCOOOCCH3N,N-dimethylpyridineis regenerated to beused as catalysthomework (3):Draw resonance hybrid of the first intermediatewith four resonance structuresApplicationStetter reaction by using nucleophilic carbene catalyst: umpolung reaction of aldehydeRNC HSRRRRbaseROHNC CSR’RRNCSRcarbeneRRNCSRylideOR HN OC CSR’RRR’OCHRONC C HSR’RRaldehyde can be considered as ORRRNR’C CSOOHACIE 1976, 15, 639.carbene (ylide) is regeneratedto be used as catalyst

rstchd–reby70on-rusalhereirreLPthed ametheonattestamuews.Frustrated Lewis Pair (FLP)generated the following question: Can one effect consecutiveBasicconcept:delivery of proton and hydride to an organic substrate? If so, thisIf Lewisandhydrogenationbase can systemnot formadductdue to stericwouldyield aacidmetal-freethat wouldregeneratetheshowFLP to uniquefurther activateH2, yieldinga lesIndeed, this hypothesis was first demonstrated to be true fornitrogen-basedunsaturatedmolecules.The mechanism of suchheterolyticcleavageof hydrogenmetal-free imine reductions has been shown to proceed viaFFof the imine, followed by hydrideFFinitial protonationtransferHH2 carbon (Scheme 1).11,12from the hydridoborate to the iminiumMestheB(C6FandB(C6F5)3ThisMesnet2Ptransfer of proton2P phosphonium5)3 hydride fromΔHborate to the imine regenerates the Lewis acid–base pair, whichFFFFare then available for subsequent activation of H2 regeneratingthe phosphonium-borate. This mechanism is consistent with theScience2006, 314,1124.observed reactivity trends in whichthe electron-richimine,tBuNvCPh(H) is reduced significantly faster than the electronpoor imine, PhSO2NvCPh(H). In addition, the phosphoniumborate (Cy3P)(C6F4)BH(C6F5)2 13 was shown not to react withimine. These results are consistent with initiation of the imineApplicationreduction via protonation.hindrance,View Article OnlineACIE 2010, 49, 46.Catalytic hydrogenation of imine, nitrile, aziridine, aromatic hydrocarbons, alkenes, and ketonesScheme 7 FLP hydrogenation of a diimine.Prof. Doug Stephan@U of Toronto, CanadaredH2ACIE 2007, 46, 8050.Scheme 1 Mechanism for FLP hydrogenation of imine.Commun.of 2012,48, heterocycles.11963.SchemeChem.9 FLP hydrogenationsnitrogen-based

Organic Molecules Containing Group 13 ElementElectronic effect of boryl substituentIn all cases, a vacant p-orbital of B atom accept an electron pairto form a negatively charged “borate” having four bonds“Inorganic benzene”: BorazineDue to B N double bond character,borazine is similar to benzeneBN-Containing aromatic moleculesACIE 2009, 48, 973.JACS 2011, 133, 11508.Polarity of B N double bond gives unique photophysical propertiesProf. Warren Piers@U of Calgary, Canadageneral review:Can. J. Chem. 2009, 87, 8.

3-Center-2-Electron BondStructure of Be(CH3)2Be or MgHWilliam LipscombNobel Prize 1976Electron deficient group 1, 2, and 13 element compoundseasily aggregate by sharing bonding electrons into vacant orbital(s)3-center-2-electron bondStructures of CH5 and B2H6HHCHHH HHBHHCHHHH3-center-2-electron bondImportant intermediatein acid-catalyzedcracking process of oilHHBHHHBHHBHHHHHBBHhydride (H–) reagent in organic synthesisGeorge OlahNobel Prize 1994homework (4):Draw the structure of (AlMe3)2 with 3c-2e bondwith description of orbitals and electronsHH

Diborane(4): Strong Lewis Acid & ReductantB–B bond in B BOB2pin2 1Cf. Nomenclature of Inorganic ChemistryIUPAC Recommendations 2005bond length (Å) BDE (kJ/mol)B–B1.75293B–C1.65372B–O1.36536J. Emsley, The Elements, 3rd ed.,Oxford University Press, New York, 1998.Diborane(4) can reduce C N triple bondHN CMes (1 equiv.) Mes COHB BB50%HMesOpinB NtButButCO 20%ButBu N C(1 atm)NNMesMes (excess)MesMesCCC B B CC BpinB OCpinB NMes pinB NMestButBuOtBuThe unsymmetrical diborane(4) compound reactedwith isocyanide to cleave C N triple bondoverlapping of two vacant orbitalslead to higher Lewis acidityAsakawa, H.; Lee, K.-H.; Lin, Z.; Yamashita, M., Nat. Commun. 2014, 5, 4245.Asakawa, H.; Lee, K.-H.; Furukawa, K.; Lin, Z.; Yamashita, M., Chem. Eur. J. 2015, 21, 4267.

Diborane(4): Strong Lewis Acid & ReductantHighly Lewis acidic diborane(4) reacted with alkyneDirect diboration of alkyne with controlled selectivityKojima, C.; Lee, K.-H.; Lin, Z.; Yamashita, M., J. Am. Chem. Soc. 2016, 138, 6662.Further higher Lewis acidity leads direct reaction with H2H2BBhexaneRT, 2 h52%BHHpyridineBHBN96%The first example of direct metathesis between B–B and H–H bondsH–H bond was reduced by reductive B–B bondTsukahara, N.; Asakawa, H.; Lee, K.-H.; Lin, Z.; Yamashita, M., J. Am. Chem. Soc. 2017, 139, 2593.

Boron Clusters via Accumulation of 3c-2e BondsWade rule: Nomenclature for cluster compoundsAccumulation ofCounting in Wade ruleKenneth Wade(1) counting all electrons from formula of the clusterex. B: 3, H: 1, charges change the # of electrons(2) SEP (skeletal electron pair) is defined as[(total electrons) – 2 (B-H unit)]/2(3) all borane clusters can be classified byn SEP – (# of B atoms)n 1: closo-, n 2: nido-, n 3: arachno(4) determining the # of verticescloso-, SEP–1; nido-, SEP–2; arachno-, SEP–3(5) # of vertices can give the structureex. B5H9all electrons 5 x 3 (B) 9 x 1 (H) 24SEP [24 – 2 5]2 7n SEP – 5 2, can be considered as nido-borane# of vertices SEP–2 5

Boron Clusters (2)Carborane: carbon-incorporated boron cluster[B12H12]2 [CB11H12] tions of carboraneuse [C2B10H12] as a surrogate ofbenzene ring in medicinal chemistryapplication in pharma (1)application in pharma (2)BNCT Boron Neutron Capture Therapyanti-inflammatoryamyloid synthesis inhibitoractivefor BNCTimportant to concentratein cancer cells

Boron Clusters (3)Application of carborane:[CB11H12]– can be used as non-coordinating anion to stabilize unstable cation species(1) X-ray crystallographicanalysis of tert-Bu cationdC 334.2(SO2)(2) model for Whelandintermediate (SEAr reaction)(3) carborane acid: the strongest acid3.530 Å3.489 ÅJACS 2005, 127, 7664.JACS 2006, 128, 3160.(4) application of carborane acid:protonation of C60C–CH3 1.429(4)–1.459(4) Å ACIE 2004, 43, 2908.Cl interacted with the vacantp-orbital of carbocation similar to the transitionstate of SN2 reactionJACS 1972, 94, 2034.JACS 2003, 125, 1796.positions of delocalizedcationic charge wereidentical to the old reportfor NMR observationScience 2000, 289, 101.

Chemistry of Boronic AcidBoronic acid: carbon-substitutedboric acid [B(OH)3] derivativesH-bonding dimerReaction with H2O to liberate H (acid)Fast formation of cyclic ester with diolApplication of cyclic ester (1): molecular recognition of sugarchelate effect makesproduct stableNature 1995, 374, 345.Formation of a complex with sugar leads fluorescenceApplication of cyclic ester (2): porous polymerJACS 2008, 130, 11872.Spontaneous shift of equilibriumthrough reversible reactionsPorous material consisting of covalent bondsBoronic Acidsedited by Deniss G. HallWiley-VCH, 2011

Hydrometallation with Group 13 ElementHydroborationRepresentative hydroboration reagentsHBOO BH3Me2S brown-hydroboration.html4-centered TSB HOcatecholboraneHerbert BrownNobel Prize 19799-borabicyclo[3.3.1]nonane(9-BBN)Oxidation of alkylboranedisiamylboraneHBB HHBHthexylboraneB Metal-catalyzed hydroborationcat Rh(PPh3)3Cl0.05 mol%, 20 min, 83%ACIE 1985, 24, 878.JACS, 1964, 86, 3565.Hydroalumination of alkeneelectron-donating groups syn additionReaction of alkenylaluminumelectron-withdrawing groups anti additionReactive C–Al bond can be usedas organometallic nucleophilehomework (5):Explain the reason why anti-additon productwas obtained with electron-withdrawing groupstogether with the structures of key intermediate(hint: after syn-addition, isomerization takes place)Can. J. Chem. 1973, 51, 2098.