Continuous flow synthesis of fullerene derivatives

Article abstract of DOI:10.1021/jo2001879

Various fullerene-based electron acceptor materials for organic photovoltaic applications were prepared via [3 + 2] and [4 + 2] cycloadditions using a continuous flow approach. The 1,3-dipolar cycloaddition of the tosylhydrazone precursor and the Diels-Alder cycloaddition of indene to either C₆₀ or C₇₀ under conventional batch reaction conditions were translated to the continuous flow process. By varying the residence time, temperature, and equivalents of cycloaddition reagent, significant improvements in yields and reaction times were achieved over conventional batch processes.

Full text of DOI:10.1021/jo2001879

NOTE
pubs.acs.org/joc
Continuous Flow Synthesis of Fullerene Derivatives
Helga Seyler, Wallace W. H. Wong,* David J. Jones,* and Andrew B. Holmes
Bio21 Institute, School of Chemistry, University of Melbourne, Victoria 3010, Australia
S Supporting Information
b
ABSTRACT: Various fullerene-based electron acceptor mate-
rials for organic photovoltaic applications were prepared via [3
þ 2] and [4 þ 2] cycloadditions using a continuous flow
approach. The 1,3-dipolar cycloaddition of the tosylhydrazone
precursor and the DielsꢀAlder cycloaddition of indene to
either C or C under conventional batch reaction conditions
6
0
70
were translated to the continuous flow process. By varying the
residence time, temperature, and equivalents of cycloaddition
reagent, significant improvements in yields and reaction times were achieved over conventional batch processes.
ullerene is one of the most widely studied n-type organic
The continuous flow reactions were performed on a commer-
28
F
semiconductor materials. Buckminsterfullerene (C ) can
cially available flow reactor (Vaportec, see Experimental Sec-
tion for details). The reactor setup consisted of polymeric or
stainless steel tubing (10 or 12 mL internal volume) and a HPLC
pump (R2þ module, Vaportec), a 2 mL loop attached to a 6-way
valve, and a backpressure regulator (BPR) fitted to the reactor
outflow. A representative reaction procedure for small scale
optimization studies is carried out by loading the sample loop
containing the fullerene substrate, cycloaddition precursor and
base, if necessary (Scheme 1A). For large scale synthesis, a single
flow channel was used to deliver either solvent or stock solution
(Scheme 1B). The effect of residence time, temperature, irradia-
tion, and equivalents of reactants on the yield was evaluated via
HPLC analysis of product mixtures (Figure 1).
60
reversibly accept six electrons, and electron mobility on the
2
1ꢀ6
order of 1 cm /(V s) has been measured.
Derivatives of
fullerenes (C60 and C ) have been used extensively in do-
70
norꢀacceptor bulk heterojunction (BHJ) solar cells due to their
7
ꢀ12
remarkable electronic properties and solution processability.
In fact, state-of-the-art BHJ devices typically consist of a poly-
13,14
meric donor material and fullerene derivatives as acceptors.
One of the main advantages of BHJ solar cells is the possibility of
cheap and fast device fabrication by employing reel-to-reel
printing techniques. However, a large quantity of material is
required to optimize the performance of printed devices.
There are numerous methods for the functionalization of full-
erenes. The most popular reactions are cyclopropanations, 1,3-
The synthesis of the most commonly used fullerene acceptor
1
5ꢀ19
dipolar cycloadditions, and DielsꢀAlder cycloadditions.
While
in organic electronics, phenyl-C -butyric acid methyl ester 3
61
these are relatively simple single-step reactions, the reaction scale
is seriously restricted by the amount of solvent required to fully
dissolve the fullerene starting material. The solubility of C60 in
toluene is only 2.8 mg/mL at 25 °C with solubility increasing to
(PC BM) and its C analogue, phenyl-C -butyric acid methyl
61 70 71
ester 6 (PC BM), was performed under continuous flow
71
conditions. The primary challenge in translating conventional
batch reactions to continuous flow methods is the solubility of
reactants and products. The synthesis of PC BM 3 is essentially
20
2
4 mg/mL in o-dichlororbenzene (o-DCB). Continuous flow
61
29,30
synthetic methods offer a solution to this problem. The advan-
tages of continuous flow reactions include superior heat transfer
and reagent control, fully contained and closed reactor system
allowing for safe handling of hazardous reagents and high
pressure reactions, ultimate reproducibility owing to precise
a one-pot reaction with three steps (Scheme 2).
In the first
step, the diazo intermediate 4 is generated by the reaction of
tosylhydrazone 1 with sodium methoxide in the presence of
pyridine. 1,3-Dipolar cycloaddition of intermediate 4 to the C60
followed by N liberation gives a mixture of two isomers of
2
21ꢀ26
control of parameters, and most importantly, scalability.
A
PC61BM, the open-cage [5,6]fulleroid and close-cage [6,6]-
isomer. The mixture can then be thermally isomerized to give
exclusively the close-cage [6,6]isomer.
In the conventional batch process, tosylhydrazone 1 and sodium
methoxide are suspended in pyridine to give the diazo intermediate 4.
This is not easily translated to the continuous flow process in which
reactants should be fully dissolved in the reaction solvent, o-DCB.
2,2,6,6-Tetramethylpiperidine 2 (TMP) proved to be a good
very recent publication showed the possibility to synthesize a
fullerene derivative using continuous flow methods on micro-
2
7
fluidic chips. However, only small scale production was exam-
ined with maximum output of 6 mg of crude product per hour.
The objective of this study is to apply continuous flow methods
to the synthesis of four fullerene derivatives that are currently
setting the benchmark in BHJ solar cell performance. Compar-
ison between the conventional batch reaction and the continuous
flow process will be made in the context of reaction time,
conversion and product purity.
Received: January 25, 2011
Published: March 10, 2011
r 2011 American Chemical Society
3551
dx.doi.org/10.1021/jo2001879
|J. Org. Chem. 2011, 76, 3551–3556

The Journal of Organic Chemistry
NOTE
a
Scheme 1. General Flow Reactor Configurations
a
Reaction setup for the (A) small scale optimization and (B) large scale fullerene functionalization via 1,3-dipolar cycloaddition.
alternative to sodium methoxide. By mixing 1 with TMP in
o-DCB, intermediate 4 was generated in situ in the tube reactor
feed of reactants from a stock solution reservoir (Scheme 1B). It
is important to note that the anomalous solubility behavior of C60
must be taken into account in large scale continuous flow
reactions. The fact that the solubility of C60 decreases (by as
much as 2/3) with increasing temperature can have significant
impact on the progress of the flow reaction. As the stock
solutions were made with near saturated room temperature
(
Scheme 1A). Intermediate 4 then reacted with C60 and even-
31
tually led to PC BM on heating. Initial small-scale optimization
6
1
experiments for the synthesis of PC BM used 2 equiv of
61
tosylhydrazone 1 with reaction temperatures up to 150 °C and
gave relatively low yields and multiadducts as the main impurity
1
(
Table 1, entries 1, 2). Additionally, H NMR analysis showed
concentrations of C60 (28 mM), precipitation of C in the tube
60
32
that the monoadduct fraction consisted of a mixture of isomers
reactor at temperature exceeding 150 °C is likely. To overcome
that can be thermally isomerized to produced the desired
this problem, the reaction temperature was increased gradually
29
33
[6,6]isomer (Figure SI-9 in Supporting Information).
from 70 °C (10 mL internal volume) to 150 °C (20 mL internal
In the presence of stoichiometric quantities of 1, the amount
volume) and 250 °C (10 mL internal volume). Additionally, the
reduction of the residence time from 100 min (Table 1, entry 4) to
80 and 40 min yielded 48% and 39% conversion, respectively.
Reducing the reaction time to less than 1 h compromises the
reaction yield by 20%, while increasing the throughput by 2.5 times.
For instance, our equipment allowed a continuous flow production
of 2.6 g (35% isolated yield after column chromato-
of multiadducts was effectively reduced (Table 1, entry 3), whereas
the increase of the reaction temperature and residence times were
translated into moderate yields and direct thermolysis to the
[6,6]isomer (Table 1, entry 4, Figure 1A). The continuous flow
approach showed a notably improved yield of 59% PC BM (94%
61
based on converted C ) in comparison with the reported 35% yield
6
0
29
(
83% based on converted C ) via the one-pot batch synthesis.
graphy) of PC BM in 8 h.
60
61
The large scale continuous flow synthesis of PC BM 3 was per-
formed with a modified reactor configuration to allow a continuous
Next, we turned our attention to the preparation of the C
analogue, PC BM 6. As for PC BM, the batch synthesis of
71 61
61
70
34
3
552
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The Journal of Organic Chemistry
NOTE
Figure 1. HPLC traces of the crude products from the continuous flow synthesis of (A) PC61BM, (B) PC71BM, (C) IC60BA (mixture of regioisomers),
and (D) IC BA (mixture of regioisomers). ICMA: indene-fullerene monoaduct. A normal phase silica gel column (Rainin Dynamax 60 Å Si-83-101-C)
70
was used with toluene (detection at 330 nm) and toluene/hexane (10:1) (detection at 313 nm) as eluents at 1 mL/min for the PCBM and indene
derivatives, respectively.
PC BM is a one-pot reaction with 3 steps (Scheme 2). The
molar ratio of indene to C70 in combination with long reaction
37
7
1
difference between the two reaction sequences lies in the final
step where irradiation is the preferred method for the isomeriza-
tion of [5,6] to [6,6] isomers of PC BM. It is important to
times were shown to be necessary for good conversions (58%).
It is important to note that both bisadducts of C60 and C70
consist of complex mixtures of regioisomers as can be observed in
the HPLC analyses (Figure 1C and D).
71
note here that although isomerization by irradiation does reduce
the number of regioisomers in the PC BM product mixture, the
One of the advantageous features of continuous flow reactions
is the ability to perform reaction under pressure with superheated
solvents. This means the high temperatures required for the
DielsꢀAlder addition of indene to fullerenes should translate
well to continuous flow methods. Indene is thermally converted
to isoindene in the tube reactor, which then reacts with C60 or
C70 via DielsꢀAlder cycloaddition (Scheme 3B). The experi-
ments were conducted with 20 to 36 equivalents of the indene
under superheated conditions at 220 °C in a stainless steel
reactor with o-DCB as a solvent. IC BA and IC BA were both
7
1
monoadduct fraction still consists of three major isomers that are
34
inseparable by conventional chromatography methods. Using
TMP as base, we found that reaction of 2 equiv of tosylhydrazone
1
with C delivered the product mixture in 42% yield after relatively
70
short irradiation times in continuous flow (Table 1, entry 5). HPLC
analysis of the relative product ratios in the reaction with equimolar
amounts of tosylhydrazone showed moderated conversions (49%)
after 60 min reaction times and 94% yield based on converted C70
(Table 1, entry 6 and Figure 1B).
60
70
Recently, DielsꢀAlder adducts of indene with fullerenes have
successfully prepared in less than 2 h in 54% and 49% yield,
respectively (Table 1, entries 7 and 8, Figures 1C and D)
achieving comparable to significantly improved yields over the
batch process.
been successfully used to improve polymer/fullerene bulk het-
erojunction (BHJ) solar cell device performance. Both indene-
3
5,36
C60 bisadduct 9 (IC BA)
and indene-C70 bisadduct 10
60
3
7
(
IC BA) are attractive fullerene acceptor materials for two
In summary, effective procedures were developed for the
preparation of fullerenes derivatives via [3 þ 2] and [4 þ 2]
cycloaddition reactions using a continuous flow approach. Elec-
tron acceptor materials PC BM, PC BM, IC BA, and IC BA
7
0
main reasons. First, the LUMO energy levels of IC BA and
6
0
IC BA are elevated compared with their PCBM counterparts
70
leading to a larger open circuit voltage in BHJ devices with donor
polymers. Second, the synthesis involves only two reactants: the
DielsꢀAlder cycloaddition of indene and fullerene (Scheme 3A).
By using 1,2,4-trichlorobenzene as solvent, the yield of the
61
71
60
70
were produced in maximum reaction times of 100 min, whereas
fullerene derivatization in batch frequently requires several hours
to days under reflux conditions. The described results, in the case
35
reported batch reaction is 34% for IC BA. For IC BA, a high
of PC BM, translate to continuous material production of up to
60
70
61
3
553
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The Journal of Organic Chemistry
Scheme 2. Synthesis of Phenyl-C -butyric Acid Methyl Ester (PC BM) and Its C analogue (PC BM) under Conventional
NOTE
6
1
61
70
71
Batch Reaction Conditions
Table 1. Optimization for the Cycloadditions of C60 and C70 with Diazo Intermediate 4 and with Indene under Flow Conditions
b
c
entry fullerene reagent diene/dipole precursor (equiv) conditions (°C) residence time (min) [lit., h] yield (%) [lit.] converted fullerenes (%)
a
1
2
3
4
5
6
7
8
C
C
C
C
C
C
C
C
60
60
60
60
70
70
60
70
1
1
1
1
1
1
2
2
130
150
150
180
hν
100
50
45
47
45
80
94
45
94
56
52
a
a
a
a
a
42
1
50
53
d
d,e
1
100 [24ꢀ29 ]
60
60
59 [35
42
]
2
e,f
1
hν
49 [59 ]
g
g
indene
indene
20
36
220
220
100[12 ]
54 [34 ]
h
h
100 [12ꢀ72 ]
49 [8ꢀ58 ]
a
b
c
d
Five equivalents of TMP were used to activate tosylhydrazone 1. Degassed o-DCB as solvent. Yield determined via HPLC. The authors isolated
intentionally the open cage fulleroid, performing the cycloaddition and N
2
extrusion at 65ꢀ70 °C for 22 h. Isomerization was induced thermally within
29 e
f
g
2
ꢀ7 h. Reported isolated yield of one-pot reaction procedures using sodium methoxide as a base. Reference 34. Isolated yield using 1,2,4-
35 h
trichlorobenzene as a solvent. Reference 37.
approximately 15 g/day with one benchtop continuous flow
reactor.
reactor setups. The Vaportec R4-pumping module was operated in the
small scale fluid connection mode with manual loaded sample loops.
The reactants were channeled into the tube reactor by pumping solvent
from a reservoir at 0.1 or 0.2 mL/min (equivalent to residence times of
between 50 and 100 min depending on the internal volume of the
reactor). All reactions were performed either thermally (R4-module,
Vaportec) or photochemically, in o-dichlorobenzene (o-DCB), at a
concentration range of 22 to 28 mM (based on fullerene component)
and under approximately 6ꢀ19 bar system pressure (Scheme SI-1 in
Supporting Information).
3
8
’
EXPERIMENTAL SECTION
General Experimental. The benzoyl propionic acid methyl ester
and the corresponding p-tosylhydrazone of methyl benzoylbutyrate
29
were prepared using standard procedures. Commercial reagents were
used as purchased without further purification. C60 (99.5%) and C70
(95%) were bought from Nano-C and BuckyUSA, respectively.
1
13
The continuous flow experiments were conducted using a Vaportec
H and C NMR measurements were and carried out from CDCl
3
28
1
13
R2þR4 unit. All solutions were degassed and reactions were per-
solutions on either 400 or 500 MHz instruments. The H and C NMR
spectrum of the fullerene derivatives are provided in the Supporting
Information. HPLC analysis was carried out using a standard HPLC
system with a UVꢀvis detector. A Rainin Dynamax 60 Å (Si-83ꢀ101-C)
formed under anaerobic conditions. Polytetrafluoroethylene PTFE
(12 mL internal volume), perfluoroalkoxy PFA (10 mL internal volume),
or stainless steel (10 mL internal volume) tubing material was used in the
3
554
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The Journal of Organic Chemistry
Scheme 3. Synthesis of Indene-C60 Bisadduct (IC BA) and Indene-C Bisadduct (IC BA) under (A) Conventional Batch
NOTE
60
70
70
Reaction and (B) Continuous Flow Conditions
analytical HPLC column was used. The product ratios and yields are
based on the percental area from the signal integrations of the HPLC
trace (detection at 330 and 313 nm). Analytical and large scale material
purification was performed following standard chromatographic purifi-
cation methods on silica gel. MALDI-TOF (matrix-assisted laser de-
sorption ionization time-of-flight) mass spectra were obtained in
positive-ion mode with trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-pro-
penylidene]malononitrile as the matrix.
Synthesis of PC71BM 6. A degassed solution of C70 (40 mg, 4.8 ꢁ
2
ꢀ
10 mmol), p-tosylhydrazone of methyl benzoylbutyrate (20 mg, 1.1
equiv), and tetramethylpiperidine (40 μL, 0.2 mmol) in 2 mL of o-DCB
was pumped through a tube reactor using a HPLC pump at the
corresponding flow rates and irradiated with a white halogen lamp. An
analytical sample was diluted with toluene, washed with water, and dried
with magnesium sulfate, and the yield was determined by analytical
HPLC. HPLC (min., 330 nm, 100% toluene, 1 mL/min) PC71BM: 6.5.
1
Functionalization of Fullerenes via 1,3-Dipolar Cy-
cloadddtion under Continuous Flow. Synthesis of PC BM 3.
H NMR (CDCl
3
, 500 MHz) δ ppm: 7.2ꢀ7.95 (m, 5 H); 3.52, 3.69
13
(major isomer), 3.76 (s, 3H, ratio 1:10:1); 2.41ꢀ2.94 (m, 4 H);
6
1
ꢀ2
A degassed solution of C60 (40 mg, 5.5 ꢁ 10 mmol), p-tosylhydrazone
of methyl benzoylbutyrate (21 mg, 1 equiv), and 2,2,6,6-tetramethylpi-
peridine (50 μL, 0.3 mmol) in 2 mL of o-DCB was pumped through a
preheated reactor (at 135 °C, 150 or 180 °C) using a HPLC pump at the
corresponding flow rate. An analytical sample was diluted with toluene,
washed with water, and dried with magnesium sulfate, and the yield was
determined by analytical HPLC. In a representative large scale experi-
ment one R4-reactor modules with four temperature controllable zones
was used: one reactor at 70 °C (10 mL internal volume), two reactors at
1.79ꢀ2.24 (m, 2 H). C NMR (CDCl
, 500 MHz) δ ppm: 173.3,
3
2
156.0, 155.3, 152ꢀ138 (forest of peaks belonging to sp carbons on the
fullerene cage, Figure SI-13 in Supporting Information), 131.6, 130.8,
128.6, 128.3, 72.9, 69.9, 51.8, 36.0, 34.2, 33.9, 21.8. MS-MALDI (m/z):
þ
calcd for C82
H
14
O
2
, 1030.10; found M , 1030.10.
Functionalization of Fullerenes via DielsꢀAlder Cy-
cloadddtion under Continuous Flow. Synthesis of IC BA 9. A
60
ꢀ2
degassed solution of C60 (40 mg, 5.5 ꢁ 10 mmol) and indene (130 μL,
1.1 mmol, 20 equiv) in 2 mL of o-DCB was pumped through a preheated
reactor (220 °C) at 100 μL/min. An analytical sample was diluted with
toluene/hexane (1:10), and the yield was determined by analytical HPLC.
After precipitation from ethanol, 40 mg of crude product was purified by
column chromatography (30% toluene in hexane). HPLC (min, 313 nm,
1
50 °C (20 mL internal volume), followed by telescopic isomerization in
one reactor at 250 °C (10 mL internal volume) at 1 mL/min flow rate
residence time = 40 min, BPR = 250 psi). Therefore, 6 g (8.33 mmol) of
60, 3.18 g (8.5 mmol) of p-tosylhydrazone of methyl benzoylbutyrate,
(
C
1
and 2,2,6,6-tetramethylpiperidine (5.7 mL, 34.3 mmol) were dissolved
in 360 mL of o-DCB and pumped through the reactor. The collected
solution at the reactor outlet was concentrated under reduced pressure
and purified by column chromatography with toluene as eluent to afford
PC BM (2.67 g, 2.93 mmol, 35%). HPLC (min., 330 nm, 100%
toluene/hexane (1:10) 1 mL/min) IC BA: 16ꢀ28. H NMR (CDCl ,
60
3
500 MHz) δ ppm: 7.91ꢀ7.20 (m, 8H), 2.57ꢀ4.44 (m, 4H), 48.08ꢀ3.22
13
(m, 2H), 3.06ꢀ2.49 (m, 2H). C NMR (CDCl
3
, 500 MHz) δ ppm:
2
161ꢀ136 (forest of peaks belonging to sp carbons on the fullerene cage,
2
Figure SI-15 in Supporting Information), 127, 124 (sp carbons on the
6
1
1
3
toluene, 1 mL/min) PC61BM: 7.5. H NMR (CDCl
3
, 500 MHz) δ
indene addend), 74, 57, 46 (sp on the indene addend). MS-MALDI (m/
þ
ppm: 7.94 (d, 2 H, J=8Hz), 7.56(t, 2H, J= 7.5 Hz), 7.48 (t, 1 H, J=7.4Hz),
z): calcd for C78
H
16, 952.13; found M , 952.18.
13
ꢀ2
3.69 (s, 3 H), 2.92 (m, 2 H), 2.54 (t, 2 H, J = 7.4 Hz), 2.2 (m, 2 H).
C
Synthesis of IC BA 10. C (40 mg, 4.7 ꢁ 10 mmol) and indene
7
0
70
NMR (CDCl , 500 MHz) δ ppm: 173.5, 148.8, 147.8, 145.2, 145.1 (2),
(200 μL, 36 equiv) were reacted following the procedure described for
3
1
1
2
44.8, 144.7, 144.4, 144.0, 143.8, 143.0 (2), 142.9, 142.2 (2), 142.1 (2),
IC60BA 5. HPLC (min, 313 nm, toluene/hexane (1:10) 1 mL/min)
1
41.0, 138.0, 137.6, 136.7, 132.1, 128.4, 128.3, 79.9, 51.9, 51.7, 33.9, 33.7,
IC70BA: 30ꢀ49. H NMR (CDCl
3
, 500 MHz) δ ppm: 7.73ꢀ7.24 (m,
þ
2.4. MS-MALDI (m/z): calcd for C H O , 910.10; found M , 910.10.
8H), 4.79ꢀ4.45 (m, 2H), 4.33ꢀ4.14 (m, 2H), 2.92ꢀ2.70 (m, 2H),
7
2 14 2
3
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The Journal of Organic Chemistry
NOTE
1
3
2
(
.50ꢀ2.37 (m, 2H). C NMR (CDCl
3
, 400 MHz) δ ppm: 162ꢀ129
Chem. 1993, 97, 3379. Doome, R. J.; Dermaut, S.; Fonseca, A.;
Hammida, M.; Nagy, J. B. Fullerene Sci. Technol. 1997, 5, 1593. Semenov,
K. N.; Charykov, N. A.; Keskinov, V. A.; Piartman, A. K.; Blokhin, A. A.;
Kopyrin, A. A. J. Chem. Eng. Data 2009, 55, 13.
2
forest of peaks belonging to sp carbons on the fullerene cage, Figure
SI-18 in Supporting Information), 127, 124 (sp carbons on the indene
addend), 68.2, 67.4, 58.0, 55.9, 46, 38.7 (sp on the indene addend). MS-
MALDI (m/z): calcd for C H , 1072.13; found M , 1072.13.
2
3
þ
(
(
21) Jas, G.; Kirschning, A. Chem.—Eur. J. 2003, 9, 5708.
22) J €a hnisch, K.; Hessel, V.; L €o we, H.; Baerns, M. Angew. Chem., Int.
88 16
Ed. 2004, 43, 406.
’
ASSOCIATED CONTENT
(23) Kirschning, A.; Solodenko, W.; Mennecke, K. Chem.—Eur. J.
2
006, 12, 5972.
S
Supporting Information. HPLC-elugrams and NMR
b
(24) Glasnov, T. N.; Kappe, C. O. Macromol. Rapid Commun. 2007,
spectra of the fullerene derivatives. This material is available free
of charge via the Internet at http://pubs.acs.org.
28, 395.
(25) Mason, B. P.; Price, K. E.; Steinbacher, J. L.; Bogdan, A. R.;
McQuade, D. T. Chem. Rev. 2007, 107, 2300.
(
(
26) Illg, T.; L €o b, P.; Hessel, V. Biorg. Med. Chem. 2010, 18, 3707.
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’
AUTHOR INFORMATION
Corresponding Author
Maggini, M. Energy Environ. Sci. 2010, 4, 725–727.
*
E-mail: wwhwong@unimelb.edu.au; djjones@unimelb.edu.au.
(28) www.vapourtec.co.uk
(
29) Hummelen, J. C.; Knight, B. W.; Lepeq, F.; Wudl, F.; Yao, J.;
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(
’
ACKNOWLEDGMENT
S. M.; Peregudov, A. S.; Kaplunov, M. G.; Lyubovskaya, R. N. Mendeleev
Commun. 2007, 17, 175.
We thank the Australian Research Council (ARC) for Dis-
covery Projects (DP0877325), the Victorian Government (DPI-
VICOSC, VSA-SPF-VICOSC), the Commonwealth Scientific
and Industrial Research Organisation (CSIRO), and the Uni-
versity of Melbourne for generous financial support.
(
31) Ruoff, R. S.; Malhotra, R.; Huestis, D. L.; Tse, D. S.; Lorents,
D. C. Nature 1993, 362, 140.
(32) Note that when performing smale scale optimization studies,
dispersion of the reaction volume within the reactor reduces the original
concentration.
(
33) This tempersture is required to convert the tosylhydrazone to
’
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