Orbital interactions in selenomethyl-substituted pyridinium ions and carbenium ions with higher electron demand

Article abstract of DOI:10.1021/jo102307v

Computational, solution phase, and crystal structure analysis of 2- and 4-organoselenylmethyl-substituted pyridinium ions (10a-c and 11a-c) provides strong evidence for C-Se hyperconjugation (σC-Se^-π*) between the C-Se σ-bond and the π-deficien

Full text of DOI:10.1021/jo102307v

ARTICLE
pubs.acs.org/joc
Orbital Interactions in Selenomethyl-Substituted Pyridinium Ions
and Carbenium Ions with Higher Electron Demand
S. Fern Lim, Benjamin L. Harris, Paul Blanc, and Jonathan M. White*
School of Chemistry and Bio-21 Institute, University of Melbourne, Parkville 3010 Melbourne, Australia
S Supporting Information
b
ABSTRACT: Computational, solution phase, and crystal structure analysis of 2- and
4-organoselenylmethyl-substituted pyridinium ions (10a-c and 11a-c) provides
strong evidence for C-Se hyperconjugation (σC-Se-π*) between the C-Se σ-bond
and the π-deficient aromatic ring and a through-space interaction (nSe-π*) between
the selenium p-type lone pair and the π-deficient aromatic ring. There is also a weak
anomeric-type interaction (nSe-σ*CC) involving the selenium p-type lone pair
electrons and the polarized CH2-C(Ar) σ-bond. NBO analysis of calculated cations
with varying electron demand (B3LYP/6-311þþG**) show that C-Se hyperconjugation
(σC-Se-π*) is the predominant mode of stabilization in the weakly electron-demanding pyridinium ions (10d, 11d, 14, and 15);
however, the through-space (nSe-π*) interaction becomes more important as the electron demand of the β-Se-substituted
carbocation increases. The anomeric interaction (nSe-σ*CC) is relatively weak in all ions.
’ INTRODUCTION
co-workers have raised similar questions regarding the nature of
sulfur participation in S-glycoside chemistry.5
We have reported previously that unimolecular solvolysis of the
conformationally biased and nonbiased β-phenylselenyl trifluoroace-
tates 1 and 2 occurs at rates which are 107 and 106 respectively with
respect to the unsubstituted derivative 3 indicating that the selenium
substituent strongly assists in the departure of the leaving group.1
Strong evidence that the C-Se bond is a good σ-donor orbital,
and therefore capable of effectively stabilizing positive charge by hy-
perconjugation, was provided by crystallographic analysis of a range
of ester and ether derivatives of the alcohol 61 using the variable
oxygen probe.6 However, whether the solvolysis of 1 involves the
bridged cation 4 the open cation 5 is still an open question.
We have found that substituted N-methyl pyridinium ions 8
provide a convenient system for investigating the effects of C-M
(M = Si, Ge) hyperconjugation.7 For example, conversion of the
trialkylsilyl-substituted pyridine derivatives 9 into the ion 8a
results in a significant downfield shift in the 29Si NMR spectrum,
and a significant decrease in the 29Si-13C one-bond coupling
constant between the silicon and the methylene carbon. These
spectroscopic effects are consistent with significant contribution
of the double-bond-no-bond resonance form 8a0 to the struc-
ture of these ions. Furthermore, X-ray structure analysis of these
ions reveals that the R3Si-CH2Pyr bond distance in ions 8a is
significantly lengthened relative to standard values.
Conventionally, participation by the selenium substituent in
these solvolyses occurs by the bridged ion intermediate 4
(Scheme 1), in which the selenium lone pair electrons facilitate
the departure of the leaving group. This is an example of
nonvertical neighboring nucleophilic participation.2 However,
we considered the possibility that participation by the selenium
substituent might occur by σC-Se-p hyperconjugation (vertical
participation)3 and involve the open carbenium ion intermediate 5,
so that the neighboring nucleophile may be the loosely held
electrons of the C-Se σ-bond rather that the selenium lone pair.
This mode of stabilization of the intermediate carbenium ion 5 is
analogous to that provided by the trimethylsilyl substituent in
the ion 7, which is the basis of the silicon β-effect.4 Woerpel and
Received: November 26, 2010
Published: February 11, 2011
r
2011 American Chemical Society
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Scheme 1. Possible Modes of Neighboring Group Participation by the β-Phenylselenyl Substituent
Scheme 2. Syntheses of Selenylmethyl-Substituted Pyridines 12a-c and 13a-c and Pyridinium Ions 10a-c and 11a-ca
a Reagents and conditions: (a) NaOH, MeOH; (b) RSeNa; (c) CH3I, or CH3OSO2CF3, or CH3OTs.
Thus to provide further evidence for stabilization by σC-Se-p
hyperconjugation we proposed to carry out an experimental and
computational study on the 2- and 4-alkyl- and aryl-selenyl-
methyl-substituted pyridinium ions 10a-c and 11a-c.
The 77Se chemical shifts, and 77Se-13C one-bond coupling
constants for 10a-c and 11a-c and the pyridine precursors
12a-c and 13a-c are presented in Table 1.
The 77Se chemical shifts for the 4-selenomethyl-substituted N-
methyl pyridinium ions 10a-c are deshielded relative to their
neutral precursors 12a-c by 45.6, 38.8, and 36.4, respectively,
consistent with dispersal of the positive charge on the pyridi-
nium ring onto the selenium substituent. Interestingly, how-
ever, while methylation of the 2-phenylselenomethylpyridine
derivative 13a also results in a downfield shift of the 77Se
chemical shift in the resulting ion 11a, the remaining two
’ RESULTS AND DISCUSSION
The precursor pyridine derivatives 12a-c and 13a-c were
prepared according to Scheme 2; these were then converted into
10a-c and 11a-c respectively by methylation using either
methyl iodide, methyl tosylate, or methyl triflate for both
solution phase and crystallographic analysis.
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derivatives 11b,c display an upfield shift upon methylation of
the precursors 13b,c. This upfield shift possibly arises due to
steric interaction of the ortho N-methyl substituent with the
selenomethyl substituent in 13b-c, an example of a 77Se γ
gauche effect,8 which has been demonstrated in other systems.
If the pyridine derivatives are converted to their corresponding
pyridinium ions by protonation rather than methylation, then
the steric environment surrounding the 4-substituted deriva-
tives and the 2-substituted derivatives becomes essentially
identical. Consistent with this, protonation of 4-substituted
pyridines 12b,c and 2-substituted pyridine derivatives 13b,c
results in a downfield shift of the 77Se by ca. 40 ppm magnitudes
for all ions (see the Experimental Section).
and some insight to this is provided in the structural and
computational studies described below.
To gain further insight into the nature of the interaction
between the selenium substituent and the electron-deficient
pyridinium ring we determined the X-ray crystal structures of
the ions 10 and 11. Crystals of suitable quality for X-ray analysis
were obtained for the N-methyl pyridinium ions 10b-c, 11a, and
11c; in addition to these we obtained crystals for the correspond-
ing protonated pyridinium ions 12aH and 13aH and 13bH as
their picrate salts. Thermal ellipsoid plots for all structures are
presented in Figure 2 while selected bond distances, bond angles,
and dihedral angles are presented in Table 2.
In all the structures the Se-CH2 bond is close to orthogonal
to the pyridinium ring, a conformation that allows for effective
overlap between the Se-CH2 σ-bond and the low-lying π*
-system (Figure 3). The mean Se-CH2 bond distance is 1.973 Å
while the mean CH2-Cipso distance is 1.485 Å; comparison of
these values for a typical Se-CH2 distance (1.960 Å) and CH2-
Ar distance (1.500 Å), which were obtained from the Cambridge
Crystallographic Database,10 provides some evidence for con-
tributions of the double-bond-no-bond resonance structures
100 and 110 to the ground state structures of these ions. Of
interest was the unusual conformation about the Se-CH2 bond,
which adopted the sterically less-favored gauche arrangement in
five of the seven structures, the exceptions being 10c and 11c
where R = But. The preference for the gauche conformation in
11a may have its origins in intramolecular π-π interactions;
however, this is not the case for the remainder of the structures.
We considered that this conformation may be favored for one or
both of the following reasons (Figure 3): (i) it allows for the
p-type lone pair on the selenium to interact with the CH2-Ar
antibonding orbital (analogous to the anomeric effect)11 and/or
(ii) it allows for a through-space interaction between the seleni-
um p-type lone-pair and the low-lying π-system of the positively
charged pyridinium ring—a similar type of through space orbital
interaction (nSe-π*CO) has been used to explain the conforma-
tional preferences of R-phenylselenylcyclohexanones.12,13 It is
compelling to propose the presence of the nSe-σ*CC as this may
help to explain the unexpected effects on the Se-CH2 coupling
constants (Table 1) which increased upon methylation of the
pyridine precursors (12a-c and 13a-c), this interaction that
would strengthen the Se-CH2 bond may offset the expected
bond weakening effects of σC-Se-π* hyperconjugation.
The downfield shift of the 77Se signal upon conversion of the
pyridine precursors 12a-c and 13a-c to their corresponding
positively charges pyridinium ion derivatives is consistent with
the dispersal of positive charge onto the selenium substituent.
However, associated with this downfield shift is a small increase
in the one-bond 77Se-13C one-bond coupling constant, in direct
contrast to the effects observed in the silicon-substituted ion 8a
where there is a significant decrease in the 29Si-13C one-bond
coupling constant compared with its neutral precursor 9a. This
result appears to conflict with the expectations of σC-Se-π
hyperconjugation in these ions, such that contributions of the
proposed double-bond-no-bond resonance forms 100 and 110
to the ground state structures of the ions 10 and 11 (Figure 1)
should weaken the Se-CH2 bond and hence decrease the
77Se-13C coupling constant. It is likely that 13C-77Se coupling
constants are influenced by factors other than hyperconjugation,
which may also change upon conversion of the neutral pyridines
into the pyridinium ions, for example the hybridization state of
the lone pairs on the selenium is known to effect both the fermi-
contact term and the spin dipole term of the 77Se-13C coupling
constant;9 these effects may mask the effects of hyperconjugation,
Table 1. δ 77Se NMR Chemical Shifts and 1J CH2-Se
Coupling Constants for the Selenylmethyl-Substituted
Pyridines 12a-c and 13a-c and the Pyridinium Ions 10a-c
and 11a-c
CMPD 1J C-Se
δ δ
77Se CMPD 1J C-Se 77Sε ΔJ (Hz) Δδ 77Se
12a
12b
12c
13a
13b
13c
61.9
65.5
67.3
61.9
64.8
67.7
361.2
10a
10b
10c
11a
11b
11c
65.5
67.0
70.9
67.7
60.3
70.5
406.8
þ3.6
þ1.5
þ2.6
þ5.8
-4.5
þ2.8
þ45.6
þ38.8
þ36.4
þ27.9
-19.1
-4.8
338.1
458.6
337.2
331.3
448.1
376.9
495.0
364.9
312.2
443.3
’ COMPUTATIONAL DETAILS
To gain further insight into the structures of these ions, and the
importance of the various orbital interactions between the selenium
substituent and the electron deficient pyridinium ring, we carried out ab
initio molecular orbital calculations on the model systems 10d and 11d
Figure 1. Hyperconjugation in 2- and 4-selenomethylpyridinium ions.
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Figure 2. Thermal ellipsoid plots for 10b, 10c, 11a, 11c, 12aH, 13aH, and 13bH. Ellipsoids are at the 20% probability level; counterions have been
omitted for clarity.
Figure 3. Possible orbital interactions involving the selenium substituent in the pyridinium ions 10a-c and 11a-c (R0 = Me) and 12aH, 13aH, and
13bH (R0 = H).
Table 2. Selected Distances (Å), Angles (deg), and Dihedral Angles (deg) for the Selenium-Substituted Pyridinium Ionsa
10b
10c
11a
11c
12aH
13aH
13bH
Se-CH2
1.959(3)
1.483(3)
112.7(3)
-61.3(3)
-67.2(3)
1.967(3)
1.483(4)
109.7(2)
93.0(2)
1.977(2)
1.479(2)
110.5(1)
-102.3(2)
44.9(1)
1.971(3)
1.495(4)
107.1(2)
98.0(2)
1.989(6)
1.486(8)
110.3(4)
-100.0(4)
76.3(4)
1.982(2)
1.483(3)
111.5(1)
84.7(1)
93.0(1)
1.969(2)
1.489(2)
112.0(2)
73.5(2)
CH2-Cipso
Se-CH2-Cipso
Se-CH2-Cipso-Cortho
R-Se-CH2-Cipso
a Estimated standard deviations are in parentheses.
-141.2(2)
154.1(2)
-77.6(2)
(R = Me); in addition to these we also carried out the calculations on
structures 14-18 in order to assess the effects that increasing the electron
demand of the cations has on the magnitude of these interactions.
Calculations were performed at the B3LYP/6-311þþG** level of
theory,14 a level of theory that has been previously employed to
investigate stereoelectronic effects of chalcogen substituents;15 energies
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are ZPE corrected. Natural Bond Orbitals (NBOs) were calculated by
using the NBO 3.0 program16 as implemented in the GAUSSIAN 03
package.17 Calculated structures for 10d and 18 are presented in
Figure 4. The remaining structures 11d and the cations 14-18 with
relevant structural parameters are available in the Supporting Informa-
tion; both the anti and gauche conformations about the Se-CH2 bond
were calculated. In all cases the gauche conformation was found to be
more stable than the anti conformation with the energy difference
between the two conformations increasing with increasing electron
demand of the carbenium ion.
12aH, 13aH, and 13bH to adopt the gauche conformation in the solid
state, and the observation that 10c and 11c with the sterically more
demanding tBu-Se substituents prefer to adopt the antiperiplanar con-
formation. As the electron demand of the cations increases (as gauged by
the decreasing pKRþ values for the parent cations), both the hypercon-
jugative σSe-C-π* and through-space nSe-π* orbital interactions
increase in strength while the nSe-σ*C-C interaction remains small
throughout the series. Increasing C-Se-π hyperconjugation with
increasing electron demand is clearly demonstrated in Figure 5, where
the Se-CH2 bond distance increases with decreasing pKRþ
.
For the pyridinium ion 10d, which has low electron demand, the anti
conformation is a local minimun that lies ca. 0.7 kJ/mol above the
gauche conformation, and a rotation barrier of 4 kJ/mol separates these
two conformations; interestingly in the cyclopropenyl cation 18 the anti
conformation is an energy maxima that is 12.4 kJ above the two
degenerate gauche conformations (see the Supporting Information for
energy barriers). Selected structural parameters and NBO interaction
energies for the σSe-C-π*, nSe-σ*CC, and nSe-π* orbital interactions
(as shown in Figure 3) for the calculated structures for 10d, 11d, and
14-18 are presented in Table 3.
Examination of the NBO interaction energies in Table 3 shows that
the most important interaction in the methylselenylmethyl-substituted
pyridines 10d and 11d is σSe-C-π* hyperconjugation, with the
through-space nSe-π* and the nSe-σ*C-C interactions being relatively
weak. The presence of the nSe-π* and nSe-σ*CC interactions, although
weak, however explains the preference of the pyridinium ions 10b, 11a,
The increasing through-space (σSe-C-π*) interaction with electron
demand of the cation manifests as a closing up of the Se-CH2-C(þ)
bond angle, which is clearly shown by the plot of the Se-CH2-C(þ)
bond angle vs pKRþ (Figure 6). This appears to represent the early stages
of bridging by the β-selenium substituent.
’ CONCLUSION
Lengthening of the Se-CH2 bond and shortening of the
CH2-C(Ar) bond in the solid state structures of selenomethyl-
substituted pyridinium ions provides evidence for carbon-
selenium hyperconjugation (σC-Se-π*) between the carbon-
selenium bonding orbital and the π* orbital of the electron-
deficient pyridinium ring. In addition there are interactions
involving the selenium p-type nonbonded pair of electrons
including a through-space nSe-π* interaction with the elec-
tron-deficient pyridinium ring and an anomeric interaction
(nSe-σ*CC) with the vicinal CH2-C(Ar) antibonding orbital.
We believe that these latter interactions are responsible for the
selenium substituent adopting the gauche conformation in 10a,b
and 11a,b, but are weak enough that the tert-butyl-substituted
derivatives (10c and 11c) adopt the sterically more preferred anti
conformation. In solution a significant downfield shift in the 77Se
NMR chemical shift upon conversion of the pyridine precursors
into the positively pyridinium ions is consistent with dispersal of
positive charge on the selenium nucleus, consistent with all the
orbital interactions discussed above. Calculations show that C-
Se hyperconjugation (σC-Se-π*) is the predominant mode of
stabilization in the pyridinium ions (10d, 11d, 14, and 15);
however, the through-space (nSe-π*) interaction becomes more
Figure 4. Calculated structures (B3LYP/6-311þþG**) for cations 10d
and 18.
Table 3. Selected Distances (Å), Angles (deg), and Dihedral Angles (deg) for the Calculated Structures of 10d, 11d, and 14-18a
10d
11d
18b
14
15
16
17
18
pKRþ
20.518
1.9995
1.4871
109.92
100.17
74.78
34.8
12.219
2.0048
1.4818
107.90
96.56
79.95
43.4
3.519
2.0091
1.4783
106.34
93.4
4.720
2.0088
1.4829
103.60
91.6
7.821
2.0074
1.4572
104.47
93.4
-7.422
2.0145
1.4462
101.13
91.2
Se-CH2
2.0038
1.4889
112.32
-99.72
71.25
34.2
CH2-Cþ
Se-CH2-Cþ
Se-CH2-Cþ-C
CH3-Se-CH2-Cþ
σSe-C- π*
nSe-π*
85.77
43.4
99.3
85.77
70.9
88.13
104.9
73.7
55.3
9.0
8.8
14.8
14.8
37.1
48.5
nSe-σ*C-C
12.6
14.8
11.9
10.6
11.8
10.1
6.0
a NBO stabilization energies for the σSe-C-π*, nSe-σ*CC, and nSe-π* orbital interactions are given in kJ mol-1. Structures were calculated at B3LYP/
6-311þþG** for all atoms except for Se, which was calculated with the SDD basis set. b An approximated value.19
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Figure 5. Plot of Se-CH2 bond distance (Å) vs pKRþ for the parent cation for the cations 10a and 14-18.
Figure 6. Plot of Se-CH2-C(þ) bond angle (deg) vs pKRþ for the parent cation, for the cations 10a and 14-18.
important as the electron demand of the β-Se-substituted
carbocation increases. The anomeric interaction (nSe-σ*CC) is
relatively weak in all ions.
Crystal data for 10c (tosylate): C18H25NO3SSe, M = 414.41, T =
130.0(2) K, λ = 0.71073 Å, monoclinic, space group P21/n, a = 6.509(2) Å,
b = 33.521(8) Å, c = 8.747(2) Å, β = 93.464(4)°, V = 1905.0(8) Å3, Z = 4,
Dc = 1.445 Mg M-3, μ(Cu KR) =2.096 mm-1, F(000) = 856, crystal size
0.5 ꢀ 0.4 ꢀ 0.03 mm3; 11914 reflections measured, 4354 independent
reflections (Rint = 0.0372), the final R was 0.0407 [I > 2σ(I)] and wR(F2)
was 0.1023 (all data).
Crystal data for 11a (triflate): C14H14F3NO3SSe, M = 412.28, T =
130.0(2) K, λ = 0.71073 Å, monoclinic, space group P21/c, a= 10.369(3) Å,
b=11.734(3) Å, c =13.532(4) Å, β = 105.156(4)°, V = 1589.2(7) Å3, Z=4,
Dc = 1.723 Mg M-3, μ(Mo KR)=2.538 mm-1, F(000) = 824, crystal size
0.40 ꢀ 0.40 ꢀ 0.30 mm3; 8157 reflections measured, 2798 independent
reflections (Rint = 0.0213), the final R was 0.0238 [I > 2σ(I)] and wR(F2)
was 0.0686 (all data).
’ EXPERIMENTAL SECTION
a. Crystallography. Intensity data were collected with an Oxford
Diffraction Sapphire CCD diffractometer, using Cu KR radiation
(graphite crystal monochromator λ = 1.54184 Å), or with a Bruker
SMART Apex CCD detector, using Mo KR radiation (graphite crystal
monochromator λ = 0.71073 Å). The temperature during data collec-
tion was maintained at 130.0(1) K for all data collections by using an
Oxford Cryostream low-temperature device.
Crystal data for 10b (triflate): C15H16F3NO3SSe, M = 426.31, T =
130.0(2) K, λ =1.5418 Å, monoclinic, space group P21/c, a=14.8030(5) Å,
b = 8.9842(3) Å, c= 13.0040(4) Å, β=99.476(3)°, V=1705.84(10) Å3, Z=
4, Dc = 1.660 Mg M-3, μ(Cu KR) =4.551 mm-1, F(000) = 856, crystal
size 0.69ꢀ0.25ꢀ04 mm3; 9296 reflections measured, 3284 independent
reflections (Rint = 0.0465), the final R was 0.0436 [I > 2σ(I)] and wR(F2)
was 0.1244 (all data).
Crystal data for 11c (tosylate):C18H25NO3SSe, M=414.41, T=130.0(2) K,
λ =1.5418 Å, monoclinic, space group P21/c, a = 17.4160(3) Å, b = 9.5355(2)
Å, c = 11.4018(2) Å, β = 90.467(2)°, V = 1893.44(6) Å3, Z = 4, Dc = 1.454
Mg M-3, μ(Cu KR) = 3.843 mm-1, F(000) = 856, crystal size 0.41ꢀ0.25ꢀ
03 mm3; 8219 reflections measured, 3690 independent reflections (Rint
=
0.0358), the final R was 0.0400 [I > 2σ(I)] and wR(F2) was 0.0964 (all data).
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Crystal data for 12aH (picrate): C18H14N4O7Se, M = 477.29, T =
130.0(2) K, λ = 0.71073 Å, monoclinic, space group P21/n, a = 7.449(3) Å,
b =13.527(4) Å, c = 19.221(6) Å, β = 99.285(5)°, V = 1911(1) Å3, Z = 4,
Dc = 1.659 Mg M-3, μ(Mo KR) = 2.016 mm-1, F(000) = 960, crystal size
0.40ꢀ 0.25 ꢀ 0.05 mm3; 9186 reflections measured, 3353 independent
reflections (Rint = 0.1140), the final R was 0.0585 [I > 2σ(I)] and wR(F2)
was 0.1190 (all data).
(m, 2H, Ar-H), 7.29 (m, 3H, Ar-H), 7.14 (d, J = 4.4 Hz, 2H, Ar-H), 4.10
(s, 2H, -CH2); 13C NMR (CDCl3, 125 MHz) δ 150.7 (Ar-C), 149.3
(Ar-C), 138.4 (Ar-C), 134.4 (Ar-C), 130.2 (Ar-C), 128.6 (Ar-C), 124.8
(Ar-C), 30.6 (1JC-Se = 61.9 Hz, -CH2); 77Se NMR (95 MHz, sample in
CD3CN, external standard: (PhSe)2 in CDCl3) δ 361.2; HRMS (ESI)
calcd for C12H12NSeþ [M þ H]þ 250.01295, found 250.01298; IR
(thin film) ν~ 3062-2927 cm-1 (pyridine ring).
Crystal data for 12bH (picrate): C18H14N4O7Se, M = 477.29, T =
130.0(2) K, λ = 0.71073 Å, triclinic, space group P1, a = 8.2176(5) Å,
b = 9.7350(6) Å, c =12.3328(8), Å, R = 82.277(1)°, β = 83.488(1)°, γ =
72.756(1)°, V = 930.9(1) Å3, Z = 2, Dc = 1.703 Mg M-3, μ(Mo KR) =
32.069 mm-1, F(000) = 480, crystal size 0.50ꢀ0.40ꢀ0.30 mm3; 4856
reflections measured, 3242 independent reflections (Rint = 0.0146), the
final R was 0.0253 [I > 2σ(I)] and wR(F2) was 0.0637 (all data).
Crystal data for 13bH (picrate): C19H16N4O7Se, M = 491.32,
T = 130.0(2) K, λ = 1.5418 Å, monoclinic, space group P21/n, a =
11.6919(2) Å, b = 8.2865(2) Å, c = 20.4393(4) Å, β = 97.802(2)°, V =
2-(Phenylselenomethyl)pyridine, 13a:. 0.21 g (86%); yellow
oil; 1H NMR (CD3CN, 500 MHz) δ 8.44 (d, J = 4.9 Hz, 1H, Ar-H),
7.59 (td, J = 7.7, 1.9 Hz, 1H, Ar-H), 7.49 (m, 2H, Ar-H), 7.25
(m, 4H, Ar-H), 7.14 (m, 1H, Ar-H), 4.25 (s, 2H, -CH2); 13C
NMR (CD3CN, 125 MHz) δ 160.0 (Ar-C), 150.2 (Ar-C), 137.5
(Ar-C), 133.6 (Ar-C), 131.3 (Ar-C), 130.1 (Ar-C), 128.1 (Ar-C),
123.9 (Ar-C), 122.8 (Ar-C), 33.9 (1JC-Se = 61.9 Hz, -CH2); 77Se
NMR (95 MHz, sample in CD3CN, external standard: (PhSe)2 in
CDCl3) δ 337.2; HRMS (ESI) calcd for C12H12NSeþ [M þ H]þ
250.01295, found 250.01291; IR (thin film) ν~ 3077-2938 cm-1
(pyridine ring).
N-Methyl 4-(phenylselenomethyl)pyridinium triflate, 10a:. A
solution of 12a (50.0 mg, 0.20 mmol) in 0.5 mL of deuterioacetonitrile was
treated with neat methyl triflate (36.4 mg, 0.22 mmol, 25.1 μL). After
evaporation of the solvent 10a as its triflate salt was obtained as a yellow oil:
1H NMR (CD3CN, 500 MHz) δ 8.40 (d, J = 6.6 Hz, 2H, Ar-H), 7.60 (d, J =
6.8 Hz, 2H, Ar-H), 7.48-7.25 (m, 5H, Ar-H), 4.25 (s, 2H, -CH2), 4.20 (s,
3H, -CH3);13CNMR(CD3CN, 125 MHz) δ161.2 (Ar-C), 150.0(Ar-C),
145.6 (Ar-C), 135.6 (Ar-C), 130.6 (Ar-C), 129.6 (Ar-C), 128.2 (Ar-C), 48.6
(-CH3), 30.2 (1JC-Se = 65.5 Hz, -CH2); 77Se NMR (95 MHz, sample
in CD3CN, external standard: (PhSe)2 in CDCl3) δ 406.8; HRMS (ESI)
calcd for C13H14NSeþ [M]þ 264.02860, found 264.02856; IR (thin film) ~ν
3062-2927 cm-1 (pyridine ring).
N-Methyl 2-(phenylselenomethyl)pyridinium triflate,
11a:. A solution of 13a (50.0 mg, 0.20 mmol) in 0.5 mL of deuter-
ioacetonitrile was treated with neat methyl triflate (36.4 mg, 0.22 mmol,
25.1 μL). X-ray quality crystals of 11a were obtained from slow
evaporation of solvent: crystalline plates; mp 118.3-120.3 °C; 1H
NMR (CD3CN, 500 MHz) δ 8.63 (d, J = 6.2 Hz, 1H, Ar-H), 8.09 (t,
J = 7.9 Hz, 1H, Ar-H), 7.75 (t, J = 7.0 Hz, 1H, Ar-H), 7.45-7.29 (m, 5H,
Ar-H), 7.24 (d, J = 7.5 Hz, 1H, Ar-H), 4.41 (s, 2H, -CH2), 4.26
(s, 3H, -CH3); 13C NMR (CD3CN, 125 MHz) δ 156.1 (Ar-C), 148.0
(Ar-C), 145.9 (Ar-C), 137.0 (Ar-C), 132.1 (Ar-C), 130.6 (Ar-C), 130.4
(Ar-C), 129.9 (Ar-C), 126.9 (Ar-C), 46.6 (-CH3), 27.8 (1JC-Se = 67.7
Hz, -CH2); 77Se NMR (95 MHz, sample in CD3CN, external standard:
(PhSe)2 in CDCl3) δ 364.9; HRMS (ESI) calcd for C13H14NSeþ [M]þ
264.02860, found 264.02856; IR (thin film) ν~ 3062-2927 cm-1
(pyridine ring).
1961.93(7) Å3, Z = 4, Dc = 1.663 Mg M-3, μ(Cu KR) = 3.066 mm-1
,
F(000) = 992, crystal size 0.6 ꢀ 0.4 ꢀ 0.2 mm3; 8689 reflections
measured, 3853 independent reflections (Rint = 0.0181), the final R
was 0.0297 [I > 2σ(I)] and wR(F2) was 0.0825 (all data).
b. Synthesis:
General. All reactions were performed in oven-dried glassware under
nitrogen atmosphere. Anhydrous ethanol was distilled from magnesium
ethoxide under nitrogen atmosphere. Deuterated solvents were stored over
4 Å sieves before use. Products were purified via crystallization with n-pen-
tane. Proton nuclear magnetic resonance spectra (1H NMR, 400 and 500
MHz) and proton decoupled carbon nuclear magnetic resonance spe-
ctra (13C NMR, 100 and 125 MHz) were obtained in deuterioacetonitrile
or deuteriochloroform with residual acetonitrile or chloroform as inter-
nal standards. Selenium nuclear magnetic resonance (77Se NMR,
95 MHz) was performed in deuterioacetonitrile or deuteriochloroform
with an external standard consisting of diphenyl diselenide in deuterio-
chloroform (100 mg/1 mL), which was referenced at 464 ppm.
Chemical shifts are reported in parts per million (ppm), followed by
(in parentheses, where applicable) multiplicity, coupling constant(s)
(J, Hz), integration, and assignments. High-resolution mass spectra
(HRMS) were obtained by ionizing samples via electron spray ioniza-
tion (ESI). Mass spectra are expressed as mass to charge ratio (m/z)
values. Melting points were uncorrected. Assignment of the methylene
carbons for the benzylselenylmethyl pyridine and pyridinium ions (10b,
11b, 12b, and 13b) was achieved by using 2-dimensional NMR tech-
niques. 1H NMR assignment was supported by gCOSY experiments and
13C NMR assignment by DEPT experiments, as well as gHSQC and
gHMBC two-dimensional experiments.
Preparation of 4-(phenylselenomethyl)pyridinium pi-
crate, 12aH:. To a solution of 12a (50.0 mg, 0.20 mmol) in 2 mL
of anhydrous ethanol was added picric acid (46.2 mg, 0.20 mmol) at
room temperature. The reaction was left to stir overnight under
nitrogen. Ethanol was removed under reduced pressure to afford the
product in solid form. X-ray quality crystals of 12aH were obtained from
chloroform/diethyl ether diffusion as yellow needles: mp 155.3-
(Phenylselenomethyl)pyridines 12a, and 13a: General
Procedure. To a solution of diphenyl diselenide (1.00 mmol) in 20
mL of anhydrous ethanol was added sodium borohydride (in excess)
portionwise until the solution turn colorless. Meanwhile, to a stirred
suspension of the appropriate bromomethyl pyridine hydrobromide
(2.00 mmol) in 25 mL of ethanol at 0 °C was added ice-cold 1 M NaOH
solution (2.00 mmol, 2 mL) in 8 mL of ethanol. This cold solution was
stirred for another 10 min then added dropwise at room temperature
into the anion solution previously generated. The reaction mixture was
left to stir overnight under nitrogen, then diluted with 25 mL of diethyl
ether and washed with water (5 ꢀ 20 mL). A 1 M HCl solution was
added to the organic phase and the product was extracted into the acidic
aqueous phase (3 ꢀ 20 mL), which was then neutralized with 1 M NaOH
solution. The pure product was extracted from the neutralized solution by
using diethyl ether (3 ꢀ 20 mL), washed with water (3 ꢀ 20 mL) and then
brine (3 ꢀ 20 mL), and dried over magnesium sulfate, then solvent was
removed under reduced pressure to afford the pure product.
1
157.3 °C; H NMR (CDCl3, 500 MHz) δ 8.58 (d, J = 7.1 Hz, 2H,
Ar-H), 7.42 (m, 4H, Ar-H), 7.31 (m, 3H, Ar-H), 4.12 (s, 2H, -CH2),
9.05 (s, 2H, Ar-H); 13C NMR (CDCl3, 125 MHz) δ 160.0 (Ar-C), 141.9
(Ar-C), 132.5 (Ar-C), 130.9 (Ar-C), 130.6 (Ar-C), 127.6 (Ar-C), 127.3
(Ar-C), 31.7 (1JC-Se = 67.0 Hz, -CH2), 161.6 (Ar-C), 140.8 (Ar-C),
136.6 (Ar-C), 127.5 (Ar-C); 77Se NMR (95 MHz, sample in CDCl3,
external standard: (PhSe)2 in CDCl3) δ 419.2; HRMS (ESI) calcd for
C12H12NSeþ [M]þ 250.01295, found 250.01298; IR (thin film) ν~
3062-2927 cm-1 (pyridine ring).
(Benzylselenomethyl)pyridines: General Procedure. To a
solution of dibenzyl diselenide (1.00 mmol) in 20 mL of anhydrous
ethanol was added sodium borohydride (in excess) portionwise until the
4-(Phenylselenomethyl)pyridine, 12a:. 0.22 g (89%); yellow
oil; 1H NMR (CD3CN, 500 MHz) δ 8.40 (d, J = 4.4 Hz, 2H, Ar-H), 7.46
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The Journal of Organic Chemistry
ARTICLE
solution turn colorless. Meanwhile, to a stirred suspension of the
appropriate bromomethyl pyridine hydrobromide (2.00 mmol) in 25
mL of ethanol at 0 °C was added ice-cold 1 M NaOH solution (2.00
mmol, 2 mL) in 8 mL of ethanol. This cold solution was stirred for
another 10 min then added dropwise at room temperature into the anion
solution previously generated. The reaction mixture was left to stir
overnight under nitrogen. Ethanol was removed under reduced pressure
and the residue was taken up in diethyl ether (25 mL), 1 M HCl solution
was added to the organic phase, and the product was extracted into the
acidic aqueous phase (3 ꢀ 20 mL), which was then neutralized with 1 M
NaOH solution. The pure product was extracted from the neutralized
solution by using diethyl ether (3 ꢀ 20 mL), washed with water (3 ꢀ
20 mL) and then brine (3 ꢀ 20 mL), and dried over MgSO4, and then
solvent was removed under reduced pressure to afford the product. Solid
product was crystallized in n-pentane.
2-(Benzylselenomethyl)pyridine, 13b:. 0.47 g (92%); crystal-
line plates; mp 28.5-29.8 °C; 1H NMR (CDCl3, 500 MHz) δ 8.53 (d,
J = 5.0 Hz, 1H, Ar-H), 7.61 (ddd, J = 8.0, 8.0, 1.5 Hz, 1H, Ar-H), 7.33-
7.19 (m, 5H, Ar-H), 7.14 (t, J = 6.0 Hz, 2H, Ar-H), 3.86 (s, 2H, -CH2),
3.85 (s, 2H, -CH2); 13C NMR (CDCl3, 100 MHz) δ 159.4 (Ar-C),
148.9 (Ar-C), 138.8 (Ar-C), 136.2 (Ar-C), 128.7 (Ar-C), 128.1 (Ar-C),
126.3 (Ar-C), 122.6 (Ar-C), 121.2 (Ar-C), 28.7 (1JC-Se = 64.8 Hz, -CH2),
27.3 (-CH2); 77Se NMR (95 MHz, sample in CDCl3, external standard:
(PhSe)2 in CDCl3) δ 331.3; HRMS (ESI) calcd for C13H14NSeþ [M þ
H]þ 264.02860, found 264.02862; IR (thin film) ~ν 3077-2938 cm-1
(pyridine ring).
NMR (95 MHz, sample in CDCl3, external standard: (PhSe)2 in CDCl3) δ
375.6; HRMS (ESI) calcd for C13H14NSeþ [M þ H]þ 264.02860, found
264.02862; IR (thin film) ~ν 3067-2910 cm-1 (pyridine ring).
N-Methyl-4-(benzylselenomethyl)pyridinium
triflate,
10b:. A solution of 12b (50.0 mg, 0.19 mmol) in 0.5 mL of deuter-
ioacetonitrile was treated with neat methyl triflate (34.0 mg, 0.21 mmol,
24 μL). X-ray quality crystals of 10b as plates were obtained by slow
1
evaporation of solvent: mp 79.2-82.2 °C; H NMR (CD3CN, 500
MHz) δ 8.39 (d, J = 6.5 Hz, 2H, Ar-H), 7.73 (d, J = 6.0 Hz, 2H, Ar-H),
7.32-7.26 (m, 5H, Ar-H), 4.21 (s, 3H, -CH3), 3.93 (s, 2H, -CH2),
3.90 (s, 2H, -CH2); 13C NMR (CD3CN, 100 MHz) δ 162.2 (Ar-C),
145.6 (Ar-C), 139.6 (Ar-C), 130.1 (Ar-C), 129.7 (Ar-C), 128.6 (Ar-C),
128.1 (Ar-C), 48.6 (-CH3), 28.9 (-CH2), 26.1 (1JC-Se = 67.0 Hz,
-CH2); 77Se NMR (95 MHz, sample in CD3CN, external standard:
(PhSe)2 in CDCl3) δ 376.9; HRMS (ESI) calcd for C14H16NSeþ [M]þ
278.04425, found 278.04422; IR (thin film) ν~ 3027-2963 cm-1
(pyridine ring).
4-(Benzylselenomethyl)pyridinium trifluoroacetate, 12bH:.
A solution of 12b (50.0 mg, 0.19 mmol) in 0.5 mL of deuteriochloro-
form was treated with neat trifluoroacetic acid (26.1 mg, 0.23 mmol, 17.5
μL): 77Se NMR (95 MHz, sample in CDCl3, external standard: (PhSe)2
in CDCl3) δ 375.1.
(tert-Butylselenomethyl)pyridine: General Procedure. To
a solution of bis(2-methyl-2-propyl) diselenide (di-tert-butyl diselenide)
(1.29 mmol) in 20 mL of anhydrous ethanol was added sodium
borohydride (in excess) portionwise until the solution turned colorless.
Meanwhile, to a stirred suspension of the appropriate bromomethyl
pyridine hydrobromide (2.58 mmol) in 25 mL of ethanol at 0 °C was
added ice-cold 1 M NaOH solution (2.58 mmol, 2.6 mL) in 9 mL of
ethanol. This cold solution was stirred for another 10 min then added
dropwise at room temperature into the anion solution previously
generated. The reaction mixture was left to stir overnight under
nitrogen. Ethanol was removed under reduced pressure and the residue
was taken up in diethyl ether (25 mL) [alternatively, the reaction
mixture was diluted with 25 mL of diethyl ether then washed with water
(5ꢀ20 mL) to remove ethanol]. A 1 M HCl solution was added to the
organic phase and the product was extracted into the acidic aqueous
phase (3 ꢀ 20 mL), which was then neutralized with 1 M NaOH
solution. The pure product was extracted from the neutralized solution
with diethyl ether (3ꢀ20 mL), washed with water (3ꢀ20 mL) and then
brine (3ꢀ20 mL), and dried over magnesium sulfate, then the solvent
was removed under reduced pressure to afford the product. Solid
product was crystallized in n-pentane.
2-(tert-Butylselenomethyl)pyridine, 13c:. 0.48 g (81%); pale
yellow oil; 1H NMR (CD3CN, 500 MHz) δ 8.44 (dd, J = 4.9, 0.7 Hz, 1H,
Ar-H), 7.65 (td, J = 7.8, 1.9 Hz, 1H, Ar-H), 7.39 (d, J = 8.0 Hz, 1H,
Ar-H), 7.15 (ddd, J = 7.4, 4.9, 0.9 Hz, 1H, Ar-H), 3.99 (s, 2H, -CH2),
1.47 (s, 9H, -C(CH3)3); 13C NMR (CD3CN, 125 MHz) δ 161.3
(Ar-C), 150.0 (Ar-C), 137.5 (Ar-C), 124.2 (Ar-C), 122.4 (Ar-C), 40.6
(-C(CH3)3), 32.7 (3C, -C(CH3)3), 28.6 (1JC-Se = 67.7 Hz, -CH2);
77Se NMR (95 MHz, sample in CD3CN, external standard: (PhSe)2 in
CDCl3) δ 448.1; HRMS (ESI) calcd for C10H16NSeþ [M þ H]þ
230.04425, found 230.04426.
4-(Benzylselenomethyl)pyridine, 12b:. 0.48 g (93%); crystal-
1
line plates; mp 33.3-34.9 °C; H NMR (CD3CN, 500 MHz) δ 8.47
(dd, J = 4.0, 1.8 Hz, 2H, Ar-H), 7.34-7.23 (m, 5H, Ar-H), 7.22 (dd, J =
4.5, 2.0 Hz, 2H, Ar-H), 3.81 (s, 2H, -CH2), 3.73 (s, 2H, -CH2); 13
C
NMR (CD3CN, 125 MHz) δ 150.8 (Ar-C), 150.1 (Ar-C), 140.4 (Ar-C),
129.9 (Ar-C), 129.6 (Ar-C), 127.8 (Ar-C), 124.9 (Ar-C), 28.4 (-CH2),
26.6 (1JC-Se = 65.5 Hz, -CH2); 77Se NMR (95 MHz, sample in
CD3CN, external standard: (PhSe)2 in CDCl3) δ 338.1; HRMS (ESI)
calcd for C13H14NSeþ [M þ H]þ 264.02860, found 264.02798; IR
(thin film) ν~ 3062-2927 cm-1 (pyridine ring).
N-Methyl-2-(benzylselenomethyl)pyridinium triflate, 11b:. A
solution of 13b (50.0 mg, 0.19 mmol) in 0.5 mL of deuterioacetonitrile
was treated with neat methyl triflate (34.0 mg, 0.21 mmol, 24 μL). After
removal of the solvent 11b was obtained as a pale yellow oil; 1H NMR
(CD3CN, 500 MHz) δ 8.57 (d, J = 5.5 Hz, 1H, Ar-H), 8.31 (td, J = 7.9,
1.5 Hz, 1H, Ar-H), 7.77 (t, J = 6.6 Hz, 1H, Ar-H), 7.46 (m, 1H, Ar-H),
7.34-7.24 (m, 5H, Ar-H), 4.17 (s, 3H, -CH3), 4.13 (s, 2H, -CH2),
3.99 (s, 2H, -CH2); 13C NMR (CD3CN, 125 MHz) δ 156.8 (Ar-C),
148.1 (Ar-C), 146.6 (Ar-C), 139.0 (Ar-C), 131.7 (Ar-C), 130.1 (Ar-C),
129.8 (Ar-C), 128.3 (Ar-C), 126.9 (Ar-C), 46.4 (-CH3), 29.5 (1JC-Se
=
61.7 Hz, -CH2), 23.4 (-CH2); 77Se NMR (95 MHz, sample in
CD3CN, external standard: (PhSe)2 in CDCl3) δ 312.2; HRMS (ESI)
calcd for C14H16NSeþ [M þ H]þ 278.04425, found 278.04428; IR
(thin film) ν~ 3072-2920 cm-1 (pyridine ring).
2-(Benzylselenomethyl)pyridinium picrate, 13bH:. To a
solution of 13b (50.0 mg, 0.19 mmol) in 2 mL of anhydrous ethanol
was added picric acid (43.7 mg, 0.19 mmol) at room temperature. Reac-
tion was left to stir overnight under nitrogen. Ethanol was removed under
reduced pressure and the resulting solids were dissolved in a mini-
mum amount of chloroform. X-ray quality crystals of 13b were obtained
from slow evaporation of solvent: yellow blocks; mp 122.1-123.0 °C; 1H
NMR (CDCl3, 500 MHz) δ8.66 (d, J= 5.5 Hz, 1H, Ar-H), 8.13 (td, J=7.9,
1.5 Hz, 1H, Ar-H), 7.63(t, J= 6.6 Hz, 1H, Ar-H), 7.48(d, J=8.1Hz, 1H, Ar-
H), 7.22-7.12 (m, 5H, Ar-H), 4.30 (s, 2H, -CH2), 3.96 (s, 2H, -CH2),
8.93 (s, 2H, Ar-H); 13C NMR (CDCl3, 125 MHz) δ 157.5 (Ar-C), 144.5
(Ar-C), 141.4 (Ar-C), 137.5 (Ar-C), 129.0 (Ar-C), 129.0 (Ar-C), 127.2
(Ar-C), 126.5 (Ar-C), 124.0 (Ar-C), 29.4 (1JC-Se = 62.7 Hz, -CH2), 22.8
(-CH2), 161.3 (Ar-C), 141.5 (Ar-C), 129.3 (Ar-C), 128.6 (Ar-C); 77Se
4-(tert-Butylselenomethyl)pyridine, 12c:. 0.46 g (78%); col-
orless plates; mp 31.9-33.5 °C; 1H NMR (CD3CN, 500 MHz) δ 8.45
(d, J = 4.4 Hz, 2H), 7.30 (d, J = 4.3 Hz, 2H), 3.85 (s, 2H), 1.48 (s, 9H);
13C NMR (CD3CN, 125 MHz) δ 150.8, 150.4, 125.1, 41.3, 32.7, 25.0
(1JC-Se = 67.3 Hz, -CH2); 77Se NMR (95 MHz, sample in CD3CN,
external standard: (PhSe)2 in CDCl3) δ 458.6; HRMS (ESI) calcd for
C10H16NSeþ [M þ H]þ 230.04425, found 230.04430.
N-Methyl-2-(tert-butylselenomethyl)pyridinium tosylate,
11c:. A solution of 13c (60.8 mg, 0.27 mmol) in 0.5 mL of deuter-
oacetonitrile was treated with neat methyl tosylate (54.6 mg, 0.29 mmol,
44.2 μL). X-ray quality crystals of 11c were obtained from slow
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The Journal of Organic Chemistry
ARTICLE
evaporation of solvent: colorless plates; mp 130.2-133.7 °C; 1H NMR
(CD3CN, 500 MHz) δ 8.66 (s, br, 1H, Ar-H), 8.36 (t, J = 7.9 Hz, 1H, Ar-
H), 8.00 (d, J = 7.8 Hz, 1H, Ar-H), 7.80 (t, J = 6.9 Hz, 1H, Ar-H), 4.30 (s,
3H, -CH3), 4.22 (s, 2H, -CH2), 1.55 (s, 9H, -C(CH3)3), 7.60 (d, J =
8.2 Hz, 2H, Ar-H), 7.15 (d, J = 8.1 Hz, 2H, Ar-H), 2.34
(s, 3H, -CH3); 13C NMR (CD3CN, 125 MHz) δ 157.5 (Ar-C),
148.3 (Ar-C), 146.7 (Ar-C), 130.4 (Ar-C), 126.9 (Ar-C), 46.5 (-
CH3), 44.3 (-C(CH3)3), 32.4 (-C(CH3)3), 21.9 (1JC-Se = 70.5 Hz,
-CH2), 146.6 (Ar-C), 139.7 (Ar-C), 129.4 (Ar-C), 126.7 (Ar-C), 21.4
(-CH3); 77Se NMR (95 MHz, sample in CD3CN, external standard:
(PhSe)2 in CDCl3) δ 443.3; HRMS (ESI) calcd for C11H18NSeþ [M]þ
244.05990, found 244.05992; IR (thin film) ν~ 3042-2856 cm-1
(pyridine ring).
extended to Dr. Colin Skene for assistance in obtaining the 2-D
NMR data for 10b, 11b, 12b, and 13b.
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(1) White, J. M.; Lambert, J. B.; Spiniello, M.; Jones, S. A.; Gable,
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(3) (a) Traylor, T. G.; Berwin, H. J.; Jerkunica, M. L. H. Pure Appl.
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2-(tert-Butylselenomethyl)pyridinium trifluoroacetate, 13cH:.
A solution of 13c (50.0 mg mg, 0.22 mmol) in 0.5 mL of chloroform was
treated with neat trifluoroacetic acid (30.0 mg, 0.26 mmol, 20.1 μL): 77Se
NMR (95 MHz, sample in CDCl3, external standard: (PhSe)2 in CDCl3) δ
491.5.
N-Methyl-4-(tert-butylselenomethyl)pyridinium tosylate,
11c:. A solution of 13c (45.0 mg, 0.20 mmol) in 0.5 mL of deuter-
ioacetonitrile was treated with neat methyl tosylate (40.4 mg, 0.22
mmol, 32.7 μL). X-ray quality crystals of 11c were obtained by slow
(5) Beaver, M. G.; Billings, S. B.; Woerpel, K. A. Eur. J. Org. Chem.
2008, 771. Beaver, M. G.; Billings, S. B.; Woerpel, K. A. J. Am. Chem. Soc.
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1
evaporation of the solvent: colorless plates; mp 161.4-162.4 °C; H
NMR (CD3CN, 500 MHz) δ 8.60 (d, J = 6.6 Hz, 2H, Ar-H), 7.87 (d, J =
6.6 Hz, 2H, Ar-H), 4.24 (s, 3H, -CH3), 4.03 (s, 2H, -CH2), 1.47 (s,
9H, -C(CH3)3); [tosylate]- 7.60 (d, J = 8.3 Hz, 2H, Ar-H), 7.15 (d, J =
8.2 Hz, 2H, Ar-H), 2.35 (s, 3H, -CH3); 13C NMR (CD3CN, 125 MHz)
δ 162.3 (Ar-C), 146.0 (Ar-C), 128.8 (Ar-C), 48.5 (-CH3), 43.2
(-C(CH3)3, 32.6 (-C(CH3)3), 24.6 (1JC-Se = 70.9 Hz, -CH2),
146.2 (Ar-C), 139.9 (Ar-C), 129.5 (Ar-C), 126.7 (Ar-C), 21.4 (-
CH3); 77Se NMR (external standard: (PhSe)2 in CDCl3, 95 MHz) δ
495.0; HRMS (ESI) calcd for C11H18NSeþ [M]þ 244.05990, found
244.05995; IR (thin film) ν~ 3047-2912 cm-1 (pyridine ring).
4-(tert-Butylselenomethyl)pyridinium trifluoroacetate, 12cH:.
A solution of 12c (50.0 mg mg, 0.22 mmol) in 0.5 mL of chloroform was
treated with neat trifluoroacetic acid (30.0 mg, 0.26 mmol, 20.1 μL):
77Se NMR (95 MHz, sample in CDCl3, external standard: (PhSe)2 in
CDCl3) δ 490.1
(6) (a) Briggs, A. J.; Glenn, R.; Jones, P. G.; Kirby, A. J.; Ramaswamy,
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Jones, P. G.; Kirby, A. J.; Parker, J. K.; Percy, J. M.; Su, M. D. J. Chem. Soc.,
Perkin Trans. 2 1992, 4, 549.
(7) (a) Karnezis, A.; O’Hair, R. A. J.; White, J. M. Organometallics
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Organometallics 2007, 26, 3094–3099. (c) Hassall, K.; Lobachevsky, S.;
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’ ASSOCIATED CONTENT
S
Supporting Information. Crystallographic information
b
files for 10b, 10c, 11a, 11c, 12aH, 13aH, and 13bH, a full listing
of geometries and energies (Gaussian Archive entries) (S1), and
NMR spectra for new compounds (S2). This material is available
free of charge via the Internet at http://pubs.acs.org. The crystal-
lographic coordinates have been deposited with the Cambridge
Crystallographic Data Centre; deposition nos. 800803-800809.
These data can be obtained free of charge from the Cambridge
Crystallographic Data Centre, 12 Union Rd., Cambridge CB2 1EZ,
UK or via www.ccdc.cam.ac.uk/conts/retrieving.html.
’ AUTHOR INFORMATION
(17) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.;
Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski,
V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick,
D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui,
Corresponding Author
*E-mail: whitejm@unimelb.edu.au.
’ ACKNOWLEDGMENT
We thank the Australian Research Council for financial support
(DP0770565) and an award of an APA to B.H. We would also like
to thank the Victorian Partnership for Advanced Computing and
the Victorian Institute for Chemical Sciences High Performance
Computing Facility for the computational time. A grateful thanks is
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The Journal of Organic Chemistry
ARTICLE
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P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A.
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