A search for dichlorocarbene ether solvent interactions

Article abstract of DOI:10.1016/j.tetlet.2003.11.009

The absolute rate constant of reaction of dichlorocarbene with pyridine and with tetramethylethylene was determined in Freon-113 (CF₂ClCFCl₂), dioxane, and tetrahydrofuran. No evidence of specific solvation was obtained.

Full text of DOI:10.1016/j.tetlet.2003.11.009

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 485–486
A search for dichlorocarbene ether solvent interactions
Stanislav I. Presolski,a Adelajda Zorba,a Dasan M. Thamattoor,a,* Eric M. Tippmannb
and Matthew S. Platzb,*
aDepartment of Chemistry, Colby College, 5750 Mayflower Hill Drive, Waterville, ME 04901, USA
bDepartment of Chemistry, The Ohio State University, 100 W. 18th Avenue, Columbus, OH 43210, USA
Received 11 August 2003; revised 4 November 2003; accepted 5 November 2003
Abstract—The absolute rate constant of reaction of dichlorocarbene with pyridine and with tetramethylethylene was determined in
Freon-113 (CF2ClCFCl2), dioxane, and tetrahydrofuran. No evidence of specific solvation was obtained.
ꢀ 2003 Elsevier Ltd. All rights reserved.
Singlet carbenes have closed shell electron configura-
tions with both a filled and empty orbital.1 This has led
chemists to wonder if singlet carbenes may form weak
complexes with coordinating solvents. Tomioka et al.,2
Ruck and Jones,3 and Moss et al.4 have probed for
evidence of complexation using product based studies.
Khan and Goodman5 have used photoacoustic spec-
troscopy to gather evidence of an interaction between
singlet methylene and benzene.
growth can be analyzed to yield an observed rate con-
stant, kobs, which can be equated to the elementary rate
constants of Scheme 1 in Eq. 1.
kobs ¼ k0 þ kpyr½pyridineꢀ
ð1Þ
A plot of kobs versus [pyridine] is linear (Fig. 2) with
slope kpyr
.
The presence of TME, at constant pyridine concentra-
tion increases kobs as shown in Eq. 2. We also carried out
independent product studies in all three solvents to
confirm that :CCl2 does indeed form the cycloadduct
with the trap, as expected, when TME is present in the
reaction mixture. In the absence of TME, the carbene
adds to the precursor itself and no products from
insertion of :CCl2 into the solvent were found.
We have reasoned that solvent complexation will reduce
the absolute bimolecular reaction rate constants of
carbenes. In previous work we found that the absolute
rate constant of reaction of arylhalocarbenes with
tetramethyethlylene (TME) is essentially the same in
coordinating and noncoordinating solvents.6;7 We
speculated that the stabilizing influence of the aryl group
weakened any carbene solvent interaction past the point
of kinetic significance. This led us to study a simpler
carbene––dichlorocarbene.
0.4
0.3
0.2
0.1
0.0
Dichlorocarbene was generated by laser flash photoly-
sis8 of diene 19 using 308 nm radiation. The carbene was
visualized by trapping with pyridine to form ylide 2,
which is easily detected at 400 nm.10
The intensity of absorption of ylide 2 increases expo-
nentially after the laser pulse (Fig. 1). The exponential
150
200
250
300
ns
350
400
450
Keywords: Singlet carbene; Laser flash photolysis; Solvent interaction.
* Corresponding authors. Tel.: +1-207-8723429; fax: +1-207-8723804;
e-mail: dmthamat@colby.edu
Figure 1. Transient absorbance of ylide 2 at 400 nm in Freon-113.
Top: 0.005 M pyridine, bottom: 0.001 M pyridine.
0040-4039/$ - see front matter ꢀ 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2003.11.009

486
S. I. Presolski et al. / Tetrahedron Letters 45 (2004) 485–486
Table 1. Values of kTME and kPYR for 1 at ambient temperature as a function of solvent
Solvent
kpyr (Mꢁ1 sꢁ1
)
s (ns)
kTME (Mꢁ1 sꢁ1
)
kTMEðFreonÞ=kTMEðsolventÞ
1
Freon-113a
4.63 · 109
3.22 · 109
6.16 · 109
7.9 · 109
684
125
172
3.13 · 109
1.20 · 109
9.28 · 108
3.81 · 109
Tetrahydrofurana
Dioxanea
2.6
3.4
Cyclohexaneb
a This work.
b Ref. 10.
kobs ¼ k0 þ kpyr½pyridineꢀ þ kTME½TMEꢀ
Plots of kTME versus [TME] are linear with slopes of
kTME (Fig. 3).
ð2Þ
Products
Cl
Cl
Cl
Cl
k
solvent
0
N
Cl
+
hν = 308 nm
N
Values of kpyr, k0 ( ¼ 1=s), and kTME are collected in
k
Cl
PYR
Table 1.
1
2
k
TME
Table 1 reveals that the lifetime of dichlorocarbene
is shorter in ether solvents than in Freon-113
(CF2ClCFCl2). Our values of kpyr and kTME in Freon-113
are very similar to that found previously in cyclohex-
ane.10 Tetrahydrofuran and dioxane have very little
influence on these values. Thus, we find no kinetic evi-
dence of specific solvation for this particular carbene,
:CCl2, by ethereal solvents.
Cl
Cl
3
Scheme 1.
3.20E+07
Acknowledgements
Support of this work by the National Science Founda-
tion and the Petroleum Research Fund is gratefully
acknowledged. S.I.P. and A.Z. also acknowledge sup-
port from the HHMI and the DeanÕs Fund at Colby
College.
1.60E+07
0.00E+00
0
0.001
0.002
0.003
0.004
0.005
0.006
[PYR] M
References and Notes
Figure 2. A plot of kobs versus [pyridine] in Freon-113 (m) and dioxane
(d) at ambient temperature.
1. Hoffmann, R.; Zeiss, G. D.; Van Dine, G. W. J. Am.
Chem. Soc. 1968, 90, 1485.
2. Tomioka, H.; Ozaki, Y.; Izawa, Y. Tetrahedron 1985, 41,
4987.
3. Ruck, R. T.; Jones, M., Jr., Tetrahedron Lett. 1998, 39,
2277.
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Soc. 1998, 120, 1088.
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2001, 105, 1158.
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1305.
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105, 8413.
4.00E+07
3.20E+07
2.40E+07
1.60E+07
8.00E+06
0.00E+00
0
0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009
[TME] M
9. Hartwig, J. F.; Jones, M., Jr.; Moss, R. A.; Lawrynowicz,
W. Tetrahedron Lett. 1986, 27, 5907.
10. Chateauneuf, J. E.; Johnson, R. P.; Kirchhoff, M. M.
J. Am. Chem. Soc. 1990, 112, 3217.
Figure 3. A plot of kobs of formation of ylide 3 versus tetramethyl-
ethylene at constant [pyridine] (0.002 M) in Freon-113 (m) and dioxane
(d) at ambient temperature.