A nonspectroscopic method to determine the photolytic decomposition pathways of 3-chloro-3-alkyldiazirine: Carbene, diazo and rearrangement in excited state

Article abstract of DOI:10.1021/ja0116876

C₆₀ acts as a mechanistic probe for the formation of carbene, diazo compound, and for the rearranged product via the excited state in the photolysis of 3-chloro-3-isopropyldiazirine and 3-chloro-3-chloromethyldiazirine. The carbene adds to C₆₀ to form methanofullerene, whereas the diazo compound adds to C₆₀ to form fulleroid. The olefin product arises as a result of the rearrangement in the excited state.

Full text of DOI:10.1021/ja0116876

Published on Web 07/19/2002
A Nonspectroscopic Method To Determine the Photolytic
Decomposition Pathways of 3-Chloro-3-alkyldiazirine:
Carbene, Diazo and Rearrangement in Excited State
Takatsugu Wakahara,† Yasuyuki Niino,‡ Takashi Kato,‡ Yutaka Maeda,†
Takeshi Akasaka,*,† Michael T. H. Liu,*,§ K. Kobayashi,| and S. Nagase*,|
Contribution from the Center for Tsukuba AdVanced Research Alliance, UniVersity of Tsukuba,
Tsukuba, Ibaraki 305-8577, Japan, Graduate School of Science and Technology, Niigata
UniVersity, Niigata 950-2181, Japan, Department of Chemistry, UniVersity of Prince Edward
Island, Prince Edward Island C1A4P3, Canada, and Department of Theoretical Studies, Institute
for Molecular Science, Myodaiji, Okazaki 444-8585, Japan
Received July 10, 2001. Revised Manuscript Received June 3, 2002
Abstract: C60 acts as a mechanistic probe for the formation of carbene, diazo compound, and for the
rearranged product via the excited state in the photolysis of 3-chloro-3-isopropyldiazirine and 3-chloro-3-
chloromethyldiazirine. The carbene adds to C60 to form methanofullerene, whereas the diazo compound
adds to C60 to form fulleroid. The olefin product arises as a result of the rearrangement in the excited state.
Scheme 1
Introduction
Carbenes have been frequently generated by the photochemi-
cal decomposition of diazirines.1 Since their introduction in
1988, pyridinium ylides2 have become popular as probes to
study the dynamics of carbene species which lack convenient
UV-vis chromophores for direct detection. In 1992, Platz and
co-workers3 discovered considerable variation in the yield of
pyridinium ylide upon laser flash photolysis of solutions of
alkylchlorodiazirines with equal optical densities. For example,
the signal obtained from cyclopropylchlorodiazirine exceeds by
more than 10-fold that obtained from isopropylchlorodiazirine.
The yield of carbene is large with cyclopropylchlorodiazirine
because the R-C-H bond is very strong. The R-C-H bond in
isopropylchlorodiazirine is weaker, so that the yield of carbene
is consistent with the fact that diazirine excited states suffer
1,2-hydrogen migration and nitrogen extrusion, in competition
with carbene formation.
pyridinium ylide absorption, is less than 20 ns at -90 °C. This
experiment was not a complete success because of the low yield
in the production of carbene upon the photolysis of 1 and also
because the carbene lifetime is close to the response time of
the detection system. In the same year, Bonneau and Liu5 also
determined the quantum yield of formation of the diazo
compound, 3, φdiazo ≈ 10-15%, in the photolysis of 1. They
concluded that the low quantum yield for 3 cannot alone explain
the low yield for the formation of carbene 2. Although these
results are in agreement with Platz’s hypothesis of an efficient
rearrangement in the excited-state (RIES) process in the case
of diazirine 1, they still await confirmation. Bonneau and Liu4
also reported the simplest interpretation of all of the existing
data. The explanation is that three pathways exist for the
formation of 4, as described in Scheme 1.
In 1996, Bonneau and Liu4 studied the 1,2-hydrogen migra-
tion in isopropyl-chlorocarbene, 2, produced by laser flash
photolysis of 3-chloro-3-isopropyldiazirine, 1. The lifetime of
carbene 2, estimated from the kinetics of growth of the
* To whom correspondence should be addressed. E-mail: T.A.,
akasaka@tara.tsukuba.ac.jp.
† University of Tsukuba.
‡ Niigata University.
§ University of Prince Edward Island.
| Institute for Molecular Science.
(1) (a) AdVances in Carbene Chemistry; Brinker, U., Ed.; JAI Press Inc.:
Stamford, Connecticut, 1994; Vol. 1; 1998; Vol. 2. (b) Chemistry of
Diazirines; Liu, M. T. H., Ed.; CRC Press: Boca Raton, Florida, 1987;
Vols. 1 and 2.
(2) Jackson, J. E.; Soundararajan, N.; Platz, M. S.; Liu, M. T. H. J. Am. Chem.
Soc. 1988, 110, 595.
(3) (a) White, W. R.; Platz, M. S. J. Org. Chem. 1992, 57, 2841. (b) Platz, M.
S.; White, W. R.; Modarelli, D. A. Res. Chem. Intermed. 1994, 20, 175.
(4) Bonneau, R.; Liu, M. T. H. J. Am. Chem. Soc. 1996, 118, 7229.
(5) Liu, M. T. H.; Bonneau, R. J. Am. Chem. Soc. 1996, 118, 8098.
9
10.1021/ja0116876 CCC: $22.00 © 2002 American Chemical Society
J. AM. CHEM. SOC. 2002, 124, 9465-9468
9465

A R T I C L E S
Wakahara et al.
Arenas and co-workers6 made a theoretical study on the
photoexcited 3H-diazirine and came to the following conclusion.
By means of dynamical calculations, they demonstrated that
carbene formation does not take place in the excited state and
it is formed on the ground-state surface after decaying through
a conical intersection.
141.06 (s), 140.04 (s), 138.99 (s), 138.50 (s), 138.09 (s), 137.27 (s),
136.24 (s), 134.67 (s), 134.52 (s), 75.90 (s), 67.56 (s), 39.35 (d), 17.76
(q). UV-vis (λmax, toluene): 339 nm. FABMS (toluene/NBA): m/z
1
810 (M), 720 (C60). Minor isomer, H NMR (500 MHz, CS2/CDCl3):
δ 2.20 (sept, 1H, J ) 6.4 Hz), 1.12 (d, 6H, J ) 6.4 Hz). 13C NMR
(CS2/CDCl3 ) 3/1, 125 MHz): δ 146.98 (s), 144.89 (s), 144.35 (s),
144.32 (s), 144.00 (s), 143.65 (s), 143.59 (s), 143.48 (s), 143.16 (s),
143.01 (s), 142.93 (s), 142.41 (s), 142.22 (s), 142.09 (s), 141.71 (s),
141.12 (s), 141.51 (s), 140.16 (s), 139.07 (s), 138.25 (s), 137.32 (s),
136.58 (s), 136.29 (s), 135.01 (s), 84.59 (s), 59.28 (s), 32.54 (d), 17.51
(q) (seven peaks of minor isomer might be overlapped by some of the
major isomer’s peaks). UV-vis (λmax, toluene): 339 nm. FABMS
(toluene/NBA): m/z 810 (M), 720 (C60).
Recently, we reported the use of C60 as a probe to distinguish
carbene/diazo partition in the photolysis of adamantanediazirine.7
C60 reacts with diazomethane to yield fulleroid. By adding onto
C60, carbene affords methanofullerene. We now wish to report
the photolysis of two diazirines in the presence of C60 with the
object of determining the contribution of various pathways in
the decomposition of alkylchlorodiazirine.
Photochemical Reaction of 3-Chloro-3-chloromethyldiazirine
with C60. We photoirradiated a toluene/o-dichlorobenzene (1:3) solution
of 3-chloromethyl-3-chlorodiazirine (8.0 mg, 3.4 × 10-3 M) and C60
(24 mg, 7.0 × 10-3 M) with a high-pressure mercury-arc lamp for 3 h
at -40 °C in a NMR tube. 1H NMR measurement of the reaction
mixture showed the yield of 1,2-dichloroethylene (E- and Z-) and
C60C(Cl)CH2Cl to be 45 and 25%, respectively. The ratio of the (E)-
and (Z)-1,2-dichloroethylene was 28/72 (E/Z ) 0.38). We also carried
out a preparative-scale experiment using diazirine 7 (44.4 mg, 8.0 ×
10-2 M) and C60 (144 mg, 2.0 × 10-2 M) to obtain an authentic sample
of the isomeric C60C(Cl)CH2Cl adduct (8). We isolated adduct 8 (7.4
mg) by HPLC separation with a Buckyprep column. Compound 8, 1H
NMR (300 MHz, CS2/C6D6): 4.68 (s, 2H). 13C NMR (125 MHz, CS2/
C6D6): 145.19 (s), 145.15 (s), 145.11 (s), 145.06 (s), 145.00 (s), 144.79
(s), 144.75 (s), 144.70 (s), 143.54 (s), 144.47 (s), 144.36 (s), 144.29
(s), 144.05 (s), 143.58 (s), 143.28 (s), 143.10 (s), 143.00 (s), 142.87
(s), 142.78 (s), 142.19 (s), 142.11 (s), 142.03 (s), 141.68 (s), 141.24
(s), 140.96 (s), 139.14 (s), 137.12 (s), 78.27 (s), 56.69 (s), 46.80 (t).
UV-vis (λmax, toluene): 328, 429, 485 nm. FABMS (toluene/NBA):
m/z 816 (M), 720 (C60).
Experimental Section
Gel permeation chromatographic separation was performed on a
recycling preparative HPLC with a series of Jaigel 1H and 2H columns
(Japan Analytical Industry Co., Ltd.) using toluene as an eluent. The
isolation of isomers was performed by using a preparative HPLC system
with a Buckyprep column (Nacalai Tesque: 20 mm φ × 250 mm)
with toluene as an eluent. The ratio of isomers was determined by HPLC
analysis using an analytical Buckyprep column (Nacalai Tesque: 4.6
mm φ × 250 mm) with toluene as an eluent. The yields of 1-chloro-
2-methyl-1-propene, 1,2-dichloroethylene, and C60CClCH2Cl were
determined by 1H NMR measurement of the reaction mixture. Bibenzyl
was used as an internal standard. The yield of C60CCl(i-Pr) was
determined by HPLC analysis. Isopropylchlorodiazirine and chlorom-
ethylchlorodiazirine were synthesized by a previously reported proce-
dure.8
Photochemical Reaction of 3-Chloro-3-isopropyldiazirine with
C60. We photoirradiated a toluene/o-dichlorobenzene (1:3) solution of
isopropylchlorodiazirine 1 (8.0 mg, 3.4 × 10-2 M) and C60 (48 mg,
3.4 × 10-2 M) with a high-pressure mercury-arc lamp for 30 min at
-40 °C in a sealed Pyrex NMR tube. The reaction mixture was allowed
to stand for 3 h in the dark at room temperature to complete N2
elimination. 1H NMR measurement of the reaction mixture showed the
yield of 1-chloro-2-methyl-1-propene to be 82%. The HPLC analysis,
using a Buckyprep column, demonstrated that adduct 5 was obtained
in 18% yield, respectively. The HPLC analysis also showed the ratio
of 5a and 5b as 28/72. We also carried out a preparative-scale
experiment using diazirine 1 (137 mg, 3.8 × 10-2 M) and C60 (72 mg,
3.3 × 10-3 M) to obtain an authentic sample of the isomeric C60CCl-
(i-Pr) adduct (5). We isolated adduct 5 (21 mg) by first-stage HPLC
separation with a GPC column and isomers 5a (6 mg) and 5b (15 mg)
by second-stage HPLC separation with a Buckyprep column. Compound
Results and Discussion
The establishment of the role of the excited state in the
chemistry of diazirine has been studied by fluorescence spec-
troscopy, as demonstrated by Platz and co-workers.9 Alkyl-
chlorodiazirines, which fluoresce weakly or not at all, have a
low fluorescence quantum yield which makes the study of
excited-state chemistry difficult. Another method entails the
analysis of the products obtained under photolysis and ther-
molysis in the presence of various amounts of a reactive olefin
at various temperatures, as performed for chloromethylchlo-
rodiazirine and n-propylchlorodiazirine.10 This method is tedious
and time-consuming. Yet a different method to study the excited
state of diazirine is the time-resolved photoacoustic calorimetry,
which monitors the amplitude and time evolution of heat
depositions following photoexcitation.10,11
Investigators now recognize that, when diazirines are used
as the source of carbenes, several processes contribute to the
formation of the final product including the rearrangement of
the excited state of the diazirine. As well, the formation of the
metastable diazo intermediate competes with the production of
carbene. The efficiency of these three ways of decomposition
of the diazirine strongly depends on the structure of the diazirine
being used. No rules exist to predict the relative efficiency of
these different pathways. Considering all of the procedures
described earlier, we found that the C60 trapping methodology
presents a simple way to determine the efficiencies of these
1
5a, H NMR (300 MHz, CS2/CDCl3): δ 3.36 (sept, 1H, J ) 6.6 Hz),
1.66 (d, 6H, J ) 6.6 Hz). 13C NMR (75 MHz, CS2/CDCl3): δ 145.98
(s), 145.05 (s), 145.02 (s), 144.99 (s), 144.95 (s), 144.87 (s), 144.82
(s), 144.64 (s), 144.45 (s), 144.41 (s), 144.31 (s), 144.27 (s), 144.17
(s), 144.16 (s), 143.50 (s), 143.43 (s), 143.09 (s), 142.91 (s), 142.90
(s), 142.84 (s), 142.78 (s), 142.72 (s), 142.68 (s), 142.21 (s), 142.03
(s), 141.94 (s), 141.56 (s), 141.02 (s), 140.76 (s), 138.73 (s), 131.42
(s), 80.24 (s), 64.30 (s), 31.08 (d), 18.62 (q). UV-vis (λmax, toluene):
331, 430 nm. FABMS (toluene/NBA): m/z 810 (M), 720 (C60).
Compound 5b, major isomer, 1H NMR (CS2/CDCl3, 500 MHz): δ 5.02
(sept, 1H, J ) 6.4 Hz), 1.51 (d, 6H, J ) 6.4 Hz). 13C NMR (CS2/
CDCl3, 125 MHz): δ 147.24 (s), 147.75 (s), 144.53 (s), 143.77 (s),
143.72 (s), 143.71 (s), 143.59 (s), 143.51 (s), 143.38 (s), 143.20 (s),
143.04 (s), 143.02 (s), 142.99 (s), 142.77 (s), 142.70 (s), 142.46 (s),
142.29 (s), 142.24 (s), 141.79 (s), 141.69 (s), 141.37 (s), 141.28 (s),
(6) Arenas, J. F.; Toco`n, I. L.; Otero, J. C.; Soto, J. J. Am. Chem. Soc. 2002,
124, 1728.
(7) Akasaka, T.; Liu, M. T. H.; Niino, Y.; Maeda, Y.; Wakahara, T.; Okamura,
M.; Kabayashi, K.; Nagase, S. J. Am. Chem. Soc. 2000, 122, 7134.
(8) Graham, W. H. J. Am. Chem. Soc. 1965, 87, 4396.
(9) Modarelli, D.; Morgan, S.; Platz, M. S. J. Am. Chem. Soc. 1992, 114, 7034.
(10) Bonneau, R.; Liu, M. T. H.; Kim, K. C.; Goodman, J. L. J. Am. Chem.
Soc. 1996, 118, 3829.
(11) LaVilla, J. A.; Goodman, J. L. J. Am. Chem. Soc. 1989, 111, 712 and 6877.
9
9466 J. AM. CHEM. SOC. VOL. 124, NO. 32, 2002

Decomposition Pathway of 3-Chloro-3-alkyldiazirine
A R T I C L E S
Scheme 2
Scheme 3
Figure 1. The optimized structure of 5a and 5b (major and minor) at the
B3LYP/3-21G* level.
Table 1. The Density Functional Calculations for 5a, 5b (Major
and Minor), and C60 at the B3LYP/3-21G Level
pathways. To test C60 as a chemical probe, we carried out the
two experiments using isopropylchlorodiazirine (1) and chlo-
romethylchlorodiazirine (7).
Photochemical Decomposition of Isopropylchlorodiazirine.
Irradiation of a o-dichlorobenzene (ODCB)/toluene solution of
C
60 (3.4 × 10-2 M) and isopropylchlorodiazirine (1, 3.4 × 10-2
M) with a high-pressure mercury-arc lamp (cutoff < 300 nm)
in a Pyrex tube at -40 °C resulted in the formation of the
corresponding adduct C60CCl(i-Pr) (5) in 18% yield, which was
purified by preparative HPLC with a GPC column. We also
observed the formation of 1-chloro-2-methyl-1-propene (4) in
82% yield (Scheme 2). Adduct 5 can be readily separated into
two isomers, 5a and 5b, by preparative HPLC with a Buckyprep
column. HPLC analysis at -40 °C after reaction showed the
formation of 6, which was converted to 5b at room temperature
by N2 elimination (Scheme 3). Compound 6 was stable at -40
°C under photoirradiation conditions. We also carried out the
irradiation of 1 in the presence of C60 at -40 °C with a λ >
400 nm, where C60 is the only light-absorbing component. In
this case, we did not observe a decomposition of 1. Thus, it is
eomers is 4:1. These results cannot be explained by thermody-
namical arguments.
We carried out the density functional calculations13 at B3LYP/
3-21G* level for 5a and two diastereomers of 5b with the
Gaussian 98 program14 (Figure 1). These three isomers have
almost identical stability (Table 1). Hence, a mechanism for
diastereoselective cluster opening reactions must account for
the kinetically controlled process. Schick and Hirsch reported
the highly diastereoselective formation of fulleroids via thermal
decomposition of the corresponding pyrazolines in the reaction
of C60 with monoalkylated diazomethanes.15 They demonstrated
that the kinetic product is the fulleroid with the bulkier
substituent located above a five-membered ring. In our case,
the difference of the two substituents (Cl and i-Pr) is small as
compared with those of monoalkylated diazomethanes. Thus,
the diastereoselectivity of 5b might be decreased.
3
evident that C60* does not play an important role in these
reactions.
FAB mass spectrometry of 5a and 5b depicts a molecular
ion peak (C64H7Cl that requires m/z 810) at m/z 814-810, as
well as one of C60 at m/z 724-720, which arises from the loss
of the i-Pr(Cl)C group. The UV-visible absorption spectra of
5a and 5b are virtually identical to that of C60 except for a subtle
difference in the 400-650 nm region. These results suggest that
5a and 5b retain the essential electronic and structural character
of C60. The UV-visible absorption spectrum of 5a has an
absorption at 430 nm, indicating a characteristic feature of a
6,6-adduct of C60.12
On the basis of these observations, the formation yields of
5a, 5b, and 4 (5, 13, and 82%) in the photoreaction of C60 with
isopropylchlorodiazirine 1 reveal the formation yields of car-
(13) For B3LYP, see: (a) Becke, A. D. Phys. ReV. 1988, A38, 3098. (b) Becke,
A. D. J. Chem. Phys. 1993, 98, 5648. (c) Lee, C.; Yang, W.; Parr, R. G.
Phys. ReV. 1988, B37, 785. For 3-21G*, see: Pietro, W. J.; Francl, M. M.;
Hehre, W. J.; DeFrees, D. J.; Pople, J. A.; Binkley, J. S. J. Am. Chem.
Soc. 1982, 104, 5039.
The spectral data of 1H and 13C NMR and 2D NMR (HMQC
1
and HMBC) clearly suggest that 5a has Cs symmetry. The H
(14) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M.
A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.; Stratmann,
R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin,
K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi,
R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.;
Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz,
J. V.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng,
C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.; Head-Gordon, M.;
Replogle, E. S.; Pople, J. A. Gaussian 98; Gaussian, Inc.: Pittsburgh, PA,
1998.
NMR spectrum of 5b showed the existence of two diastereo-
mers. The proton of the isopropyl group of the major isomer
appears as a septet at 5.02 ppm, which is a typical chemical
shift for a location above the five-membered ring of the fullerene
subunit. The chemical shift of the same H atom of the minor
isomer appears at 2.20 ppm, indicating that the isopropyl group
is located on the six-membered ring. The ratio of two diaster-
(12) Hirsch, A.; Gro¨sser, T.; Skiebe, A.; Soi, A. Chem. Ber. 1993, 126, 1061.
(15) Hirsch, A.; Schick, G. Tetrahedron 1998, 54, 4283.
9
J. AM. CHEM. SOC. VOL. 124, NO. 32, 2002 9467

A R T I C L E S
Wakahara et al.
Scheme 4
derivatization of C60 by 7 are in agreement with these findings,
especially that the E/Z ratio (28/72) of 9 is very close to
Bonneau’s results (25/75) indicating that all 9 is formed via
RIES process in our reaction. This experiment reiterates that
our C60 trapping methodology acts as a probe for the partitioning
of carbene, diazo and excited-state chemistry in the photolysis
of diazirines.
Table 2. Redox Potentialsa in V of C60
, 5a, and 5b
b
compound
ox E1
red E1
red E2
red E3
C60
+1.21c,d
+1.24c
+1.11c
+1.07c
+1.10c
+1.29c
-1.12
-1.14
-1.14
-1.21
-1.18
-1.13
-1.50
-1.51
-1.51
-1.58
-1.55
-1.54
-1.95
-2.10
Electrochemical Properties of Fullerene Derivatives. In
view of the electron-acceptor character of C60, there is a great
interest in the electrochemical behavior of C60 derivatives
bearing an organic addend.16 We studied the redox potentials
of the prepared compounds by cyclic voltammetry at room
temperature. The data are collected in Table 2, together with
C60, C60CClPh, and C60Ad as reference compounds. Adduct 5a
exhibits three one-electron reversible reduction waves and one
irreversible oxidation, such as that observed for the parent C60.
However, we observed two reversible reduction waves and one
irreversible oxidation for 5b. The salient feature is that the 5,6-
adduct 5b has a low oxidation potential (+1.11 V) as compared
to that of the 6,6-adduct 5a (+1.24 V). Interestingly, the 6,6-
adduct of C60Ad has a low oxidation potential (+1.16 V) as
compared to that of the 5,6-adduct of C60Ad (+1.45 V).
Meanwhile, the first reduction potentials related to C60 are
cathodically shifted, which indicates that the introduction of a
i-Pr(Cl)C group results in decreasing the electron-accepting
properties. This finding agrees with that previously observed
for other dihydrofullerenes. It may be explained by the raising
of the LUMO energy of the adducts.
6,6-C60CCl(i-Pr) (5a)
5,6-C60CCl(i-Pr) (5b)
6,6-C60Ade
-2.06
-2.02
-2.02
5,6-C60Ade
C60CClPhe
a Half-cell potentials unless otherwise stated. Values are relative to
ferrocene/ferrocenium couple. b Reference 17. c Irreversible. d Value was
obtained by differential pulse voltammogram. e Reference 7.
bene, diazo compound, and RIES process during the reaction.
Bonneau and Liu have already determined that approximately
13% goes to diazo compounds from 1 in the laser flash
photolysis of 1.5 On the other hand, Platz claims that the
quantum yield of the carbene is only 10% for i-PrClCN2
photolysis.3 He assumed that the RIES for this diazirine must
be high, for example, 70-80%. Present results obtained from
chemical derivatization of C60 by 1 are in agreement with these
findings. We are now convinced that C60 can be used as a
chemical probe for the photochemical reaction of diazirine.
Photochemical Decomposition of Chloromethylchlorodi-
azirine. We irradiated a o-dichlorobenzene (ODCB)/toluene
solution of C60 (3.4 × 10-2 M) and chloromethylchlorodiazirine
(7, 3.4 × 10-2 M) under the same conditions as diazirine 1 to
afford the corresponding adduct C60CCl(CH2Cl) (8), which was
purified by preparative HPLC with a Buckyprep column. We
also observed the formation of 1,2-dichloroethylene (9) (Scheme
4). The 8/9 ratio is 36/64. Hence, the RIES process for diazirine
7 is 64%. The E/Z ratio of 9 is 28/72. The HPLC analysis and
spectroscopic investigation by means of NMR measurements
verify that 8 is a 6,6-adduct of C60.
Bonneau and co-workers reported the determination of the
carbene formation (R) and the RIES efficiency (1 - R) of 7 by
time-resolved photoacoustic calorimetry (R ) 0.49) as well as
by the thermolysis and photolysis of 7 in the presence of olefins
(R ) 0.54 - 0.42).10 They also reported that the rearrangement
of free carbene ClCH2CCl gives ∼6% of 9-E and ∼94% of
9-Z from a thermolysis experiment. Photolysis of the same
diazirine gives ∼15% of 9-E and ∼85% of 9-Z. This was
explained by the RIES process which produced 9 with a much
larger E/Z ratio than that of the free carbene. If the efficiency
of RIES is ∼52%, then the RIES process gives ∼25% of 9-E
and ∼75% of 9-Z. Present results obtained from chemical
Conclusion
Our proposal uses C60 to measure carbene/diazo partitioning
functions not only in the carbene/diazo case but also in the
measurement of RIES, which is neither a carbenic nor a diazo
process. This method complements Platz’s fluorescence experi-
ment and Bonneau and Liu’s relative rate and time-resolved
photoacoustic studies. We believe that this paper presents the
first set of unambiguous results in the assignment of decomposi-
tion pathways in diazirine.
Acknowledgment. This work was supported in part by a grant
from the Asahi Glass Foundation and by a Grant-in-Aid from
the Ministry of Education, Science, Sports, and Culture of Japan.
M. T. H. Liu thanks NSERC of Canada for financial support.
JA0116876
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