ꢀ
LanhuiꢀRenꢀetꢀal.ꢀ/ꢀChineseꢀJournalꢀofꢀCatalysisꢀ37ꢀ(2016)ꢀ1216–1221ꢀ
1217ꢀ
clicꢀketones,ꢀmostꢀcatalystsꢀreportedꢀtoꢀdateꢀforꢀtheseꢀoxidativeꢀ
transformationsꢀ areꢀ homogeneous.ꢀ Theseꢀ catalystsꢀ areꢀ there‐
foreꢀdifficultꢀtoꢀrecycleꢀandꢀoftenꢀrequireꢀhighꢀreactionꢀtemper‐
atures,ꢀ whichꢀ hasꢀ furtherꢀ limitedꢀ theirꢀ scopeꢀ andꢀ application.ꢀ
Theꢀdevelopmentꢀofꢀeconomicallyꢀandꢀenvironmentallyꢀfriendlyꢀ
alternativesꢀtoꢀtheseꢀexistingꢀproceduresꢀisꢀthereforeꢀstronglyꢀ
desired.ꢀHeterogeneousꢀcatalystsꢀareꢀpreferredꢀtoꢀhomogenousꢀ
systemsꢀbecauseꢀtheyꢀcanꢀbeꢀreadilyꢀrecoveredꢀandꢀreused.ꢀInꢀ
Schemeꢀ1.ꢀPreparationꢀofꢀtheꢀMnO ‐N@Cꢀcatalysts.ꢀ
x
2
2
012,ꢀ Akhlaghiniaꢀ etꢀ al.ꢀ [26]ꢀ reportedꢀ theꢀ oxidationꢀ ofꢀ
‐benzylpyridineꢀ toꢀ 2‐benzoylpyridineꢀ usingꢀ ceriaꢀ nanoparti‐
wouldꢀhaveꢀevaporationꢀ(theꢀboilingꢀpointꢀofꢀ1,10‐
phenanthro‐
ꢀ
lineꢀisꢀ365ꢀ°Cꢀatꢀ1ꢀatm).ꢀTheꢀcarbideꢀgraduallyꢀdecomposedꢀatꢀ
temperaturesꢀ overꢀ 600ꢀ °C.ꢀ Takenꢀ together,ꢀ theꢀ resultsꢀ ofꢀ thisꢀ
analysisꢀ revealedꢀ thatꢀ 600ꢀ °Cꢀ wasꢀ theꢀ mostꢀ appropriateꢀ tem‐
clesꢀasꢀaꢀcatalyst.ꢀUnfortunately,ꢀthisꢀreactionꢀusedꢀKBrO
ꢀasꢀanꢀ
3
oxidant,ꢀ whichꢀ isꢀ highlyꢀ toxic,ꢀ makingꢀ itꢀ harmfulꢀ toꢀ humanꢀ
healthꢀandꢀtheꢀenvironment.ꢀThisꢀcatalystꢀsystemꢀalsoꢀrequiredꢀ
theꢀ useꢀ ofꢀ anꢀ organicꢀ solvent,ꢀ makingꢀ itꢀ environmentallyꢀ un‐
friendly.ꢀHerein,ꢀweꢀreportedꢀtheꢀ developmentꢀofꢀaꢀnovel,ꢀ re‐
usableꢀ MnO
mationsꢀofꢀCsp3–HꢀbondsꢀtoꢀketonesꢀusingꢀTBHPꢀasꢀanꢀoxidant.ꢀ
Notably,ꢀ thisꢀ MnO ‐N@Cꢀ catalystꢀ isꢀ inexpensiveꢀ withꢀ severalꢀ
notablyꢀ advantagesꢀ overꢀ existingꢀ systems,ꢀ includingꢀ aꢀ lowꢀ
loading,ꢀ goodꢀ functionalꢀ groupꢀ tolerance,ꢀ highꢀ selectivityꢀ andꢀ
goodꢀ reusability.ꢀ Mostꢀ notably,ꢀ thisꢀ newꢀ MnO ‐N@Cꢀ catalystꢀ
peratureꢀforꢀtheꢀpreparationꢀofꢀtheꢀMnO
Aꢀ 50ꢀ mLꢀ round‐bottomꢀ flaskꢀ (RBF)ꢀ wasꢀ chargedꢀ withꢀ
Mn(NO ꢀ(2.3ꢀg,ꢀ6.4ꢀmmol,ꢀ50%ꢀinꢀwater),ꢀ1,10‐phenanthrolineꢀ
2.3ꢀ g,ꢀ 12.8ꢀ mmol)ꢀ andꢀ EtOHꢀ (40ꢀ mL).ꢀ Theꢀ flaskꢀ wasꢀ thenꢀ
x
‐N@Cꢀcatalyst.ꢀ
)
3 2
x
‐N@Cꢀ catalystꢀ forꢀ theꢀ directꢀ oxidativeꢀ transfor‐
(
sealed,ꢀandꢀtheꢀmixtureꢀwasꢀstirredꢀatꢀ80ꢀ°Cꢀforꢀ12ꢀh.ꢀTheꢀreac‐
tionꢀ mixtureꢀ wasꢀ cooledꢀ toꢀ roomꢀ temperatureꢀ andꢀ filteredꢀ
throughꢀaꢀpadꢀofꢀCelite.ꢀTheꢀfilterꢀcakeꢀwasꢀsubsequentlyꢀcol‐
lectedꢀandꢀdriedꢀatꢀ120ꢀ°Cꢀforꢀ2ꢀhꢀtoꢀgiveꢀcomplexꢀAꢀinꢀ93%ꢀ
yield.ꢀ
x
x
canꢀ beꢀ usedꢀ underꢀ solvent‐freeꢀ conditionsꢀ atꢀ lowerꢀ reactionꢀ
temperaturesꢀ(Fig.ꢀ1).ꢀ
Complexꢀ Aꢀ (3.3ꢀ g)ꢀ wasꢀ subsequentlyꢀ pyrolyzedꢀ atꢀ 500ꢀ °Cꢀ
underꢀ anꢀ atmosphereꢀ ofꢀ nitrogenꢀ forꢀ 2ꢀ hꢀ toꢀ giveꢀ theꢀ
Theꢀ resultsꢀ ofꢀ ourꢀ previousꢀ workꢀ showedꢀ thatꢀ 2,3‐
pentenopyridineꢀmayꢀbeꢀoxidizedꢀtoꢀ6,7‐dihydro‐5H‐cyclopen‐
ta[b]pyridin‐5‐oneꢀusingꢀMn(OTf) ꢀasꢀaꢀcatalystꢀ[23].ꢀHowever,ꢀ
ꢀ
cyclo‐
MnO
Severalꢀ otherꢀ MnO
00,ꢀ 800ꢀ andꢀ 900ꢀ °C)ꢀ wereꢀ alsoꢀ preparedꢀ accordingꢀ toꢀ thisꢀ
x
‐N@C‐catalystꢀ(pyrolysisꢀatꢀ500ꢀ°C)ꢀinꢀ32%ꢀyield.ꢀ ꢀ
ꢀ
x
‐N@C‐catalystsꢀ (pyrolyzedꢀ atꢀ 400,ꢀ 600,ꢀ
2
7
thisꢀparticularꢀcatalystꢀsystemꢀwasꢀdifficultꢀrecycleꢀandꢀexpen‐
sive,ꢀ therebyꢀ limitingꢀ itsꢀ potentialꢀ forꢀ industrialꢀ applications.ꢀ
Furthermore,ꢀthisꢀoxidationꢀreactionꢀrequiredꢀaꢀlargeꢀexcessꢀofꢀ
TBHPꢀ(5ꢀequiv.).ꢀToꢀaddressꢀtheseꢀissues,ꢀweꢀdevelopedꢀaꢀnewꢀ
generalꢀoxidationꢀprocedure.ꢀ ꢀ
Aꢀ 15‐mLꢀ RBFꢀ wasꢀ chargedꢀ withꢀ substrateꢀ (0.5ꢀ mmol),ꢀ
x
MnO ‐N@Cꢀcatalystꢀ(1ꢀmg,ꢀpyrolysisꢀatꢀ600ꢀ°C)ꢀandꢀTBHPꢀ(1.5ꢀ
2
mmol,ꢀ65%ꢀinꢀH O).ꢀTheꢀflaskꢀwasꢀthenꢀsealed,ꢀandꢀtheꢀmixtureꢀ
MnO
muchꢀsmallerꢀamountꢀofꢀTBHPꢀ(3ꢀequiv.).ꢀWeꢀchoseꢀMn(NO
asꢀ theꢀ metalꢀ sourceꢀ becauseꢀ nitrylꢀ isꢀ aꢀ goodꢀ elec‐
tron‐withdrawingꢀ anion,ꢀ justꢀ likeꢀ trifluoromethanesulfonate,ꢀ
andꢀ Mn(NO ꢀ isꢀ commerciallyꢀ inexpensive.ꢀ Theꢀ MnO ‐N@Cꢀ
catalystsꢀwereꢀpreparedꢀbyꢀtheꢀcomplexationꢀofꢀMn(NO ꢀwithꢀ
,10‐phenanthroline,ꢀfollowedꢀbyꢀpyrolysisꢀatꢀaꢀhighꢀtempera‐
tureꢀ (400–900ꢀ °C)ꢀ forꢀ 2ꢀ hꢀ underꢀ anꢀ atmosphereꢀ ofꢀ nitrogenꢀ
Schemeꢀ 1).ꢀ First,ꢀ theꢀ pyrolysisꢀ characteristicsꢀ ofꢀ complexꢀ Aꢀ
fromꢀ Mn(NO ꢀ andꢀ 1,10‐phenanthrolineꢀ wereꢀ studiedꢀ underꢀ
anꢀatmosphereꢀofꢀnitrogenꢀbyꢀthermogravimetricꢀanalysisꢀ(Fig.ꢀ
).ꢀ Theꢀ resultꢀ ofꢀ thisꢀ analysisꢀ showedꢀ thatꢀ theꢀ weightꢀ ofꢀ theꢀ
complexꢀ remainedꢀ stableꢀ forꢀ temperaturesꢀ inꢀ theꢀ rangeꢀ ofꢀ
00–600ꢀ °C.ꢀ Furthermore,ꢀ theꢀ carbonizationꢀ ofꢀ theꢀ complexꢀ
x
‐N@Cꢀ catalyst,ꢀ whichꢀ isꢀ highlyꢀ reusableꢀ andꢀ requiresꢀ aꢀ
wasꢀheatedꢀatꢀ60ꢀ°Cꢀforꢀ12ꢀh.ꢀTheꢀreactionꢀwasꢀcooledꢀtoꢀroomꢀ
temperatureꢀandꢀdilutedꢀwithꢀethylꢀacetateꢀ(4ꢀmL),ꢀbeforeꢀbe‐
ingꢀcentrifugedꢀatꢀ10000ꢀr/minꢀforꢀ1ꢀminꢀtoꢀseparateꢀtheꢀcata‐
lyst.ꢀ Theꢀ supernatantꢀ wasꢀ removedꢀ andꢀ theꢀ catalystꢀ wasꢀ
washedꢀ withꢀ ethylꢀ acetateꢀ (5ꢀ ×ꢀ 4ꢀ mL).ꢀ Theꢀ supernatantꢀ wasꢀ
subsequentlyꢀ combinedꢀ theꢀ ethylꢀ acetateꢀ washꢀ solutionsꢀ andꢀ
evaporatedꢀtoꢀdrynessꢀtoꢀgiveꢀaꢀresidue,ꢀwhichꢀwasꢀpurifiedꢀbyꢀ
flashꢀ columnꢀ chromatographyꢀ overꢀ silicaꢀ gelꢀ (ethylꢀ ace‐
tate/n‐hexaneꢀ=ꢀ1:10,ꢀv/v).ꢀ
3 2
) ꢀ
)
3 2
x
)
3 2
1
(
)
3 2
Theꢀoxidationꢀofꢀ2‐benzylpyridineꢀtoꢀgiveꢀ2‐benzoylpyridineꢀ
(2a)ꢀ wasꢀ selectedꢀ asꢀ aꢀ modelꢀ reactionꢀ toꢀ studyꢀ theꢀ catalyticꢀ
2
activityꢀofꢀnewꢀMnO
x
‐N@Cꢀmaterials.ꢀItꢀisꢀnoteworthyꢀthatꢀallꢀofꢀ
4
110
100
90
occurredꢀinꢀthisꢀtemperatureꢀrange.ꢀHowever,ꢀtheꢀmassꢀofꢀtheꢀ
complexꢀrapidlyꢀdecreasedꢀ byꢀ53.99%ꢀwhenꢀ theꢀtemperatureꢀ
reachedꢀ365ꢀ°C.ꢀThisꢀchangeꢀwasꢀattributedꢀtoꢀtheꢀdecomposi‐
tionꢀofꢀtheꢀcomplexꢀwithꢀtheꢀlossꢀofꢀ1,10‐phenanthroline,ꢀwhichꢀ
8
0
0
7
N
N
O
60
X=N or CH
R1
50
X
X
1
) Heterogeneous MnOx-N@C-catalyst
0.79 mol% Mn)
) TBHP (3 equiv.), 60 oC, 12 h
(
R1
40
30
2
3
R2
N
R2
O
) Solvent-free
0
200
400
600
o
800
1000
Temperature ( C)
N
Fig.ꢀ1.ꢀDirectꢀoxidationꢀofꢀtheꢀCsp3–HꢀbondsꢀofꢀN‐heterocyclicꢀsystems
usingꢀaꢀreusableꢀheterogeneousꢀMnO ‐N@Cꢀcatalyst.ꢀ
Fig.ꢀ2.ꢀTheꢀthermogravimetricꢀanalysisꢀofꢀtheꢀcomplexꢀAꢀfromꢀMn(NO
andꢀ1,10‐phenanthroline.ꢀ
3 2
)
x