Formation and characterization of zwitterionic stereoisomers from the reaction of B(C6F5)3 and NEt2Ph: (E)- and (Z)-[EtPhN+=CHCH2-B- (C6F5)3]

Article abstract of DOI:10.1002/1099-0682(200212)2002:12<3328::AID-EJIC3328>3.0.CO;2-P

The stoichiometric reaction of B(C₆F₅)₃ and NEt₂Ph I, at room temperature, in an aromatic solvent, has been investigated by 1D and 2D NMR spectroscopy (¹H, ¹¹B, ¹³C, ¹⁵

Full text of DOI:10.1002/1099-0682(200212)2002:12<3328::AID-EJIC3328>3.0.CO;2-P

FULL PAPER
Formation and Characterization of Zwitterionic Stereoisomers from the
Reaction of B(C6F5)3 and NEt2Ph: (E)- and
(Z)-[EtPhN؉؍CHCH2-B؊(C6F5)3]
Nicolas Millot,[a] Catherine C. Santini,*[a] Bernard Fenet,[b] and Jean Marie Basset[a]
Keywords: Boranes / Aniline / Zwitterions / NMR spectroscopy
The stoichiometric reaction of B(C6F5)3 and NEt2Ph I, at room
C5H9)7O12Si8, or silanol group of silica], all the equilibria in-
temperature, in an aromatic solvent, has been investigated volved in solutions of I are quantitatively displaced towards
by 1D and 2D NMR spectroscopy (1H, 11B,13C, 15N and 19F).
No Et2PhN·B(C6F5)3 adduct was observed. An equilibrium
between free B(C6F5)3, NEt2Ph, [HB(C6F5)3]−(HNEt2Ph)+ and
two zwitterionic stereoisomers (E)- and (Z)-[EtPhN+=CH-
CH2-B−(C6F5)3] (30%) in an E/Z ratio of 3:2 was observed.
Whatever the protic reagent Z-OH [Z = H, SiPh3, (c-
the ionic form [Z-O-B(C6F5)3]−(HNEt2Ph)+. In the case of di-
methylaniline, besides free B(C6F5)3 and Me2NPh, the 1:1 ad-
duct (C6F5)3B·NMe2Ph and an iminium salt [PhCH3N=
CH2]+[HB(C6F5)3]− have been identified.
( Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany,
2002)
Introduction
We report in this paper the results obtained by multinu-
clear 1D and 2D NMR spectroscopy (1H, 11B, 13C, 15N,
19F) on stoichiometric solutions of B(C6F5)3 and NR2Ph
(R ϭ Et, Me).
In homogeneous metallocene-based olefin polymeriz-
ation catalysis, ammonium salts are known to activate neut-
ral alkyl precursors into highly active metallocenium cat-
ions by irreversible protonolysis. These salts are generally
composed of a tertiary ammonium cation [HNR2RЈ]ϩ (R ϭ
Me, Et; RЈ ϭ Ph, Et) and various non-coordinating anions
such as metallacarboranes[1] or borates.[2Ϫ6] From the latter,
the non-coordinating character of pentafluorophenylbor-
ates {[XB(C6F5)3], X ϭ -C6F5,[7] -OH,[8] -OR,[9] (c-
C5H9)7O12Si8 [10]}, and their resistance towards anion de-
composition, even though pentafluorophenylborates are far
less stable towards decomposition when X ϭ OR,[11] have
allowed the successful enhancement of the activity of metal-
locenium catalysts.[12]
Results and Discussion
The addition of one equivalent of NEt2Ph to B(C6F5)3 in
aromatic solvents led instantaneously to a pink coloration
of the solution I. The 11B NMR spectrum of I shows three
resonance at δ ϭ Ϫ13.7, Ϫ23.6 and 60 ppm indicating the
presence of at least three different species in the reaction
mixture. In order to determine their structure, a study was
performed using multinuclear 1H, 11B, 13C, 15N and 19F
NMR spectroscopy.
1
In the H NMR spectrum of solution I (Figure 1), the
major peaks at δ ϭ 0.82 (CH3), 2.8 (CH2) and 6.5Ϫ7 ppm
Cp2ZrMe2 ϩ [HNR2RЈ]ϩ[B(C6F5)4]Ϫ
Ǟ
[Cp2ZrMe]ϩ[B(C6F5)4]Ϫ ϩ MeH ϩ NR2RЈ
Interestingly, despite the fact that anilines are commonly
used with tris(pentafluorophenyl)borane [B(C6F5)3] in the
preparation of heterogeneous cocatalysts for olefin
polymerization,[13Ϫ16] no reports exist on the Lewis acid/
base reactivity of such compounds in solution and the pos-
sible formation of aniline·B(C6F5)3 adducts. Like boron tri-
halides,[17,18] the strong Lewis acid B(C6F5)3 is known to
form stable adducts with amines or pyridines.[19]
[a]
´
Laboratoire de Chimie Organometallique de Surface, UMR
9986 CNRS Ϫ ESCPE Lyon,
43, bd du 11 Novembre 1918, 69626 Villeurbanne Cedex France
Centre de RMN, UMR 5012 UCB Lyon 1 Ϫ ESCPE Lyon,
43 bd du 11 Novembre 1918, 69626 Villeurbanne Cedex France
[b]
1
Figure 1. H NMR spectrum (500 MHz, 25 °C, C6D6) of solution
I; N indicates peaks due to free Et2NPh
3328  2002 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1434Ϫ1948/02/1212Ϫ3328 $ 20.00ϩ.50/0 Eur. J. Inorg. Chem. 2002, 3328Ϫ3335

Zwitterionic Stereoisomers from the Reaction of B(C6F5)3 and NEt2Ph
FULL PAPER
(aromatic protons) are characteristic of the free amine in
solution. Additional peaks appear in the region of methyl
(a1, a2), methylene (b1, b2; c1, c2) and aromatic (d1, d2, e2)
protons. Two deshielded overlapping triplets (g1, g2) and a
very broad signal are also observed at δ ϭ 7.8 and 3.9 ppm,
respectively. The intensities of these peaks, relative to those
of the free amine, do not exceed 30%, and are sensitive to
the concentration of the solution, suggesting the existence
of an equilibrium or equilibria between NEt2Ph and other
species in solution. In all experiments, a ratio of 3:2 is ob-
served for the areas of the peaks x1/x2 (x ϭ aϪg).
In the 2D-COSY NMR spectrum of I (Figure 2) the trip-
lets a1 and a2 are correlated to the quadruplets b1 and b2,
respectively, supporting the fact that two different -CH2-b
-
CH3-a fragments are present. A correlation is also detected
between (c1, c2) and (g1, g2), indicating that the Hg protons
are coupled to the -CH2-c-X fragments (Figure 2a). Analysis
of the aromatic proton region of the spectrum (Figure 2b)
shows the presence of two types of non-equivalent phenyl
groups (in a d1/d2 ratio of 3:2). At lower levels, a weak cor-
relation can be detected between the (b1, b2) quadruplets
and the (g1, g2) triplets.
The solution 13C NMR spectrum of I (Figure 3) shows
the characteristic peaks for the methyl (δ ϭ 11.4 ppm),
methylene (δ ϭ 49.4 ppm) and aromatic carbons (δ ϭ
116Ϫ142 ppm) of diethylaniline, as well as doublets repres-
entative of the pentafluorophenyl carbons (δ
ϭ
1
138Ϫ149 ppm) of B(C6F5)3. As in the H NMR spectrum,
two sets of additional peaks appear in the 13C NMR spec-
trum of I for each methyl, methylene and aromatic carbon
atom. Two new peaks are also present near δ ϭ 190 ppm
that can be attributed to a CϭY group, where Y is an elec-
tron-withdrawing center (O, N).
The upfield shift of the methyl and ipso carbons, as well
as the downfield shifts of the methylene, ortho and para
carbons of the diethylaniline (see Exp. Sect.) could indicate
a protonation[20,21] or a weakly coordinative interaction be-
tween NEt2Ph and B(C6F5)3, as described for other boron-
aniline complexes.[17]
More accurate structural information on the species pre-
Figure 2. a) 1H-1H COSY NMR spectrum (500 MHz, 25 °C, C6D6)
of solution I; b) expanded [δ ϭ 7.2Ϫ5.7 ppm] region
1
sent in I can be obtained by a H-13C HSQC NMR experi-
ment (Figure 4). The carbons of the methyl (a1, a2) and
methylene (b1, b2) groups of the two -CH2-b-CH3-a frag-
ments can be assigned. The two broad methylene protons
(c1, c2) are correlated to a broad carbon resonance at δ ϭ
34.5 ppm, suggesting the proximity of a boron atom. The
aromatic resonances associated with the ortho (d1, d2), meta
(e1, e2) and para (f1, f2) hydrogen atoms confirm the pres-
ence of two distinct phenyl groups in addition to the phenyl
ring of the free aniline (Figure 4b). The two most deshi-
elded carbons (δ ϭ 190 ppm) exhibit a correlation with the
triplets (g1, g2, δ ϭ 8 ppm), supporting the presence of an
Hg-CϭY group (Y ϭ O, N). In accordance with the results
1
1
obtained by H-1H COSY NMR experiments, the H-13C
HSQC NMR experiment confirms the existence of two dif-
ferent -CH2-b-CH3-a, phenyl and Hg-(CϭY)-CH2-c-X frag-
ments.
Figure 3. 13C NMR spectrum (500 MHz, 25 °C, C6D6) of solution
I; N and B indicate peaks due to free Et2NPh and B(C6F5)3, re-
spectively
Eur. J. Inorg. Chem. 2002, 3328Ϫ3335
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N. Millot, C. C. Santini, B. Fenet, J. M. Basset
FULL PAPER
Figure 4. a) 1H-13C HSQC NMR spectrum (500 MHz, 25 °C,
Figure 5. a) 1H-13C HMBC NMR spectrum (500 MHz, 25 °C,
C6D6) of solution I; b) expanded [δ ϭ 8.3Ϫ2.3/δ ϭ 144 to
Ϫ114 ppm] region
C6D6) of solution I; b) expanded [δ
132Ϫ115 ppm] region
ϭ
7.3Ϫ6.0/δ
ϭ
1
The H-13C HMBC NMR experiments on I (Figure 5) acteristic of tetracoordinate anionic boron centers[22] and a
allow the ipso carbons of the two distinct phenyl rings to broad resonance at δ ϭ 60 ppm assigned to free B(C6F)3
[23Ϫ25]
be assigned (Figure 5b), and show their couplings with the
(Figure 6). No resonance characteristic of a
methylene protons (b1, b2
Ϫ
3JC-H), with the deshielded (C6F5)3B·NEt2Ph adduct is observed in the region between
triplets (g1, g2 Ϫ JC-H), and with aromatic meta (e1, e2 Ϫ 0 and Ϫ5 ppm.[22] The resonance at δ ϭ Ϫ23.6 ppm is un-
3
3JC-H) and ortho (d1, d2 Ϫ JC-H) hydrogens. The coupling ambiguously assigned to [HB(C6F5)3]Ϫ due to the observed
2
between the deshielded triplets (g1, g2 Ϫ 3JC-H) and methyl- 11B-1H coupling constant (1JB-H ϭ 77.5 Hz[22,26]). This as-
3
2
ene protons (b1, b2 Ϫ JC-H) and, (c1, c2 Ϫ JC-H) is also signment is consistent with the presence of a broad signal
1
evident (Figure 5a).
at δ ϭ 3.9 ppm characteristic of the hydride[27] in the H
The 11B NMR spectrum of I on a 300 MHz spectrometer NMR spectrum of I. The third resonance at δ ϭ
shows two sharp peaks at δ ϭ Ϫ13.7 and Ϫ23.6 ppm, char- Ϫ13.7 ppm is assigned by comparison to related
3330
Eur. J. Inorg. Chem. 2002, 3328Ϫ3335

Zwitterionic Stereoisomers from the Reaction of B(C6F5)3 and NEt2Ph
FULL PAPER
systems[8,28Ϫ30] to a [R-B(C6F5)3]Ϫ fragment (where R is an
alkyl group with an sp3 carbon bound to boron). The 11B
NMR spectrum of I on a 500 MHz spectrometer shows that
there are two signals at δ ϭ Ϫ13.1 (B2) and Ϫ13.5 ppm
(B1) in an approximate B2/B1 ratio of 2:5 (Figure 6). This
indicates the presence of two types of anionic boron com-
pound in which the boron atoms are located in very sim-
ilar environments.
Figure 7. H-11B NMR HMBC NMR spectrum (500 MHz, 25 °C,
1
C6D6) of solution I
Figure 6. 11B NMR spectrum (500 MHz, 25 °C, C6D6) of solution I
1H-11B HMBC NMR experiments show a 2JB-H coupling (I) at ambient temperature, several species are present:
between the [R-B(C6F5)3]Ϫ boron atoms and the (c1, c2) B(C6F5)3, NEt2Ph, [HB(C6F5)3]Ϫ(HNEt2Ph)ϩ and two new
protons (Figure 7). In spite of the short T2 of the quadru- species (A1, A2 in Scheme 1) in a constant A1/A2 ratio of
polar 11B nucleus, 1H-11B HMBC experiments were at- 3:2. In none of the experiments is formation of the
tempted to confirm the linkage of the -CH2- B(C6F5)3. The (C6F5)3B·NEt2Ph adduct observed. The zwitterionic stereo-
quality of the 2D matrix was surprisingly good and allowed isomeric species A1 (E isomer) and A2 (Z isomer) come
1
us to attribute the broad resonances c1 and c2 in the H closest to explaining the 2D NMR experimental data.
(δc1 ϭ 3.15, δc2 ϭ 3.45 ppm) and 13C NMR spectra
In the 1H-11B HMBC NMR spectra, the long range
(δc1,c2 ϭ 34.5 ppm) to be attributed to the -CH2-B(C6F5)3 coupling between the boron resonance B1 and the methyl-
3
moieties.[30Ϫ32] A JB-H coupling of the [-CH2-B(C6F5)3]Ϫ ene protons b1 is only possible for the trans-isomer A1 (E
boron atoms with the (g1, g2) protons is an additional proof isomer) in a particular conformation. According to the rel-
1
for the structure of H-(CϭX)-CH2-B(C6F5)3. Furthermore, ative intensities of the peaks associated with A1 in the H,
a third coupling is observed between the major boron res- 11B and 15N NMR spectra, this result definitively proves
onance B1 and the methylene protons b1, while there is no that A1 (E isomer) is the major species, as expected on the
correlation between B2 and the methylene protons b2.
basis of steric considerations.
Multinuclear NMR studies performed on I at ambient
1H-15N HMBC NMR experiments indicate that three dif-
ferent nitrogen resonances are present at δ ϭ 74, 209.5 and temperature enable the other boron species, besides un-
210.2 ppm (Figure 8 and 9). The major peak at δ ϭ 74 ppm changed B(C6F5)3, to be identified as [HB(C6F5)3]Ϫ and the
(N) corresponds to the nitrogen atom of NEt2Ph. The res- two stereoisomers A1 and A2 of [RCH2-B(C6F5)3]Ϫ. The
onances at δ ϭ 209.5 for (N1) and δ ϭ 210.2 ppm (N2) are formation of the [HB(C6F5)3]Ϫ anion can be explained by
characteristic of an sp2-hybridized nitrogen atom, such as a reversible abstraction of the α-hydrogen from NEt2Ph by
an iminium center.[22] Correlations are observed between B(C6F5)3 affording the iminium cations (B) (reaction 1 in
3
these peaks and the methyl (a1, a2 Ϫ JN-H), the methylene Scheme 2). This hydride abstraction by B(C6F5)3 could be
2
3
3
(b1, b2 Ϫ JN-H; c1, c2 Ϫ JN-H), the ortho (d1, d2 Ϫ JN-H
)
facilitated by conjugation with the lone pair of the nitrogen
and imino (g1, g2 Ϫ 2JN-H) protons, indicating the existence atom, and has already been reported for organic sub-
of two types of iminium center in slightly different environ- strates[33] and for organometallic complexes.[26,27] However,
ments, as observed in the 11B NMR spectrum.
there is no evidence for the presence of the iminium cations
The 19F NMR spectrum of I reveals a complex pattern (B) in solution. It is likely that, in the presence of NEt2Ph,
of non-equivalent pentafluorophenyl groups at ambient the iminium salt (B) initially formed is rapidly converted
temperature, three types of pentafluorophenyl ligand (a, b, into enamine (C) and an anilinium salt (reaction 2,
c) bound to anionic boron centers are present[32] (Table 1). Scheme 2). The conversion of tertiary iminium salts into
No pentafluorobenzene is formed in solution.
enamines in presence of a base is well documented.[34] At
Thus, multinuclear NMR studies indicate that in solu- this stage, an electrophilic addition of B(C6F5)3 to the en-
tions containing equimolar amounts of B(C6F5)3 ϩ NEt2Ph amine intermediate yields the zwitterions (A1, A2) (reaction
Eur. J. Inorg. Chem. 2002, 3328Ϫ3335
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N. Millot, C. C. Santini, B. Fenet, J. M. Basset
FULL PAPER
Table 1. 19F NMR chemical shifts of C6F5 ligands in I
Attribution
Chemical shifts[a]
∆(δm,p)
o-C6F5
p-C6F5
m-C6F5
[b]
B(C6F5)3
Ϫ128.7
Ϫ132.6
Ϫ132.2
Ϫ133.5
Ϫ141.7
Ϫ158.6
Ϫ159.5
Ϫ161.2
Ϫ160.0
Ϫ164.8
Ϫ164.3
Ϫ165.4
18.3
6.2
4.8
4.2
a[b]
b[b]
c[b]
[a]
[b]
δ in ppm. At 25 °C in C6D6.
Scheme 1. Structure of the two stereoisomers (A1) and (A2) present
in solution I
instead of diethylaniline. The reaction of equimolar
amounts of B(C6F5)3 and NMe2Ph in concentrated
[D6]benzene solution was monitored by 11B NMR spectro-
scopy at room temperature. The spectra of the pale pink
solution of IMe show the presence of a sharp peak at δ ϭ
Ϫ24 ppm characteristic of the [HB(C6F5)3]Ϫ anion. This in-
dicates the formation of the iminium (BMe) by α-hydrogen
abstraction with B(C6F5)3 (reaction 5, Scheme 3). It should
be noted that there is also a peak at δ ϭ Ϫ3 ppm which is
assigned to the Lewis acid-base complex (C6F5)3B·NMe2Ph
(V). The fact that no peak characteristic of zwitterions A1
and A2 is present at δ ϭ Ϫ13 ppm proves that electrophilic
addition of B(C6F5)3 does not proceed for dimethylaniline.
This can be rationally explained by the fact that formation
of an enamine intermediate is not possible in the case of
dimethylaniline. Thus, the reaction pathway is stopped at
the stage of the formation of the ternary iminium salt
(BMe).
1
Figure 8. a) H-15N NMR HMBC NMR spectrum (500 MHz, 25
°C, C6D6) of solution 1; b) expanded [δ ϭ 199Ϫ220 ppm] region
The overall equilibria observed in solutions I and IMe are
summarized in reaction 4 (Scheme 2) and reaction 6
(Scheme 3) respectively. It should be noted that in the 11B
NMR spectrum of I (Figure 9) the intensity ratio of 1:0.9
between the two sharp peaks at δ ϭ Ϫ13.7 and Ϫ23.6 ppm,
that is [CH2-B(C6F5)3]Ϫ/[HB(C6F5)3]Ϫ, is in good agree-
ment with the stoichiometry expected from reaction 4 in
Scheme 2. However, in all cases, the reaction of R-OH com-
pounds [R ϭ H, Ph3Si, (c-C5H9)7O12Si8 or silanol group of
silica] with [B(C6F5)3 ϩ NEt2Ph] solutions leads quantitat-
Figure 9. 11B NMR spectrum (300 MHz, 25 °C, C6D6) of: a) solu-
tion I; b) solution IMe
3, Scheme 2), as already reported for other Lewis acids such ively to the formation of [RO-B(C6F5)3]Ϫ(HNEt2Ph)ϩ con-
as GeCl4, SnCl4,[35] and TiCl4.[36,37]
firming that all equilibria involved in solutions of I are dis-
The involvement of the iminium ion (B) as an interme- placed towards the ionic form [RO-B(C6F5)3]Ϫ(HNEt2Ph)ϩ
diate is demonstrated by using dimethylaniline as a base in the presence of protic compounds.[39]
3332
Eur. J. Inorg. Chem. 2002, 3328Ϫ3335

Zwitterionic Stereoisomers from the Reaction of B(C6F5)3 and NEt2Ph
FULL PAPER
Scheme 2. Proposed mechanism to explain the formation of stereoisomers (A1) and (A2)
Scheme 3. Structure of the compounds of the reaction of B(C6F5)3 and Me2NPh, solution IMe
Eur. J. Inorg. Chem. 2002, 3328Ϫ3335
3333

N. Millot, C. C. Santini, B. Fenet, J. M. Basset
FULL PAPER
3
8.2 Hz, 2 H, o-C6H5), 2.80 (q, JH-H ϭ 7.1 Hz, 4 H, CH2), 0.82 (t,
Conclusion
3JH-H ϭ 7.1 Hz, 6 H, CH3) ppm. 13C NMR: δ ϭ 142.4 (s, i-C6H5),
130.3 (s, m-C6H5), 123.1 (br. s, p-C6H5), 116.4 (s, o-C6H5), 49.4 (s,
CH2), 11.4 (s, CH3) ppm. 15N NMR: δ ϭ 71 (s, NEt2Ph) ppm.
The presence of several species in equilibrium in a solu-
tion of (C6F5)3B and R2NPh (1: 1) has been established by
several NMR experiments. In the case of dimethylaniline,
besides free B(C6F5)3 and Me2NPh, the 1:1 adduct
(C6F5)3B·NMe2Ph and an iminium salt [PhCH3Nϭ
CH2]ϩ[HB(C6F5)3]Ϫ have been identified. With diethyl-
aniline, 40% of the products were unchanged (C6F5)3B
B(C6F5)3: 11B NMR: δ ϭ 59 (br. s, B(C6F5)3] ppm. 13C NMR: δ ϭ
1
1
148.8 (d, JC-F ϭ 243 Hz, o-C6F5), 141.5 (d, JC-F ϭ 230 Hz, p-
C6F5), 137.7 (d, JC-F ϭ 247 Hz, m-C6F5) ppm. 19F NMR: δ ϭ
1
Ϫ128.6 (br. s, 6 F, o-C6F5), Ϫ141.7 (br. s, 3 F, p-C6F5), Ϫ160.0 (br.
s, 6 F, m-C6F5) ppm.
[A1, (E)-isomer]: 1H NMR (20%): δ ϭ 7.88 (t, 3JH-H ϭ 7.9 Hz, 1 H,
and
Et2NPh,
30%
were
the
iminium
salt
3
H-CϭN), 6.92 (m, m- and p-C6H5), 6.17 (d, JH-H ϭ 7.2 Hz, 2 H,
[HB(C6F5)3]Ϫ(HNEt2Ph)ϩ, and the remaining 30% were
converted into the zwitterionic stereoisomers (E)- and (Z)-
[PhEtNϩϭCH-CH2BϪ(C6F5)3] in a 3:2 ratio. In the pres-
ence of a protic compound this equilibrium is totally dis-
placed towards the ionic form [RO-B(C6F5)3]Ϫ[HNEt2Ph]ϩ.
3
o-C6H5), 3.15 (br. m, 2 H, CH2-B), 2.60 (q, JH-H ϭ 7.25 Hz, 2 H,
CH2), 0.40 (t, JH-H ϭ 7.2 Hz, 3 H, CH3) ppm. 11B NMR: δ ϭ
3
Ϫ12.9 (s, [-CH2-B(C6F5)3]Ϫ) ppm. 13C NMR: δ ϭ 188.6 (s, CϭN),
136.5 (s, i-C6H5), 131 (s, m-C6H5), 130.2 (s, p-C6H5), 124.2 (s, o-
C6H5), 58.5 (s, CH2), 34.5 (br, CH2-B), 12.7 (s, CH3) ppm; C6F5
signals not resolved. 15N NMR: δ ϭ 209.5 (s, EtPhNϩϭCH-) ppm.
3
19F NMR: δ ϭ Ϫ132.6 (d, JF-F ϭ 19 Hz, 6 F, o-C6F5), Ϫ158.6
Experimental Section
(br. s, 3 F, p-C6F5), Ϫ164.8 (br. s, 6 F, m-C6F5) ppm.
3
[A2, (Z)-isomer]: 1H NMR (10%): δ ϭ 7.91 (t, JH-H ϭ 8.5 Hz, 1
All operations were carried out under an argon atmosphere using
glovebox (Jacomex or MBraun) or vacuum-line techniques. Tolu-
ene and pentane were distilled under argon from Na/K alloy, de-
gassed and stored under argon over Na (toluene) or 3 A molecular
sieves (pentane). C6D6 (SDS Ϫ 99.6%) and CD2Cl2 (SDS Ϫ 99.6%)
3
H, H-CϭN), 6.92 (m, m-C6H5), 6.85 (t, JH-H ϭ 7.7 Hz, 1 H, p-
3
C6H5), 6.36 (d, JH-H ϭ 7.9 Hz, 2 H, o-C6H5), 3.45 (br.m, 2 H,
3
3
CH2-B), 3.10 (q, JH-H ϭ 7.4 Hz, 2 H, CH2), 0.35 (t, JH-H
ϭ
˚
7.2 Hz, 3 H, CH3) ppm. 11B NMR: δ ϭ Ϫ12.6 (s, [-CH2-
B(C6F5)3]Ϫ) ppm. 13C NMR: δ ϭ 189.2 (s, CϭN), 142.4 (s, i-C6H5),
130.9 (s, m-C6H5), 130.5 (s, p-C6H5), 122.9 (s, o-C6H5), 48.3 (s,
CH2), 34.5 (br, CH2-B), 11.8 (s, CH3) ppm; C6F5 signals not re-
were degassed by three ‘‘freeze-pump-thaw’’ cycles and dried over
˚
freshly regenerated 3 A molecular sieves. NEt2Ph (Aldrich Chem-
icals, 98%) and NMe2Ph (Aldrich Chemicals, 99%) were dried over
KOH, distilled under vacuum and used immediately. B(C6F5)3
(Merck Chemicals, Ͼ 97%) was dried using Me3SiCl,[38] purified
by vacuum sublimation and controlled by 19F NMR spectroscopy
before use. The NMR spectra were recorded with Bruker AC
200 MHz (19F), AC 300 MHz (1H, 13C), DRX 300 MHz (11B) and
DRX 500 MHz (1H, 13C, 11B, 15N 2D NMR) spectrometers. Chem-
ical shifts are reported in ppm and referenced to residual solvent
resonances (C6D6: δ ϭ 7.15 ppm for 1H, δ ϭ 128 ppm for 13C;
3
solved. 19F NMR: δ ϭ Ϫ132.6 (d, JF-F ϭ 19 Hz, 6 F, o-C6F5),
Ϫ158.6 (br. s, 3 F, p-C6F5), Ϫ164.8 (br. s, 6 F, m-C6F5) ppm. 15N
NMR: δ ϭ 210.2 (s, EtPhNϩϭCH-) ppm.
1
[HB(C6F5)3]؊: H NMR: δ ϭ 3.90 (br, 1 H) ppm. 11B NMR: δ ϭ
1
3
Ϫ23.6 (d, JB-H ϭ 77.5 Hz) ppm. 19F NMR: δ ϭ Ϫ132.2 (d, JF-
3
ϭ 22 Hz, 6 F, o-C6F5), Ϫ159.5 (t, JF-F ϭ 22 Hz, 3 F, p-C6F5),
F
Ϫ164.3 (m, 6 F, m-C6F5) ppm; δ ϭ Ϫ133.5 (br. m, 6 F, o-C6F5),
Ϫ161.2 (br. m, 3 F, p-C6F5), Ϫ165.4 (br. m, 6 F, m-C6F5) ppm.
1
CD2Cl2: δ ϭ 5.32 ppm for H, δ ϭ 53.8 ppm for 13C), or external
Preparation of IMe: In an NMR tube, B(C6F5)3 (97 mg, 0.19 mmol)
was dissolved in 0.4 mL of C6D6. NMe2Ph (24 µL, 0.19 mmol) was
then added with a syringe to give a pale pink solution.
standards (19F: CFCl3; 11B: BF3·OEt2; 15N: N,N-dimethylformam-
ide).
1
3
2D COSY experiments were acquired with the standard Bruker
COSYgp experiment and processed in absolute mode. 2D HSQC
experiment were acquired with the standard Bruker inviegts experi-
NMe2Ph: H NMR: δ ϭ 7.31 (dd, JH-H ϭ 7.0 Hz, 2 H, m-C6H5),
3
3
6.88 (t, JH-H ϭ 7.0 Hz, 1 H, p-C6H5), 6.72 (d, JH-H ϭ 8.5 Hz,
2 H, o-C6H5), 2.62 (s, 3 H, CH3) ppm. 15N NMR: δ ϭ 43.7 (s,
ment and processed in phases mode. 2D HMBC experiment were NMe2Ph) ppm.
acquired with the standard Bruker inv4gplrnd and processed in ab-
3
(C6F5)3B·NMe2Ph: 1H NMR: δ ϭ 7.17 (d, JH-H ϭ 8.5 Hz, 2 H, o-
solute mode, as shown in Table 2.
3
3
C6H5), 6.8 (t, JH-H ϭ 8.2 Hz, 1 H, p-C6H5), 6.67 (t, JH-H
ϭ
8.4 Hz, 2 H, m-C6H5), 2.55 (s, 6 H, CH3) ppm. 11B NMR: δ ϭ
Ϫ2.9 (s, (C6F5)3B-NMe2Ph) ppm. 15N NMR: δ ϭ 52.3 [s, (C6F5)3B-
Table 2. Standard parameters for the 2D NMR experiments
NMe2Ph] ppm. 19F NMR: δ ϭ Ϫ132.7 (d, JF-F ϭ 20 Hz, 6 F, o-
3
1H-13C
1H-15N
1H-11B
3
C6F5), Ϫ159.1 (t, JF-F ϭ 20 Hz, 3 F, p-C6F5), Ϫ165.4 (m, 6 F, m-
C6F5) ppm.
D6
50ms
100 ms
25 ms
[PhMe(N؍CH2)]؉[HB(C6F5)3]؊: 11B NMR:
δ ϭ Ϫ23.9 (s,
Gradients
Row data size
20Ϫ20Ϫ10
4096 ϫ 1024
70Ϫ30Ϫ50
4096 ϫ 256
60Ϫ20Ϫ6567
2048 ϫ 512
3
[HB(C6F5)3]Ϫ) ppm. 19F NMR: δ ϭ Ϫ132.1 (d, JF-F ϭ 22 Hz, 6
3
F, o-C6F5), Ϫ159.7 (t, JF-F ϭ 22 Hz, 3 F, p-C6F5), Ϫ164.4 (m, 6
F, p-C6F5); δ ϭ Ϫ133.3 (br. m, 6 F, o-C6F5), Ϫ161.6 (br. m, 3 F,
p-C6F5), Ϫ165.4 (br. m, 6 F, m-C6F5) ppm.
Reactions of Equimolar Amounts of [B(C6F5)3؉NEt2Ph] (I) and
[B(C6F5)3؉NMe2Ph] (IMe
)
Preparation of I: In an NMR tube, B(C6F5)3 (75 mg, 0.15 mmol) Acknowledgments
was dissolved in 0.4 mL of C6D6. NEt2Ph (23.3 µL, 0.15 mmol) was
We thank Dr. R. Andersen, Pr. M. Ciufolini and Pr. A. Smith for
then added with a syringe to give a pink solution after agitation.
fruitful discussions. We are also grateful to CNRS and ESCPE
Lyon for financial support, and to the French Ministry for Educa-
tion and Research for a fellowship (N. M.).
1
3
NEt2Ph: H NMR (C6D6): δ ϭ 7.17 (dd, JH-H ϭ 7.9 Hz, 2 H, m-
3
3
C6H5), 6.9 (t, JH-H ϭ 7.2 Hz, 1 H, p-C6H5), 6.66 (d, JH-H
ϭ
3334
Eur. J. Inorg. Chem. 2002, 3328Ϫ3335

Zwitterionic Stereoisomers from the Reaction of B(C6F5)3 and NEt2Ph
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