One-pot synthesis and unpredicted hydrogen bonds of the guanidinium triflates from readily available amines, carbodiimides, and Zn(OTf)2

Article abstract of DOI:10.1021/om2006613

The first synthesis of trisubstituted guanidinium triflates has been achieved by a simple one-step procedure from readily available amines, carbodiimides, and Zn(OTf)₂. X-ray analysis revealed they adopt 1-D chain-like or novel 3-D hydrogen-bon

Full text of DOI:10.1021/om2006613

ARTICLE
pubs.acs.org/Organometallics
One-Pot Synthesis and Unpredicted Hydrogen Bonds of the
Guanidinium Triflates from Readily Available Amines, Carbodiimides,
and Zn(OTf)2
Dongzhen Li,† Yang Wang,† Wen-Xiong Zhang,*,†,‡ Shaoguang Zhang,† Jie Guang,† and Zhenfeng Xi*,†
†Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular Engineering of
Ministry of Education, College of Chemistry, Peking University, Beijing 100871, China
‡State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin, 300071, China
S Supporting Information
b
ABSTRACT: The first synthesis of trisubstituted guanidinium triflates
has been achieved by a simple one-step procedure from readily
available amines, carbodiimides, and Zn(OTf)2. X-ray analysis re-
vealed they adopt 1-D chain-like or novel 3-D hydrogen-bonded
networks, which have not been reported previously in the solid
structure of guanidinium salts. Isolation of a binuclear zinc complex
and its subsequent carbodiimide insertion provide the insight into the
mechanism for the formation of guanidinium triflates.
Scheme 1. Methodology for the Preparation of Guanidinium
Salts
’ INTRODUCTION
0
0
Multi0substituted guanidinium salts, [C(NR1R1 )(NR2R2 )-
(NR3R3 )][X] (X = Cl, OTf, PF6, BF4, etc.), are an important
class of “CN3”-core-containing ion-pair compounds.1,2 These
guanidinium salts can serve as building blocks of many biologi-
cally active compounds3 and of ionic liquids,4 and also as base
catalysts in many organic transformations.5 The classical meth-
ods for their preparation employ protonation or alkylation of
a pre-existing guanidine core (Scheme 1, a).6,4b Guanidinium
salts are also obtained by reaction of amines with guanidine
precursors, such as chloroformamidinium salts (Scheme 1, b).7
Mioskowski et al. reported the synthesis of guanidinium chlor-
ides using nonguanidine precursors, such as phosgeniminium
chlorides (Scheme 1, c).8 These three types of methods generally
involve the preparation of guanidinium halides. Guanidinium
salts having other anionic species, such as OTf, PF6, and BF4,
have to employ the halide exchange between guanidinium halides
and the corresponding metal salts MX (M = Li, Na, K or Ag, X =
OTf, PF6, BF4, etc.). In 1981, Stang et al. reported the two-step
synthesis of guanidinium triflates from the starting ureas in the
presence of triflic anhydride (Scheme 1, d).9 Generally, the triflate
ion in guanidinium triflates is introduced by anion exchange. All
reported methods for the preparation of guanidinium salts involve
the synthesis of guanidine or non-guanidine precursors. Two or
more synthetic steps are required for guanidinium triflates.
complex was isolated from the reaction system and confirmed
the true intermediate for the formation of guanidinium triflates.
’ RESULTS AND DISCUSSION
Synthesis. The neat aniline could not react with N,N0-
diisopropylcarbodiimide (iPrNdCdNiPr) at room temperature
or higher temperatures. Very recently we have found that
Zn(OTf)2 could serve as a good catalyst for addition of amine
NꢀH bonds to carbodiimides, yielding efficiently guanidines.13c
In this initial step, the active catalyst species containing a ZnꢀN
bond is produced by release of a guanidinium triflate. So we
pondered that a guanidinium triflate could be prepared from
We have been interested in the reaction chemistry of
carbodiimide.10ꢀ14 Herein we report the one-pot synthesis of
the guanidinium triflates from readily available amines, carbodii-
mides, and Zn(OTf)2. X-ray analysis of two different substituted
guanidinium triflates revealed they adopt 1-D chain-like or novel
3-D hydrogen-bonded networks. The active binuclear zinc
i
the reaction system of aniline, PrNdCdNiPr, and Zn(OTf)2.
Received: July 21, 2011
Published: September 09, 2011
r
2011 American Chemical Society
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Table 1. Formation of Guanidinium Triflates from Two
a,b
Amines, Carbodiimides, and Zn(OTf)2
Figure 1. Hydrogen bond pattern between the guanidinium cation and
triflate anion in 1b. Hydrogen atoms except those on the nitrogen atoms
are omitted for clarity. Selected bond length (Å) and angles (deg):
N1ꢀC1 1.362(6), N2ꢀC1 1.327(6), N3ꢀC1 1.338(6), N1ꢀC1ꢀN2
120.0(4), N1ꢀC1ꢀN3 119.0(4), N2ꢀC1ꢀN3 120.9(4). Hydrogen
bonds: dH3
= 2.02 Å, dN3
= 2.825 Å, —N3ꢀH3 O2
0 3 3 3
O2
O2
3 3 3
0
3 3 3
151.6ꢀ; dH2A O1 = 2.16 Å, dN2 O1 = 2.997 Å, —N20ꢀH2A
O1
0
159.2ꢀ. = x 3+3 31, y, z. C gray, H3 l3i3ght gray, O red, N blue, F green, S
3 3 3
0
orange.
new protocol was established. Thus, after Zn(OTf)2 was first
treated with a THF solution of 2 equiv of aniline in a closed
Schlenk tube at 100 ꢀC for 3 h, then reacted with iPrNdCdNiPr
at room temperature for 2 h, guanidinium triflate 1a was obtained
in 91% isolated yield (Table 1, entry 1).
Under the optimized conditions the scope of this protocol was
further explored by using different substituted anilines. As shown
in Table 1, almost all of the substrates produced the guanidinium
triflates 1bꢀh in excellent yields (entries 2ꢀ6). The presence of
an electron-donating tert-butyl group (entry 3) and weakly
electron-withdrawing fluoro (entry 2) or chloro (entry 6) groups
at para or meta position of this phenyl ring produced the
expected guanidinium triflates. Sterically hindered ortho-substi-
tuted anilines also smoothly provided the corresponding guani-
dinium triflates 1d and 1e in excellent yields (entries 4 and 5).
These results demonstrated that the present reaction was
insensitive to the steric nature of the substituents on the phenyl
ring. In addition to anilines, aliphatic amine is suitable for this
reaction (entry 7). Furthermore, N,N0-diaryl-substituted carbo-
diimides were also applicable (entry 8).
All guanidinium triflates 1aꢀh were fully characterized by
their 1H and 13C NMR spectroscopy as well as FTMS. The 1H
NMR spectrum of 1c in THF-d8 revealed two broad singlets at δ
7.09 (2H) and 8.77 ppm (1H), which were assigned to the NꢀH
protons of BuC6H4NH and PrNH, respectively. In the 13C
NMR spectroscopy, the singlet at δ 154.0 ppm corresponded to
the central carbon atom of the “CN3” core. The quartet at 121.7
ppm with a 1JC,F = 318 Hz was unambiguously assigned to the
CF3 carbon atom of the triflate.
t
i
a Conditions: amines, 2.25 mmol; carbodiimides, 1 mmol; Zn(OTf)2,
1 mmol; THF, 5 mL. b Isolated yield.
Crystallography and Hydrogen Bonds. The structures of
guanidinium triflates 1b and 1d were characterized by X-ray
diffraction analysis. 1b crystallized in the triclinic P1 space group;
however, 1d crystallized in the non-centrosymmetric orthor-
hombic space group Pna2(1).15 1b and 1d have one crystal-
lographically independent cationꢀanion pair in the asymmetric
unit. The sum of the angles at the central carbon equals 359.9ꢀ
(1b) and 359.98ꢀ (1d), indicating complete planarity within the
range of errors. The CꢀN bond lengths are in the range
1.32ꢀ1.36 Å within the “CN3” core of both structures, which
At the beginning, we tried to heat a 1:1:1 mixture of aniline,
iPrNdCdNiPr, and Zn(OTf)2 in different solvents such as
THF, benzene, and toluene. The guanidine was obtained almost
quantitatively, suggesting that the catalytic addition of aniline to
iPrNdCdNiPr occurred once the ZnꢀN active species was
produced by release of a guanidinium triflate. This result also
suggested the guanidine remained inert to Zn(OTf)2. To avoid
the formation of guanidine, after many screening experiments, a
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Figure 2. 1-D chain-like packing motif in crystalline 1b via hydrogen bonds viewed along the c axis. Only “SO3” and “CN3H3” units are shown, and other
atoms are omitted for clarity. C gray, H light gray, O red, N blue, S orange.
Figure 3 showed the interaction of hydrogen bonds among the
cationꢀanion pair in 1d. Being different from 1b, each guanidi-
nium cation in 1d forms three hydrogen bonds to oxygen lone
electron pairs on each of three neighboring triflate anions. There
is no hydrogen-bond interaction between the guanidinium cation
and triflate anion in the same independent unit. A brick-like
unit was composed of five alternate cationꢀanion pairs. Three
guanidinium cations and three triflate anions are positioned on
the corners of the bricks and extend to form a two-dimensional
brick wall monolayer viewed along the c axis in crystalline 1d via
hydrogen bonds (Figure 4a). The brick wall monolayers are
linked by NꢀH O hydrogen bonds to form the 3-D network
3 3 3
(Figure 4b).
Several guanidinium sulfonates, especially for the guanidinium
+
cation C(NH2)3 , have been reported, and their X-ray analyses
reveal that they adopt dimers, ribbons, or 2-D sheets.17 As far as
we are aware, this is the first example of efficient preparation of
well-defined trisubstituted guanidinium triflates, and also the 3-D
hydrogen-bonded network in 1d has not been reported pre-
Figure 3. Hydrogen bond pattern between the guanidinium cation and
triflate anion in 1d. Hydrogen atoms except those on the nitrogen atoms
are omitted for clarity. Selected bond lengths (Å) and angles (deg):
N(1)ꢀC(7) 1.357(3), N(2)ꢀC(7) 1.332(3), N(3)ꢀC(7) 1.325(3),
N(1)ꢀC(7)ꢀN(2) 119.94(19), N(1)ꢀC(7)ꢀN(3) 118.93(19), N-
viously in the solid structure of guanidinium salts.
Mechanism. A possible mechanism for the formation of
guanidinium triflates was proposed in Scheme 2. Initially, the
reaction of Zn(OTf)2 with 2 equiv of anilines in THF yielded the
amine-coordinated binuclear zinc intermediate 2. 2 might under-
go coordination of a carbodiimide to the Zn center, yielding
intermediate A. A would undergo 2-fold protonation toward the
nitrogen atoms of a carbodiimide, affording the final guanidinium
triflates by the release of the ZnꢀN amido species.
O20
O100
O1000
(2)ꢀC(7)ꢀN(3) 121.11(19). Hydrogen bonds: dH1
= 2.08 Å,
= 2.07 Å,
= 2.11 Å,
3 3 3
3 3 3
3 3 3
= 2.882 Å, —N1ꢀH1 O20 151.9ꢀ; dH2
O20
O100
O1000
dN1
dN2
dN3
3 3 3
3 3 3
3 3 3
= 2.907 Å, —N2ꢀH2 O100 158.1ꢀ, dH3
3 3 3
= 2.899 Å, —N3ꢀH3 O3000 149.5ꢀ. 0 = x, y + 1, z, 00 = ꢀx,
ꢀ y3+3 31, z ꢀ 1/2, 000 = ꢀx + 1/2, y + 1/2, z ꢀ 1/2. C gray, H light gray,
3 3 3
The proposed mechanism is further confirmed by isolation
and reaction of the amine-coordinated binuclear zinc complex 2-F.
We successfully isolated the zinc complex 2-F (Scheme 2, Ar =
4-F-C6H4) from the reaction mixture of Zn(OTf)2 and 2 equiv of
4-fluoroaniline in THF at refluxing temperature. An X-ray
structure analysis of 2-F revealed that it adopts a dimeric
structure, in which two Zn atoms are bridged by the oxygen
atoms of two triflates (Figure 5). The isolated 2-F was allowed to
react with iPrNdCdNiPr at room temperature for 3 h to yield
quantitatively the guanidinium triflate 1b (Ar = 4-F-C6H4).
O red, N blue, F green, S orange.
are shorter than a pure CꢀN single bond (1.41 Å) and longer
than a pure CdN double bond (1.27 Å).16 This suggested the
delocalization within the π-system of the “CN3” core of the
guanidinium cation.
Owing to the good ability of the triflate anion acting as a weak
hydrogen-bond acceptor, the different NꢀH O hydrogen
3 3 3
bonds and networks were observed in the solid structures of
1b and 1d and provided the major driving force for their crystal
packing.
Figure 1 showed the interaction of hydrogen bonds among the
cationꢀanion pair in 1b. There are only two hydrogen bonds
between each guanidinium cation and each triflate anion in 1b.
’ CONCLUSION
We have reported a simple and convenient one-step procedure
from readily available amines, carbodiimides, and Zn(OTf)2,
providing efficiently for the first time the trisubstituted guanidi-
nium triflates. Two different substituted guanidinium triflates
were characterized by X-ray diffraction analysis. The 4-fluoroani-
line-substituted guanidinium triflate 1b adopts 1-D chain-like
packing motif; however, 2-isopropylaniline-substituted guanidi-
nium triflate 1d adopts a 3-D hydrogen-bonded network in the
solid structure. The reason for the different hydrogen-bonded
One hydrogen bond, such as N3ꢀH3 O2, comes from the
3 3 3
interaction in the same unit of the guanidinium cation and triflate
anion, the other N20ꢀH2A0
O1 hydrogen bond from a
3 3 3
different unit of the guanidinium cation and triflate anion. One
NꢀH bond of the guanidinium cation and one oxygen atom of
the triflate anion do not involve a hydrogen-bond interaction.
The guanidinium cation and triflate anion are linked in a 1-D
chain by two NꢀH O hydrogen bonds (Figure 2).
3 3 3
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Figure 4. (a) Two-dimensional brick wall motif in crystalline 1d via hydrogen bonds viewed along the c axis. (b) Three-dimensional network in
crystalline 1d via hydrogen bonds. Only “SO3” and “CN3H3” units are shown, and other atoms are omitted for clarity. C gray, H light gray, O red, N blue,
S orange.
Scheme 2. Possible Mechanism for the Formation of Gua-
’ EXPERIMENTAL SECTION
nidinium Triflates
General Method. Unless otherwise noted, all starting materials and
solvents were commercially available and were used without further
purification. 1H and 13C NMR spectra were recorded on a JEOL JNM-
AL300 spectrometer (FT, 300 MHz for 1H; 75 MHz for 13C) at room
temperature, unless otherwise noted. High-resolution mass spectra
(HRMS) were recorded on a Bruker Apex IV FTMS mass spectrometer
using electrospray ionization.
Typical Procedure for the Preparation of Guanidinium
Triflates 1aꢀf. In a Schlenk tube, Zn(OTf)2 (363 mg, 1 mmol) was
added to a solution of aniline (2.25 mmol) in THF (5 mL). The Schlenk tube
was sealed, and the mixture was stirred at 100 ꢀC for 3 h. N,N0-Diisopro-
pylcarbodiimide (1 mmol) was then allowed to react with the above reaction
mixture at room temperature for 2 h. The reaction mixture was quenched by
water at room temperature and extracted with ether. The combined organic
layer was dried over anhydrous MgSO4. Solvent was removed under reduced
pressure, and the residue was recrystallized to provide colorless solid 1.
[C(PhNH)(iPrNH)2][OTf] (1a). Colorless solid, isolated yield 91%
1
networks is not clear, but are probably due to the steric and
substituent effects on the aromatic ring. A binuclear zinc complex
was characterized by X-ray diffraction analysis and confirmed to
be an active intermediate in the formation of guanidinium
triflates.
(336 mg); mp 102.9ꢀ103.6 ꢀC; H NMR (300 MHz, THF-d8) 1.22
(d, J = 6.0 Hz, 12H, CH3), 3.91ꢀ4.00 (m, 2H, CH), 7.17ꢀ7.40 (m, 7H,
5CH, 2NH), 8.73 (br, 1H, NH); 13C NMR (75 MHz, THF-d8) 22.5,
46.2, 121.7 (q, J = 318 Hz), 124.1, 126.7, 130.4, 137.9, 154.2; HRMS
calcd for C13H22N3 [M ꢀ HOTf]+ 220.1803, found 220.1808.
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[C(C6H5NH)(C6H4NH)2][OTf] (1h). Colorless solid, isolated yield 82%
(358 mg); mp 107.7ꢀ108.3 ꢀC; 1H NMR (300 MHz, THF-d8) 6.53 (br,
3H, NH), 6.90ꢀ7.42 (m, 15H, CH); 13C NMR (75 MHz, THF-d8)
121.4 (q, J = 316 Hz), 124.3, 127.2, 130.2, 136.7, 153.3; HRMS calcd for
C19H18N3 [M ꢀ HOTf]+ 288.1500, found 288.1495.
Isolation of 2-F. In a Schlenk tube, Zn(OTf)2 (726 mg, 2 mmol)
was added to a solution of 4-fluoroaniline (500 mg, 4.5 mmol) in THF
(5 mL), and the mixture was stirred at 100 ꢀC for 3 h. The solvent of the
reaction mixture was evaporated under vacuum, and the residue was
washed by THF (5 mL) three times. The thus obtained colorless powder
as amine-coordinated binuclear zinc complex 2-F was pure enough for
NMR analysis. Single crystals suitable for X-ray analysis were grown in
THF/hexane at room temperature for 2 days. Colorless solid, isolated
yield 95% (1246 mg); 1H NMR (300 MHz, THF-d8) 2.17ꢀ2.26 (m, 4H,
CH2), 4.03ꢀ4.10 (m, 4H, CH2), 6.04 (br, 8H, NH), 7.32ꢀ7.53 (m,
16H, CH); 13C NMR (75 MHz, THF-d8) 26.2, 68.2, 116.2 (d, J = 22.4 Hz),
120.9 (q, J = 316 Hz, 2CF3), 121.6 (d, J = 8.0 Hz), 138.7 (d, J = 2.5 Hz),
159.8 (d, J = 239 Hz).
Figure 5. ORTEP drawing of 2-F with 30% thermal ellipsoids. Hydro-
gen atoms except those on the nitrogen atoms are omitted for clarity.
Selected bond lengths (Å): Zn(1)ꢀN(1) 2.096(3), Zn(1)ꢀN(2)
2.079(3), Zn(1)ꢀO(1) 2.284(3), Zn(1)ꢀO(3) 2.235(3), Zn(1)ꢀO-
(4) 2.118(3), Zn(1)ꢀO(7) 2.088(3), S(1)ꢀO(1) 1.450(3), S(1)ꢀO-
(2) 1.444(2), S(2)ꢀO(4) 1.460(3), S(2)ꢀO(5) 1.445(3), S(2)ꢀO(6)
1.422(3). 0 = ꢀx + 2, ꢀy + 2, ꢀz.
Reaction of 2-F with N,N0-Diisopropylcarbodiimide. N,N0-
Diisopropylcarbodiimide (126 mg, 1.0 mmol) was added to a solution of
complex 2-F (658 mg, 0.5 mmol) in THF (5 mL). The reaction was
carried out at room temperature for 2 h. After the normal workup, the
reaction provided quantitatively a colorless solid, 1b.
[C(4-F-C6H4NH)(iPrNH)2][OTf] (1b). Single crystals suitable for X-ray
analysis were grown in THF/hexane at room temperature for 12 h.
Colorless solid, isolated yield 85% (329 mg); mp 158.1ꢀ159.0 ꢀC; 1H
NMR (300 MHz, THF-d8) 1.23 (d, J = 6.0 Hz, 12H, CH3), 3.89ꢀ3.98
(m, 2H, CH), 7.10ꢀ7.33 (m, 7H, 5CH, 2NH); 13C NMR (75 MHz,
THF-d8) 22.5, 46.2, 117.2 (d, J = 23 Hz), 121.8 (q, J = 319 Hz), 126.9 (d,
J = 8.0 Hz), 134.0 (d, J = 2.5 Hz), 154.3, 161.7 (d, J = 243 Hz); HRMS
calcd for C13H21FN3 [M ꢀ HOTf]+ 238.1714, found 238.1714.
[C(4-tBu-C6H4NH)(iPrNH)2][OTf] (1c). Colorless solid, isolated yield
’ ASSOCIATED CONTENT
1
Supporting Information. Copies of H and 13C NMR
S
b
spectra for all isolated compounds and crystallographic data for
1a, 1d, and 2-F. This material is available free of charge via the
Internet at http://pubs.acs.org.
1
96% (408 mg); mp 176.5ꢀ176.8 ꢀC; H NMR (300 MHz, THF-d8)
’ AUTHOR INFORMATION
1.23 (d, J = 6.6 Hz, 12H, CH3), 1.30 (s, 9H, CH3), 3.95ꢀ4.02 (m, 2H,
CH), 7.09 (br, 2H, NH), 7.19ꢀ7.44 (m, 4H, CH), 8.77 (br, 1H, NH);
13C NMR (75 MHz, THF-d8) 22.5, 31.6, 35.0, 46.0, 121.7 (q, J = 318
Hz), 123.7, 127.2, 135.2, 149.4, 154.0; HRMS calcd for C17H30N3 [M ꢀ
HOTf]+ 276.2435, found 276.2434.
Corresponding Author
*E-mail: wx_zhang@pku.edu.cn; zfxi@pku.edu.cn. Fax: (+86)10-
62751708.
[C(2-iPr-C6H4NH)(iPrNH)2][OTf] (1d) (ref 13c). Colorless solid, iso-
lated yield 95% (390 mg); mp 122.8ꢀ123.7 ꢀC; 1H NMR (300 MHz,
THF-d8) 1.20ꢀ1.24 (m, 18H, CH3), 3.09ꢀ3.18 (m, 1H, CH),
3.91ꢀ4.00 (m, 2H, CH), 6.74 (br, 2H, NH), 7.23ꢀ7.44 (m, 4H,
CH), 8.52 (br, 1H, NH); 13C NMR (75 MHz, THF-d8) 22.5, 23.6,
28.7, 45.9, 121.4 (q, J = 317 Hz), 128.1, 128.5, 129.6, 133.5, 146.4, 154.7;
HRMS calcd for C16H28N3 [M ꢀ HOTf]+ 262.2278, found 262.2278.
[C(2,6-Me2-C6H3NH)(iPrNH)2][OTf] (1e). Colorless solid, isolated
yield 94% (373 mg); mp 157.5ꢀ158.3 ꢀC; 1H NMR (300 MHz,
THF-d8) 1.20 (d, J = 5.4 Hz, 12H, CH3), 2.24 (s, 6H, CH3),
3.96ꢀ4.05 (m, 2H, CH), 6.52 (br, 2H, NH), 7.11ꢀ7.16 (m, 3H,
CH), 8.37 (br, 1H, NH); 13C NMR (75 MHz, THF-d8) 18.1, 22.6,
45.5, 121.7 (q, J = 318 Hz), 129.4, 129.7, 132.8, 137.6, 153.4; HRMS
calcd for C15H26N3 [M ꢀ HOTf]+ 248.2116, found 248.2121.
[C(3-Cl-C6H4NH)(iPrNH)2][OTf] (1f). Colorless solid, isolated yield
’ ACKNOWLEDGMENT
This work was supported by the Natural Science Foundation
of China and the “973” program from MOST of China
(2011CB808601). We also thank Dr. Shangda Jiang of Peking
University for useful discussions.
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1
94% (379 mg); mp 129.0ꢀ129.8 ꢀC; H NMR (300 MHz, THF-d8)
1.25 (d, J = 6.6 Hz, 12H, CH3), 3.92ꢀ4.01 (m, 2H, CH), 7.19ꢀ7.40 (m,
6H, 4CH, 2NH), 8.91 (br, 1H, NH); 13C NMR (75 MHz, THF-d8) 22.5,
46.4, 121.4 (q, J = 318 Hz), 122.1, 123.7, 126.3, 131.8, 135.5, 139.7, 153.8;
HRMS calcd for C13H21ClN3 [M ꢀ HOTf]+ 254.1418, found 254.1419.
[C(CyNH)(iPrNH)2][OTf] (1g). Colorless solid, isolated yield 95%
(308 mg); mp 164.4ꢀ165.2 ꢀC; 1H NMR (300 MHz, THF-d8)
1.15ꢀ1.26 (m, 6H, CH3), 1.30ꢀ1.43 (m, 6H, CH3), 1.60ꢀ1.64 (m,
2H, CH2), 1.76ꢀ1.79 (m, 4H, CH2), 2.01ꢀ2.05 (m, 4H, CH2),
3.09ꢀ3.19 (m, 3H, CH), 6.71 (br, 3H, NH); 13C NMR (75 MHz,
THF-d8) 22.5, 25.1, 25.6, 45.2, 51.7, 121.6 (q, J = 318 Hz), 153.4; HRMS
calcd for C13H28N3 [M ꢀ HOTf]+ 226.2279, found 226.2278.
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Organometallics
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(15) The X-ray structure of 1d was mentioned in ref 13c, and its
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