Supporting InformationGerman Edition: DOI:A Highly Efficient
Gold-Catalyzed Photoredox a-C(sp3)HAlkynylation of Tertiary
Aliphatic Amines with SunlightJin Xie, Shuai Shi, Tuo Zhang, Nina
Mehrkens, Matthias Rudolph, and A. Stephen K.
Hashmi*anie_201412399_sm_miscellaneous_information.pdf1 Content
General information2 Optimization of the reaction conditions2-3
General procedure for the gold-catalyzed -sp3 C-H alkynylation
reaction 3-13 Mechanistic studies14-27 Copiesofthe 1H, 13Cand
19FNMR spectra 28-90 2
GeneralInformation:Allthereactionswereperformedundernitrogenorargon
atmosphere.Chemicals(Aldrich,Fluka,Lancaster,andMerck)wereusedwithout
furtherpurification.Dichloromethane,MeOHandMeCNweredriedfromdried
machine. NMR spectra were recorded on Bruker, Avance 300 (300 MHz)
and Avance
500(500MHz)spectrometers.Chemicalshiftswerereferencedtoresidualsolvent
protons and reported in ppm. Signal multiplicity as follows: s
(singlet), d (doublet), t
(triplet),q(quartet),m(multiplet).GC-MSspectrawererecordedusingaAgilent
5890SeriesIIPlusmodel,coupledwithaHP5972MassSelectiveDetector.As
column, a HP-1 column was used and helium was carrier gas. Unless
stated otherwise,
thefollowingtemperatureprogramwasused:injectiontemperature60C,heating
rate: 10 C/min, 5 min solvent delay. IR spectra were recorded on a
Bruker Vector 22,
andtheabsorptionmaximaweregiveninwavelengthincm-1units.Thin-layer
chromatography(TLC)wasperformedonprecoatedpolyestersheets(POLYGRAM
SIL /GUV254), and components were visualized by observation under
UV light or by treating the plates with KMnO4 solution followed by
heating. The 1-iodoalkynes were
preparedaccordingtotheliterature.[1]
Thephotocatalyst[Au2(-dppm)2]2Xwas obtained according to the
literature.[2] Optimization of the reaction conditions Table 1:
Optimization of the reaction conditions.[a] EntryPhotocatalyst
[mol%] XAdditives (2.0 equiv) SolventTime [h] Yield of 4aa[%][b]
11a (3%)BXK2HPO4MeCN6trace 21a (3%)BrK2HPO4MeCN6trace 31a
(3%)IK2HPO4MeCN653% 41a (3%)I-MeCN640% 51b (3%)IK2HPO4MeCN662% 61c
(3%)IK2HPO4MeCN660% 3 71b (3%)ICsFMeCN672% 81b (3%)IDMAPMeCN669%
91b (3%)IPyridineMeCN666% 101b (3%)INaOAcMeCN665% 111b
(3%)I2,6-lutidineMeCN668% 121b (3%)IimidazoleMeCN665% 131b
(1%)I-MeCN1.581% 141b (1%)I-MeCN1.581% 151b
(1%)I-MeOH6AbundanceScan 867 (10.048 min):
JX253-2.D\data.ms114.172.086.056.1128.199.9 228.2 169.0 207.0 The
mass spectrum (EI) of standard sample 7 (in library) (mainlib)
1,2-Bis-(2-diisopropylaminoethyl) ethane30 40 50 60 70 80 90 100
110 120 130 140 150 160 170 180 190 200 210 220 230
240050100394143565870728498114128155 169 228NN 18
ThecomparisonoftwoEIspectrainthemasslibrary(Redrepresentsthereaction
byproduct and blue represents the standard compound 7) Scan 867
(10.048 min): JX253-2.D\ data.ms 1,2-Bis-(2-diisopropylaminoethyl)
ethane50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200
210 220 230 2400501005010051565670707272848488
9898114114128128155169169180 207 228228 Name:
1,2-Bis-(2-diisopropylaminoethyl) ethaneFormula: C14H32N2 MW: 228
CAS#: 104017-39-2 NIST#: 226557 ID#: 68927 DB: mainlibOther DBs:
None Contributor: Dennis Rohrbaugh, CBDCOM/ERDEC, Edgewood, MD
Scheme4.Reactionconditions:1b(1mol%),3c(0.2mmol),8(0.2mmol),2a(5.0
equiv), MeCN (0.5 mL), rt, sunlight, 3 hours. Theyields in brackets
indicate the GC yield with decane as an internal standard. For
characterization data for compound 9: 1H NMR (CDCl3, 300 MHz): =
6.06 (d, J = 3.5 Hz, 1 H), 5.48 (s, 1 H), 3.68 (s, 3 H), 3.02-2.88
(m, 2 H), 2.51-2.30 (m, 4 H), 0.94 (d, J= 6.6 Hz, 12 H); 13C
NMR(CDCl3, 100 MHz): = 167.8, 139.4, 125.6, 51.7, 48.6, 45.1, 34.7,
20.7; HRMS (ESI) calculated for C12H24NO2 [M+H]+ m/z 214.18016,
found 214.18027.
Insummary,theaboveexperimentsprovideadirectexperimentalproofforan
-aminoalkyl radical and an alkynyl radical intermediate during the
reaction process.
Basedontheaboveresults,itiscleartoconcludethattheradical-radicalC-C
couplingofan-aminoalkylradicalandanalkynylradicalisahighlypossible
pathway. 19 1H NMR spectrum of product 9 13C NMR spectrum of
product 9 E) EPR experiment 20
Scheme5.EPRspectra(Xband,9.4GHz,160K-220K)ofreactionsystem:
[Au2(-dppm)2]2OTf1b(1mol%),N,N-diisopropylmethylamine(5.0equiv),
(iodoethynyl)benzene(0.1mmol),MeCN(1mL)underargon(1atm).Thereaction
mixturewasvigorouslystirredatroomtemperaturebyirradiationwithUVAlight
(instead of sunlight)for5 min. Subsequently, 0.2 mL of the
reactionyellow mixture was taken out into the EPR tube under argon
atmosphere, and the tube was frozen in liquid nitrogen for
measurement (The low temperature is essential for the normal EPR
machinetoobservetheradicalsignalbecausetheradicalsdisappearedrapidlyby
reaction).Then,thismixturewasanalyzedbyEPRunder160K,200Kand220K
respectively.Itwasfoundthattheobservedradicalsignaldisappearedrapidlywhen
the temperature was increased.
Scheme6.EPRspectra(Xband,9.4GHz,160-200K)ofcontrolexperiment:
[Au2(-dppm)2]2OTf 1b (0.1 mmol), (iodoethynyl)benzene (0.1 mmol),
MeCN (1 mL) under argon (1 atm). The reaction mixture was
vigorously stirred at room temperature by irradiation with UVA
light for 5 min. Subsequently, 0.2 mL of the reaction mixture was
taken out into the EPR tube under argon atmosphere, and the tube
was frozen in
liquidnitrogenformeasurement.Then,thismixturewasanalyzedbyEPRunder
160-200 K. No any positive signal was observed in this condition.
Typical spectrometer parameters are shown as follows, scan range:
from 2600-3600 G;
centerfieldset:3100G;timeconstant:5.12ms;scantime:0.08192s;modulation
amplitude:0.0001;modulationfrequency:9.443691GHz;receivergain:70;
microwave power: 6.359 mW.
FromtheaboveEPRexperiments,thepossibilityofalkynylradicalfortheobserved
EPR signals would be ruled out. At present, although the assignment
remains a matter
ofconjecture,wepostulatetheobservedsignalsistheproducedalpha-aminoalkyl
radical intermediate. To further determine the real real existence
of alpha-aminoalkyl
radicalsinourreaction,inthelightofrecentpublications(J.Am.Chem.Soc.2012,
134,3338-3341;Org.Lett.2012,14,672-675;J.Am.Chem.Soc.2013,135,
1823-1829), we add Michael acceptor 8 into the model reaction to
trap the generated 21
alpha-aminoalkylradical.Pleasingly,besidethenormalcouplingproduct4aa,the
-aminoalkylradicaladditionproduct9wasproduced,whichwasisolatedand
characterized by 1H, 13C and HRMS. Also see page 18-19 for details.
F) Sunlight-dark experiment of the model reaction
Scheme7.Time-profileofthemodelreaction(1).Reactionconditions:
[Au2(-dppm)2](OTf)2(1mol%),3c(0.2mmol),2a(5.0equiv),MeCN(0.5mL),
roomtemperature,N2,sunlight.ThereactionmixturewassubjectedtoGC-MS
analysis. G) Determination of the potential of photocatalyst, 3c
and amine
Cyclicvoltammetryexperimentswerecarriedoutinaconventionalthree-electrode
electrochemicalcellusingVersaSTAT3Instrument(PrincetonAppliedresearch).A
gold electrode in PEEK (Serial #: ET076-0240) and Pt/Ti titanium
wire anode (Serial
#:ET078-0264)wereusedastheworkingandcounterelectrodes,respectively.A
silverwirewasusedasapseudo-referenceelectrodeatascanrateof0.2V/s.The
redox potentials were determined through cyclicvoltammetry by
employing 1.0 mM
[Au2(-dppm)2]2OTf,2.0mM(iodoethynyl)benzeneand2.0mM
diisopropylmethylamineina0.1MsolutionofBu4NPF6indryMeCNwithagold
working electrode at a scan rate of 0.2 V/s. Prior to each
measurement, solutions were purged with N2.
Figure1.Cyclicvoltammogram(twosegment):(a)[Au2(-dppm)2]2OTf;(b) 22
(iodoethynyl)benzene; (c) diisopropylmethylamine. The current peak
was determined
byusingtheblankmeasurementandcorrectedwiththeredoxpotentialofFeCp2
(Fc/Fc+)asaninternalstandard(defineditspotentialasE1/2=0V).Theredox
potentials for the irreversible processes were determined from
onset potential (Es) and
Ep.TheEsfor(a)and(b)wasdeterminedfromtheintersectionofthetwotangents
drawnatthedecreasingcurrentandbaselinechargingcurrentoftheCVtraces.The
Es for (c) was determined form the intersection of the two tangents
drawn at the rising current and baseline charging current of the CV
traces. About the Es calculation, also
seetheSupportingInformationofLeespaper(Angew.Chem.Int.Ed.2012,51,
12303).
Toinvestigatethethermodynamicaspectoftheelectrontransferreactionbetween
thegoldcatalyst,(iodoethynyl)benzeneanddiisopropylmethylamine,acyclic
voltammetricstudywasstudied.Inelectrochemicalexperiments,
[Au2(-dppm)2]2OTfunderwentanirreversiblereductionprocess,andthereduction
potentialofgoldcatalystisaround1.70V(Fig1a).Accordingtothecyclic
voltammetry, the Es of gold catalyst was determined as -1.64 V. In
the same way, the
reductionpotentialandhalfpotentialof(iodoethynyl)benzene3cwasdeterminedas
-1.38 V and 1.29 V respectively (Fig 1b), which are more positive
than the reduction
potentialandhalfpotentialofgoldcatalyst.Furthermore,thereductionpotentialfor
Eo(Au23+/Au22+*)isalsorangedfrom-1.6
0.1V.[7]Theseresultssuggestthatthe
electrontransferfromboth[Au21+]and[Au22+]*to3cmightbepossibleunderthe
photocatalyticreactionconditions.Interestingly,when[Au2(-dppm)2]2OTfand3c
weremixedtogetherintheabsenceofelectrondonordiisopropylmethylamine,and
thenirradiatedwithsunlight,the
31PNMRspectrumsuggestedthatthegoldcatalyst [Au2(-dppm)2]2+ was
desymmetrized (four 31P signal peaks). There doesnt have the
similardesymmetricphenomenoneitherwhenonlythegoldcatalystwasirradiated
withsunlightorthegoldcatalystand3cmixturewasplacedatroomtemperature
without sunlight irradiation. These experiments strongly support
the electron transfer from [Au22+]* to 3c (see experiments below).
Finally, the cyclic voltammetric result of diisopropylmethylamine
demonstrated that it could undergo an oxidation process with E1/2 =
0.30 V (Fig 1c). It could donate electron easily. H) The electron
transfer evidence from [Au22+]* to3c 1)Photocatalyst
[Au2(-dppm)2]2OTf (5 mol) in CD3CN (0.5 mL) 2)Photocatalyst
[Au2(-dppm)2]2OTf (5 mol),(5 mol) in CD3CN (0.5 mL), argon, room
temperature, 3 hours 23 The 1H NMR (300 MHz, CD3CN) spectrum The
31P NMR (121 MHz, CD3CN) spectrum 3)Photocatalyst [Au2(-dppm)2]2OTf
(5 mol) in CD3CN (0.5 mL), sunlight, argon, room temperature, 2
hours 4)Photocatalyst [Au2(-dppm)2]2OTf (5 mol),(5 mol) in CD3CN
(0.5 mL), sunlight, argon, room temperature, 2 hours 24 The 1H NMR
(300 MHz, CD3CN) spectrum The GC-MS analysis of reaction (4),
ethynylbenzene was also observed. The 31P NMR (121 MHz, CD3CN)
spectrum Suggested intermediate for explaining the desymmetric
signals I) The evidence for ligand exchange 5)Photocatalyst
[Au2(-dppm)2]2OTf (1 mol) in CD3CN (0.5 mL)
6)Photocatalyst[Au2(-dppm)2]2OTf(1 mol),n-Bu4NI(10equiv)inCD3CN(0.5
mL), argon, room temperature, 15 min 25 The 1H NMR (300 MHz, CD3CN)
spectrum 31P NMR (121 MHz, CD3CN) spectrum
WhenthemixturewassubjectedtoHRMS(ESI)analysis,nopeaksof
[Au2(-dppm)2]2OTf was found, and only [Au2(-dppm)2]2I was found.
HRMS (ESI) calcd for [M-I]+: [C50H44Au2IP4]+ = 1289.07692, found:
1289.07591.
Moreover,underthesamereactionconditions,onlytheliganddppmdidntundergo
thechemicalshiftin1HNMRand 31PNMRspectra.Whenthemodelreactionof
iPr2NMeand(iodoethynyl)benzenefinished, 31PNMRanalysisofthereaction
mixture,alsogaveasignificantpeakat27.6ppm,supportingtheligandexchanging
process of photocatalyst 1b. J) Calculation about the SOMO energy
of radicals Firstly, to determine the accuracy of chosen
calculation method, two known SOMO energy of some radicals were
performed. 26 Cal.Literature[8]Calculated CH3 radical-10.42-9.8 ev
Benzene radical-9.63 -9.2 ev Method: DFT/UM06-2X/6-311++g(d,p)//
DFT/UMP2/6-311++g(d,p) Use the same method to get the SOMO energy
of -aminoalkyl radical and alkynyl radical. SOMO energy : -7.12 ev
SOMO energy: -10.07 ev K) Quantum yield measurement The quantum
yield () was determined by the known ferrioxalate actinometry
method.
AferrioxalateactinometrysolutionwaspreparedbyfollowingtheHammond
variationoftheHatchardandParkerprocedureoutlinedinHandbookof
Photochemistry.[9]OwingtotheUV/VISabsorptionofgoldphotocatalystinUVA
region, to determine the quantumyield, 240 W UVA lamps (PRP-3500 ,
purchased
fromSouthernNewEnglandUltravioletCompany)wereused.Theirradiatedlight
intensitywasestimatedto3.54x10-7
einsteinS-1byusingK3[Fe(C2O4)3]asan actinometer. Model reaction
solution: [Au2(-dppm)2]2OTf (1 mol%), (iodoethynyl)benzene 3c (3.1
mmol), iPr2NMe (5 equiv) were added to a 10 mL volumetric flask,
and then filled to the mark with anhydrous acetonitrile. [c = 0.31
mmol/mL]
Foreverytube,1mLmodelreactionsolutionwastakenoutintofour10mLdried
pyrex screw-top reaction tube, respectively, and degassed under
nitrogen by sparging 27 for5-10minat0
oC.Then,thereactionmixtureswereirradiationwith240WUVA
lampsforspecifiedtimeintervals(5min,10min,15min,20min).Themolesof
products formed weredetermined by GC-MS measurementwith decaneas
reference
standard.Thenumberofmolesofproducts(yaxis)perunittimeisrelatedtothe
numberofphotons(xaxis,calculatedfromthelightintensity).Theslopegivesthe
quantum yield () of the photoreaction, 0.614. Reference:
[1]Y.Gao,M.Yin,W.Wu,H.HuangandH.Jiang,Adv.Synth.Catal.2013,355,
2263. [2] G. Revol, T. McCallum, M. Morin, F. Gagosz, L. Barriault,
Angew. Chem. Int. Ed. 2013, 52, 13342. [3] R. F. Parcell, C. B.
Pollard, J. Am. Chem. Soc. 1950, 72, 3312. [4] Q. Shen, L. Zhang,
Y.-R. Zhou, J.-X. Li, Tetrahedron Lett. 2013, 54, 6725. [5] Z.-P.
Li, C.-J. Li, J. Am. Chem. Soc. 2004, 126, 11810. [6] A. McNally,
C. K. Prier, D. W. C. MacMillan, Science 2011, 334, 1114. [7] C.-M.
Che, H.-L. Kwong, K.-C. Poon, V. W.-W. Yam, J. Chem. Soc. Dalton
Trans. 1990, 3215-3219. [8] I. Fleming,, Frontier Orbitals and
Organic Chemical Reactions, John Wiley (1976), New York, NY. [9] S.
Murov, L., Handbook of Photochemistry, Marcel Dekker, New York,
1973. 28 1H NMR spectrum of 4aa 29 13C NMR spectrum of 4aa 30 1H
NMR spectrum of 4ab 31 13C NMR spectrum of 4ab 32 1H NMR spectrum
of 4ac 33 13C NMR spectrum of 4ac 34 1H NMR spectrum of 4ad 35 13C
NMR spectrum of 4ad 36 1H NMR spectrum of 4ae 37 13C NMR spectrum
of 4ae 38 19F NMR spectrum of 4ae 39 1H NMR spectrum of 4af 40 13C
NMR spectrum of 4af 41 19F NMR spectrum of 4af 42 1H NMR spectrum
of 4ag 43 13C NMR spectrum of 4ag 44 19F NMR spectrum of 4ag 45 1H
NMR spectrum of 4ah 46 13C NMR spectrum of 4ah 47 1H NMR spectrum
of 4ai 48 13C NMR spectrum of 4ai 49 1H NMR spectrum of 4aj 50 13C
NMR spectrum of 4aj 51 1H NMR spectrum of 4ak 52 13C NMR spectrum
of 4ak 53 19F NMR spectrum of 4ak 54 1H NMR spectrum of 4al 55 13C
NMR spectrum of 4al 56 19F NMR spectrum of 4al 57 1H NMR spectrum
of 4am 58 13C NMR spectrum of 4am 59 1H NMR spectrum of 4an 60 13C
NMR spectrum of 4an 61 1H NMR spectrum of 4ao 62 13C NMR spectrum
of 4ao 63 1H NMR spectrum of 4ap 64 13C NMR spectrum of 4ap 65 1H
NMR spectrum of 4ar 66 13C NMR spectrum of 4ar 67 1H NMR spectrum
of 4ba 68 13C NMR spectrum of 4ba 69 1H NMR spectrum of 4ca 70 13C
NMR spectrum of 4ca 71 1H NMR spectrum of 4da 72 13C NMR spectrum
of 4da 73 1H NMR spectrum of 4ea 74 13C NMR spectrum of 4ea 75 1H
NMR spectrum of 4fa 76 13C NMR spectrum of 4fa 77 1H NMR spectrum
of 4ha 78 13C NMR spectrum of 4ha 79 1H NMR spectrum of 4ia 80 13C
NMR spectrum of 4ia 81 1H NMR spectrum of 4ja 82 13C NMR spectrum
of 4ja 83 1H NMR spectrum of 4ka 84 13C NMR spectrum of 4ka 85 1H
NMR spectrum of 4ma 86 13C NMR spectrum of 4ma 87 1H NMR spectrum
of 4na 88 13C NMR spectrum of 4na 89 1H NMR spectrum of 4oa 90 13C
NMR spectrum of 4oa
