Reversible heterolytic Si-H bond activation by an intramolecular frustrated Lewis pair

Article abstract of DOI:10.5560/ZNB.2012-0181

The intramolecular frustrated P/B Lewis pair Mes₂PCH ₂CH₂B(C₆F₅)₂ (7) reacts readily with phenylsilane by heterolytic cleavage of the Si-H bond to give the zwitterion [Mes₂(PhH

Full text of DOI:10.5560/ZNB.2012-0181

Reversible Heterolytic Si–H Bond Activation by an Intramolecular
Frustrated Lewis Pair
Wanli Niea,b, Hendrik F. T. Klarea, Martin Oestreichc, Roland Fro¨hlicha, Gerald Kehra,
and Gerhard Erkera
a
Organisch-Chemisches Institut, Westfa¨lische Wilhelms-Universita¨t Mu¨nster, Corrensstraße 40,
48149 Mu¨nster, Germany
College of Chemistry & Materials Science, Northwest University, 229 North Taibai Road,
b
Xi’an 710069, Shaanxi Province, P. R. China
Institut fu¨r Chemie, Technische Universita¨t Berlin, Straße des 17. Juni 115, 10623 Berlin,
c
Germany
Reprint requests to Prof. Dr. Gerhard Erker. Fax: +49 251 83 36503. E-mail: erker@uni-muenster.de
Z. Naturforsch. 2012, 67b, 987 – 994 / DOI: 10.5560/ZNB.2012-0181
Received July 3, 2012
Dedicated to Professor Heribert Offermanns on the occasion of his 75th birthday
The intramolecular frustrated P/B Lewis pair Mes2PCH2CH2B(C6F5)2 (7) reacts read-
ily with phenylsilane by heterolytic cleavage of the Si–H bond to give the zwitterion
[Mes2(PhH2Si)P+CH2CH2B−H(C6F5)2] (8a), which has been fully characterized and its structure
confirmed by X-ray crystal structure analysis. Variable-temperature NMR studies revealed that the
reaction is reversible. Adduct 8a is the predominant species (ca. 98%) in CD2Cl2 solution at low
temperature (193 K), whereas at ambient temperature (299 K) it exists in a ca. 7 : 3 equilibrium with
unreacted 7 and PhSiH3. Diphenylsilane reacted similarly with the frustrated Lewis pair 7, however,
the equilibrium was found to favor the starting materials in the investigated temperature range.
Key words: Frustrated Lewis Pairs, Silanes, Si–H Bond Activation, Silylphosphonium Ions
Introduction
tivated former carbonyl carbon atom then closes the
catalytic cycle to give the respective hydrosilylation
Hydrosilylation is an important method of re- product.
ducing organic π-functionalities [1 – 3]. While many Related to the mechanism of the B(C6F5)3-mediated
transition metal complexes are known to catalyze Si–H bond activation, frustrated Lewis pairs (FLPs)
the Si–H addition to polar as well as nonpolar or- have been shown to activate dihydrogen heterolytically
ganic π-substrates, alternative protocols using main- under mild reaction conditions [32 – 36]. Therefore, it
group catalysts are limited [4]. A remarkable ex- was expected that FLPs would also cleave the Si–H
ception in this context is the strong Lewis acid bond of organic hydrosilanes. In a recent example, Al-
tris(pentafluorophenyl)borane, B(C6F5)3 [5 – 7] which carazo and co-workers reported the activation of the
serves as a potent catalyst [8 – 12], e. g., in the hydrosi- Si–H bonds in ethyldimethylsilane (EtMe2SiH) and
lylation of ketones and imines [12 – 27]. Piers et al. had diphenylsilane (Ph2SiH2) by the carbon(0)/borane-
shown that the role of B(C6F5)3 is not to activate the based FLP hexaphenylcarbodiphosphorane/B(C6F5)3
carbonyl function, as one might have thought [28, 29], (1) (Scheme 1, upper part) [37]. Klankermeyer et
but that it activates the silane by an abstractive coordi- al. extended the scope by showing that the inter-
nation of the hydridic Si–H bond to the Lewis acidic molecular frustrated P/B Lewis pair tBu3P/B(C6F5)3
boron atom [30]. Concomitant silyl transfer to the car- (3) is also capable of cleaving the Si–H bond in
bonyl group via an SN2-Si mechanism [31] followed dimethylphenylsilane (Me2PhSiH) under mild condi-
by hydride transfer from the borohydride to the ac- tions [38] (Scheme 1, lower part). The resulting zwit-
c
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988
W. Nie et al. · Reversible Heterolytic Si–H Bond Activation
Scheme 1. Heterolytic Si–H bond activation by intermolecular frustrated Lewis pairs.
terion 4 was characterized by X-ray diffraction. These in pentane (5 → 7, Scheme 2). During stirring for
results prompted us to describe the results of our study 15 min, the hydroboration reaction went to comple-
of the reaction of the intramolecular frustrated P/B tion, and a yellow solution of FLP 7 was obtained.
Lewis pair 7 with silanes. Herein, we describe the re- To this solution a 10 fold excess of phenylsilane was
versible heterolytic Si–H bond cleavage of phenylsi-
HB(C6F5)2
lane (PhSiH3) and of diphenylsilane (Ph2SiH2) by FLP
7 and report the solid-state structure of the resulting
silylphosphonium hydridoborate 8a.
6
Mes2P
Mes2P
B(C6F5)2
pentane
25 °C
5
7
Results and Discussion
H
PhSiH3
Synthesis and molecular structure of the
silylphosphonium hydridoborate 8a
B(C6F5)2
Mes2P
PhSiH2
To test the potential of the ethylene-bridged frus-
trated P/B pair 7 [39 – 41] in the Si–H bond activa-
tion of phenylsilane, FLP 7 was generated in situ by
treatment of dimesitylvinylphosphane (5) with Piers’
borane HB(C6F5)2(6) [42, 43] at ambient temperature
8a
Scheme 2. Synthesis of intramolecular FLP 7 and het-
erolytic Si–H bond cleavage of Ph3SiH (Mes = 2,4,6-
trimethylphenyl).
Fig. 1. Molecular structure of the zwitterion
˚
8a. Selected bond lengths (A), angles (deg),
and dihedral angles (deg): P1–Si1 2.309(1),
P1–C1 1.829(2), C1–C2 1.538(2), C2–B1
1.635(2); C1–P1–Si1 103.94(6), C11–P1–Si1
122.76(6), C21–P1–Si1 99.41(5), C41–B1–
C51 108.6(1), P1–Si1–C31 102.61(6), C31–
Si1–H1 112.2(9), C31–Si1–H2 113.8(8), H1–
Si1–H2 113.9(12); P1–C1–C2–B1 176.1(1).
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W. Nie et al. · Reversible Heterolytic Si–H Bond Activation
989
added dropwise, whereupon the reaction mixture im- der these conditions, resulting in the observed dou-
mediately turned colorless and a colorless precipitate blet of doublets pattern with 29Si satellites (1JSiH
≈
2
formed, which was identified as the product of the 240 Hz) and JPH coupling constants of 20.1 and
heterolytic cleavage of PhSiH3 by FLP 7 (7 → 8a, 22.3 Hz, respectively (Fig. 2). Similarly, the hydro-
Scheme 2). The highly hygroscopic silylphosphonium gen atoms at the –CH2–CH2– linkage are pair-
hydridoborate 8a [44 – 63] was isolated as a color- wise diastereotopic as are the C6F5 substituents at
less solid in 81% yield and characterized by elemental the boron atom. The 11B NMR spectrum of 8a
analysis, spectroscopic methods, and X-ray diffraction. shows a signal at δ = −20 ppm, which is in the
Single crystals were obtained from a toluene solution typical [HBR(C6F5)2]− borate range, and the 31P
by slow evaporation of the solvent at ambient temper- NMR spectrum shows a resonance at δ = −9.9 ppm.
ature.
The 29Si NMR signal occurs at δ = −30.0 ppm,
The X-ray crystal structure analysis of zwitterion significantly downfield shifted compared to PhSiH3
8a (Fig. 1) confirmed that the reaction of FLP 7 with (δ = −60.2 ppm, C6D6, 299 K), with a coupling con-
PhSiH3 had resulted in heterolytic splitting of one Si– stant of 1JPSi = 59.5 Hz.
H bond of the silane with formation of a silylphos-
Warming the solution of 8a to ambient temperature
phonium cation intramolecularly connected to a hy- allows for free rotation around the P–C(mesityl) bonds.
dridoborate anion. The bulky [Mes2(PhH2Si)P]+ and Most significantly, this results in the observation of
[HB(C6F5)2]− groups are oriented in an antiperipla- a singlet with 29Si satellites of the P–SiH2 unit and
nar conformation at the bridging –CH2–CH2– unit a single set of signals of the pair of mesityl groups at
1
(θP1−C1−C2−B1 = 176.1(1)◦).
the phosphorus atom in the H NMR spectrum. Con-
currently, only three 19F NMR resonances of the now
symmetry-equivalent C6F5 groups at the boron atom
are observed.
NMR solution studies
The NMR spectra of compound 8a in CD2Cl2 so-
The heterolytic Si–H bond cleavage is reversible,
lution are strongly temperature dependent. At suf- and the equilibrium 7 + PhSiH3 ꢀ 8a shifts toward the
ficiently low temperature (193 K) we found the ro- side of the starting materials with increasing tempera-
tation around the P–C(mesityl) bonds frozen on ture. While we have monitored a ca. 98% composition
the NMR time scale. Consequently, a total of six of addition product 8a in CD2Cl2 solution at 193 K, the
mesityl CH3 singlets and four aromatic m-mesityl pro- ratio of 8a to unreacted FLP 7 and PhSiH3 changed to
ton resonances are detected in the 1H NMR spec- approximately 7 : 3 at 299 K (Scheme 3).
trum of 8a at 193 K (Fig. 2). The hydrogen atoms
We next treated the in situ generated FLP 7 with a 10
of the P-bound SiH2 unit are diastereotopic un- fold excess of diphenylsilane. In this case, the reaction
Fig. 2. 1H NMR spectrum
(500 MHz) of compound
8a in CD2Cl2 (*) at
193 K (p = pentane, cp =
cyclopentane).
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990
W. Nie et al. · Reversible Heterolytic Si–H Bond Activation
H
B(C6F5)2
Mes2P
+
PhSiH3
Mes2P
B(C6F5)2
CD2Cl2
PhSiH2
7
8a
:
:
193 K ca.
299 K ca. 30
2
98
70
Scheme 3. Temperature-dependent equilibrium between FLP 7, PhSiH3 and the zwitterionic adduct 8a in CD2Cl2 solution.
H
B(C6F5)2
+
Ph2SiH2
Mes2P
Mes2P
B(C6F5)2
CD2Cl2
Ph2SiH
7
8b
:
:
193 K
299 K
ca. 60
ca. 89
40
11
Scheme 4. Temperature-dependent equilibrium between FLP 7, Ph2SiH2 and the zwitterionic adduct 8b in CD2Cl2 solution.
mixture in pentane remained yellow at room tempera- m-mesityl singlets. Compound 8b is characterized at
ture, but turned colorless with formation of a colorless 193 K by a 31P NMR signal at δ = −8.6 ppm, a 11B
precipitate upon cooling to −35 ◦C. After additional NMR signal at δ = −20 ppm, and a 29Si NMR res-
2 h at this temperature, we isolated silylphosphonium onance at δ = −15.2 ppm (1JPSi = 48.5 Hz). Warm-
hydridoborate 8b as an amorphous colorless solid in ing the sample to 299 K results in a further shift of
83% yield. The product was characterized by spec- the 7 + Ph2SiH2 ꢀ 8b equilibrium toward the starting
troscopy and elemental analysis.
materials.
A solution of the salt 8b in CD2Cl2 showed a low-
1
temperature H NMR spectrum at 193 K that already Conclusion
contained a 3 : 2 mixture of the starting materials
and the zwitterionic product 8b (Scheme 4). The lat-
Many FLPs activate dihydrogen under mild condi-
ter features the typical 1H NMR resonances of the tions [64, 65]. However, the heterolytic FLP splitting
separated mesityl methyl groups and four aromatic of dihydrogen is rarely reversible. The systems 9 [66]
F
F
F
F
F
F
F
H2
H
25 °C
Mes2P
Ph2P
Mes2P
H
B(C6F5)2
B(C6F5)2
150 °C
– H2
F
9
10
PPh2
H
H2
25 °C
PPh2
Ph2P
[HB(C6F5)3]–
/
B(C6F5)3
60 °C
– H2
11
12
Scheme 5. Reversible H2 activation by FLPs 9 and 11/B(C6F5)3.
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W. Nie et al. · Reversible Heterolytic Si–H Bond Activation
991
and 11 [67] are notable exceptions (Scheme 5), and 0.10 mmol, 1.00 equiv.) were suspended in pentane (4 mL),
and the reaction mixture was stirred for 15 min at ambient
temperature. To the resulting yellow solution phenylsilane
(123 µL, 108 mg, 1.00 mmol, 10.0 equiv.) was added drop-
wise, whereupon the reaction mixture turned colorless, and
a colorless solid precipitated. After an additional 15 min at
ambient temperature the precipitate was isolated by filtration,
washed with pentane (3 × 1 mL) and dried briefly in vacuo to
yield 8a as a colorless powder (61 mg, 81%). Single crystals
suitable for X-ray diffraction were obtained from a toluene
solution of 8a by slow evaporation of the solvent at ambi-
ent temperature; m. p. 144 ◦C (decomposition at 150 ◦C). –
1H NMR (500 MHz, CD2Cl2, 193 K): δ = 7.47 (m, 1 H, p-
there are a few other reversible H2-activating FLP sys-
tems known [68 – 72]. Often silanes are more reac-
tive in hydrosilylation chemistry than dihydrogen is in
the related catalytic hydrogenation of polar substrates.
Therefore, our disclosure of a particularly mild and
reversible Si–H bond cleavage of the silanes PhSiH3
and Ph2SiH2 by our reactive intramolecular frustrated
P/B Lewis pair Mes2PCH2CH2B(C6F5)2 (7) is quite
remarkable. The reversibility of Si–H bond breaking
needs to be taken into account when planning FLP-
catalyzed hydrosilylation reactions and can become
a favorable feature when FLP-induced transformations
of silanes themselves are considered [15, 31, 38]. In
this context, fundamental understanding of the Si–H
bond activation mode by FLPs will provide an experi-
mental basis for useful developments.
4
Ph), 7.10 (m, 2H, m-Ph), 7.06 (dm, JPH = 4.0 Hz, 1H, m-
4
MesA), 6.88 (dm, JPH = 2.5 Hz, 1H, m-MesB), 6.81 (dm,
4JPH = 2.9 Hz, 1H, m’-MesA), 6.66 (br, 2H, o-Ph), 6.65 (m,
1
2
1H, m’-MesB), 5.47 (dd, JSiH = 242.5 Hz, JPH = 20.1 Hz,
2JHH = 9.2 Hz, 1H, SiH2), 5.06 (ddd, JSiH = 236.9 Hz,
1
2JPH = 22.3 Hz, JHH = 9.2 Hz, JHH = 1.5 Hz, 1H, SiH2),
2.76 (s, 3H, o-CHM3 esA), 2.61, 2.20 (each m, each 1H, PCH2),
2.26 (s, 3H, p-CH3MesA), 2.23 (s, 3H, p-CHM3 esB), 1.84 (s,
3H, o-CHM3 esB), 1.74 (s, 3H, o’-CHM3 esA), 1.35, 0.71 (each
br, each 1H, BCH2), 1.30 (s, 3H, o’-CHM3 esB), n. o. (BH). –
13C{1H} NMR (126 MHz, CD2Cl2, 193 K): δ = 147.2 (dm,
1JFC ≈ 234 Hz, m-C6F5), 143.3 (d, 4JPC = 2.7 Hz, p-MesA),
2
4
Experimental Section
All reactions were carried out in flame-dried glassware
under an argon atmosphere using a glove box or stan-
dard Schlenk techniques. Solvents were dried using a sol-
vent purification system [73]. Deuterated dichloromethane
used for NMR spectroscopy was dried over CaH2, vac-
uum transferred to a dry Schlenk flask and subsequently de-
gassed by freeze-pump-thaw technique. Dimesitylvinylphos-
phane (5) [39 – 41] and Piers’ borane HB(C6F5)2 (6) [42, 43]
were prepared according to literature procedures. Commer-
cially available silanes PhSiH3 and Ph2SiH2 were dried
over CaH2 and distilled prior to use. NMR spectra were
recorded on a Varian Inova 500 MHz and a Unity Plus
600 MHz spectrometer. 1H NMR and 13C NMR chemical
shifts are reported in parts per million (ppm) and are ref-
erenced to the residual solvent signal as the internal stan-
dard (CD2Cl2: δ = 5.32 ppm for 1H and δ = 53.8 ppm for
143.0 (d, JPC = 2.7 Hz, p-MesB), 142.9 (d, JPC = 7.9 Hz,
4
2
o’-MesB), 141.6 (d, JPC = 11.1 Hz, o-MesA), 141.1 (d,
2
2JPC = 6.4 Hz, o’-MesA), 140.7 (d, JPC = 9.7 Hz, o-
2
MesB), 136.9 (dm, JFC ≈ 243 Hz, p-C6F5), 136.1 (o-
1
1
Ph), 135.7 (dm, JFC ≈ 247 Hz, o-C6F5), 132.4 (p-Ph),
131.4 (d, JPC = 9.8 Hz, m-MesB), 131.4 (d, JPC = 9.8 Hz,
3
3
3
m’-MesB), 131.3 (d, JPC = 9.3 Hz, m’-MesA), 130.1
(d, JPC = 11.3 Hz, m-MesA), 128.0 (m-Ph), 125.4 (br
3
2
m, i-C6F5), 122.1 (d, JPC = 9.5 Hz, i-Ph), 117.9 (d,
1JPC = 66.0 Hz, i-MesA), 115.9 (d, 1JPC = 49.5 Hz, i-MesB),
27.4 (d, JPC = 22.0 Hz, PCH2), 24.9 (d, JPC = 5.0 Hz,
1
3
o-CHM3 esA), 23.3 (d, JPC = 6.2 Hz, o-CHM3 esB), 22.5 (o’-
3
13C). A unified scale was used for reporting the NMR CHM3 esB), 21.2 (d, JPC = 5.7 Hz, o’-CHM3 esA), 20.62 (p-
chemical shifts of all other nuclei relative to the 1H CH3MesA), 20.56 (p-CH3MesB), 15.8 (br, BCH2). – 31P{1H}
NMR resonance of tetramethylsilane as recommended by NMR (202 MHz, CD2Cl2, 193 K): δ = −9.9 (ν1/2 ≈ 30 Hz).
the IUPAC [74]. Elemental analyses were performed using
3
–
19F NMR (470 MHz, CD2Cl2, 193 K): δ = −133.5 (m,
2F, o-C6FA5 ), −133.9 (m, 2F, o-C6FB5 ), −162.7 (m, 1F,
a Foss-Heraeus CHNO-Rapid analyzer. Electrospray ioniza-
tion (ESI) mass spectra were measured on a Bruker Mi-
croTof instrument. Melting points (decomposition temper-
atures) were determined using a DSC 2010 apparatus by
TA Instruments. IR spectra were recorded on a Varian 3100
FT-IR (Excalibur Series) spectrophotometer using KBr pel-
lets.
p−C6FA5 ), −163.2 (m, 1F, p−C6FB5 ), −165.4 (m, 2F, m-
C6FA5 ), −166.0 (m, 2F, m-C6FB5 ), [∆δ
F
m,p
= 2.7, 2.8].
19
–
11B{1H} NMR (160 MHz, CD2Cl2, 193 K): δ = −20
(ν1/2 ≈ 360 Hz). – 29Si(dept) NMR (99 MHz, CD2Cl2,
1
193 K): δ = −30.0 (d, JPSi = 59.5 Hz).
– IR (KBr):
ν = 3440 (br), 3070 (w), 2972 (m), 2933 (m), 2848 (w), 2323
(s), 2273 (w), 2154 (s), 1637 (s), 1605 (s), 1559 (m), 1509 (s),
1457 (s), 1391 (m), 1379 (m), 1275 (s), 1259 (s), 1180 (s),
1135 (s), 1124 (s), 1094 (s), 1082 (s), 1029 (m), 973 (s), 946
(s), 925 (s), 873 (s), 857 (s), 808 (w), 768 (m), 749 (m), 739
Preparation of 8a
Dimesitylvinylphosphane (5) (29.7 mg, 0.10 mmol, 1.00
equiv.) and bis(pentafluorophenyl)borane (6) (34.6 mg,
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W. Nie et al. · Reversible Heterolytic Si–H Bond Activation
(s), 723 (w), 699 (s), 643 (s), 609 (m), 604 (m), 569 (w), 557 193 K): δ = −20 (ν1/2 ≈ 350 Hz). – 29Si(dept) NMR
(m), 467 (w), 452 (m), 411 (m) cm−1. – HRMS ((+)-ESI):
(119 MHz, CD2Cl2, 193 K): δ = −15.2 (d, 1JPSi = 48.5 Hz).
m/z = 789.1943 (calcd. 789.1949 for C38H34BF10PSiONa,
[M+ONa]+). – C38H34BF10PSi (750.53): calcd. C 60.81, H
4.57; found C 61.06, H 4.61.
– IR (KBr): ν = 3432 (br), 3070 (w), 3049 (w), 3001 (w),
2975 (w), 2925 (m), 2853 (w), 2363 (m), 2345 (m), 2138
(m), 1654 (w), 1637 (m), 1605 (m), 1560 (w), 1541 (w),
1508 (s), 1458 (s), 1430 (m), 1379 (w), 1272 (m), 1180 (m),
1119 (m), 1082 (s), 1027 (w), 972 (s), 855 (m), 842 (m), 824
(m), 769 (w), 736 (m), 700 (m), 642 (w), 608 (w), 555 (w),
492 (w), 444 (w) cm−1. – HRMS ((+)-ESI): m/z = 865.2254
(calcd. 865.2263 for C44H38BF10PSiONa, [M+ONa]+). –
C44H38BF10PSi (826.63): calcd. C 63.93, H 4.63; found C
64.42, H 5.13.
Preparation of 8b
Dimesitylvinylphosphane (5) (29.7 mg, 0.10 mmol, 1.00
equiv.) and bis(pentafluorophenyl)borane (6) (34.6 mg,
0.10 mmol, 1.00 equiv.) were suspended in pentane (4 mL),
and the reaction mixture was stirred for 15 min at ambient
temperature. To the resulting yellow solution, diphenylsi-
lane (186 µL, 184 mg, 1.00 mmol, 10.0 equiv.) was added.
Upon cooling to −35 ◦C the reaction mixture turned color-
less and a colorless solid precipitated. After an additional
2 h at this temperature, the precipitate was isolated by fil-
tration, washed with cold pentane (3 × 1 mL) and dried
briefly in vacuo to yield 8b as a colorless powder (69 mg,
83%); m. p. 81 ◦C. – 1H NMR (600 MHz, CD2Cl2, 193 K):
δ = 7.52 (br, 1H, p-PhB), 7.51 (br, 1H, p-PhA), 7.48 (br
m, 2H, o-PhB), 7.37 (br, 2H, m-PhB)1, 7.24 (br, 4H, o,m-
X-Ray crystal structure determination
The data set for the X-ray crystal structure analysis
of compound 8a was collected with a Nonius KappaCCD
diffractometer. Programs used were: COLLECT for data col-
lection [75], DENZO-SMN for data reduction [76], DENZO
for absorption correction [77], SHELXS-97 for structure so-
lution [78, 79], SHELXL-97 for structure refinement [80,
81], and SCHAKAL for graphical visualization [82].
4
PhA), 6.94 (dm, JPH = 4.0 Hz, 1H, m-MesA), 6.87 (dm,
4
4JPH = 2.4 Hz, 1H, m-MesB), 6.81 (dm, JPH = 2.4 Hz, 1H,
X-Ray crystal structure analysis of 8a
m’-MesB), 6.73 (dm, 4JPH = 2.6 Hz, 1H, m’-MesA), 5.92 (d,
2
1JSiH = 235.8 Hz, JPH = 25.4 Hz, 1H, SiH), 2.71 (s, 3H,
Formula C38H34BF10PSi, Mr = 750.52, colorless crys-
tal, 0.30 × 0.25 × 0.10 mm3, triclinic, space group P1
o-CHM3 esA), 2.66, 2.36 (each m, each 1H, PCH2)1,2, 2.30
(s, 3H, p-CH3MesB), 2.19 (s, 3H, p-CHM3 esA), 1.65 (s, 3H,
o’-CH3MesA), 1.45, 0.75 (each br, each 1H, BCH2)2, 1.42
(s, 3H, o’-CH3MesB), 1.27 (s, 3H, o-CHM3 esB), n.o. (BH),
[1 from the ghmbc experiment; 2 from the ghsqc experiment].
¯
˚
(no. 2), a = 10.4968(3), b = 13.4561(5), c = 13.6874(5) A,
α = 94.254(2)◦, β = 109.081(2)◦, γ = 99.584(2)◦, V =
3
1784.33(11) A , Z = 2, Dcalcd = 1.40 g cm−3
,
µ =
˚
1.7 mm−1
, F(000) = 772 e, empirical absorption cor-
13C{1H} NMR (126 MHz, CD2Cl2, 193 K): δ = 143.3
˚
rection (0.627 ≤ T ≤ 0.847), λ = 1.54178 A, T = 223 K,
–
(d, JPC = 2.9 Hz, p-MesB), 142.8 (d, JPC = 7.3 Hz, o’-
MesB), 142.8 (d, 4JPC = 2.5 Hz, p-MesA), 141.7 (o-MesB)1,
141.6 (d, 2JPC = 11.0 Hz, o-MesA), 140.8 (d, 2JPC = 6.2 Hz,
o’-MesA), 136.3 (o-PhB), 135.8 (o-PhA), 132.3 (p-PhA),
4
2
ω and ϕ scans, 25935 reflections collected ( ± h, ± k, ± l),
[(sinθ)/λ]max = 0.60 A−1, 6133 independent (Rint = 0.043)
˚
and 5522 observed reflections [I > 2σ(I)], 475 refined
parameters, R = 0.037, wR2 = 0.103, max. (min.) residual
−3
132.2 (p-PhB), 132.0 (d, JPC = 9.6 Hz, m’-MesB), 131.5
3
˚
electron density 0.31 (−0.21) e A
.
(d, JPC = 9.4 Hz, m-MesB), 131.1 (m’-MesA), 129.9 (d,
3
CCDC 888686 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data request/cif.
3JPC = 11.5 Hz, m-MesA), 128.4 (m-PhB), 128.2 (m-PhA),
125.9 (d, JPC = 8.2 Hz, i-PhB), 125.6 (d, JPC = 14.3 Hz,
2
2
i-PhA), 119.8 (d, JPC = 63.8 Hz, i-MesA), 116.0 (d,
1
1JPC = 48.2 Hz, i-MesB), 28.6 (1JPC = 22.5 Hz, PCH2)1,2
,
25.6 (d, JPC = 5.2 Hz, o-CHM3 esA), 25.3 (d, JPC = 6.3 Hz,
3
3
Supporting information
o-CHM3 esB), 23.0 (d, JPC = 1.4 Hz, o’-CHM3 esB), 21.4 (d,
3
Additional experimental and spectroscopic details, in
particular pictures of the most prominent NMR spec-
tra, are given as Supporting Information available online
(DOI: 10.5560/ZNB.2012-0181).
3JPC = 5.4 Hz, o’-CH3MesA), 20.7 (p-CHM3 esB), 20.6 (p-
CHM3 esA), 15.6 (br, BCH2)2, [1 from the ghmbc exper-
2
iment;
–
from the ghsqc experiment; C6F5 not listed].
31P{1H} NMR (243 MHz, CD2Cl2, 193 K): δ = −8.6
(ν1/2 ≈ 30 Hz). – 19F NMR (564 MHz, CD2Cl2, 193 K):
δ = −133.6 (m, 2F, o-C6FA5 ), −134.0 (m, 2F, o-C6FB5 ),
−162.8 (m, 1F, p−C6FA5 ), −163.3 (m, 1F, p−C6FB5 ),
Acknowledgement
Financial support from the Deutsche Forschungsgemein-
−165.5 (m, 2F, m-C6F5A), −166.0 (m, 2F, m-C6FB5 ), schaft and the Alexander von Humboldt Foundation (fellow-
19
[∆δ
F
m,p
= 2.7, 2.7]. – 11B{1H} NMR (192 MHz, CD2Cl2, ship to W. N.) is gratefully acknowledged.
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