Thermochemical properties of iodinated cubane derivatives

Article abstract of DOI:10.1016/j.tca.2009.10.015

Since the initial synthesis of cubane, numerous derivatives have been made with a diverse range of physical, chemical, and biological properties. Some iodinated cubane derivatives have been reported to be thermolytically unstable and/or rearrange in situ. An iodinated cubane-containing, norbornene-based polymer showed rapid thermo-decomposition during TGA studies. Bis-(4-iodocubylmethyl)-dialkoxy disulfide undergoes fragmentation more easily than its non-iodinated counterpart. The synthesis and thermal behaviour of a library of iodinated cubane compounds are herein reported. Most of the iodinated cubane derivatives showed melting/decomposition with no exotherm upon cooling. 4-Iodo-1-vinylcubane was observed to rearrange to 4-vinyl-trans-β-iodostyrene and its cyclooctatetraene intermediate during DSC analysis. TGA studies on 1-iodo-4-(hydroxymethyl)-cubane suggest that this particular iodinated cubane scaffold is mostly prone to rapid thermo-decomposition.

Full text of DOI:10.1016/j.tca.2009.10.015

Thermochimica Acta 499 (2010) 15–20
Contents lists available at ScienceDirect
Thermochimica Acta
journal homepage: www.elsevier.com/locate/tca
Thermochemical properties of iodinated cubane derivatives
Justin R. Griffithsa, John Tsanaktsidisb, G. Paul Savageb, Ronny Priefera,∗
a Department of Chemistry, Biochemistry, and Physics, Niagara University, NY 14109, USA
b CSIRO Molecular and Health Technologies, Clayton South MDC 3169, Australia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 August 2009
Received in revised form 19 October 2009
Accepted 23 October 2009
Available online 13 November 2009
Since the initial synthesis of cubane, numerous derivatives have been made with a diverse range of phys-
ical, chemical, and biological properties. Some iodinated cubane derivatives have been reported to be
thermolytically unstable and/or rearrange in situ. An iodinated cubane-containing, norbornene-based
polymer showed rapid thermo-decomposition during TGA studies. Bis-(4-iodocubylmethyl)-dialkoxy
disulfide undergoes fragmentation more easily than its non-iodinated counterpart. The synthesis and
thermal behaviour of a library of iodinated cubane compounds are herein reported. Most of the
iodinated cubane derivatives showed melting/decomposition with no exotherm upon cooling. 4-Iodo-
1-vinylcubane was observed to rearrange to 4-vinyl-trans-␤-iodostyrene and its cyclooctatetraene
intermediate during DSC analysis. TGA studies on 1-iodo-4-(hydroxymethyl)-cubane suggest that this
particular iodinated cubane scaffold is mostly prone to rapid thermo-decomposition.
Keywords:
Iodinate cubane
TGA
DSC
4-Vinyl-trans-␤-iodostyrene
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
[12–14], however specific focus on iodinated cubane compounds
has not been reported. This thus inspired us to examine the ther-
Cubane and its derivatives have excited chemists since the first
successful synthesis by Eaton and Cole in 1964 [1]. Numerous pub-
lications have highlighted the great diversity and utility of this
simple scaffold [2]. Heteroatom bonding to the cube has revealed
some rather unique phenomena. For example, nitrated cubane
derivatives are explosive [3], whereas cubylamines are reported
to possess anti-viral activity [2]. Cubanol undergoes spontaneous
cage opening to yield vinylcyclobutenylketene [4]; whereas dicubyl
disulfide [5] and its derivatives [6] are stable, and have unique
bond lengths and intramolecular H-bonding. Cubyl halides have
been demonstrated to be useful intermediates for subsequent
transformations. In general, iodine is the most versatile halide as
it can be easily attached to the cage from the cubyl carboxylic
acid precursor via a Moriarty reaction [7], and can be transmet-
allated to magnesium [8] or lithium [5,9] for subsequent reactions.
There are two reports of greater stability of non-iodofunctionalized
cubane derivatives compared to their iodinated counterparts. One
was with the dialkoxy disulfide functionality [10] and the other
with a cubane-containing, norbornene-based polymer [11]. The
latter revealed through thermogravimetric analysis that the iodi-
nated cubane polymer underwent rapid decomposition at ∼250 ◦C.
Extensive work has been done on cubane and its derivatives
molytic behaviour of a family of iodinated cubane derivatives.
2. Experimental
2.1. Materials, preparation and characterization of compounds
All chemicals were reagent grade. 1,4-Dioxane was distilled
over potassium benzophenone ketyl immediately prior to use.
Melting points were obtained on a Gallenkamp apparatus and
are uncorrected. 1H (400 MHz) NMR spectra were obtained on a
Varian instrument with solvent indicated with tetramethylsilane
(TMS) as an internal standard and compared to authentic sam-
ples. Chemical shifts (s) are given in ppm, coupling constants (J)
in Hz, and spin multiplicities as s (single), d (doublet), and m
(multiplet).
2.1.1. Cyclopentanone ethylene ketal (2)
Cyclopentanone (1, 250 mL, 3.0 mol), ethane-1,2-diol (200 mL,
3.59 mol), and Dowex 50W-X8 (H) cation exchange resin (3 g) were
heated at reflux in benzene (500 mL) with simultaneous azeotropic
removal of water over 30 h. The yellow solution which remained
was cooled to room temperature, filtered, and washed with 4%
aqueous NaOH (250 mL) and brine (500 mL), dried with MgSO4
and concentrated by distillation through a Vigreux column (35 cm).
Simple distillation of the residue (59–63 ◦C/23 mmHg) (Lit [15]
57 ◦C/18 mmHg) yielded the ketal (2, 326.2 g, 90%) as a colorless
liquid.
∗
Corresponding author at: Department of Chemistry, Biochemistry, and Physics,
Niagara University, 206 DePaul Hall, Niagara University, NY 14109, USA.
Tel.: +1 716 286 8261; fax: +1 716 286 8254.
E-mail address: rpriefer@niagara.edu (R. Priefer).
1H NMR (400 MHz, CDCl3): ı = 1.58–1.81 (m, 8H), 3.87 (s, 4H).
0040-6031/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2009.10.015

16
J.R. Griffiths et al. / Thermochimica Acta 499 (2010) 15–20
2.1.2. Endo-2,4-dibromodicyclopentadiene-1,8-dione
2.1.5. Cubane-1,4-dicarboxylic acid (6)
bisethyl-ene ketal (3)
Dimethyl 1,4-cubanedicarboxylate (5, 5.04 g, 22.9 mmol) was
added to a dissolved solution of NaOH (3.72 g, 93.0 mmol) in MeOH
(150 mL) and H2O (10 mL). After 10 min, 5 was completely dis-
solved. The mixture was heated at reflux for 4.5 h, at which time the
solution was cloudy white. The solvent was removed via evapora-
tion. The white residue was dissolved in H2O (100 mL), and acidified
to pH ∼1 with conc. HCl. The white precipitate was vacuum fil-
tered, washed with water and dried under vacuum to constant
weight affording cubane-1,4-dicarboxylic acid (6, 4.35 g, 99%). mp.
dec. 220–222 ◦C (Lit [18] 220 ◦C).
Anhydrous 1,4-dioxane (25 kg) was transferred into a 100 L reac-
tion vessel under an atmosphere of nitrogen. To this was added
cyclopentanone ethylene ketal (6.3 kg, 49.2 mol) and the mixture
stirred under nitrogen. The system was cooled to 10 ◦C while stir-
ring at 200 rpm. Anhydrous bromine (25 kg, 156 mol) was added
slowly under nitrogen to the vigorously stirred reaction mixture
keeping the temperature between 10 and 15 ◦C and ensuring the
bromine was added directly into the stirred solution. Addition of
bromine was complete after 6 h. The mixture was left stirring at
room temperature with nitrogen blowing through the delivery ves-
sel and over the reaction mixture to ensure removal of HBr. Sodium
hydroxide (11 kg, 275 mol) in methanol (55 L) was added slowly
maintaining the temperature below 10 ◦C. After half the NaOH solu-
tion had been added, the mixture turned a dark green color. After 4 h
the addition was complete with the color having turned to brown.
The mixture was then heated to reflux and left stirring for 16 h
then subsequently cooled to room temperature and pumped out
of the reactor into ice water (80 L). The precipitate was collected
by vacuum filtration, washed with deionized water (90 L) and cold
methanol (5 L), then the solid was then air-dried to yield the biske-
tal (3, 7.46 kg, 74.7%). mp. 174–176 ◦C (Lit [16] mp. 172–174 ◦C).
1H NMR (400 MHz, CDCl3): ı = 2.69–2.76 (m, 1H), 3.02–3.13 (m,
1H), 3.46–3.55 (m, 1H), 3.83–4.30 (m, 8H), 5.84 (d, J = 6.5 Hz, 1H),
6.07 (d, J = 2.3 Hz, 1H), 6.19 (dd, J = 3.5, 6.5 Hz, 1H).
1H NMR (400 MHz, MeOD): ı = 4.18 (s, 6H, cubyl H).
2.1.6. 1,4-Diiodocubane (7)
Dry benzene (350 mL) was added to cubane-1,4-dicarboxylic
acid (6, 3.50 g, 18.3 mmol) under N2, forming a suspension. To this
IBDA (17.62 g, 54.7 mmol) and I2 (14.40 g, 56.7 mmol) were added.
The dark purple solution was refluxed for 6 h. After cooling to room
temperature, sat. Na2SO3 (100 mL) was added, and the mixture was
stirred until the top organic layer was light yellow (15–20 min).
The layers were separated, the organic layer was washed with sat.
Na2SO3 (2× 100 mL), H2O (2× 100 mL), and brine (100 mL). The
solution was dried with MgSO4, filtered, and evaporated. The sus-
pension that remained was triturated with cold hexanes to remove
iodobenzene, affording the desired 1,4-diiodocubane (7, 5.45 g,
84%) as a white solid; mp. 225–227 ◦C (Lit [19] 226–227 ◦C).
1H NMR (400 MHz, CDCl3): ı = 4.39 (s, 6H, cubyl H).
2.1.3. Endo-2,4-dibromodicyclopentadiene-1,8-dione (4)
2.1.7. Iodocubane (7)
The bisketal 3 (14 kg, 34.5 mol) was slowly added to 98%
sulphuric acid (45 L) keeping the temperature below 25 ◦C. The mix-
ture was stirred at room temperature for 24 h then pumped from
the reactor onto ice water (120 L) while stirring. The precipitate
was collected by vacuum filtration, washed with water (2× 20 L),
and then air-dried to yield the dione, 4, as a colorless solid (10.8 kg,
98.4%). mp. 156–157 ◦C (Lit [16] mp. 155–155.5 ◦C).
1,4-Diiodocubane (8, 4.28 g, 12.0 mmol) was dissolved in dry
THF (130 mL) under N2. A 1.0 M EtMgBr in THF (48 mL) solution
was added and cooled to −78 ◦C whereby the solution became off-
white cloudy. A 1.6 M n-BuLi in hexanes (31 mL) solution was added
till the mixture turned bright yellow. The mixture was stirred for
an additional 5 min at −78 ◦C, whereupon cold MeOH (30 mL) was
added. The cloudy white mixture was slowly warmed to room tem-
perature and sodium methoxide in methanol (25 wt%, 35 mL) was
added. The system was refluxed for 1 h to destroy the iodobutane
by-product. After cooling to room temperature, pentane (200 mL)
and H2O (100 mL) were added. The mixture was acidified to pH
1 with concentrated HCl, extracted with pentane, and the com-
bined organic layers were washed with H2O (2× 100 mL) and brine
(100 mL). The solution was dried with MgSO4, filtered and evapo-
rated. Column chromatography with pentane as eluent afforded
iodocubane (8, 2.38 g, 86%) as a white low-melting solid; mp.
31–33 ◦C (Lit [20] 32–34 ◦C).
1H NMR (400 MHz, CDCl3): ı = 3.15–3.25 (m, 1H), 3.48–3.63 (m,
2H), 6.24–6.36 (m, 2H), 7.67 (d, J = 2.9 Hz, 1H).
2.1.4. Dimethyl 1,4-cubanedicarboxylate (5)
The dione, 4 (4.00 kg, 12.6 mol) was dissolved in methanol (68 L),
deionized water (12 L) and conc. sulphuric acid (103 mL) in a 100 L
reactor. The solution was pumped and circulated through a Syman-
tec large scale photolysis unit irradiating the solution with UV light
(2 kW Hg vapor lamp). Cooling was applied to the reactor to main-
tain a temperature of 25 ◦C. Conversion to the caged dione is quite
slow with a maximum conversion rate of ca. 10 g per hour (mon-
itored by 1H NMR). When conversion was complete the reaction
solution was concentrated to dryness under reduced pressure. The
crude solid caged dione was dissolved in a 30% aq. sodium hydrox-
ide solution (38 L) and the mixture was heated at reflux for 3 h.
The solution was then cooled to 0 ◦C and acidified by the slow
addition of conc. HCl (24 L) with vigorous stirring while maintain-
ing the temperature below 10 ◦C. The resulting precipitate, crude
cubane diacid, was collected by vacuum filtration and washed with
ice-cold water (2× 2 L), and then air-dried. The cubane diacid was
dissolved in methanol (15 L), to which Dowex ion exchange resin
(pre-washed with 500 mL methanol) was added, and the solution
was heated at reflux overnight. The mixture was cooled to room
temperature, filtered, and the filtrate evaporated to dryness under
reduced pressure. The crude product was then purified by sublima-
tion to afford a white solid of 5 (563 g, 78.7%). mp. 161–162 ◦C (Lit
[17] mp. 161–162 ◦C).
1H NMR (300 MHz, CDCl3): ı = 4.17 (m, 4H, H-3,4,5,7), 4.31 (m,
3H, H-2,6,8).
13C NMR (75.5 MHz, CDCl3): ı = 38.7, 47.9, 48.5, 58.1.
2.1.8. 4-(Methoxycarbonyl)cubane carboxylic acid (9)
A solution of NaOH (0.438 g, 10.9 mmol) dissolved in MeOH
(7.1 mL) was added dropwise to a solution of dimethyl 1,4-
cubanedicarboxylate, (5, 2.498 g, 11.3 mmol) in THF (85 mL) at
room temperature. The mixture was stirred overnight and then
evaporated to dryness. The resulting white solid was dissolved
in water (100 mL), extracted with CHCl3 (3× 25 mL), dried with
MgSO4, filtered and evaporated. This afforded unreacted starting
material (0.125 g, 5.5%). The aqueous layer from the extraction
was acidified with conc. HCl to pH ∼1, extracted with CHCl3 (3×
50 mL), dried with MgSO4, filtered and evaporated, to afford 4-
(methoxycarbonyl)cubane carboxylic acid (9, 1.70 g, 73.0%). mp.
181–183 ◦C (Lit [9a] mp. 182–183 ◦C).
1H NMR (400 MHz, CDCl3): ı = 3.70 (s, 6H, CH3), 4.24 (s, 6H, cubyl
H).
1H NMR (400 MHz, MeOD): ı = 3.71 (s, 3H, CH3), 4.20 (s, 6H, cubyl
H).

J.R. Griffiths et al. / Thermochimica Acta 499 (2010) 15–20
17
1H NMR (400 MHz, CDCl3): ı = 4.31 (m, 3H, cubyl H), 4.53 (m,
3H, cubyl H), 9.76 (s, 1H, CHO).
2.1.9. 4-Iodo-methyl-cubane carboxylate (10)
Iodobenzenediacetate (23.5 g, 72.2 mmol)
(18.5 g, 72.8 mmol) were added to suspension of 4-
and
I2
a
(methoxycarbonyl)cubane carboxylic acid (5.00 g, 24.3 mmol)
in dry benzene (390 mL) under argon. The mixture was heated at
reflux for 7 h, cooled to room temperature, and hexane (175 mL)
was added. The solution was washed with sat. Na2SO3 (2× 60 mL),
H2O (2× 60 mL), and brine (60 mL), dried over MgSO4, and evap-
orated down to a reddish-brown oil. Column chromatography
[EtOAc/hexanes (1:1)] afforded methyl 4-iodocubanecarboxylate
(10, 4.89 g, 70%). mp. 115–117 ◦C (Lit [21] mp. 111–112 ◦C, [19]
124–125 ◦C).
2.1.13. 4-Iodo-1-vinylcubane (14)
To a suspension of methyltriphenylphosphonium bromide
(0.76 g, 2.21 mmol) in dry THF (20 mL), at −78 ◦C, under N2, 2.50 M
n-BuLi in hexanes (0.60 mL, 1.50 mmol) was slowly added. The
yellow mixture was stirred for 20 min, whereupon 1-iodocubane-
4-carboxaldehyde (13, 0.26 g, 1.01 mmol) dissolved in dry THF
(10 mL), under N2, was cannulated in and maintained at −78 ◦C
for 1 h. After an additional hour at room temperature the mix-
ture was quenched with H2O (15 mL). Hexanes (25 mL) were added
and the layers were separated. The aqueous layer was extracted
with hexanes (2× 25 mL), and the combined organic layer was
washed with H2O (2× 25 mL) and brine (25 mL), dried with MgSO4,
filtered, and evaporated to dryness. Column chromatography (hex-
anes) afforded 4-iodo-1-vinylcubane (14, 0.23 g, 88%) as a white
solid. mp. 77–79 ◦C (Lit [22] mp. 77–79 ◦C).
1H NMR (400 MHz, CDCl3): ı = 3.71 (s, 3H, CH3), 4.30 (m, 3H,
cubyl H), 4.39 (m, 3H, cubyl H).
13C NMR (100 MHz, CDCl3): ı = 36.1, 50.2, 51.7, 54.9, 56.1, 172.2.
2.1.10. 4-Iodocubanecarboxylic acid (11)
Iodobenzenediacetate
(9.06 g,
28.1 mmol)
and
I2
1H NMR (300 MHz, CDCl3): ı = 4.09 (m, 3H), 4.19 (m, 3H), 4.92
(dd, 1H, J = 1.95, 17.10 Hz), 5.06 (dd, 1H, J = 1.95, 10.60 Hz), 6.05 (dd,
1H, 10.60, 17.10 Hz).
(7.14 g, 28.1 mmol) were added to
a
suspension of 4-
(methoxycarbonyl)cubane carboxylic acid (9, 1.94 g, 9.38 mmol)
in dry benzene (150 mL) under argon, and the mixture heated at
reflux for 7 h. The mixture was then cooled to RT and hexanes
(75 mL) were added. The solution was washed with saturated
Na2SO3 (2× 25 mL), H2O (25 mL), and brine (25 mL), dried with
MgSO4, filtered, and evaporated to near dryness. The resulting
red-brown liquid was dissolved in THF (50 mL) and a mixture of
NaOH (3.75 g, 93.8 mmol) dissolved in MeOH (40 mL) and H2O
(15 mL) was added and the mixture stirred overnight. The solution
was evaporated to near dryness then dissolved in water (25 mL),
acidified with concentrated HCl to pH < 1, whereby a white precip-
itate formed which was collected under vacuum filtration, yielding
4-iodocubanecarboxylic acid (11, 1.91 g, 74.3%). mp. 212 ◦C (dec.)
(Lit [9a] mp. 215 ◦C (dec.)).
2.1.14. Measurements
Thermal properties were examined by thermogravimetric anal-
ysis, TGA, with TA instruments TGA Q50 System in a N2 atmosphere
and heated at a rate of 10 K/min. The differential scanning calorime-
try, DSC, was run with a Perkin-Elmer Pyris 6 calorimeter in a N2
atmosphere. The solid sample was placed in an aluminum capsule,
heated and cooled at the rate of 5 K/min. All results were taken
from the multiple heating and cooling runs, detecting the level of
enthalpy change that is associated with a respective phase transi-
tion. The transition enthalpy, ꢀH (kJ/mol), was determined from
the peak area of the DSC thermogram. The transition entropy, ꢀS
(kJ/mol K), was calculated with the equation ꢀS = ꢀH/T, where T
was the transition temperature corresponding to the DSC max-
imum. The thermodynamic data were mean values of several
independent measurements carried out on different samples.
1H NMR (400 MHz, MeOD): ı = 4.24 (m, 3H, cubyl H), 4.36 (m,
3H, cubyl H).
2.1.11. 1-Iodo-4-(hydroxymethyl)cubane (12)
4-Iodocubanecarboxylic acid (11, 676 mg, 2.46 mmol) was dis-
solved in dry THF (25 mL) under argon and cooled to 0 ◦C. To it,
borane dimethyl sulfide complex (0.78 mL, 3.91 mmol) was added
and stirred for 20 min at 0 ◦C, then at RT for 4 h. The solution was
quenched with water and stirred overnight. After adding EtOAc
(20 mL), the solution was washed with water (2× 15 mL) and brine
(20 mL), dried with MgSO4, filtered, and evaporated to dryness.
Column chromatography (1:1 CHCl3:EtOAc) afforded the white
solid, 1-iodo-4-(hydroxymethyl)cubane (12, 438 mg, 68.4%). mp.
109–111 ◦C (Lit [9a] mp. 109–111 ◦C).
3. Results and discussion
3.1. Synthesis
As Aldrich no longer sells any cubane starting materials, we
synthesized the dimethyl 1,4-cubanedicarboxylate from cyclopen-
tanone directly (Scheme 1) [23]. The synthesis of the cubane frame
was accomplished by initial ketalization of cyclopentanone, 1,
with ethane-1,2-diol in presence of a Dowex 50W-X8 (H) cation
exchange resin to give 2. The ketal, 2, was treated with bromine
in 1,4-dioxane and the unpurified tribromide was dimerized to
yield endo-2,4-dibromodicyclopentadiene-1,8-dione bisethyl-ene
ketal, 3, upon refluxing in MeOH. Stirring in concentrated H2SO4
afforded the dione, 4, which upon irradiation underwent two
consecutive Favorskii ring contractions, and subsequent esteri-
fication to afford the dimethyl 1,4-cubanedicarboxylate, 5. The
simple monoiodocubane, 8, was synthesized from the dimethyl 1,4-
cubanedicarboxylate, 5, by initially performing a base hydrolysis
with excess NaOH to yield the diacid, 6 [18]. After a Mori-
arty reaction we obtained the diiodocubane, 7 [19], whereby we
selectively removed one iodine to yield the monoiodocubane, 8
[20]. By only reacting one equivalent of NaOH with the starting
dimethyl 1,4-cubanedicarboxylate, 5, we obtained the acid/ester,
9. A Moriarty reaction yielded the iodo/ester, 10. Base hydrol-
ysis afforded the iodo/acid, 11, which could be further reacted
with borane to give the iodo/alcohol, 12. Swern oxidation provided
the iodo/aldehyde, 13, followed by Wittig gave the iodo/vinyl, 14
[22].
1H NMR (400 MHz, CDCl3): ı = 3.80 (s, 2H, CH2), 4.07 (m, 3H,
cubyl H), 4.23 (m, 3H, cubyl H).
2.1.12. 1-Iodocubane-4-carboxaldehyde (13)
A stirring solution of oxalyl chloride (0.16 mL, 1.89 mmol) in
dry CH2Cl2 (4 mL) was prepared under argon at −78 ◦C. To it, dry
DMSO (0.28 mL, 3.86 mmol) in dry CH2Cl2 (4 mL) was added drop-
wise. After 20 min at −78 ◦C, 1-iodo-4-(hydroxymethyl)cubane (12,
403 mg, 1.56 mmol) dissolved in dry CH2Cl2 (17 mL) under argon
was added dropwise to the system. The mixture was maintained at
−78 ◦C for 1.5 h and then dry Et3N (0.42 mL, 7.02 mmol) was added
via syringe. The mixture was warmed to RT and quenched with
water (15 mL). The aqueous layer was extracted with CH2Cl2 (2×
15 mL) and the organic layers were combined and washed with
water (15 mL) and brine (15 mL), dried with MgSO4, filtered, and
evaporated to dryness. Column chromatography (CH2Cl2) afforded
1-iodocubane-4-carboxaldehyde as a white solid (13, 326 mg,
80.9%). mp. 106–109 ◦C (Lit [20] mp. 108–110 ◦C).

18
J.R. Griffiths et al. / Thermochimica Acta 499 (2010) 15–20
Scheme 1. Synthetic path for all iodinated cubane derivatives.
3.2. Thermogravimetric analysis
(12), and iodo/aldehyde (13) had a small amount of residual mate-
rial remaining of 1.68, 2.84, 1.64, and 3.82% of weight, respectively.
What was most remarkable was the onset to end temperature range
was 35–47 K, for all but one of the iodinated cubane compounds.
Iodo/alcohol (12) had a relatively steep 2nd tangent, hence a nar-
row onset to end temperature range of 28 K. This phenomenon was
also observed with the cubane-containing, norbornene-based poly-
mer synthesized from the iodo/alcohol [14]. It appears that this
particular cubane scaffold is prone to rapid thermo-decomposition.
The thermogravimetric analysis on the iodinated cubane deriva-
tives (7, 8, 10–14, Fig. 1) all showed no weight loss prior to
decomposition curve, suggesting that no crystal and/or hygroscop-
ically bound solvent was present. From Table 1, it can be seen that
monoiodo, 8, and iodo/vinyl, 14, had the lower onset of degradation
temperature of 376 and 386 K, respectively; while iodo/acid, 11,
had the highest at 479 K. Monoiodo (8), iodo/acid (11), iodo/alcohol

J.R. Griffiths et al. / Thermochimica Acta 499 (2010) 15–20
19
Table 1
Temperature at onset, inflection, and end for iodinated cubane derivatives, 7, 8, 10–14.
Compound
Extrapolated onset temperature
for degradation (K)
Temperature of inflection
point (K)
Extrapolated end temperature
for degradation (K)
Diiodo (7)
441
376
417
479
438
418
386
468
405
448
507
460
448
416
479
418
460
514
466
465
427
Monoiodo (8)
Iodo/ester (10)
Iodo/acid (11)
Iodo/alcohol (12)
Iodo/aldehyde (13)
Iodo/vinyl (14)
Fig. 2. DCS thermogram of iodo/ester, 10.
Fig. 1. TGA curves for 7, 8, 10–14.
DSC NMR revealed no detectable degradative products. The ꢀH
for 7, 8, 10, and 12 were between 9 and 22 kJ/mol. In comparison
cubane itself has a reported ꢀH of fusion of 8.7 kJ/mol [24], whereas
dimethyl 1,4-cubanedicarboxylate (5) has a ꢀH of ∼38 kJ/mol [14].
Interestingly, both iodo/acid, 11, and iodo/aldehyde, 13, yielded an
exotherm upon heating at 516 and 465 K respectively. Both of these
temperatures were virtually identical to the extrapolated end tem-
perature for degradation from the TGA (Table 1). Post-DSC NMRs
revealed that no starting cubane remained. When the residues
were partially dissolved in water, the pH was ∼4 and a precipi-
tate was formed when AgNO3 was added suggesting the formation
of hydroiodic acid. The dissolved residue was also active to starch
paper which indicated the presence of iodine. Mass spectrometry
did indeed reveal signals that correspond to I2 (254) and HI (128).
Iodo/vinyl, 14, gave the most unique data (Fig. 3). On the first DSC
cycle an endotherm at 357 K (ꢀH = 13.4 kJ/mol; ꢀS = 37.6 J/mol K)
and an exotherm upon cooling at 344 K (ꢀH = −52.6 kJ/mol;
ꢀS = −153.0 J/mol K) was observed. This heating/cooling was
repeated three more times. Each time there was a decrease in
the temperature of the endotherm, ꢀH and ꢀS upon heating. On
the cooling runs the temperature of the exotherm decreased as
3.3. DSC analysis
Only the iodo/ester, 10, demonstrated the classic melt-
ing/freezing DSC thermogram profile of a pure compound (Fig. 2).
An endotherm was observed at 395 K with a ꢀH of 22.3 kJ/mol and
a ꢀS of 56.4 J/mol K. Upon cooling, an exotherm was observed at
380 K with a ꢀH of −103.2 kJ/mol and a ꢀS of −271.5 J/mol K. The
sample could be heated and cooled repeatedly and exhibited tem-
perature hysteresis. Diiodo, 7, and iodo/alcohol, 12, both yielded
endotherms at 499 and 393 K, respectively; however, neither pro-
duced an exotherm upon cooling (Table 2). This is not surprising
as these temperatures were near the inflection points of degra-
dation from the TGA results (Table 1). The aluminum capsules
were opened and NMR spectra were run on the material, reveal-
ing no starting cube compound. Monoiodo (8) gave an endotherm
at 301 K with no exotherm upon cooling. It was assumed that this
was due to the low-melting point of this compound. Even upon
cooling the sample in dry ice and then re-running, the DSC did
not provide an endotherm on a second run. When the aluminum
capsule was opened indeed monoiodo, 8, was a liquid and post-
Table 2
Transition temperatures, T, enthalpies, ꢀH, and entropies, ꢀS for iodinated cubane derivatives, 7, 8, 10–14.
Compound
Heating
Cooling
T (K)
ꢀH (kJ/mol)
ꢀS (J/mol K)
T (K)
ꢀH (kJ/mol)
−103.2
ꢀS (J/mol K)
−271.5
Diiodo (7)
499
301
395
516
393
465
357
351
350
349
16.7
9.0
22.3
33.5
29.9
56.4
Monoiodo (8)
Iodo/ester (10)
Iodo/acid (11)
Iodo/alcohol (12)
Iodo/aldehyde (13)
Iodo/vinyl (14)
380
−485.4
−940.7
22.4
57.1
−302.6
13.4
11.7
10.9
10.7
−651.1
37.6
33.3
31.1
30.6
344
335
331
319
−92.6
−87.7
−85.7
−80.3
−273.0
−261.6
−259.3
−251.5

20
J.R. Griffiths et al. / Thermochimica Acta 499 (2010) 15–20
vent as observed from TG analysis. Iodo/alcohol, 12, showed the
most rapid thermo-decomposition as was previously reported from
a polymer containing this moiety. The iodo/vinyl, 14, underwent
cage opening/rearrangement to 4-vinyl-trans-␤-iodostyrene, 16,
during the heating with DSC.
Acknowledgment
The authors thank the Niagara University Academic Center for
Integrated Science and the Rochester Academy of Science for their
financial support.
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4. Conclusion
A range of iodinated cubane derivatives were successfully syn-
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