New azoniaboratacyclopropanes from (F3C)2BNMe2 and diazomethane derivatives - Structure of cyclo-(F3C)2B-Cph2-NMe2 and HOB(CF3)2- CHC6F5-NHMe2

Article abstract of DOI:10.1002/(SICI)1099-0682(19990202)1999:2<255::AID-EJIC255>3.0.CO;2-F

1,1-Dimethyl-2,2-bis(trifluoromethyl)azoniaboratacyclopropanes, cyclo- (F₃C)₂B-CR¹R²-NMe₂ [R¹ = R² = C₆H₅ (2a); R¹/R² = C₁₂H₈ (2b); R¹ = H, R² = C₆H₅ (2c), 4-FC₆H₄ (2d), 3FC₆H₄ (2e), 2-FC₆H₄ (2f), C₆F₅ (2g), iPr (2h), tBu (2i); R¹ = Me, R² = C(=O)OMe (2j), C(=O)OEt (2k)] have been obtained from (F₃C)₂BNMe₂ (1) and diazomethanes R¹R²CN₂. In contrast to compound 2a, the B-N bonds of 2b-2k hydrolyze to form the zwitterionic species Me₂NH-CR¹R²-B(CF₃)₂OH (3b-3k). The diazoacetic acid esters HC(N₂)C(=O)OMe and HC(N₂)C(=O)OtBu react with 1 to form three-membered rings, which hydrolyze rapidly to form Me₂NH- CR¹R²B(CF₃)₂OH [R¹ = H, R² = C(=O)OMe (31), C(=O)OtBu (3m)]. F₃CSiF₃ reacts under elimination of CF₂ with 1 to form the acyclic derivative (F₃C)₂BF-CF=NMe₂ (4). The structures of 2a and 3g have been investigated crystallographically. A nearly eclipsed conformation is found for the central B-C bond of 3g, which is 0.097(7) A longer than the B-C bond length in the three-membered ring of 2a.

Full text of DOI:10.1002/(SICI)1099-0682(19990202)1999:2<255::AID-EJIC255>3.0.CO;2-F

FULL PAPER
New Azoniaboratacyclopropanes from (F3C)2BNMe2 and Diazomethane
Derivatives – Structure of cyclo-(F3C)2B–CPh2–NMe2 and
HOB(CF3)2–CHC6F5–NHMe2
David J. Brauer,[a] Hans Bürger,*[a] Silke Buchheim-Spiegel,[a] and Gottfried Pawelke[a]
Dedicated to Professor H. D. Lutz on the occasion of his 65th birthday
Keywords: Boron / Small rings / Trifluoromethyl group / Crystal structure
1,1-Dim ethyl-2,2-bis(triflu orom ethyl)azon ia bora ta cyclo-
propanes, cyclo-(F3C)2B–CR1R2–NMe2 [R1 = R2 = C6H5 (2a);
R1/R2 = C12H8 (2b); R1 = H, R2 = C6H5 (2c), 4-FC6H4 (2d), 3-
HC(N2)C(=O)OtBu react with 1 to form three-membered
rings, which hydrolyze rapidly to form Me2NH–CR1R2–
B(CF3)2OH [R1 = H, R2 = C(=O)OMe (3l), C(=O)OtBu (3m)].
F3CSiF3 reacts under elimination of CF2 with 1 to form the
acyclic derivative (F3C)2BF–CF=NMe2 (4). The structures of
2a and 3g have been investigated crystallographically. A
nearly eclipsed conformation is found for the central B–C
FC6H4 (2e), 2-FC6H4 (2f), C6F5 (2g), iPr (2h), tBu (2i); R1
=
Me, R2 = C(=O)OMe (2j), C(=O)OEt (2k)] have been obtained
from (F3C)2BNMe2 (1) and diazomethanes R1R2CN2. In
contrast to compound 2a, the B–N bonds of 2b–2k hydrolyze
to form the zwitterionic species Me2NH–CR1R2–B(CF3)2OH
(3b–3k). The diazoacetic acid esters HC(N2)C(=O)OMe and
˚
bond of 3g, which is 0.097(7) A longer than the B–C bond
length in the three-membered ring of 2a.
(Dimethylamino)bis(trifluoromethyl)borane, (F3C)2BNMe2
(1), possesses chemical properties that are unique in amino-
borane chemistry.[1] Owing to a balance of pronounced
electrophilic character and steric protection of the boron
atom, the reactivity of its strong BϭN bond bears a degree
of resemblance to an olefinic CϭC bond. On the other
hand its polarity is related to that of a CϭN bond in a
dimethyliminium cation. In a preceding paper we reported
on reactions of diazomethane derivatives with 1.[2] While
diazomethane itself, trimethylsilyldiazomethane and tri-
methylsilyl(benzyl)diazomethane formed novel heterocyclo-
propane derivatives, diazoacetic acid ethyl ester underwent
an ene-type reaction to form an extraordinary stable, boryl-
ated diazomethane species (Scheme 1). In contrast to the
BϪN bond in dimethylamineϪbis(trifluoromethyl)boranes,
R(F3C)2B · NMe2H, which is not only stable to dissociation
but also to displacement reactions at room temperature, the
BϪN bond in the azoniaboratacyclopropanes, which are
formed from reactions of 1 with diazomethane or trimethyl-
silydiazomethane, is rather reactive.
Scheme 1. Diazomethane derivatives and (dimethylamino)bis(tri-
fluoromethyl)borane
What is the influence of the substituents R1 and R2 on the
formation, reactivity and stability of azoniaboratacyclopro-
panes? (2) Can other potential carbene sources (e. g.,
F3CSiF3) be used to form such three-membered rings? (3)
Will diazoacetic acid esters other than HC(N2)C(ϭO)OEt
also enter into ene-type reactions or will they form three-
membered rings? Here we report on our results.
Thus, water cleaves their BϪN bonds to form
Me2NHϪCHRϪB(CF3)2OH while nitriles like H3CCN or
carbonyl compounds like acetone insert into the BϪN bond
to yield the five-membered heterocycles cyclo-Me2NϪ
CHRϪB(CF3)2NϭCMe
and
cyclo-Me2NϪCHRϪB-
(CF3)2OϪCMe2, respectively.[3] On the other hand cyclo-
(F3C)2BϪC(SiMe3)(CH2C6H5)ϪNMe2 was far less reactive
than the other three-membered rings.
The reasons for the varying reactivity were not fully
understood, and there were questions left unanswered: (1)
Results
The reactivity of compound 1 towards many solvents and
reagents prohibits in situ generation of diazomethanes. Fur-
thermore the diazomethanes must be accessible as neat ma-
[a]
Anorganische Chemie, FB 9, Universität-GH,
D-42097 Wuppertal, Germany
E-mail: buerger1@wrcs3.urz.uni-wuppertal.de
Eur. J. Inorg. Chem. 1999, 255Ϫ261
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
1434Ϫ1948/99/0202Ϫ0255 $ 17.50ϩ.50/0
255

D. J. Brauer, H. Bürger, S. Buchheim-Spiegel, G. Pawelke
FULL PAPER
F3C-SiF3 Ǟ {CF2} ϩ SiF4
(1)
terial in high purity. These demands limit the number of
possible candidates to a small number of stable, isolable di-
azomethanes. Of these candidates, R1R2CN2, those with R1
and R2 as defined in Scheme 2 were prepared and dissolved
in dry pentane. Compound 1 was condensed onto these
frozen solutions at Ϫ196°C. Upon warming decolorization
and evolution of nitrogen was observed as soon as 1 melted
and mixed with the diazomethane solutions.
Indeed trifluoro(trifluoromethyl)silane reacts rapidly
with 1 at Ϫ60°C; however, instead of the expected three-
membered ring, the acyclic isomer (F3C)2BFϪCFϭNMe2
(4) was obtained (Scheme 3). We assume that difluorocar-
bene adds primarily to the BϭN bond of 1; however, the
three-membered ring is unstable and rearranges by a 1,2-
dyotropic shift to form 4.
Scheme 3. Difluorocarbene and (dimethylamino)bis(trifluorome-
thyl)borane
Properties and Spectra
Compounds 2aϪ4 are colorless solids. Except for com-
pound 2a the three-membered heterocycles 2bϪ2k are sen-
sitive to moisture Ϫ their BϪN bond being cleaved. At first
it is surprising that 2a is stable to water whereas 2b hydro-
lyses readily. In both species two phenyl rings are bonded
to the ring carbon atom. However, electronically both
groups in the ring are different. Heterolytic breaking of the
CϪN bond in 2a and 2b would generate either a borylated
diphenylmethyl (2a) or a borylated fluorenyl cation (2b). If
it is accepted that the diphenylmethyl cation is more stable
than the fluorenyl cation and that this is also true for a
borylated species, then the C13H8 substituent attracts more
Scheme 2. Formation of azoniaboratacyclopropanes and hydrolytic
cleavage of their BϪN bond
All of the investigated diazomethanes act as carbene electron density from the BϪN bond in 2b than the
sources, and though their reactivity towards 1 varied, no C(C6H5)2 group does in 2a. Thus, the BϪN bond in 2b is
competing reactions were observed. The relatively stable di- more polar than in 2a and hence more reactive towards
phenyldiazomethane and fluorenyldiazomethane react less water.
rapidly than the less stable phenyl and alkyldiazomethanes.
1
The H-, 19F-, 11B- and 13C-NMR spectra of 2aϪ4 were
On the other hand trifluoromethyldiazomethane, F3CHCN2, recorded. The shift data which are set out in Table 1 are
did not react with 1. consistent with the proposed structures, and only a few
While HC(N2)COOEt undergoes an ene-type reaction comments will be necessary. The 13C resonances of the CF3
with 1, the corresponding diazoacetic acid esters groups in 2aϪ2k are not detectable due to quadrupolar
HC(N2)COOMe and HC(N2)COOtBu reacted differently broadening by the boron atom. In 3bϪ4 they appear as
Ϫ three-membered rings were formed with elimination of extremely broadened signals. Therefore these resonances are
N2. Due to their sensitivity towards water, these ring com- not included in Table 1. Compounds 2cϪ2k and 3cϪ3m
pounds were not isolated in a pure state and therefore are have an asymmetric carbon atom which causes a splitting
missing in the list of Scheme 2. However, their hydrolysis of the NMR signals of both the N(CH3)2 and B(CF3)2
products 3l and 3m were obtained in high yields.
groups. For compound 3g five 19F and five 13C resonances
The reactivity of 2aϪ2k was tested by reaction with water are found for the pentafluorophenyl ring. This splitting is
(Scheme 2). Except for compound 2a all of the three-mem- due to hindered rotation of the ring relative to the NMR
bered rings hydrolyze within minutes to form the zwit- time scale which was confirmed by recording the NMR
terionic species 3bϪ3m. Because neat F2CϭN2 is difficult spectra at different temperatures. While 2aϪ2k show only
to prepare and because all of the diazomethanes tested here broad signals for the ring carbon atoms, in the zwitterions
reacted as carbene sources, we were interested in testing the 3bϪ3m the 13C resonances of these carbon atoms appear
1
reactivity of a suitable difluorocarbene source with com- as 1:1:1:1 quadruplets with J(BC) ϭ 42Ϫ51 Hz. The 19F
pound 1. Such a difluorocarbene source is trifluoro(tri- chemical shift of the boron-bonded fluorine atom in 4 oc-
fluoromethyl)silane, F3CSiF3, which is known to decom- curs at unusually high field, δ ϭ Ϫ220.9. This shift is larger
pose at 30°C according to Equation 1.[4]
than that for Mes(F3C)BFϪCFϭNMe2 [δ(BF) ϭ Ϫ202.7][5]
256
Eur. J. Inorg. Chem. 1999, 255Ϫ261

New Azoniaboratacyclopropanes from (F3C)2BNMe2 and Diazomethane Derivatives
FULL PAPER
Table 1. NMR-spectral data of 2aϪ2k and 3bϪ4[a]
2a
2b
2c
2d
2e
2f
2g
2h
2i
2j
2k
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
4
1H
δ(NCH3) 3.00 3.02 2.48 2.46 2.51 2.86 2.65 2.77 2.82 2.81 2.85 2.64 2.59 2.62 2.91 2.88 2.73
2.76 2.88 2.86 2.64 3.16 2.93 3.35
2.88 2.99 3.10 2.93 3.25 3.08 3.60
3.04 3.02 3.04 3.03 3.09 2.82 2.91 2.96 2.99
3.48 3.42 3.44 3.37 3.11 1.82 2.01
1.00 1.17 1.72 1.28
2.74 2.77 3.00 2.99 3.02
3.63 3.66 3.76 4.21 4.03
δ(BCHn)
δ(CCH3)
2.30 2.62
3.62 3.40
1.45
1.03 1.17 1.53 1.27
1.13
2.05
1.75
1.17
2.15
1.46
δ(CHnC)
δ(OCHn)
δ(C6Hn) 7.25 7.50 7.3
3.71 4.20
3.67 4.15 3.64
7.07 7.03 7.1
7.37 7.49 7.12 7.11 7.16
7.47 7.36 7.56 7.39 7.40
и
и
и
7.30 7.08
и
7.45 7.80 7.42
7.37 7.4
7.12
7.37
7.82
7.87
7.45 7.93
δ(NH)
δ(OH)
19F
7.2
7.05 7.0
7.68 7.72 7.2
8.4
2.2
ca. 8.7 ca. 7.8 ca. 7.2 ca. 8.0 ca. 7.1
ca. 2.3 2.09 ca. 2.2 ca. 2 ca. 1.8
2.16 1.71 2.2
2.1
2.2
2.30
δ(CF3) Ϫ55.0 Ϫ53.8 Ϫ55.5 Ϫ55.5 Ϫ56.0 Ϫ56.2 Ϫ59.6 Ϫ57.7 Ϫ53.1 Ϫ58.2 Ϫ56.1 Ϫ65.2 Ϫ60.2 Ϫ66.3 Ϫ66.1 Ϫ66.5 Ϫ69.4 Ϫ65.1 Ϫ64.3 Ϫ64.7 Ϫ64.9 Ϫ67.3 Ϫ65.9 Ϫ70.5
Ϫ60.1 Ϫ60.2 Ϫ60.7 Ϫ60.6 Ϫ60.9 Ϫ60.5 Ϫ58.9 Ϫ60.0 Ϫ57.5
Ϫ63.7 Ϫ69.4 Ϫ69.4 Ϫ69.6 Ϫ69.5 Ϫ68.2 Ϫ67.3 Ϫ67.2 Ϫ66.8 Ϫ70.7 Ϫ70.4
δ(BF)
δ(ϭCF)
δ(C6Fn)
Ϫ220.9
Ϫ6.6
Ϫ112.3Ϫ112.8Ϫ113.1Ϫ137.2
Ϫ116.3Ϫ115.7Ϫ117.1Ϫ136.2
Ϫ151.6
Ϫ161.2
Ϫ143.0
Ϫ157.4
Ϫ164.8
Ϫ165.5
11B
δ(B)
13C
Ϫ14.0 Ϫ11.6 Ϫ15.1 Ϫ14.6 Ϫ16.8 Ϫ16.9 Ϫ15.7 Ϫ15.5 Ϫ17.3 Ϫ17.2 Ϫ17.1 Ϫ6.6 Ϫ6.9 Ϫ6.8 Ϫ8.1 Ϫ8.0 Ϫ8.0
Ϫ9.2 Ϫ7.8 Ϫ7.4 Ϫ7.5 Ϫ3.5 Ϫ3.5 Ϫ4.1
38.9 ca. 41.8 42.3 41.7 41.8 40.3
δ(NCH3) 45.1 45.2 41.9 41.8 42.0 41.1 41.8 40.1 41.7 42.2 42.7 41.8 41.6 41.6 42.6 42.5 44.4
42.5
47.8 ca. 41.9 45.1 44.9 41.0
48.1
70.5 74.7 70.4 70.8 62.6 63.4 ca. 189
49.0 48.9 49.1 48.3 48.8 49.2 51.0 45.5 46.0
45.7 45.8 46.8 46.8 47.3
δ(BC)
69
65
57 56 55.8 50.7 43.6 60.7 65 ca. ca.
75.9 68.7 67.9 69.0 59.1 57.2
55.3 55.9
20.6 30.6 15.0 14.1
δ(CCH3)
21.7 30.6 11.2 11.5
27.3
81.8
23.9
24.8 33.2
15.5
24.7
27.3 35.3
14.3
δ(CCH3)
δ(OCHn)
52.2 62.2
52.4 62.9 50.7
δ(C6Hn) 127.5 119.8 128.6 115.6 116.0 115.0 106.1
128.5 127.1 128.8 126.5 118.8 118.6 137.9
129.5 128.8 130.7 133.8 127.7 124.5 142.0
139.1 138.3 131.9 163.0 130.2 131.3 146.7
120.8 128.9 115.6 116.3 116.5 112.3
128.0 129.2 130.4 120.9 122.4 138.4
128.1 133.7 135.8 130.5 125.1 141.4
129.7 134.0 163.8 130.9 131.7 ca. 146.2
142.5
133.1 134.3
162.6 163.4
142.8
143.3
138.0 135.9 ca. 146.9
163.8 163.5
δ(CϭO)
171.1 171.4
174.3 174.2 171.4 169.8
[a] 2aϪ2h, 2j, 2k in CDCl3, 2i in CD2Cl2, 3bϪ3d, 3gϪ3k, 3m, 4 in [D3]acetonitrile, 3e, 3f, 3l in [D6]acetone.
[7Ϫ9]
˚
which was previously believed to be the upper limit for a Ϫ all of which exceed 1.61 A.
Secondly, the NϪC(1)
˚
fluorine bonded directly to boron.
linkage [1.556(5) A] is markedly longer than the NϪCH3
EI mass-spectral data are set out in Table 2. Mϩ peaks bonds [av. 1.484(5) A], but examples of long bonds between
are generally weak, but the fragments [Mϩ Ϫ CF3] and [Mϩ quaternary nitrogen and carbon atoms have been registered
Ϫ C2F5] give reliable indications of the molecular mass. The in five-membered heterocycles involving the (F3C)2B group
˚
base peak of the three-membered rings 2cϪ2h is such as cyclo-(F3C)2BϪNMe2ϪCMe2ϪS(ϭO)ϪO [1.543(3)
[8]
[(CH3)2NCHRϩ], which is less prominent in 2i due to the
A ] and cyclo-(F3C)2BϪCH(SiMe3)ϪNMe2ϪCMe2ϪO
˚
instability of the tBu group. In the corresponding hy- [1.582(4) A[3]]. In this connection we note that the BϪC,
drolyzed products 3cϪ3h the fragment [CH3NHCHRϩ] is BϪN and NϪC(1) [1.556(5) A] bond lengths in 2a agree to
˚
˚
in general the base peak.
within experimental error with the values [1.595(5), 1.560(5)
and 1.567(4) A] found for the corresponding linkages in
˚
cyclo-(F3C)2BϪC(SiMe3)(CH2C6H5)ϪNMe2 (5).[2] Thirdly,
the exocyclic substituent planes of the B and C(1) atoms do
not bisect the NϪBϪC(1) and BϪC(1)ϪN angles, respec-
tively, but rather are pivoted away from the bisecting posi-
tions by 8.8(5)° and 9.7(5)°, respectively, towards the NMe2
group. A similar distortion was found in 5. Fourthly, the
bond angles defined at the ring atoms by their two exocyclic
substituents average 109.1(8)°, which is similar to the
108.0(3)° value found in 5. These angles seem small in view
of the relatively high s character ascribed to the hybrid or-
bitals used by a cyclopropyl ring atom in its exocylic
bonds.[10]
Description of the Crystal Structures of 2a and 3g
The structure of 2a is shown in Figure 1. The three-mem-
bered ring defines a non-crystallographic mirror plane,
which is obeyed by the exocyclic bonds to within exper-
imental error and is followed by the angles and the magni-
tude of the torsion angles to within 4°. The phenyl groups
are oriented parallel to the BϪN bond and are thus not
capable of conjugation with the tangential Walsh ring or-
bitals.[6]
Several features of the ring geometry deserve comment.
˚
Firstly, the BϪN bond length [1.568(6) A] is clearly shorter
than those reported between quaternary nitrogen atoms
A drawing of 3g is given in Figure 2. The nearly eclipsed
and (F3C)2B entities in four-, five- and six-membered rings conformation about the BϪC(3) bond and its great length,
Eur. J. Inorg. Chem. 1999, 255Ϫ261
257

D. J. Brauer, H. Bürger, S. Buchheim-Spiegel, G. Pawelke
FULL PAPER
Table 2. EI mass-spectral data for 2aϪ2i and 3bϪ4
m/z (%) [fragmentϩ]
2a 165 (100) [C13H9ϩ], 74 (43) [F2BN(CH3)2ϩ], 77 (33) [C6H5ϩ], 240(31) [Mϩ Ϫ C2F5], 91(26) [C7H7ϩ], 290(25) [Mϩ Ϫ CF3], 162(19)
[Mϩ Ϫ C2F5ϪC6H5], 359(5) [Mϩ]
2b 165 (100) [C13H9ϩ], 91 (15) [C7H7ϩ], 74 (12) [F2BN(CH3)2ϩ], 357 (1) [Mϩ]
2c 134 (100) [(CH3)2NCHC6H5ϩ], 74 (80) [F2BN(CH3)2ϩ], 42 (77) [CH3NCHϩ], 91 (19) [C7H7ϩ], 164 (33) [Mϩ Ϫ C2F5], 168 (23)
[C6H5BFCFNHCH3ϩ], 77 (17) [C6H5ϩ], 214 (15) [Mϩ Ϫ CF3], 182 (10) [C6H5BFCFN(CH3)2ϩ], 283 (3) [Mϩ]
2d 152 (100) [(CH3)2NCHC6H4Fϩ], 42 (68) [CH3NCHϩ], 74 (60) [F2BN(CH3)2ϩ], 109 (30) [C7H6Fϩ], 232 (21) [Mϩ Ϫ CF3], 182 (15)
[Mϩ Ϫ C2F5], 301 (3) [Mϩ]
2e 152 (100) [(CH3)2NCHC6H4Fϩ], 42 (20) [CH3NCHϩ], 74 (22) [F2BN(CH3)2ϩ], 186 (18) [FC6H4BFCFNHCH3ϩ], 109 (5) [C7H6Fϩ],
232 (4) [Mϩ Ϫ CF3], 182 (4) [Mϩ Ϫ C2F5], 301 (2) [Mϩ]
2f 152 (100) [(CH3)2NCHC6H4Fϩ], 42 (21) [CH3NCHϩ], 186 (19) [FC6H4BFCFNHCH3ϩ], 74 (18) [F2BN(CH3)2ϩ], 109 (6) [C7H6Fϩ],
232 (7) [Mϩ Ϫ CF3], 182 (4) [Mϩ Ϫ C2F5], 301 (3) [Mϩ]
2g 224 (100) [(CH3)2NCHC6F5ϩ], 230 (43) [F2CCHC6F5ϩ], 42 (38) [CH3NCHϩ], 258 (29) [Mϩ Ϫ C2F4 Ϫ CH3], 74 (27) [F2BN-
(CH3)2ϩ], 254 (5) [Mϩ Ϫ C2F5], 304 (5) [Mϩ Ϫ CF3]
ϩ
2h 100 (100) [(CH3)2NCHCH (CH3)2ϩ], 44 (66) [(CH3)2Nϩ], 106 (60) [Mϩ Ϫ C2F4 Ϫ (CH3)2CH], 148 (5) [F2BCCH(CH3)2N(CH3)2
]
2i 57 (100) [(CH3)3Cϩ], 44 (79) [(CH3)2Nϩ], 70 (51) [(CH3)3CCHϩ], 106 (39) [Mϩ Ϫ C2F4 Ϫ (CH3)3C], 114 (21) [(CH3)2NCHC-
(CH3)3ϩ], 148 (7) [F2BCCH(CH3)2N(CH3)2ϩ], 156 (5) [Mϩ Ϫ CF2 Ϫ (CH3)3C], 213 (4) [Mϩ Ϫ CF2], 263 (2) [Mϩ]
3b 194 (100) [CH3NHC13H8ϩ], 209 (76) [(CH3)2NHC13H8ϩ], 211 (64) [Mϩ Ϫ C2F5 Ϫ NH(CH3)2], 165 (46) [C13H9ϩ], 44 (22) [CH3)2Nϩ],
256 (20) [Mϩ Ϫ C2F5], 306 (3) [Mϩ Ϫ CF3]
3c 42 (100) [CH3NCHϩ], 120 (88) [CH3NHCHC6H5ϩ], 44 (76) [(CH3)2Nϩ], 137 (35) [Mϩ Ϫ C2F5 Ϫ NH(CH3)2], 91 (19) [C7H7ϩ], 182
(26) [Mϩ Ϫ C2F5], 135 (25) [(CH3)2NHCHC6H5ϩ], 77 (13) [C6H5ϩ], 232 (2) [Mϩ Ϫ CF3]
3d 138 (100) [CH3NHCHC6H4Fϩ], 42 (88) [CH3NCHϩ], 44 (67) [(CH3)2Nϩ], 155 (42) [Mϩ Ϫ C2F5 Ϫ NH(CH3)2], 200 (24) [Mϩ
C2F5], 152 (23) [(CH3)2NCHC6H4Fϩ], 109 (13) [C7H6Fϩ], 250 (2) [Mϩ Ϫ CF3]
Ϫ
3e 138 (100) [CH3NHCHC6H4Fϩ], 44 (66) [(CH3)2Nϩ], 42 (45) [CH3NCHϩ], 200 (44) [Mϩ Ϫ C2F5], 155 (42) [Mϩ Ϫ C2F5
NH(CH3)2], 152 (16) [(CH3)2NCHC6H4Fϩ], 109 (7) [C7H6Fϩ], 250 (3) [Mϩ Ϫ CF3]
Ϫ
3f 138 (100) [CH3NHCHC6H4Fϩ], 200 (65) [Mϩ Ϫ C2F5], 155 (65) [Mϩ Ϫ C2F5 Ϫ NH(CH3)2], 44 (45) [(CH3)2Nϩ], 42 (24)
[CH3NCHϩ], 152 (21) [(CH3)2NCHC6H4Fϩ], 109 (6) [C7H6Fϩ], 250 (6) [Mϩ Ϫ CF3]
3g 210 (100) [CH3NHCHC6F5ϩ], 44 (86) [(CH3)2Nϩ], 272 (77) [Mϩ Ϫ C2F5], 225 (55) [(CH3)2NHCHC6F5ϩ], 227 (34) [Mϩ Ϫ C2F5
NH(CH3)2], 42 (30) [CH3NCHϩ], 322 (9) [Mϩ Ϫ CF3]
Ϫ
3h 86 (100) [CH3NHCHC3H7ϩ], 148 (68) [Mϩ Ϫ C2F5], 198 (11) [Mϩ Ϫ CF3]
3i 46 (100) [(CH3)2NH2ϩ], 100 (97) [CH3NHCHC4H9ϩ], 44 (93) [(CH3)2Nϩ], 162 (76) [Mϩ Ϫ C2F5], 106 (64) [Mϩ Ϫ C2F5
(CH3)2CCH2], 57 (50) [C4H9ϩ], 115 (26) [(CH3)2NHCHC4H9ϩ], 212 (13) [Mϩ Ϫ CF3]
Ϫ
3j 72 (100) [CH3NH2CHCOϩ], 131 (30) [(CH3)2NHCCH3CO2CH3ϩ], 116 (15) [(CH3)2NHCCH3CO2ϩ], 178 (7) [Mϩ Ϫ C2F5], 228 (3)
[Mϩ Ϫ CF3]
3k 72 (100) [CH3NH2CHCOϩ], 116 (43) [(CH3)2NHCCH3CO2ϩ], 100 (33) [(CH3)2NHCCH3COϩ], 192 (24) [Mϩ Ϫ C2F5], 145 (15)
[(CH3)2NHCCH3CO2C2H5ϩ], 242 (8) [Mϩ Ϫ CF3]
3l 86 (100) [(CH3)2NHCHCOϩ], 58 (62) [(CH3)2NCH2ϩ], 102 (50) [(CH3)2NHCHCO2ϩ], 164 (38) [Mϩ Ϫ C2F5], 117 (35)
[(CH3)2NHCHCO2CH3ϩ], 214 (8) [Mϩ Ϫ CF3]
3m 86 (100) [(CH3)2NHCHCOϩ], 150 (47) [Mϩ Ϫ C2F5 Ϫ C4H8], 103 (45) [(CH3)2NHCHCO2Hϩ], 57 (26) [(CH3)3Cϩ], 58 (14)
[(CH3)2NCH2ϩ], 200 (8) [Mϩ Ϫ CF3 Ϫ C4H8], 256 (2) [Mϩ Ϫ CF3], 206 (1) [Mϩ Ϫ C2F5]
4
124 (100) [Mϩ Ϫ C2F5], 56 (15) [C3H6Nϩ], 49 (13) [BF2ϩ], 60 (10) [H3CNCFϩ], 108 (6) [Mϩ Ϫ C2F5 Ϫ CH4], 174 (1) [Mϩ Ϫ CF3]
tively. Each compound exhibits
a
synperiplanar
OϪBϪC(3)ϪN torsion angle Ϫ their values of 20.3(5)° and
19.6(5)° in 6 and 7, respectively, being significantly larger
than in 3g, 11.6(3)°. While the conformation in 6 and 7
is stabilized by moderately strong intramolecular NϪH···O
˚
hydrogen bonds of 1.88(2) and 1.82(3) A, respectively, the
˚
corresponding distance in 3g, 2.41(3) A, is too long to be
bonding. Here the nitrogen atom donates its proton to an
˚
oxygen atom of an inversion-related molecule, 2.03(3) A;
thus, centrosymmetric, hydrogen-bonded dimers are formed
in the solid state. Perhaps the absence of intramolecular hy-
drogen bonding in 3g accounts for its OϪBϪC(3) and
BϪC(3)ϪN angles [110.2(2)° and 111.4(2)°, respectively]
being on the average 5(1)° larger than the analogous angles
of 6 and 7.
Figure 1. A perspective drawing of 2a
Because hindered rotation was detected by NMR spec-
troscopy for the C6F5 group, we note that the aryl group in
˚
1.683(4) A, are reminiscent of the structures reported pre- 3g is oriented roughly parallel to the C(3)ϪH(3) bond Ϫ
viously for B(CF3)2(OH)CH(Ph)NH(Bz)(tBu) (6)[11] and the H(3)ϪC(3)ϪC(6)ϪC(11) torsion angle being 17(2)°. A
B(CF3)2(OH)CH(SiMe3)NHMe2 (7)[3] Ϫ the corresponding similar orientation was found for the corresponding phenyl
˚
BϪC bond lengths being 1.673(4) and 1.690(4) A, respec- substituent of 6. In 3g the aryl group protrudes into a cavity
258
Eur. J. Inorg. Chem. 1999, 255Ϫ261

New Azoniaboratacyclopropanes from (F3C)2BNMe2 and Diazomethane Derivatives
FULL PAPER
and R ϭ Et (Cs symmetry)], and the conformation governs
the distances between the lone pair, the carbon atom and
the hydrogen atom and thus the reaction pathway. Route b
is, however, also dependent on the acidity of the abstracted
proton. Therefore this route is only observed for diazocar-
bonyl derivatives.
The failure to synthesize the three-membered ring cyclo-
(F3C)2BϪCF2ϪNMe2 animated us to compare the differ-
ence in its calculated energy and that of 4 to the analogous
difference of cyclo-(F3C)2BϪCH2ϪNMe2 versus (F3C)2-
BHϪCHϭNMe2. According to semi-empirical AM1 calcu-
lations the energy of cyclo-(F3C)2BϪCH2ϪNMe2 is ca. 2
kcal/mol lower than that of (F3C)2BHϪCHϭNMe2 while 4
is ca. 30 kcal/mol more stable than cyclo-(F3C)2BϪ
CF2ϪNMe2
Figure. 2. A perspective drawing of 3g
Experimental Section
in which the CH3 group of C(4) and the CF3 group of C(1)
are on opposites sides of the ring plane.
General: NMR: Bruker ARX 400 (400 MHz, 100.6 MHz and 376.5
1
MHz, for H, 13C and 19F respectively), Bruker AC 250 (79.8 MHz
for 11B). [D3]Acetonitrile as solvent and internal standard (1H:
δH ϭ 1.95; 13C: δC ϭ 1.30), CDCl3 as solvent and internal standard
(1H: δH ϭ 7.27; 13C: δC ϭ 77.0), [D6]acetone as solvent and internal
standard (1H: δH ϭ 2.05; 13C: δC ϭ 29.8), CD2Cl2 as solvent and
internal standard (1H: δH ϭ 5.35; 13C: δC ϭ 53.8), 19F external
standard CFCl3, 11B external standard BF3 ·OEt2. Ϫ IR: Bruker
IFS 25. Ϫ MS: Varian MAT 311 (70 eV).
Discussion
The divergent behavior of the three diazoacetic acid es-
ters HC(N2)COOR (R ϭ tBu, Et and Me) is not fully
understood. The acetic acid esters H3CCOOR with R ϭ
tBu, Et undergo an ene-type reaction with 1 regardless of
their substituent R. Therefore we speculate that the mecha-
nism which leads to ene-type products of acetic acid esters
and the diazoacetic acid ethyl ester are different. The reac-
tion of all diazomethane derivatives with 1 is obviously in-
itiated by a nucleophilic attack of boron at the diazo carbon
atom (Scheme 4). The transient complex thus formed has
two ways to gain stabilization. In pathway a the nitrogen
lone pair attacks the diazomethane carbon atom, dinitrogen
is eliminated and the three-membered ring is fused. In path-
way b the lone pair abstracts a proton bonded to the diazo-
methane carbon atom Ϫ the diazo group being preserved.
X-ray Structure Determinations: Crystals of 2a and 3g were grown
from solutions in CHCl3 and acetone/H2O, respectively. While crys-
tals of 2a were sealed in glass capillaries under nitrogen, those of
3g were glued to glass fibers. The structures were solved and refined
using absorption-corrected X-ray data with the SHELXTL pro-
gram package.[12] While the H(N) and H(O) atoms of 3g were re-
fined freely, the positions of all other hydrogen atoms were ideal-
ized. Crystal data are summarized in Table 3. Crystallographic data
(excluding structure factors) have been deposited with the Cam-
bridge Crystallographic Data Centre as supplementary publication
no. CCDC-102694 for 2a and -102695 for 3g. Copies of the data
can be obtained free of charge on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK [Fax: int. code ϩ 44(1223)336-
033; E-mail: deposit@ccdc.cam.ac.uk].
1,1-Dimethyl-3,3-diphenyl-2,2-bis(trifluoromethyl)-1-azonia-2-
boratacyclopropane (2a), 3-Fluorenyl-1,1-dimethyl-2,2-bis(trifluoro-
methyl)-1-azonia-2-boratacyclopropane (2b), 1,1-Dimethyl-3-phenyl-
2,2-bis(trifluoromethyl)-1-azonia-2-boratacyclopropane (2c), 3-(4-
Fluorophenyl)-1,1-dimethyl-2,2-bis(trifluoromethyl)-1-azonia-2-
boratacyclopropane (2d), 3-(3-Fluorophenyl)-1,1-dimethyl-2,2-bis-
(trifluoromethyl)-1-azonia-2-boratacyclopropane (2e), 3-(2-Fluoro-
phenyl)-1,1-dimethyl-2,2-bis(trifluoromethyl)-1-azonia-2-borata-
cyclopropane (2f), 1,1-Dimethyl-3-(pentafluorophenyl)-2,2-bis(tri-
fluoromethyl)-1-azonia-2-boratacyclopropane (2g), 3-Isopropyl-1,1-
dimethyl-2,2-bis(trifluoromethyl)-1-azonia-2-boratacyclopropane
(2h), 3-tert-Butyl-1,1-dimethyl-2,2-bis(trifluoromethyl)-1-azonia-2-
boratacyclopropane (2i), 3-(Methoxycarbonyl)-1,1,3-trimethyl-2,2-
bis(trifluoromethyl)-1-azonia-2-boratacyclopropane (2j), 3-(Ethoxy-
carbonyl)-1,1,3-trimethyl-2,2-bis(trifluoromethyl)-1-azonia-2-bor-
atacyclopropane (2k). ؊ General Procedure: 10 ϫ 10Ϫ3 mol of the
respective neat diazomethane (Scheme 2) and 10Ϫ15 ml of pentane
(stored over P4O10) were condensed at Ϫ196°C into a U-shaped
reaction vessel connected to a vacuum line. By warming the vessel,
Scheme 4. Formation of azoniaboratecyclopropanes and ene-type
reaction products with 1 and diazomethane derivatives
A small conformational change in the transition com-
plex, as determined by the NϪBϪCϪH torsional angle, is
presumably responsible for the formation of azoniaborata-
cyclopropanes (route a) or ene-products (route b). The con-
formation about the BϪC bond should be affected by the
varying shape of the groups R [R ϭ Me, tBu (C3 symmetry) pentane and the diazomethane were mixed. The vessel was cooled
Eur. J. Inorg. Chem. 1999, 255Ϫ261 259

D. J. Brauer, H. Bürger, S. Buchheim-Spiegel, G. Pawelke
FULL PAPER
Table 3. Crystal data and structure refinement
Table 4. Elemental analyses of 2aϪ2c and 3bϪ3m
Compound
2a
3g
Compound Formula
found/(calcd.)
Formula
C17H16BF6N
359.12
C11H9BF11NO
391.00
C
H
N
Mr
2a
2b
2c
3b
3c
3d
3e
3f
C17H16BF6N
C17H14BF6N
C11 12BF6N
56.5/(56.86) 4.4/(4.49) 3.9/(3.90)
55.3/(57.18) 4.1/(3.95) 4.0/(3.92)
46.0/(46.68) 4.3/(4.27) 4.7/(4.95)
Crystal system
Space group
orthorhombic
P212121
7.592(2)
12.836(3)
17.539 (4)
90
monoclinic
P21/n
H
˚
a [A]
8.409(1)
14.179(2)
12.417(2)
91.52(1)
4
1.755
294(2)
C17H16BF6NO 54.2/(54.43) 4.6/(4.30) 3.7/(3.73)
C11H14BF6NO 43.8/(43.89) 4.6/(4.69) 4.4/(4.65)
C11H13BF7NO 41.4/(41.41) 4.3/(4.11) 4.6/(4.39)
C11H13BF7NO 40.8/(41.41) 4.3/(4.11) 4.5/(4.39)
C11H13BF7NO 41.1/(41.41) 4.0/(4.11) 4.5/(4.39)
C11H9BF11NO 33.4/(33.79) 2.3/(2.32) 3.2/(3.58)
C8H16BF6NO 35.0/(35.99) 5.2/(6.04) 5.6/(5.25)
C9H18BF6NO 36.9/(38.46) 6.0/(6.46) 5.5/(4.98)
˚
b [A]
˚
c [A]
β [°]
Z
4
D(calcd.) [g cmϪ3
T [K]
]
1.396
3g
3h
3i
297(2)
Diffractometer
Siemens AED 1
0.71073
Zr filter
2.3Ϫ25.0
h, ±k, ±l
3475
Siemens P3
1.54184
graphite
4.7Ϫ69.0
h, k, ±l
2879
˚
λ [A]
3j
C8H BF6NO3 32.4/(32.35) 4.8/(4.75) 4.1/(4.72)
14
Monochromation
θ range [°]
3k
3l
C9H BF6NO3 34.0/(34.76) 5.0/(5.19) 4.7/(4.50)
16
C7H BF6NO3 29.6/(29.71) 4.3/(4.27) 5.3/(4.95)
12
Quadrants
3m
C10H18BF6NO3 36.8/(36.95) 5.4/(5.58) 3.6/(4.31)
Reflections collected
Unique
1738
2750
Observed [I > 2σ(I)]
1028
2184
µ (λ) [mmϪ1
]
0.127
1.890
3d: M.p. 100°C. Ϫ IR: ν˜ ϭ 3663 cmϪ1 (OH), 3262 (NH), 1092
Crystal size [mm]
Transmission
Parameters
0.46 ϫ 0.24 ϫ 0.13 0.36 ϫ 0.34 ϫ 0.11
(CF).
0.971Ϫ0.984
232
0.606Ϫ0.825
243
3e: M.p. 104°C. Ϫ IR: ν˜ ϭ 3643 cmϪ1 (OH), 3270 (NH), 1086
RF (observed)
0.044
0.085
0.054
0.158
wRF2 (all data)
(CF).
Ϫ3
˚
Final diff. density [e A
]
0.15 to Ϫ0.16
0.53 to Ϫ0.40
3f: M.p. 102°C. Ϫ IR: ν˜ ϭ 3646 cmϪ1 (OH), 3272 (NH), 1086,
1025 (CF).
3g: M.p. 110°C. Ϫ IR: ν˜ ϭ 3661 cmϪ1 (OH), 3257 (NH), 1091
(CF).
again to Ϫ196°C and 2 g (11 ϫ 10Ϫ3 mol) of (F3C)2BNMe2 and ca
10 ml of pentane were condensed onto the diazomethane/pentane
mixture. The reaction vessel was gassed with dry nitrogen and al-
lowed to warm to room temperature under stirring. After 10 min
at 20°C, all volatile material was removed in vacuo. According to
NMR spectra the reaction was quantitative and the products were
analytically pure.
3h: M.p. 60°C. Ϫ IR: ν˜ ϭ 3671 cmϪ1 (OH), 3277 (NH), 1074,
1021 (CF).
3i: M.p. 92°C. Ϫ IR: ν˜ ϭ 3663 cmϪ1 (OH), 3269 (NH), 1094,
1074 (CF).
3j: M.p. 120°C. Ϫ IR: ν˜ ϭ 3164 cmϪ1 (NH), 1708 (CϭO), 1086
3-Fluorenyl-5,5,5-trifluoro-4-hydroxy-2-methyl-4-(trifluoromethyl)-
2-azonia-4-boratapentane (3b), 5,5,5-Trifluoro-4-hydroxy-2-methyl-
3-phenyl-4-(trifluoromethyl)-2-azonia-4-boratapentane (3c), 5,5,5-
Trifluoro-3-(4-fluorophenyl)-4-hydroxy-2-methyl-4-(trifluorometh-
yl)-2-azonia-4-boratapentane (3d), 5,5,5-Trifluoro-3-(3-fluorophen-
yl)-4-hydroxy-2-methyl-4-(trifluoromethyl)-2-azonia-4-boratapen-
tane (3e), 5,5,5-Trifluoro-3-(2-fluorophenyl)-4-hydroxy-2-methyl-4-
(trifluoromethyl)-2-azonia-4-boratapentane (3f), 5,5,5-Trifluoro-4-
hydroxy-2-methyl-3-(pentafluorophenyl)-4-(trifluoromethyl)-2-
azonia-4-boratapentane (3g), 5,5,5-Trifluoro-4-hydroxy-3-isopropyl-
2-methyl-4-(trifluoromethyl)-2-azonia-4-boratapentane (3h), 3-tert-
Butyl-5,5,5-trifluoro-4-hydroxy-2-methyl-4-(trifluoromethyl)-2-azo-
nia-4-boratapentane (3i), 5,5,5-Trifluoro-4-hydroxy-3-(methoxycar-
bonyl)-2,3-dimethyl-4-(trifluoromethyl)-2-azonia-4-boratapentane
(3j), 3-(Ethoxycarbonyl)-5,5,5-trifluoro-4-hydroxy-2,3-dimethyl-4-
(trifluoromethyl)-2-azonia-4-boratapentane (3k), 5,5,5-Trifluoro-4-
hydroxy-3-(methoxycarbonyl)-2-methyl-4-(trifluoromethyl)-2-
azonia-4-boratapentane (3l), 3-(tert-Butoxycarbonyl)-5,5,5-trifluoro-
4-hydroxy-2-methyl-4-(trifluoromethyl)-2-azonia-4-boratapentane
(3m). ؊ General Procedure: A solution (3 ϫ 10Ϫ3 mol) of the corre-
sponding azoniaboratacyclopropane in 10 ml of CH2Cl2 was stirred
with 20 ϫ 10Ϫ3 mol of H2O for 12 h at ambient temperature. After
removal of the solvent and the water in vacuo, pure 3bϪ3m were
obtained in quantitative yield.
(CF).
3k: M.p. 106°C. Ϫ IR: ν˜ ϭ 3161 cmϪ1 (NH), 1705 (CϭO), 1106,
1081 (CF).
3l: M.p. 124°C. Ϫ IR: ν˜ ϭ 3670 cmϪ1 (OH), 3082 (NH), 1716 (Cϭ
O), 1086 (CF).
3m: M.p. 140°C. Ϫ IR: ν˜ ϭ 3435 cmϪ1 (OH), 3254 (NH), 1688
(CϭO), 1088 (CF).
3,4,5,5,5-Pentafluoro-2-methyl-4-(trifluoromethyl)-2-azonia-4-
boratapent-2-ene (4): 1 g (6.5 ϫ 10Ϫ3 mol) of F3CSiF3 and 1.25 g
(6.5 ϫ 10Ϫ3 mol) of 1 were condensed at Ϫ196°C into an ampoule
fitted with a PTFE valve. The ampoule was slowly warmed to room
temperature and all volatile material was removed in vacuo. The
brown residue was crystallized from a CH2Cl2/CHCl3 mixture.
Yield 89%; decomp. ca. 40°C. Ϫ IR: ν˜ ϭ 1684 cmϪ1 (CϭN), 1112,
1081, 1051 (CF). Ϫ For elemental analyses see Table 4.
Acknowledgments
Financial support by the Fonds der Chemischen Industrie is grate-
fully acknowledged.
3b: M.p. 160°C. Ϫ IR: ν˜ ϭ 3636 cmϪ1 (OH), 3270 (NH), 1078
(CF).
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3c: M.p. 96°C. Ϫ IR: ν˜ ϭ 3638 cmϪ1 (OH), 3278 (NH), 1107,
1083 (CF).
260
Eur. J. Inorg. Chem. 1999, 255Ϫ261

New Azoniaboratacyclopropanes from (F3C)2BNMe2 and Diazomethane Derivatives
FULL PAPER
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Received September 21, 1998
[I98322]
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261