Hans-Beat Bürgi in Strasbourg – the story of an encounter 2022 Jean-Marie Lehn.pdf

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Hans-BeatBu¨rgiinStrasbourg–the
storyofanencounter
ISSN2052-5206
Jean-MarieLehn*
InstituteforAdvancedStudy(USIAS),UniversityofStrasbourg,BP70028,8Alle´e
GaspardMonge,Strasbourg,Alsace67083Cedex,France.*Correspondencee-mail:
******@
Received17January2022
Accepted1March2022
IthappenedthatthescientificpathofHans-BeatBu¨rgi
.
,UniversityofBern,From1968to1980,wehadbeenpursuingabinitiomol-
Switzerland
ecularquantumcomputationalstudiesusingtheabinitio
SCF-LCAO-MO(Hartree–Fock)
Keywords:Hans-BeatBu¨rgi;Strasbourg;
-1960sbyEnrico
ClementiatIBMwiththecollaborationofAlainVeillard,who
subsequentlyjoinedourChemistryDepartmentatthe
UniversityofStrasbourgandbroughttheprogramto
Strasbourg(thusinitiatingquantumchemistryatour
university).ThankstotheavailabilityoftheIBMOL
program,aseriesofabinitioquantumchemicalstudies
werepursuedinmygroup,concerningespeciallynitrogen
inversionbarriers,electronicstructuresandstereo-
electroniceffectsinorganicmolecules[forareview,seeLehn
(1970)].
Atthebeginningofthe1970s,Hans-BeatBu¨rgi,thenaPhD
studentinthelaboratoryofJackDunitzattheETHinZurich,
Switzerland,wasexaminingtheworkinghypothesisthatdata
obtainedfromstaticcrystalstructuresmayprovideapicture
ofthechangesthatoccuralongthepathwayofachemical
-
energypathwaysfortwotypesofinorganicreaction,ligand
addition(Bu¨rgi,1973)andligandremoval(Bu¨rgietal.,1975),
atnon-carbontetrahedralcentres,aswellasfornucleophilic
addition/eliminationreactionsatcarbonyl(Bu¨rgietal.,1973).
Theresultssuggestedthatimportantfeaturesoftheminimum-
energypathswerelargelyindependentofthenatureofthe
centralatomandoftheligandsbutwerecharacteristicofthe
reactiontype.
In1973,Hans-Beatspentseveralmonthsinmygroupin
Strasbourgtoperformquantumchemicalcomputationsusing
theIBMOLprogram,withthegoalofprovidingtheoretical
supportinfavouroftheconjecturethatcrystalstructures
couldindeedprovideinformationaboutthepathwayof

onthepositioningofnitrogensiteswithrespecttocarbonyl
groupsinvariouscrystalstructures,thetrajectoryofthefirst
step,theapproachofthetworeagents,inthecondensationof
anaminewithanaldehydeoraketonecouldbepictured
(Bu¨rgietal.,1973).Thecrystalstructuresweretakenasfrozen
snapshotsonadynamicevolutionfromthestartingreactants

course,theconjecturewouldacquireamuchbroadersignifi-
canceifitcouldbeextendedtoawholesetofdifferent
chemicalreactions.
ActaCryst.(2022).B78,295–297/S2052520622002372295
Hans-BeatBu¨rgitribute
Figure1
(Left)Theminimum-,B,C,D,EcorrespondtoHÀÁÁÁ,,
˚À
,,respectively,forwhichthecalculatedbindingenergies(relativetoinfinitelyseparatedH+CH2O),,,
À1,À1higherthantheminimum-energypath.(Right)
¨rgietal.(1974),copyright(1974)Elsevier.
Figure2
.(1974),copyright(1974),JohnWiley&SonsInc.
ThestudyperformedbyHans-˚.Theseresultswerereportedintwo
Wipff,thenagraduatestudentinmygroup,concernedthepapers[Buergietal.(1974)andBu¨rgietal.(1974)].
‘idealized’caseoftheapproachofahydrideionHÀtotheThetetrahedralintermediateresultingfromtheadditionof
-anucleophiletoacarbonylgroupalsohasamajorsignificance
tersmadesuchdrasticsimplificationcompulsoryforabinitiointhereactivityofimines,estersand,mostimportantly,


thepathwayledtotheidentificationofthreesteps:(i)formedinesterandamidehydrolysisandtheireffecton
electrostaticguidedapproachalongthedirectionofthereactivity,susceptibletooperatingontheintimatefeaturesof
carbonylgroupintheplaneofthemoleculeatadistanceenzymaticreactionsonesterandpeptidebonds,werethe
largerthan3A˚;(ii)contactwiththeHatomsoftheformal-subjectofextensivetheoreticalstudiesbyGeorgesWipffinhis
dehydemoleculeleadingtothepathcurvingoutoftheplanePhDwork,usingasmodelstheadductofwaterwithformic
˚;(iii)finally,acidandformamide(Lehnetal.,1974;Lehn&Wipff,1974;
bondformationatanangleleadingtoamethoxideionatshort1980).Inthiscontext,Hans-Beattookpartinstudieson
296Jean-MarieLehnHans-BeatBu¨rgiinStrasbourgActaCryst.(2022).B78,295–297
Hans-BeatBu¨rgitribute
hydroxymethanes,wheremethanetriolmaybetakenasaReferences
modelofthetetrahedralintermediateinesterhydrolysisBuergi,.,Lehn,J.-M.&Wipff,G.(1974).,
()(Lehnetal.,1974).1956–1957.
Theamine–carbonylcondensationprocess,apillarofBu¨rgi,.(1973).,2321–2325.
organicreactions,anditselectronicfeatureshavegainedBu¨rgi,.,Dunitz,.,Lehn,J.-M.&Wipff,G.(1974).
furthersignificanceasanemblematicreversiblereactionintheTetrahedron,30,1563–1572.
Bu¨rgi,.,Dunitz,.&Murray-Rust,P.(1975)..
,921–922.
ThuswasourveryenjoyablecommonscientificstoryattheBu¨rgi,.,Dunitz,.&Shefter,E.(1973).,
triplemeetingpointofchemicalreactivity,crystalstructures5065–5067.
,J.-M.(1970).TopicsinCurrentChemistry,,–377.
greatpleasuretowishHans-BeataveryHappy80thBirthday!Heidelberg:SpringerVerlag.
Lehn,J.-M.&Wipff,G.(1974).,4048–4050.
IthappensthatithasalsobecomeafittingoccasiontopayLehn,J.-M.&Wipff,G.(1980).,1347–1354.
tributetothegreatscientistandsharpmind,JackDunitz,whoLehn,J.-M.,Wipff,G.&Bu¨rgi,.(1974).,57,
–496.
ActaCryst.(2022).B78,295–297Jean-MarieLehnHans-BeatBu¨rgiinStrasbourg297