DTIC ADA528068: Bridged Heterocyclium Dicationic closo-Icosahedral Perfluoroborane, Borane, and Carborane Salts via Aqueous, Open-Air Benchtop Synthesis (Postprint)

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11-03-2010 Journal Article
4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER
Bridged Heterocyclium Dicationic closo-Icosahedral Perfluoroborane, Borane, and 5b. GRANT NUMBER

Carborane Salts via Aqueous, Open-Air Benchtop Synthesis (Postprint)
5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S) 5d. PROJECT NUMBER
S. Shackelford, J. Boatz, S. Schneider (AFRL/RZSP); J. Belletire, A. Wheaton, B. Wight
(ERC); H. Ammon (Univ. of Maryland); D. Peryshkov, S. Strauss (Colorado State Univ.) 5e. TASK NUMBER

5f. WORK UNIT NUMBER
NAVY053Y
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION
REPORT NUMBER
Air Force Research Laboratory (AFMC)
AFRL/RZSP AFRL-RZ-ED-JA-2010-090
10 E. Saturn Blvd.
Edwards AFB CA 93524-7680

9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S
ACRONYM(S)

Air Force Research Laboratory (AFMC)
AFRL/RZS 11. SPONSOR/MONITOR’S
5 Pollux Drive NUMBER(S)
Edwards AFB CA 93524-70448 AFRL-RZ-ED-JA-2010-090
12. DISTRIBUTION / AVAILABILITY STATEMENT

Approved for public release; distribution unlimited (PA #10106).

13. SUPPLEMENTARY NOTES
Published in Organic Letters, 2010, Vol. 12, No. 12, 2714-2717. © 2010 American Chemical Society.
14. ABSTRACT

Thirteen bridged triazolium and imidazolium dicationic salts, which uniquely pair closo-icosahedral perfluoroborane [B F ]2–, borane
12 12
[B H ]2–, or carborane [CB H ]– anionic species with unsaturated bridged heterocyclium dications, were synthesized using an aqueous
12 12 11 12
benchtop method. This considerably extends the scope of a reported aqueous synthesis of binary [heterocyclium][B H ] and
2 12 12
[heterocyclium][CB H ] salts. Also, the one-step preparation of five new precursor bridged heterocyclium dihalide salts using conventional
11 12
procedures and in one case a microwave-assisted method is described.
15. SUBJECT TERMS

16. SECURITY CLASSIFICATION OF: 17. LIMITATION 18. NUMBER 19a. NAME OF RESPONSIBLE
OF ABSTRACT OF PAGES PERSON
Dr. Scott A. Shackelford
a. REPORT b. ABSTRACT c. THIS PAGE 19b. TELEPHONE NUMBER
SAR 5 (include area code)
Unclassified Unclassified Unclassified N/A
Standard Form 298 (Rev. 8-98)

Prescribed by ANSI Std. 239.18
ORGANIC
LETTERS
Bridged Heterocyclium Dicationic 2010
Vol. 12, No. 12
closo-Icosahedral Perfluoroborane, 2714-2717
Borane, and Carborane Salts via
Aqueous, Open-Air Benchtop Synthesis
Scott A. Shackelford,* John L. Belletire,† Jerry A. Boatz, Stefan Schneider,
Amanda K. Wheaton,† Brett A. Wight,† Herman L. Ammon,‡
Dmitry V. Peryshkov,§ and Steven H. Strauss§
Air Force Research Laboratory, Propellants Branch (AFRL/RZSP), 10 East Saturn
BlVd., Edwards AFB, California 93524-7680, Department of Chemistry and
Biochemistry, UniVersity of Maryland, College Park, Maryland 20742, and Department
of Chemistry, Colorado State UniVersity, Fort Collins, Colorado 80523
[email protected]
ReceivedApril6,2010
ABSTRACT
Thirteenbridgedtriazoliumandimidazoliumdicationicsalts,whichuniquelypaircloso-icosahedralperfluoroborane[B F ]2-,borane[B H ]2-,
12 12 12 12
or carborane [CB H ]- anionic species with unsaturated bridged heterocyclium dications, were synthesized using an aqueous benchtop
11 12
method.Thisconsiderablyextendsthescopeofareportedaqueoussynthesisofbinary[heterocyclium][B H ]and[heterocyclium][CB H ]
2 12 12 11 12
salts.Also,theone-steppreparationoffivenewprecursorbridgedheterocycliumdicationicdihalidesaltsusingconventionalproceduresand
inonecaseamicrowave-assistedmethodisdescribed.
Comparedtoneutralorganiccompounds,heterocyclicsalts tion of heterocyclium borane and dinitrate salts to an air-
enhancetheflexibilitytoattainrationalstructuraldesignand sustained combustion is one example,2 as explained by a
resultant predicted ingredient properties, which can permit current initiation sensitivity concept.3
atailorablebehavioralresponse.1,2Tailoringthermalinitia-
We report the first synthesis of heterocyclium perfluo-
roborane [B F ]2- salts and the first pairing of [B F ]2-,
†ERC,Inc.atAFRL/RZSP. 12 12 12 12
‡UniversityofMaryland. [B12H12]2-,and[CB11H12]-anionicspecieswithunsaturated
§ColoradoStateUniversity. bridged[heterocycliumdications]2+in89-98%yields.The
(1) Shackelford, S. A.; Belletire, J. L.; Boatz, J. A.; Schneider, S.;
functionalunsaturatedsitecenteredinthealkyl-basedbridge
Wheaton,A.K.;Wight,B.A.;Hudgens,L.M.;Ammon,H.L.;Strauss,
S.H.Org.Lett.2009,11,2623. structure, which in turn possesses a heterocylium cation
(2) (a)Shackelford,S.A.;Belletire,J.L.Centr.Europ.J.Energ.Mater.
2009,6,219.(b)Shackelford,S.A.;Belletire,J.L.12thNewTrendsin
ResearchofEnergeticMaterials(NTREM)InternationalSeminar,Pardubice,
CzechRepublic,April1-32009. (3) Shackelford,S.A.Centr.Europ.J.Energ.Mater.2008,5,75.
10.1021/ol100752y 2010AmericanChemicalSociety
PublishedonWeb05/25/2010
tethered at each terminal end, is a unique dication feature [B F ]2-dianionfirstwassynthesizedin1992asthecesium
12 12
(Scheme 1). salt in 38% yield.12 Recently, the K [B F ] salt was
2 12 12
The aqueous, open-air benchtop synthesis of 13 unique synthesizedbyK [B H ]perfluorinationin74%yieldand
2 12 12
high-energy bridged heterocyclium dication salts of 99.5%+ purity by continuously bubbling 20/80 F /N in
2 2
[B12F12]2-,[B12H12]2-,and[CB11H12]-byarapid,one-step, CH3CN solvent using ordinary glassware.13 Two bridged
high-yieldmetathesisreactionsignificantlyextendsthescope [heterocyclium][B F ] salts 16 and 17 were synthesized
12 12
of the recently reported preparation of high-energy binary using the K [B F ] reactant salt, and a third 18 was
2 12 12
triazolium and imidazolium closo-icosahedral borane
synthesizedtwice,oncewiththeCs [B F ]salt(Table2).
[B H ]2-andcarborane[CB H ]-saltsinwatersolvent.1 2 12 12
12 12 11 12 Thebridged[B H ],and[CB H ]saltsweresynthesized
12 12 11 12
Anopen-airmetathesismethodforsimilarbinarytriazolium
usingtheK [B H ]andK[CB H ]reactantsalts,respec-
2 12 12 11 12
and tetrazolium borane based salts of high water solubility
tively, in the correct stoichiometry.14
andformixedboranesaltsthatpairtwodifferentheterocy-
clium cations in a 1:1 ratio also is possible.4 All five
precursorbridgedheterocycliumdicationdihalidesalts1-5
(Figure 1) used in the aqueous metathesis reaction were
obtained by a one-step alkylation in CH CN solvent. Salts
3
1-4 have no literature precedent.
Twobridged2-butenylheterocycliumdicationicdihalide
salts,suchassalt5,havebeenreported,5,6andbothcontain
an N-methylimidazolium cation at the terminal ends of the
alkenylbridgestructure.Nobridgedheterocycliumdicationic
salts based on the 2-butynyl bridge structure or terminal
triazolium cations, seen in salts 1-4, have been described.
Scheme1.Two-StepSynthesisofBridgedHeterocyclium
DicationicSaltsof[B F ]2-,[B H ]2-,and[CB H ]-
12 12 12 12 11 12
Figure1.Fivebridgedheterocycliumdicationicdihalidereactant
saltspreparedwithyieldsobtained.
These132-alkenyl-and2-alkynyl-basedbridgedhetero-
cyclium dicationic salts of [B F ]2-, [B H ]2-, and
12 12 12 12
[CB H ]-weresynthesizedinatwo-stepsequence(Scheme
11 12
1). First, five new intermediate bridged heterocyclium
dicationic dihalogen salts 1-5, needed to prepare the final
bridged heterocyclium dicationic salts 6-18, precipitated
from refluxing CH CN solution during a high-yield, one-
3
step alkylation of 1,4-dihalo-2-butene or 1,4-dibromo-2-
butyne with the selected neutral triazole or imidazole
compound (Figure 1). Intermediate salts 1-5, once filtered
Analogous to the closo-icosahedral [B12H12]2- and and dried, were pure enough for direct use in the second
[CB H ]-anionicspeciespreviouslyreported7-11andseen
11 12 metathesisstep(e.g.,salt1).Oneintermediate,bridgedsalt
in the bridged heterocyclic salts 6-15 (Table 1), the 4 (Figure 1), contained 6-7% of unreacted 4-amino-1,2,4-
triazole(4AT),butwatersolventremovedthe4ATimpurity
(4) Belletire, J. L.; Shackelford, S. A.; Schneider, S.; Wight, B. A.;
during the subsequent metathesis reaction. Reaction times
Strauss,S.H.Synth.Commun.Submittedforpublication.
(5) Zhang,Y.;Ngeow,K.C.;Ying,J.Y.Org.Lett.2007,9,3495. neededtosynthesizeintermediatebridgeddihalidesalts1-5
D.(T6o)xiJcookla.nLoevtitc.,1M99.;6M,8a5k,si3m5o.vic,M.;Killbarda,V.;Jovanovic,D.;Savic, varied.Atypicalprocedureforsalts1-4isgivenbytrans-
(7) Pitochelli, A. R.; Hawthorne, M. F. J. Am. Chem. Soc. 1960, 82,
3228.
(8) Kaszynski,P.Collect.Czech.Chem.Commun.1999,64,895,and (12) Solntsev,K.A;Mebel,A.M.;Votinova,N.A.;Kuznetsov,N.T.;
referencestherein. Charkin,O.P.Koord.Khim.1992,18,340.
(9) Muetterties,E.L.;Knoth,W.H.PolyhedralBoranes;MarcelDekker: (13) Peryshkov,D.V.;Popov,A.A.;Strauss,S.HJ.Am.Chem.Soc.
NewYork,1969. 2009,131,18393.
(10) Grimes,R.N.Angew.Chem.Int.Ed.2003,42,1198,andreferences (14) TheK[B H ]andK[CB H ]reactantsaltswerepurchasedfrom
2 12 12 11 12
therein. KatchemLtd.,E.Krasnohorske6,11000Prague1,CzechRepublicand
(11) Knoth,W.H.J.Am.Chem.Soc.1967,89,1274. wereusedasreceived.
Org.Lett.,Vol.12,No.12,2010 2715
Table1.PropertiesDataforBridgedHeterocycliumDicationic Table2.PropertiesDataforBridgedHeterocycliumDicationic
Salts6-15of[B H ]2-and[CB H ]- Salts16-18of[B F ]2-
12 12 11 12 12 12
Bridgedintermediatesalt5required6hconventionallybut
only 45 min at 100 °C in the microwave. A key advantage
existed in the synthesis of intermediate bridged salt 3.
Whereasaconventionalone-stepalkylationyieldedaccept-
ably pure bridged salts 1, 2, 4, and 5, intermediate salt 3
was obtained in a 90% crude yield and contained 11% of
1,4-di(4-amino-1,2,4,-triazolium-1N)-2-butenedibromide2.15 unreacted 1-amino-1,2,3-triazole (1AT) and other trace
Synthesisdetailsforsalts1-5areinSupportingInformation. impurities. The neutral 1AT heterocycle was removed by
Synthesis of the intermediate bridged heterocyclium reprecipitationfromamethanol/ethanolmixedsolventwith
dichloride salt analogue of dibromide salt 1 was possible an 82% recovery, but the other trace impurities remained.
using1,4-dichloro-2-butyne,butanoticeableamountofthe Microwave-assisted synthesis precipitated 1AT-free salt 3
4-amino-1,2,4-triazole (4AT) reactant (11-16%) remained as a pure white solid.17,18
in the isolated dichloride salt. Two tedious reprecipitations While microwaving the reaction solution in a defined
in a MeOH/CH CN mixed solvent, with large losses, concentrationat100°Cfor45minaffordedthebestreaction
3
removedthe4AT.Theavailabilityof1,4-dibromo-2-butyne, conditions,a22%yieldofprecipitatedintermediatesalt3must
however,provided4AT-freebridgeddibromidesalt1inhigh be an acceptable option.17 A parametric study that increased
yield and purity.16 concentration, increased or decreased reaction time, and in-
Microwave-assistedsynthesisreducedalkylationreaction creasedordecreasedtemperaturegaveeitheralowerpurified
time and gave a comparable yield and purity. Bridged yield or a less pure tan-colored, gummy solid salt 3 that was
intermediate dibromide salt 2 was synthesized in 6.5 h similartotheconventionalalkylationreactionresults.
conventionally in refluxing CH CN (98% yield) but in 50
3
min at 100 °C under microwave conditions (96% yield). (17) [trans-1,4-Di(1-amino-1,2,3-triazolium-3N)-2-butene][Br] (3).Six
2
Biotage (nee Personal Chemistry) Initiator Emrys 10-20 mL vials with
Teflon-coated magnetic stir bars were each charged with 0.600 g (2.72
(15) [trans-1,4-Di(4-amino-1,2,4,-triazolium-1N)-2-butene][Br] (2).A mmol) of 97% trans-1,4-di(1-amino-1,2,3,-triazolium-3N)-2-butene di-
2
100mLsingle-neckedrecoveryflaskwithTeflon-coatedstirbarwascharged bromide,0.472g(0.561mmol)of1-amino-1,2,3-triazole,18and20mLof
with1.506g(6.831mmol)of97%trans-1,4-dibromo-2-butene,1.160g CHCN.Eachcappedvialwasmicrowavedat100°Cfor45minandthen
3
(13.658mmol)of99%4-amino-1,2,4-triazole,and40mLofCHCNand was cooled in a freezer (-13.5 °C). The suspensions of each vial were
3
wasrefluxedfor6.5h.Theresultantsuspensionwascooledtort,vacuum combinedandvacuumfiltered.Vacuumdryingat50°Cfor3dyielded
filtered,andvacuumdriedtoyield2.560g(98%)ofwhitesolidsalt2. 1.398g(22%)ofwhitesolidsalt3.
(16) The 1,4-dibromo-2-butyne was purchased from BromOrganics (18) Kaplan, G.; Drake, G.; Tollison, K.; Hall, L.; Hawkins, T.
Corporation,P.O.Box722,ElkGrove,IL60009. J.HeterocyclicChem.2005,42,19.
2716 Org.Lett.,Vol.12,No.12,2010
Thechemicalstructureofbridgedsalts1-5demonstratethe pycnometry density values despite two unusually large
flexibiltythatthesesaltsprovideforsystematicstructuredesign variances with salts 14 and 15.
toachievepropertiesmodificationsthatareneededfortailoring
chemical performance behavior.1,2 The unsaturated bond at
thebridgecentercanbevaried,thechemicalstuctureofthe
tethered heterocyclium cation can be altered, the terminal
heterocycliumcationscanbechangedforanothertype,and/
orthepairedanionicspeciescanbeexchangedfromdihalides
to a perfluoroborane, borane, carborane, or a dinitrate.2
A second aqueous, open-air, one-step metathesis reacted
intermediate salts 1-5 with either K[B F ], K[B H ], or
2 12 12 2 12 12
K[CB H ] to produce the 13 new bridged heterocyclium
11 12
dicationcloso-icosahedralsaltsof[B H ]2-,[CB H ]-6-15
12 12 11 12
(Table1),andof[B F ]2-16-18(Table2)assolidprecipi-
12 12
tates.Atypicalsynthesisprocedureisgivenforthe[1,4-di(4-
amino-1,2,4-triazolium-1N)-2-butyne][B F ]salt16.19Detailed
12 12
dataforsalts6-18arefoundinSupportingInformation.
Initially, smaller scale metatheses (47-320 mg of inter-
mediate bridged salts 1-5) were conducted at rt by im-
mediately mixing the two aqueous reactants. To minimize
the presence of possible KBr or KCl byproduct residue,
subsequentlargerscaleaqueousmetatheses(849-1550mg)
were run at 78-80 °C by a dropwise addition of aqueous
Kof2[sBa1lt2sF112-],5K.2[ABf1t2eHr1p2]r,ecoirpKita[CtiBon11Han1d2]fisoltlruattiioonns,ttoheasporloudtiuocnt Faisgluigrhetl2y.CtilrtyesdtaclrpyasctaklilnoggroafpbhricidRge-adx[iBs.12F12]salt16viewedalong
salt suspension was digested 30 min at 78-80 °C in fresh
deionized water before final isolation.
As expected, bridged [heterocyclium dication][B F ]
12 12
Becauseintermediatebridgedheterocycliumdichloridesalt salts 16-18 (Table 2) displayed a single crystal X-ray
4 is a clear dark brown glass-like solid with a hard rock densityatrtthatissignificantlyhigherthantheanalogous
candy texture, weighing the exact mass needed for subse- bridged [heterocyclium dication][B H ] and [heterocy-
12 12
quent aqueous metathesis reactions is difficult. Therefore, clium dication][CB H ] salts 6-15 (Table 1). Limited
11 12 2
the amount of salt 4 needed to synthesize bridged hetero- K [B F ] reactant initially dictated that bridged [hetero-
2 12 12
cyclium dication salts of [B12H12]2- 12 and [CB11H12]- 13 cyclium dication][B12F12] salts 16-18 be synthesized at rt
was prepared individually in two portions. on a 44-49 mg scale based on reactant salts 1-3. Bridged
Isolated yield, density, and melting/decomposition point salts 16 and 18 later were scaled to 773 and 821 mg,
data for each bridged heterocyclium dication borane, car- respectively, using the 78-80 °C digestion procedure.19
borane, and perfluoroborane salt are listed in Tables 1 and The similar densities for the bridged salts 16-18 (Table
2. Pycnometry-determined densities at rt, and predicted 2) result from the formation of planar perpendicular inter-
valuesarecomparedforsalts6-15usinganewlydeveloped sectingbridged[heterocycliumdication]2+layersthatalter-
predictivedensityadditivitycode(Table1).20Thisadditivity nate with icosahedral [B F ]2- dianion layers (Figure 2).
12 12
code predicts an average 3.3% variance from the 10 Therefore, the structure of the unsaturated bridged hetero-
cycliumdicationexertslittleeffectinalteringcrystalpacking
and resultant density values.
(19) [1,4-Di(4-amino-1,2,4-triazolium)-trans-2-butene-1N]B F ]16.A
12 12
50mLbeakerwaschargedwithaTeflon-coatedmagneticstirbarand0.773
g(2.02mmol)ofsalt2thatwasdissolvedin4mLofDIwater.Another Acknowledgment. AFRL/RZ Chief Scientist, Dr. Alan
50mLbeakerwaschargedwith0.865g(1.98mmol)ofK[B F ]that
was dissolved in 6 mL of DI water. Both beakers were pla2ced12on12a hot Garscadden, Wright-Patterson AFB, OH, entrepreneurial
platethatmaintainedwaterat78-80°C.Thewatervolumewasmaintained researchfunds.AFRL/RZS,EdwardsAFB,CA,funding,Dr.
for15minbyaddingDIwaterasneeded.Theaqsalt2solutionwasstirred
Robert Corley and Mr. Shaun Raquedan, technical and
vigorously, and the aq K[B F ] occasionally was swirled. The aq
2 12 12
K[B F ]solutionwasaddeddropwisetothestirredaqsolutionofsalt2 logistics support. ERC, Inc., Huntsville, AL, for CSU
2 12 12
withadisposablecapillarypipetteplus2×1mLrinsesoftheaqK[B F ],
2 12 12 financial assistance.
beaker(9mintotaladdtime).Theaqsuspensionwascooledtortandplaced
intoarefrigerator(3.0°C).Vacuumfiltrationandrinsingofthesolidcake Supporting Information Available: Experimental pro-
with2×1mLofpre-chilled(3.0°C)DIwaterfollowed.Thesemi-dried
cedures, spectroscopy data, HRMS (all salts), ion chroma-
cakewasplacedinthesame50mLbeakerwiththesamestirbar,and6
mLoffreshDIwaterwereadded.Thestirredsuspensionwasdigestedat tography Cl-/Br- analyses, melting/decomposition points,
78-80°Cfor30min,cooledtort,andplacedintotherefrigerator16h. singlecrystalX-ray(salts16-18).Thismaterialisavailable
Vacuumfiltration,rinsingofthesolidcakewith2×1mLofpre-chilled
DIwater,andhighvacuumdryingto18mTorratrtyielded1.060g(92%) free of charge via the Internet at http://pubs.acs.org.
ofwhitesalt16.
(20) Ammon,H.L.Propellants,Explos.,Pyrotech.2008,33,92. OL100752Y
Org.Lett.,Vol.12,No.12,2010 2717