S37
31P{1H} NMR (CD2Cl2, Room Temperature)
31P{1H} NMR (CD2Cl2, -70 °C)
Ru
PP
P
Si
Me
t-Bu
Me
Me
t-BuMet-Bu
6
Cl
DMSO Cl
Ru
PP
P
Si
Me
t-Bu
Me
Me
t-BuMet-Bu
6
Cl
DMSO Cl
Chem622:OrganometallicChemistry
Class:MWF,1030–1120AM,Bilger341CInstructor:MattCain
Textbook(s):Crabtree,6thEdition,TheOrganometallicChemistryoftheTransitionMetalsAND
Elschenbroich,3rdEdition,OrganometallicsOrganometallicChemistrybridgestheimaginarygapbetweenorganicandinorganicchemistry. Despite being a rather new field (Ferrocene 1951), its utility andpracticality are undeniable. The production of L-DOPA, S-Metolachlor, and (–)-Mentholare justsomeof thecommoditiesproducedonacolossalscaleduetotheemployment of organometallics catalysts. This class will focus on the entirePeriodicTableofElements andwill introduce the fundamental trends inboth theMainGroupandTransitionMetals.Studentsshouldgainanunderstandingofthesefundamentals and be able to apply them to published research,with the ultimategoal of applying it to their own! In addition, some topics/complexes will beevaluated fromahistoricalprospective, inwhich they first appearedas structuralanomalies and have evolved (through synthesis, etc.) to become highly usefulligands, intermediates,orcatalysts. Acommonthemethroughouttheclasswillbetoconnectthematerialfromtheclassroomtorelevantandpublishedresearch,withthe hope that students will recognize that although many fields of chemistry(organic, inorganic, physical, supramolecular, etc.) are taught separately, they areinterdisciplinaryandoftentimes,directlylinkedbyorganometallicchemistry.
Fe FePPh2
PPh2Fe
PR2
PR'2
dppf Josiphos
N
OCl
H3CO
S-MetolachlorFerrocene
R
LiLi
Li
RR
R
Li
LiLiLi
Li R
Structure and Bonding
PR1 R2
R3R1
SR2
O
Chiral MoleculesNMR Spectroscopy
Reactivity
ZnEt2 in air
History, Development, Evolution, and Application Main Group
Organometallics and Catalysis
N
N
H
H
Main Group Applications
31P NMR 19F NMR6Li NMR7Li NMR
Olefin MetathesisR
M
R
M
R R
+R
MR
Asymmetric Hydrogenation
OEt
O O
OEt
OH O
M C O
Ligands and Bonding
CO: σ-donor / π-acceptor DCD ModelM OC M C
C
Isolobal Analogyd7–ML5 CH3
(CO)5Mn CH3(CO)5Mn Mn(CO)5
H3C CH3
M RX
MX
RM
R'
R
R'-M'M'-X
RR'Cross Couplings
MP P
H/D
FG
Symmetry and ChiralityKineticIsotopeEffects
Electron Counting
PtP
P Ph
Cl
CpTa
Cp CH2
CH3
dialkylphosphoric,dialkylphosphinic,6andnitric7acids).Thelow
barriertoprotontransferbetweentwominimaofadouble-well
potentialfunctionisresponsiblefortheappearanceofabroad
absorptionforO
-H‚‚‚Ostretching,forexample,inthe3000-1500
cm-1rangeforstrongphosphoricaciddimers.7Inthepresentcase
ofCl-H‚‚‚Clbonding,withastrongeracidandheavieratoms,the
absorptionliesatlowerfrequency,inthe2200
-1100cm
-1range.
Thedimericform
ofH(CHB 1
1Cl 11)canbeobtaineddirectlyby
rapidsublimationusinghighsublimationtemperatures(200-260
°C)andimmediatecondensationontocoldcellwindows(Figure
4a). Withmoregradualsublimationoverlongertimeperiods(g1h)
atlowertemperatures(180-200°C),anewIRspectrumofavisibly
crystallinesolidphaseisobserved(Figure4b,c).Theappearance
ofsharp
νCHbandsfromthecarboraneanionat3039and3024
cm-1(Figure4inset)indicatesthepresenceoftwodifferent
crystallinephases.Therelativeintensityofthesetwobandsvaries
accordingtothesublimationconditionswiththe3039cm
-1band
typicallybeingmoreabundant,althoughoccasionallyabsent(Figure
4c).TheCl-H‚‚‚Clvibrationsdonotdiffersignificantlybetween
thetwophases,indicatingtheyhaveverysim
ilarstructures.The
carboraneclusterbands(rightinsetofFigure2)onlydistinguish
betweenmonomeranddimer/polymerstructures.
Afragmentofthecrystallinephase(having
νCHat3039cm
-1 )
wasusedforsingle-crystalX-raydetermination.AsshowninFigure
5,thestructurecontainslinearpolymericchainswithprotonbridges
betweenClatomsatthe7-11positionsofthecarboraneanions.
Theseareindicatedby
shortinter-anion
Cl‚‚‚Clcontactsand
lengtheningoftheassociatedB-
Clbonds.TheCl‚‚‚Cldistances
involvedinthetwocrystallographicallyindependentCl‚‚‚H
‚‚‚Cl
bridgesare3.171(3)and3.209(3)Å,whereasallotherCl‚‚‚Cl
nonbonding
contactsare>3.36
Å.TheB-
Clbond
lengthsof
unprotonatedClatomslieintherangeof1.745(10)-1.796(10)Å,
whereasthoseassociatedwithprotonbridgesare1.831(10)-1.845-
(10)Å.Thebindingofthecarboraneanionstotheacidicproton
viaClatomsfromthe7-11pentagonalbeltratherthantheslightly
morebasic
12position(seemonomerA,Figure2)isprobablya
consequenceofpackingefficiencyandstatisticaladvantage.The
samebiasinthecrystallinestatetowardthe7ratherthanthe12
positionwasseenintheX-raystructureofi-Pr(CHB 1
1Me 5Br
6).5
TheHatomswerelocatedintheX-rayrefinementof[H(CHB 1
1-Cl11)] nwiththefollowingdimensions:foroneCl-H-Clbridge,
Cl-H
)1.28(9)and1.92(10)Å,∠Cl-H-Cl
)166(7)°;andfor
theother,Cl-H
)1.74(11)and1.47(11)Å,∠Cl-H-Cl
)179-
(8)°.Whilenotconclusive,thesedataareconsistentwithsomewhat
unsymmetricalH-bondingandeasydisplacementofHalongthe
trajectorybetweentheClatoms.
IftheCl-H-Clgroupsinthepolymericacidweresymmetric
with
localD∞hsymmetry,onlythedoublydegeneratebend(ν2)
andtheantisymmetricCl-H-Clstretch(ν3)wouldbeIRactive.
BandscorrespondingtothesevibrationsareobservedintheIR
spectrumofthebichlorideion,HCl2-,whichisagoodstructural
modelforthepolymeric(anddimeric)carboraneacid.Inthesolid
state,thebichlorideioncanbeasymmetricorsymmetricdepending
uponthecation,8,9andwhenasymmetric,the
ν 1symmetricCl‚‚‚
ClstretchbecomesweaklyIRactive(∼200cm
-1 ).Thepolymeric
acidhasquitesim
ilarbands(Figure4).Thus,theverybroadand
distortedbandwithmaximum
at∼1100cm
-1isassignedto
ν 3,
thehigh
intensity,broadband
at∼615cm
-1whoseshapeis
distortedby
Evansholes10isassignedto
ν 2,andaweaklow-
frequencybandat225cm
-1canbeattributedto
ν 1.TheIRactivity
ofν 1isconsistentwith
theX-raystructurewhichindicatestwo
typesofClHCl
groups
with
differentdegreesofasymmetry.
Together,theIRandX-raydataindicatestrong,low-barrier,nearly
symmetricH-bonding.
Insummary,thegasandsolid
phasestructuresofH(CHB11-
Cl11)havebeendetermined.RelateddataforH(CHB 1
1H5Br 6)(see
TableinSupportingInformation)indicatethatthesestructuresare
generalforcarboraneacids.Thedifferentstructureshaveimplica-
tionsforacidity.WiththehighestνHClfrequencyandthesmallest
Cl-H‚‚‚Clanglereflectingbondstrain,themonomericacidshould
show
thehighestacidity.Uponthermodynamicallyfavoreddimer-
ization,anglestrainintheCl-H‚‚‚Clgroupispresumablyrelieved,
thestrengthoftheH‚‚‚Clbond
increases,andtheacidshould
expressdiminishedacidity.Inthepolymericcrystallinephases,the
Cl-H-Cl
bondingismorenearlysymmetricalandsomewhat
strongerthanthedimer,soaciditywillbefurtherdiminished.These
differencesmaybeimportantconsiderationswhenusinggasand
solidphasecarboraneacidstoprotonatetheweakestbases.
Acknowledgment.WethankDr.FookTham
fordetermining
theX-raystructure.Thisworkwassupportedby
NSF
(CHE-
0349878)andNIH(GM23851).
SupportingInformationAvailable:
Experimentaldetails,IR
spectra,DFTcalculations,andX-raystructuredetails.Thismaterialis
availablefreeofchargeviatheInternetathttp://pubs.acs.org.
References
(1)Reed,C.A.;Kim,K.-C.;Bolskar,R.D.;Mueller,L.J.Science2000,
122,4660-4667.
(2)Reed,C.A.C
hem.C
ommun.2005,1669-1677.
(3)Juhasz,M
.;Hoffmann,S.P.;Stoyanov,E.S.;Kim,K.-C.;Reed,C.A.
Angew.C
hem.,Int.Ed.2004,43,5352-5355.
(4)Koppel.I.A.;Burk,P.;Koppel,I.;Leito,I.;Sonoda,T.;Mishima,M.J.
Am.C
hem.Soc.2000,122,5114-5124.
(5)Kato,T.;Stoyanov,E.S.;Geier,J.;Grutzmacher,H.;Reed,C.A.J.Am.
Chem.Soc.2004,126,12451-12457.
(6)Stoyanov,E.S.;Popov,V.M
.;Mikhailov,V.A.Zh.Prikl.Spectrosk.
1984,40,77-84.
(7)Guillory,W
.A.;Bernstein,M.L.J.Chem.Phys.1975,62,1058-1060.
(8)Evans,J.C.;Lo,G.Y.-S.J.Phys.Chem.1966,70,11-19.
(9)Ault,B.S.Acc.Chem.Res.1982,15,103-109.
(10)EvansJ.C.
Spectrochim.Acta1960,16,994-1000.
JA058581L
Figure4.IRspectraofdifferentsublimedfilmsofH(CHB 1
1Cl 11):(a)the
dimericform
(black,dashed)andtwopolymericforms(b)with
νCHat
3039cm
-1(red,studiedbyX-ray)and(c)at3024cm
-1(blue).
Figure5.Perspectiveview
oftheproton-bridgedX-raycrystalstructure
ofH(CHB 1
1Cl 11)lookingdowntheC-
Hbondsofthecarboraneanions
(green
)Cl,orange)B,gray
)C,white
)H).
COMMUNIC
ATIO
NS
J.AM
.CHEM.SOC.
9VO
L.128,NO
.10,2006
3161
TopicsIntroduction/HistoricalPerspective
- Landmark compounds and reactions, Evolution ofInorganic/OrganometallicChemistry,NobelPrizeWinners
MainGroup
- StructureandBondingofGroups1,2,13–16- SynthesisofMainGroupCompounds- DOSYNMRspectroscopy- ReactivityandhandlingofMainGroupCompounds- Trends in bond strength/length, polarity of M-C bond,
comparisontotransitionmetalcomplexes- NMRactivenuclei(6Li,7Li,31P,19F,etc.)andNMRassignments
ofcomplexes- InertPairEffect,increasingenergyseparationofs/porbitals- P-andS-Stereogenicmolecules,synthesisandresolution,and
importance- Tolman,BiteAngle,etc.à Describingligands- AsymmetricDeprotonationwiths-BuLi/(–)-Sparteine- Carboranes:Synthesis,Reactivity,Applications- FrustratedLewisPairs,NBcomplexes,othernewresearch- Unusual,unexpectedMainGroupcomplexes
OrganometallicstoCatalysis
- Introduction: 16/18-electron rule,σ-,π-, andδ-bonding andtheorbitals,DCDmodel,etc.
- Tour of the ligands: σ-donors, σ-donors/π-acceptor, π-donors,commonligands(CO,PR3,halides,etc.),backbondingand its effect (IR spectroscopy, quantification of electrondensity)
- Isolobal Analogy and its Application: understanding andpredictingbonding,RoaldHoffman(1981NobelPrize)
- Reactions at the Metal: Ligand Dissociation/Association,OxidativeAddition/ReductiveElimination,and the impactofstericsandelectronics
- Reactions involving the Ligands: Insertion/β-hydrideelimination, nucleophilic/electrophilic attack, and how topromote or inhibit these processes. Examination of Bredt’sRule,agosticinteractions,etc.
- Kinetic Isotope Effects: Deuterium Labeling, CrossoverExperiments,etc.
- HomogeneousCatalysis1:Hydrogenation- Chirality: Types (Point, planar, axial, helical, etc.), effect of
symmetry,examplesofchiralmolecules
- Asymmetric Catalysis: Hydrogenation and its mechanisticunderlyings,prochiraltochiral,howtogetenantioinduction,NobelPrize2001
- Homogeneous Catalysis 2: Pd-Cross Coupling,TransmetalationAgent (B, Sn,Cu, Si, etc.),2010NobelPrize,RecentDevelopments(BuchwaldLigands,etc.)
- Homogeneous Catalysis 3: Metathesis, Its development,mechanism, and applications, 2005 Nobel Prize, DickSchrock/BobGrubbs,Mo/Wvs.Ru
- Future:HypotheticalDirections,whattoexpect,etc.Grading
- 5BriefExams(80%,20%each,droplowest)- Final(OralPresentation)à20%total
