Electronic control of frustrated lewis pair behavior: Chemistry of a geminal alkylidene-bridged per-pentafluorophenylated P/B pair

Article abstract of DOI:10.1021/om200569k

"Markovnikov" hydroboration of bis(pentafluorophenyl)(propynyl) phosphine (12) with Piers' borane [HB(C₆F₅)₂] gives the frustrated Lewis pair (FLP) (C₆F₅) ₂P-(μ-C=CHCH₃)-B(C

Full text of DOI:10.1021/om200569k

ARTICLE
pubs.acs.org/Organometallics
Electronic Control of Frustrated Lewis Pair Behavior: Chemistry of a
Geminal Alkylidene-Bridged Per-pentafluorophenylated P/B Pair
Christoph Rosorius, Gerald Kehr, Roland Fr€ohlich, Stefan Grimme, and Gerhard Erker*
Organisch-Chemisches Institut der Universit€at M€unster, Corrensstrasse 40, 48149 M€unster, Germany
S Supporting Information
b
ABSTRACT: “Markovnikov” hydroboration of bis(pen-
tafluorophenyl)(propynyl)phosphine (12) with Piers' bor-
ane [HB(C6F5)2] gives the frustrated Lewis pair (FLP)
(C6F5)2PÀ(μ-CdCHCH3)ÀB(C6F5)2 (13) as the major pro-
duct in good yield. FLP 13 adds cleanly to 1-alkynes to form the
five-membered heterocyclic products 15 (two examples). It adds to the CdN double bond of arylisocyanates to yield the five-
membered heterocycles 16 (two examples), and it regioselectively adds to aldehydes to yield the BÀO/PÀC bonded heterocycles
17 (from benzaldehyde) and 18 (from trans-cinnamic aldehyde), respectively. Dynamic 19F NMR spectroscopy indicates a rapidly
occurring reversible PÀC bond dissociation process taking place in 17 and 18 [17: ΔGqdiss(328 K) = 14.7 ( 0.3 kcal/mol; 18:
ΔGqdiss(368 K) = 11.9 ( 0.2 kcal/mol]. The products 15a, 15b, 17, and 18 were characterized by X-ray diffraction. This chemistry
indicates that frustrated Lewis pair behavior can be induced electronically by the choice of suitable substituents at the Lewis base.
Chart 1
’ INTRODUCTION
Lewis acids and bases usually quench each other by strong
adduct formation when brought together in solution.1 The
adducts may have interesting properties in themselves,2 but they
usually do not exhibit any of the typical chemical features of their
individual components. The adduct formation may be hindered
or even be made impossible by introducing sterically bulky
substituents at either of the components.3 The resulting coex-
isting Lewis acid/Lewis base pairs can show the individual pro-
perties of their respective antagonists,4 but, more importantly,
they may exhibit cooperative behavior toward a variety of sub-
strates. With the introduction of RÀB(C6F5)2-type Lewis acids
this rather new field of frustrated Lewis pair chemistry5 has taken
up an enormous development.6,7 Frustrated Lewis pairs (FLPs)
have shown to activate dihydrogen and to add to alkenes or
alkynes and even to CO2 or N2O.8,9
With the intramolecular ethylene-bridged P/B system 1 we
have early on contributed an intramolecular FLP whose char-
acteristic features were to a large extent determined by sterics.10
It is a weakly interacting Lewis pair.11 Compound 1 currently is
one of the most active metal-free activators of dihydrogen. It has
served as an active hydrogenation catalyst toward selective
unsaturated substrates.12 It adds to carbon dioxide8 and to a
variety of carbonyl compounds.13 It competitively reacts with
terminal alkynes by either proton abstraction or addition (see
Chart 1).13b,14
The increasing number of reports about the chemistry of
sterically determined FLPs posed the question whether it would
be possible to design and generate frustrated Lewis pairs whose
properties would be governed by electronic effects rather than
the ubiquitous steric control. We found a first successful leading
answer in the following system: hydroboration of the very electron
poor alkenylphosphine 7 with Piers' borane [HB(C6F5)2]15 took
an unusual course.16 We isolated the “Markovnikov” 1,2 addition
product (8) featuring a geminal pair of a strongly electro-
philic ÀB(C6F5)2 group and a weakly basic ÀP(C6F5)2 moiety
(Chart 2). The system 8 so far was not active in the H2 activation,
but it showed a number of typical FLP reactions with a variety of
unsaturated organic substrates. We have now found a second
example of such an electronically controlled frustrated Lewis pair
system that shows that this new approach to generate Lewis acid/
Lewis base pairs that feature typical frustrated Lewis pair behavior
might be rather general. This recent development in FLP
Received: June 30, 2011
Published: July 14, 2011
r
2011 American Chemical Society
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chemistry will be illustrated in this article with this new example
of an electronically controlled P/B Lewis pair.
11B NMR resonance at δ 60, which is typical for tricoordinated
boron in a RB(C6F5)2-type system. Consequently, we observe a
set of the ÀB(C6F5)2-derived 19F NMR signals at δ À128.9 (o),
À146.2 (p), and À160.2 (m) with the typical large Δδm,p
separation18 of 14.0 ppm. The corresponding 19F NMR signals
of the P(C6F5)2 moiety occur at δ19F À128.1 (o), À148.0 (p),
and À159.7, respectively.
’ RESULTS AND DISCUSSION
Generation of the New Frustrated Lewis Pair. For generat-
ing the new FLP (13) we first reacted bis(pentafluorophenyl)
chlorophosphine (11)17 with propynyllithiumto yield thereagent
12 (Scheme 1). Its treatment with Piers' borane [HB(C6F5)2]15
at room temperature gave a ca. 7:1 mixture of the two regioiso-
meric products 13 and 14 isolated in a combined yield of close to
90%. The major product is the “Markovnikov” addition product
We used this mixture, containing the geminal FLP 13 as the
dominating major product, for the addition reactions that are
subsequently described in this article. The presence of the minor
product (14) did not pose any problem. It was removed from the
respective addition products during the typical workup proce-
dures of the reaction mixtures.
1
13. It features a very typical set of H NMR spectral data of
the dCHCH3 moiety [methyl: doublet at δ 1.58 (3JH,H = 6.9 Hz)
and doublet of quartets with 3JP,H ≈24 Hz at δ6.73(seeFigure1)].
The minor product (14) in contrast features a broad methyl signal
at δ 2.00 and a broad dCH resonance at δ 7.50. The major
product (13) features a 31P NMR signal at δ À62.8 and a broad
Reactions with 1-Alkynes. We first reacted the FLP 13 with
1-pentyne. The reaction was carried out in pentane solution at
ambient temperature. After 12 h stirring a white precipitate
had formed, which was collected by filtration and was shown
to be the pure 1-pentyne addition product (15a) to the FLP
13. Product 15a was isolated in a yield of 62%. It was
characterized by C, H elemental analysis, by spectroscopy,
and by X-ray crystal structure analysis (single crystals were
obtained from a solution in d6-benzene by slow evaporation of
the solvent).
Chart 2
The structure determination of 15a has confirmed that the
major hydroboration product (see Scheme 1) was indeed the
“Markovnikov” addition product 13. This part of the structure of
15a features a trisubstituated olefin with a Z-orientation of the
methyl group at C2 and phosphorus at C3. Boron is found
geminal to phosphorus. The P/B pair has been 1,2-added to the
alkyne with a “Markovnikov”-like orientation. The central five-
membered heterocycle is close to planar with a sum of endocyclic
bond angles of 539.2° (molecule A) [crystallographically inde-
pendent molecule B: 539.4°]. The BÀC(sp2) bond lengths
around B1 are in a range between 1.599(8) and 1.660(8) Å
(see Table 1). At phosphorus the pair of endocyclic P1ÀC(sp2)
bonds is slightly shorter than the adjacent P1ÀC6F5 σ-bonds
(see Table 1).
Scheme 1
The product 15a features a 31P NMR resonance at δ 0.9, which
3
shows a complex pattern due to the partially relaxed JP,B
coupling. The 11B NMR signal appears as a doublet at δ À9.8
(3JP,B ≈ 40 Hz), a typical chemical shift of tetracoordinated
1
boron (19F NMR: Δδp,m [of B(C6F5)2] = 5.1). The H NMR
Figure 1. 1H NMR spectrum (500 MHz, C6D6, 298 K) of the 13/14 mixture (7:1) obtained by HB(C6F5)2 hydroboration of (C6F5)2PÀCtCÀCH3.
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Table 1. Selected Structural Data of the FLP/Alkyne Adducts
15a and 15ba
15ab
15b
C2ÀC3
1.327(7)
1.774(5)
1.792(5)
1.821(5)
1.824(5)
1.314(7)
1.651(7)
1.599(8)
1.651(8)
1.660(8)
106.5(3)
99.9(2)
1.329(7)
1.766(5)
1.789(5)
1.819(5)
1.821(5)
1.322(8)
1.642(7)
1.611(8)
1.646(7)
1.652(8)
107.1(3)
100.0(3)
102.8(4)
107.6(4)
121.9(5)
1.330(4)
1.785(3)
1.785(3)
1.813(3)
1.817(3)
1.341(4)
1.657(4)
1.617(4)
1.631(5)
1.653(4)
104.6(2)
98.5(1)
P1ÀC3
P1ÀC4
P1ÀC11
P1ÀC21
C4ÀC5
B1ÀC3
B1ÀC5
B1ÀC31
B1ÀC41
P1ÀC3ÀB1
C3ÀP1ÀC4
C3ÀB1ÀC5
P1ÀC4ÀC5
B1ÀC5ÀC4
Figure 3. Molecular structure of compound 15b.
Scheme 3
103.0(4)
107.5(4)
122.3(4)
102.0(2)
108.5(2)
119.6(3)
a Bond length in Å, angles in deg. b Two independent molecules in the
unit cell.
close to planar five-membered P/B-containing heterocycle (the
sum of internal bonding angles is 533.2°) are similar to those of
its congener 15a.
Compound 15b features NMR resonances at δ 11B: À10.1
(d, 3JP,B ≈ 39 Hz) and δ 31P: À2.8 (partially relaxed 1:1:1:1 q,
3JP,B ≈ 39 Hz). It shows 1H NMR signals of the olefinic 5-H at δ
8.73 (with 3JP,H = 57.3 Hz) and 2-H at δ 6.86 (with 3JP,H = 63.6
1
Hz). Its adjacent methyl group gives rise to a H NMR dd at
δ 1.93 (with 3JH,H = 7.1 Hz and 4JP,H = 3.5 Hz).
Reactions with Carbonyl Compounds. Frustrated Lewis
pairs react with a variety of carbonyl compounds. Even less
reactive FLPs are known to add to very reactive organic carbonyl
substrates, such as alkyl- or arylisocyanates.13,19 Therefore, we
first treated the new electronically modified FLP 13 with
phenylisocyanate and p-tolylisocyanate, respectively. The reac-
tion of 13 with PhÀNdCdO in pentane at room temperature
produced compound 16a as a white solid, which was isolated in
65% yield. The product showed a 13C NMR carbonyl carbon
Figure 2. Molecular structure of the heterocycle 15a.
Scheme 2
1
resonance at δ 159.1 (with a JP,C coupling of ca. 119 Hz). It
exhibits a corresponding intensive ν(CdO) stretching band in
the IR spectrum at 1699 cmÀ1. The system features NMR signals
3
of the heteroatoms at δ 31P: À30.1 (with a JP,H coupling
constant of ca. 61 Hz to the olefinic 2-H proton of the backbone)
and δ 11B: À4.7. These data indicate that we have encountered a
rare example of a FLP addition to the CdN moiety of the
isocyanate reagent and not to the mostly preferred OdC group
of the heterocumulene, analogously to that observed by us upon
treatment of the related geminal FLP 8 with an arylisocyanate.16,20
The reaction of 13 with p-tolylisocyanate took a similar course to
yield 16b [65% isolated; δ 11B: À4.5; δ 31P: À32.0; δ 13C
(CdO): 158.7 (d, 1JP,C = 115.4 Hz); ν(CdO) = 1699 cmÀ1].
We eventually reacted the FLP 13 with aldehydes. This
revealed the same interesting new features in the addition
reaction of frustrated Lewis pairs. Treatment of 13 with benzal-
dehyde at room temperature in pentane resulted in a precipitate
olefin 2-H resonance occurs at δ 7.02 with a typical large 3JP,H
62.3 Hz, while the corresponding 5-H signal is at δ 8.27 (3JP,H
61.5 Hz).
The reaction of the FLP 13 with phenylacetylene was carried
out analogously, and we isolated the addition product 15b in 64%
yield. The compound was also characterized by X-ray diffraction
(see Figure 3 and Table 1). The overall structural features of the
=
=
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Scheme 4
Figure 4. View of the molecular structure of the FLP/benzaldehyde
addition product 17.
Table 2. Selected Structural Data of the Aldehyde/FLP
Addition Products 17 and 18a
17
18
C2ÀC3
1.313(8)
1.773(5)
1.886(6)
1.807(5)
1.803(5)
1.670(8)
1.498(8)
1.643(9)
1.627(8)
1.398(6)
104.1(4)
94.6(2)
1.336(4)
1.777(2)
1.910(2)
1.818(2)
1.823(3)
1.650(4)
1.501(3)
1.643(4)
1.654(4)
1.387(3)
104.4(2)
95.4(1)
P1ÀC3
P1ÀC4
P1ÀC11
P1ÀC21
B1ÀC3
B1ÀO1
Figure 5. Molecular structure of compound 18.
B1ÀC31
four sets of three broad 19F NMR resonances, two ortho-, two
para-, and two meta-signals for the P(C6F5)2 substituent, like the
six resonances for the B(C6F5)2 unit. Heating the sample to 363
K resulted in a pairwise coalescence of the 19F NMR resonances
of the diastereotopic C6F5 groups at phosphorus and boron. This
observation indicates the loss of chirality, probably by the
reversible cleavage of the C4ÀP1 bond to get the aldehyde
adduct 19 as a reactive intermediate. From the dynamic 19F
B1ÀC41
O1ÀC4
P1ÀC3ÀB1
C3ÀP1ÀC4
P1ÀC4ÀO1
C4ÀO1ÀB1
O1ÀB1ÀC3
a Bond length in Å, angles in deg.
96.6(3)
99.0(2)
111.1(5)
102.6(4)
111.7(2)
103.6(2)
NMR spectra we estimated a Gibbs activation energy of ΔGq
(328 K) = 14.7 ( 0.3 kcal/mol (based on the p-C6F5
diss
B
of the addition product 17, which was isolated as a white solid in
65% yield. Single crystals of 17 suited for X-ray crystal structure
analysis were obtained from d2-dichloromethane by slow eva-
poration of the solvent at À34 °C. The structure (see Figure 4) of
compound 17 shows that the P/B pair has added to the CdO
functionality of benzaldehyde, forminga new boron-to-oxygen and
phosphorus-to-carbon bond. The five-membered heterocycle at-
tainsa twist-like conformation that deviates from planarity (sum of
internal bond angles inside the five-membered ring: 509.0°). We
note that the PÀC4 bond is markedly elongated, as judged by
comparison with the adjacent three PÀC bonds inside com-
pound 17 (see Table 2).
resonance) for the PÀC bond cleavage process in 17. In a
crossover experiment we could show that the formation of the
aldehyde addition product 17 was reversible (for details see the
Experimental Section and the Supporting Information).
Treatment of the FLP 13 with trans-cinnamic aldehyde in
pentane rapidly resulted in the formation of a white precipitate of
the product 18, which was isolated as a solid in 74% yield. The
X-ray crystal structure analysis (see Figure 5 and Table 2)
confirmed that the FLP 13 had 1,2-added to the carbonyl
function of the reagent to give a five-membered heterocyclic
structure with a pendant PhÀCHdCH functional group. The
ring is slightly twisted (sum of internal bond angles: 514.1°). In
compound 18 the P1ÀC4 bond to the former aldehyde carbon
atom is even longer than in 17. In fact, at P1ÀC4 = 1.910(2) Å it
is by more than 0.13 Å longer than the adjacent P1ÀC3 bond and
by ca. 0.09 Å longer than the P1ÀC6F5 linkages.
In solution compound 17 exhibits chemical shifts of the NMR-
active heteroatoms at δ 11B: 0.7 and δ 31P: À5.5. It shows the
1
typical H NMR features of the exocyclic dCHCH3 unit at
δ 7.28 [dq, 3JP,H = 61.5 Hz, 3JH,H = 7.0 Hz (1H)] and δ 1.95 [dd,
3JH,H = 7.0 Hz, 4JP,H = 3.5 Hz (3H)].
Compound 18 also contains a newly formed chirality center
inside the five-membered heterocycle at C4. Therefore, there
should be two pairs of diastereotopic C6F5 groups, one at
phosphorus and one at boron. At 233 K in d2-dichloromethane
Compound 17 contains a newly formed chirality center at C4.
Therefore, both the C6F5 groups at phosphorus and the C6F5
groups at boron are pairwise diastereotopic. At 298 K we observe
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we monitored in the 19F NMR spectra of compound 18 the
o-fluorine signals of two different C6F5 groups at P and the
o-fluorine NMR signals of two different C6F5 groups at B.
However, on raising the monitoring temperature of the NMR
experiment, we observed that the signals of all the respective
diastereotopic pairs coalesce and eventually give rise to the
observation of a single set of P(C6F5)2 and another one of the
B(C6F5)2 moiety (see Figure 6). We assume the analogous
dynamic process to that for 17: a rapid and reversible cleavage
of the P1ÀC4 bond resulting in the reversible formation of
the intermediate 19. The easy formation of this carbonyl adduct
by PÀC bond dissociation might be indicated by the uniquely
long phosphorus carbon linkage, as observed in the solid-state
structure of compound 18. From the dynamic 19F NMR spectra
we calculated a Gibbs activation energy of ΔGqdiss(268 K) =
11.9 ( 0.2 kcal/mol (based on the p-C6F5B resonance) for the
PÀC bond cleavage process in 18 (for details see the Supporting
Information).
Quantum Chemical Calculation. Quantum-chemical calcu-
lations were performed at the dispersion-corrected meta-GGA
level employing large triple-ζ type basis sets (abbreviated here as
TPSS-D3/def2-TZVP21), as outlined in detail in the Supporting
Information. Inclusion of bulk solvation effects by continuum
solvation models (COSMO22) has been considered in test calcu-
lations, but the energetic effects in the relatively nonpolar
solvents used in the experiments are generally small (except for
one case, see below) and thus not considered in most of the
treatments.
We first performed a conformational search for the new
FLP 13. Four conformers within an energy window of 4 kcal/
mol have been found. From these, only the lowest two with an
energy difference of 0.9 kcal/mol are relevant under ambient
conditions. The structures are shown in Figure 7.
Both conformers have a PÀB distance (2.84 and 3.04 Å) that is
larger by more than 0.5 Å compared to that in more common
FLPs, for which these distances have been computed (e.g., 1, for
which r(PÀB) is 2.24 Å at the same theoretical level). They can
be interconverted by rotation around the PÀC(B) bond vector.
In the energetically more favored one (13A, left in Figure 7) the
lone pair on the phosphorus atom is pointing “away” from the
boron atom and is probably not reactive in addition reactions.
This situation, however, is reversed in 13B, which should be
thermally accessible under the experimental conditions. Accord-
ing to population analysis, electronic communication between
the B and P atoms in both conformers takes place mainly
“through-bond” (i.e., via the C1 bridge), but is weak, as indicated
by small covalent PÀB (Wiberg) bond orders of 0.13 and 0.06 for
13A and 13B, respectively (the corresponding value for 1 is
0.72). 13A is significantly stabilized by noncovalent stacking
interactions between two C6F5 rings located on the P and B
Figure 6. Temperature-dependent 19F NMR spectra of compound 18
(in d2-dichloromethane, 470 MHz).
atoms, respectively (shortest C C contact of about 3.2 Å).
3 3 3
According to very accurate ab initio estimated CCSD(T)/CBS
Figure 7. Optimized structures (TPSS-D3/def2-TZVP) of the two energetically lowest conformers 13A and 13B of FLP 13 (the left one (A) is favored
energetically by 0.9 kcal/mol). The BÀP distances are given in Å.
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results, the hexafluorobenzene dimer interaction provides about
5.7 kcal/mol stabilization (for comparison the corresponding
TPSS-D3/def2-TZVP value is 5.6 kcal/mol).
zwitterionic product from 1 (1,4-distance) compared to 13 (1,3-
distance). In any case, our theoretical results for 13 indicate that
it behaves electronically and thermodynamically very similar to
other FLPs despite its larger PÀB distance and the electron-
accepting aryl substituents on phosphorus.
Finally, we have investigated the origin of the observed
dynamical behavior of 17. Besides the experimentally observed
closed form of the addition product, we could locate a second
minimum by rotation around the BÀO bond vector. As can be
seen in Figure 8, in this open isomer the PÀC bond is completely
broken. At the TPSS-D3/def2-TZVP level, this form is higher in
energy by only 13.7 kcal/mol. This value has been checked by
single-point calculations with the more accurate PWPB95 dou-
ble-hybrid functional,23 which yields an almost identical isomer-
ization energy of 13.5 kcal/mol. This value is in excellent
agreement with the barrier of ca. 14 kcal/mol, as estimated from
temperature-dependent NMR experiments (see above).
The reactions of PhÀNdCdO, PhÀCHdO, and PhÀ
CHdCHÀCHdO with FLP 13 were also investigated theore-
tically. The optimized structures of the corresponding products
16a, 17, and 18 in general agree very well with the X-ray data
(computed structures are given in the Supporting Information).
For example, the relatively long, newly formed P1ÀC4 bond in
17 and 18 (exptl: 1.89 and 1.91 Å) is reproduced by the
calculations (theory: 1.922 and 1.949 Å). The reaction energies
for the experimentally observed carbonyl substrates are given
in Table 3 in comparison to the corresponding value for dihy-
drogen addition.
As can be seen in Table 3, the reactions of 13 with all carbonyl
compounds are strongly exothermic, with large absolute values
for the two aldehydes and a significantly smaller (but still large)
value of À16 kcal/mol for PhÀNdCdO. The reaction with
dihydrogen is much less exothermic (À7.3 kcal/mol), but only
slightly less favorable than the corresponding reaction for the
four-membered-ring FLP 1 (À8.3 kcal/mol). Although this
qualitatively agrees with the observed inability of 13 to activate
H2 under the applied typical reaction conditions, the ΔΔE
of only 1 kcal/mol is small, and kinetic reasons may be also
responsible. In this case, inclusion of bulk solvation effects by
COSMO for a dielectric constant of 10 increases the exothermi-
city of H2 addition to À10.8 kcal/mol for 13 but to À13.9 kcal/
mol for 1; that is, the difference between FLPs 13 and 1 increases
to 3 kcal/mol, which better explains the observations. The clear
reason for this is the larger separation of the formal charges in the
’ CONCLUSIONS
Our study shows that FLP behavior not only can be induced
by the introduction of steric bulk, as it is usually done, but can
also be achieved by suitable electronic means. Attaching the
strongly electron-withdrawing pair of C6F5 substituents at the
phosphorus Lewis base component results in a drastic reduction
of the basicity and the nucleophilicity of the phosphorus atom.
Consequently, we see no Lewis acid/Lewis base quenching in the
Lewis pair 13, although the P and the B centers are spacially close
together. Nevertheless, the typical spectroscopic features of a free
tricoordinated strongly electrophilic boron Lewis acid are ob-
served for 13, and the DFT calculation confirms that.
Although the (C6F5)2P Lewis base is weak—it does for instance
not deprotonate the 1-alkynes, in contrast to many other FLPs—
the P/B pair in 13 shows typical frustrated Lewis pair behavior. It
adds to unsaturated organic substrates to form the respective
heterocyclic five-membered-ring adducts. Some of the reactiv-
ities and selectivities of these addition reactions are reversible.
From the dynamic NMR behavior of an example it has become
apparent that the PÀC bond formation of the aldehyde addition
is reversible. At the same time preferred CdN addition over
OdC addition to the isocyanates is rather uncommon. Both
features may be explained by respective stabilized carbocation-
like borane adducts as reactive intermediates.
Table 3. Energies for Reaction of FLP (13) with Various
Substrates (TPSS-D3/def2-TZVP)a
E (kcal/mol)
H2
À7.3
À8.3
H2 (1)
PhÀNdCdO
PhÀCHdO
PhÀCHdCHÀCHdO
À16.1
À25.6
À24.8
a For comparison, the value for reaction of 13 and the conventional FLP
(1) with dihydrogen are also given.
Figure 8. Optimized structures (TPSS-D3/def2-TZVP) of the two isomers of PhÀCHdO adduct 17. Distances are given in Å.
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The fact that the introduction of the strongly electron-with-
drawing C6F5 substituents at phosphorus still leads to a pro-
nounced frustrated Lewis pair behavior in the P/B pair 13
indicates that electronic steering of FLP properties might become
a viable alternative to the usually determining steric features. We
think that this observation will further increase the scope of
frustrated Lewis pair formation and utilization of their specific
chemical properties.
colorless to slightly yellow. The solvent was removed in vacuo, and a
mixture of the Markovnikov and the anti-Markovnikov product (13:14 =
7:1; from the 1H NMR experiment) was obtained as a yellow, viscous
foam (5.97 g, 7.96 mmol, 88%). Mp: 88 °C. Anal. Calcd for C27H4BF20P
(750.1 g/mol): C 43.23, H 0.54. Found: C 43.20, H not detected. IR ν~
(KBr)/cmÀ1: 2922 w, 1647 s, 1520 s, 1477 s, 1316 s, 1289 m, 1208 m,
1151 m, 1090 s, 979 s, 873 w, 829 w, 782 w, 694 w, 640 w, 507 w, 420 w.
1
Major compound 13. H NMR (500 MHz, [D6]-benzene, 298 K):
δ 1.58 (d, 3JH,H = 6.9 Hz, 3H, CH3), 6.73 (dq, 3JP,H = 24.4 Hz, 3JH,H
=
6.9 Hz, 1H, CH). 13C{1H} NMR (126 MHz, [D6]-benzene, 298 K):
’ EXPERIMENTAL SECTION
3
δ 19.7 (d, JP,C = 22.6 Hz, CH3), 108.0 (m, i-PC6F5), 113.2 (m,
i-BC6F5), 137.6 (dm, 1JF,C ≈ 254 Hz, o-C6F5), 137.7 (dm, 1JF,C ≈ 256 Hz,
General Information. All reactions were carried out under argon
atmosphere with Schlenk-type glassware or in a glovebox. Solvents
(including deuterated solvents used for NMR spectroscopy) were dried
and distilled under argon prior to use. The following instruments were
used for physical characterization of the compounds. Elemental ana-
lyses: Foss-Heraeus CHNO-Rapid. Mass spectrometry: Orbitrap LTQ
XL (Thermoscientific) for ESI measurements. NMR: Bruker AV 300
(1H: 300 MHz, 13C: 76 MHz, 31P: 122 MHz, 19F: 282 MHz, 11B: 96
MHz), Bruker AV 400 (1H: 400 MHz, 13C: 101 MHz, 31P: 162 MHz),
Varian 500 MHz INOVA (1H, 500 MHz, 13C, 126 MHz, 31P: 162 MHz,
19F: 470 MHz, 11B: 160 MHz), Varian UNITY plus NMR spectrometer
(1H, 600 MHz, 13C, 151 MHz, 31P: 243 MHz, 19F: 564 MHz, 11B: 193
MHz). Assignments of the resonances are supported by 2D experiments.
Melting points/decomposition temperature: DSC 2010 (TA-In-
struments) apparatus, determined by the baseline method. Infrared
spectroscopy: Varian 3100 FT-infrared spectroscopy (ExcaliburSeries)
spectrometer. X-ray diffraction: Data sets were collected with a Nonius
KappaCCD diffractometer. Programs used: data collection COLLECT
(Nonius B.V., 1998), data reduction Denzo-SMN (Z. Otwinowski, W.
Minor, Methods Enzymol. 1997, 276, 307À326), absorption correction
Denzo (Z. Otwinowski, D. Borek, W. Majewski, W. Minor, Acta
Crystallogr. 2003, A59, 228À234), structure solution SHELXS-97
(G. M. Sheldrick, Acta Crystallogr. 1990, A46, 467À473), structure
refinement SHELXL-97 (G. M. Sheldrick, Acta Crystallogr. 2008, A64,
112À122), graphics SCHAKAL (E. Keller, Universit€at Freiburg, 1997).
R-values are given for the observed reflections, wR2-values for all
independent ones. All figures are drawn with 50% probability.
B
1
o-C6F5), 142.2 (br, CP), 142.9 (dm, JF,C ≈ 258 Hz, p-C6F5), 143.7
1
1
(dm, JF,C ≈ 255 Hz, p-C6F5), 147.1 (dm, JF,C ≈ 247 Hz, m-C6F5),
147.7 (dm, 1JF,C ≈ 253 Hz, m-C6F5), 163.8 (d, 2JP,C = 22.2 Hz, CH).
11B{1H} NMR (160 MHz, [D6]-benzene, 298 K): δ60.2 (ν1/2 ≈1400 Hz).
19F NMR (470 MHz, [D6]-benzene, 298 K): δ À160.2 (2F, m), À146.2
(1F, p), À128.9 (2F, o) (BC6F5) [Δδ19Fmp = 14.0], À159.7 (2F, m),
À148.0 (1F, p), À128.1 (2F, o) (PC6F5) [Δδ19Fmp = 11.7], [assignment
supported by 19F{31P} NMR experiment]. 31P{1H} NMR (202 MHz, [D6]-
benzene, 298 K): δ À62.8 (m).
Minor compound 14. 1H NMR (500 MHz, [D6]-benzene, 298 K):
δ 2.00 (s, 3H, CH3), 7.50 (s, 1H, CH). 13C{1H} NMR (126 MHz, [D6]-
benzene, 298 K): δ 18.3 (d, 3JP,C = 28.0 Hz, CH3), 143.1 (d, 2JP,C = 22.2
Hz, CH)a, 161.4 (PCB)b [a from the ghsqc NMR experiment, b from the
ghmbc NMR experiment]. 19F NMR (564 MHz, [D6]-benzene, 298 K):
δ À160.2 (2F, m), À144.5 (1F, p), À128.9 (2F, o) (BC6F5), À159.8
(2F, m), À148.4 (1F, p), À130.4 (2F, o) (PC6F5) [assignment supported
by 19F{31P} NMR experiment]. 31P{1H} NMR (202 MHz, [D6]-
benzene, 298 K): δ À66.6 (quint, 3JP,F = 26.4 Hz).
Reactions of 13 with Small Molecules. General Procedures.
The mixture 13/14 (1 equiv) was dissolved in n-pentane (5 mL) and
then treated with a solution of the respective substrate (1 equiv) in
n-pentane (1À2 mL) at room temperature. Upon stirring the reaction
mixture for 12 h at room temperature, the resulting precipitate was
collected and washed with n-pentane (3 Â 5À10 mL). Subsequently the
obtained solid was dried in vacuo to get the respective product.
Preparation of Compound 15a. Mixture 13/14 (200 mg, 0.27 mmol,
1 equiv) reacted with 1-pentyne (18.0 mg, 0.27 mmol, 1 equiv) to give
15a as a white solid (135 mg, 0.165 mmol, 62%). Crystals suitable for the
X-ray crystal structure analysis were obtained by slow evaporation of a
saturated solution of 15a in [D6]-benzene. Anal. Calcd for C32H12BF20P
(818.2 g/mol): C 46.97, H 1.48. Found: C 46.56, H 1.60. Mp: 225 °C.
1H NMR (500 MHz, [D6]-benzene, 298 K): δ 0.73 (t, 3JH,H = 7.1 Hz,
Materials. The compounds propynyllithium,24 bis(pentafluorophenyl)
chlorophosphine (11),17 and bis(pentafluorophenyl)borane [HB(C6F5)2]15
were prepared according to modified literature procedures.
Preparation of Bis(pentafluorophenyl)propynylphosphine
(12). A solution of bis(pentafluorophenyl)chlorophosphine (11) (9.81 g,
24.5 mmol, 1 equiv) in n-pentane (4 mL) was added to a suspension of
propynyllithium (1.13 g, 24.5 mmol, 1 equiv) in dry THF (80 mL) at
À78 °C. The resulting slightly yellow suspension was warmed to room
temperature and stirred for two hours. The solvent of the resulting
yellow solution was removed in vacuo, and the orange-red residue was
dissolved in n-pentane before being filtrated over Celite to remove the
formed lithium chloride. The solvent of the filtrate was removed in vacuo,
and the resulting residue was purified by distillation (p = 0.11 mbar,
97 °C) to get 12 as a colorless oil (4.04 g, 10 mmol, 41%). Anal. Calcd for
C15H3F10P (404.1 g/mol): C 44.58, H 0.75. Found: C 44.19, H 0.69. IR
3H, CH2CH3), 1.36 (m, 2H, CH2CH3), 1.45 (dd, 3JH,H = 7.1 Hz, 4JP,H
=
3
3.6 Hz, 3H, CH3), 1.94 (q, JP,H
=
3JH,H = 7.8 Hz, 2H, CH2),
7.02 (dq, 3JP,H = 62.3 Hz, 3JH,H = 7.1 Hz, 1H, dCH), 8.27 (d, 3JP,H
=
61.5 Hz, 1H, dCHB). 13C{1H} NMR (126 MHz, [D6]-benzene,
3
298 K): δ 13.7 (CH2CH3), 20.8 (d, JP,C = 7.8 Hz, CH2CH3), 21.9
3
2
(d, JP,C = 17.2 Hz, CH3), 31.2 (d, JP,C = 16.7 Hz, CH2), 124.6
1
P
(d, JP,C = 89.1 Hz, dCP), 132.9 (br, CB), 155.9 (br, dCH), 180.6
(br, dCHB) [C6F5 not listed]. 11B{1H} NMR (160 MHz, [D6]-
benzene, 298 K): δ À9.8 (br d, 3JP,B ≈ 40 Hz). 19F NMR (470 MHz,
[D6]-benzene, 298 K): δ À164.2 (m, 2F, m), À159.1 (m, 1F, p), À132.7
(m, 2F, o) (BC6F5) [Δδ19Fmp = 5.1], À156.7 (m, 2F, m), À138.6
(m, 1F, p), À130.0 (m, 2F, o) (PC6F5) [Δδ19Fmp = 18.1]. 31P{1H}
NMR (202 MHz, [D6]-benzene, 298 K): δ 0.9 (m, patially relaxed 3JP,B).
X-ray Crystal Structure Analysis of 15a: formula C32H12BF20P, M =
818.20, colorless crystal 0.25 Â 0.12 Â 0.07 mm, a = 11.1848(4) Å, b =
15.8115(6) Å, c = 18.1557(10) Å, β = 103.037(3)°, V = 3128.0(2) Å3,
1
ν~ (KBr)/cmÀ1: 2197 [st, ν(CtC)] w. H NMR (400 MHz, [D6]-
benzene, 296 K): δ 1.45 (d, 4JP,H = 2.8 Hz, 1H, CH3). 13C{1H} NMR
(101 MHz, [D6]-benzene, 296 K): δ 4.8 (d, 3JP,C = 1.2 Hz, CH3), 67.6
(m, PCt)t, 107.7 (m br, i-C6F5), 109.2 (d, 2JP,C = 14.3 Hz, tC)t, 137.6
1
1
(dm, JF,C ≈ 255 Hz, o-C6F5), 142.8 (dm, JF,C ≈ 257 Hz, p-C6F5),
147.6 (dm, 1JF,C ≈ 251 Hz, m-C6F5), [t tentative assignment].
Preparation of Compounds 13 and 14. A solution of bis-
(pentafluorophenyl)propynylphosphine (12) and n-pentane (10 mL)
was added to a suspension of bis(pentafluorophenyl)borane (3.14 g,
9.11 mmol, 1 equiv) in n-pentane (150 mL) at À78 °C. Upon warming
to room temperature and stirring for two hours, the color turned from
F
calc = 1.737 g cmÀ3, μ = 2.144 mmÀ1, empirical absorption correction
(0.616 e T e 0.864), Z = 4, monoclinic, space group P21 (No. 4),
λ = 1.54178 Å, T = 223 K, ω and j scans, 28 344 reflections collected
((h, Àk, Àl), [(sin θ)/λ] = 0.60 ÅÀ1, 9090 independent (Rint = 0.059)
4217
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Organometallics
ARTICLE
3
3
and 7709 observed reflections [I g 2σ(I)], 977 refined parameters, R =
0.049, wR2 = 0.125, Flack parameter 0.04(3), max. residual electron
density 0.36 (À0.24) e ÅÀ3, hydrogen atoms calculated and refined as
riding atoms.
6.87 (dq, JP,H = 60.6 Hz, JH,H = 6.9 Hz, 1H, dCH), 7.37 (m, 2H,
o-Tol). 13C{1H} NMR (126 MHz, [D6]-benzene, 298 K): δ 20.7
(CH3Tol), 21.9 (br d, 4JP,C = 17.5 Hz, CH3), 125.1 (o-Tol), 126.3 (br,
PCB)b, 129.6 (m-Tol), 137.2 (p-Tol), 138.5 (d, 3JP,C = 12.0, Hz, i-Tol),
156.4 (m, dCH), 158.7 (d, 1JP,C = 115.4 Hz, CdO) [C6F5 not listed, b
from the ghmbc NMR experiment]. 11B{1H} NMR (160 MHz, [D6]-
benzene, 298 K): δ À4.5 (ν1/2 ≈ 100 Hz). 19F NMR (470 MHz, [D6]-
benzene, 298 K): δ À163.7 (m, 2F, m), À156.6 (m, 1F, p), À132.2 (br,
2F, o) (BC6F5) [Δδ19Fmp = 7.1], À155.6 (m, 2F, m), À136.2 (m, 1F, p),
À127.0 (br, 2F, o) (PC6F5) [Δδ19Fmp = 19.4]. 31P{1H} NMR (202
MHz, [D6]-benzene, 298 K): δ À32.0 (ν1/2 ≈ 30 Hz).
Preparation of Compound 15b. Mixture 13/14 (200 mg, 0.27 mmol,
1 equiv) reacted with phenylacetylene (28 mg, 0.27 mmol, 1 equiv) to
get 15b as a white solid (146 mg, 0.17 mmol, 64%). Crystals suitable for
X-ray crystal structure analysis were obtained by slow evaporation of a
saturated solution of 15b in [D2]-dichloromethane at À34 °C. Anal.
Calcd for C35H10BF20P (852.2 g/mol): C 49.33, H 1.18. Found: C
48.71, H 0.79. MS-ESI-EM: calcd. for (C35H10BF20P)H 853.0378,
1
found 853.03749. Mp: 111 °C. H NMR (400 MHz, [D2]-dichloro-
Preparation of Compound 17. Mixture 13/14 (200 mg, 0.27 mmol,
1 equiv) reactedwith benzaldehyde(28.0 mg, 0.27 mmol, 1 equiv) toform
a slightly yellow reaction solution. After 12 h the product 17 was obtained
as a white solid (148 mg, 0.172 mmol, 65%). Crystals suitable for X-ray
crystal structure analysis were obtained by slow evaporation of a
saturated solution of 17 in [D2]-dichloromethane at À34 °C. Anal. Calcd
for C35H10BF20P (856.2 g/mol): C 47.70, H 1.18. Found: C 47.98, H
1.39. Mp: 95 °C. 1H NMR (500 MHz, [D2]-dichloromethane, 298 K): δ
1.95 (dd, 3JH,H = 7.0 Hz, 4JP,H = 3.5 Hz, 3H, CH3), 6.34 (d, 2JP,H = 15.3
methane, 296 K): δ 1.93 (dd, 3JH,H = 7.1 Hz, 4JP,H = 3.5 Hz, 3H, CH3),
6.86 (dm, 3JP,H = 63.6 Hz, 1H, dCH), 7.20 (m, 2H, o-Ph), 7.31 (m, 3H,
m-, p-Ph), 8.73 (dm, 3JP,H = 57.3 Hz, 1H, dCHB). 13C{1H} NMR (101
3
MHz, [D2]-dichloromethane, 296 K): δ 21.7 (br d, JP,C = 18.2 Hz,
CH3), 126.5 (d, 2JP,C = 94.8 Hz, PCd), 127.2 (d, 3JP,C = 5.6 Hz, o-Ph),
129.2 (d, J = 1.1 Hz, p-Ph), 129.3 (m-Ph), 132.7 (br, PCB)b, 133.9 (dm,
2JP,C = 18.3 Hz, i-Ph), 154.3 (dCH), 184.3 (br, dCHB) [C6F5 not
listed, b from the ghmbc NMR experiment]. 11B{1H} NMR (160 MHz,
[D2]-dichloromethane, 298 K): δ À10.1 (d, 3JP,B ≈ 39 Hz). 19F NMR
(470 MHz, [D2]-dichloromethane, 298 K): δ À165.3 (2F, m), À160.6
Hz, 1H, CH), 7.23 (m, 2H, o-Ph), 7.27 (m, 2H, m-Ph), 7.28 (dq, 3JP,H
=
61.5 Hz, 3JH,H = 7.0 Hz, 1H, dCH), 7.36 (m, 1H, p-Ph). 13C{1H} NMR
(151 MHz, [D2]-dichloromethane, 298 K): δ 22.9 (br d, 3JP,C = 15.0 Hz,
CH3), 85.5 (br d, 1JP,C = 40.9 Hz, CH), 126.7 (d, 3JP,C = 5.7 Hz, o-Ph),
129.0 (d, J = 4.0 Hz, m-Ph), 130.4 (d, J = 4.8 Hz, p-Ph), 133.6 (d, 2JP,C = 3.6
Hz, i-Ph), 133.8 (br, PCB)b, 158.0 (br, dCH) [C6F5 not listed, b from the
ghmbc NMR experiment]. 11B{1H} NMR (160 MHz, [D2]-dichloro-
methane, 298 K): δ 0.7 (ν1/2 ≈ 80 Hz). 19F NMR (470 MHz,
[D2]-dichloromethane, 298 K): δ À165.4 (m, 2F, m), À160.4 (m, 1F,
3
(t, JF,F = 20 Hz, 1F, p), À133.2 (2F, o) (BC6F5) [Δδ19Fmp = 4.7],
À157.0 (2F, m), À140.6 (1F, p), À127.9 (2F, o) (PC6F5) [Δδ19Fmp
=
16.4]. 31P{1H} NMR (202 MHz, [D2]-dichloromethane, 298 K):
δ À2.8 (1:1:1:1 q, 3JP,B ≈ 39 Hz).
1
X-ray Crystal Structure Analysis of 15b: formula C35H10BF20P
/
2
3
CH2Cl2, M = 894.67, colorless crystal 0.35 Â 0.20 Â 0.10 mm, a =
33.3804(8) Å, b = 40.8995(9) Å, c = 9.9755(4) Å, V = 13619.0(7) Å3,
F
calc = 1.745 g cmÀ3, μ = 2.740 mmÀ1, empirical absorption correction
p), À135.1 (m, 2F, o) (BC6F5 ) [Δδ19Fmp = 5.0], À165.4 (m, 2F, m),
A
À159.4 (m, 1F, p), À132.5 (m, 2F, o) (BC6F5 ) [Δδ19Fmp = 6.0],
B
(0.447 e T e 0.771), Z = 16, orthorhombic, space group Fdd2 (No. 43),
λ = 1.54178 Å, T = 223 K, ω and j scans, 14 647 reflections collected
((h, Àk, Àl), [(sin θ)/λ] = 0.60 ÅÀ1, 5675 independent (Rint = 0.041)
and 5458 observed reflections [I g 2σ(I)], 543 refined parameters, R =
0.037, wR2 = 0.094, Flack parameter 0.47(2), max. residual electron
density 0.44 (À0.25) e ÅÀ3, hydrogen atoms calculated and refined as
riding atoms.
A
À158.2 (m, 2F, m), À139.6 (m, 1F, p), À126.6 (m, 2F, o), (PC6F5
)
[Δδ19Fmp = 18.6], À155.4 (m, 2F, m), À139.4 (m, 1F, p), À124.6
(m, 2F, o) (PC6F5 ) [Δδ19Fmp = 16.0]. 31P NMR (202 MHz, [D2]-
A
dichloromethane, 298 K): δ À5.5 (dm, JP,H ≈ 62 Hz). 31P{1H}
3
NMR (202 MHz, [D2]-dichloromethane, 298 K): δ À5.5 (ν1/2
≈
60 Hz).
Preparation of Compound 16a. Mixture 13/14 (200 mg, 0.27 mmol,
1 equiv) reacted with phenylisocyanate (28.0 mg, 0.27 mmol, 1 equiv) to
yield the product 16a as a white solid (148 mg, 0.17 mmol, 65%). Anal.
Calcd for C32H12BF20P (869.2 g/mol): C 46.98, H 1.04, N 1.61. Found:
C 46.87, H 1.22, N 1.54. Decomp.: 174 °C. 1H NMR (500 MHz, [D2]-
dichloromethane, 298 K): δ 2.01 (dd, 3JH,H = 7.0 Hz, 4JP,H = 3.6 Hz, 3H,
CH3), 7.11 (m, 2H, o-Ph), 7.12 (m, 1H, p-Ph), 7.16 (dq, 3JP,H = 61.3 Hz,
3JH,H = 7.0 Hz, 1H, dCH), 7.21 (m, 2H, m-Ph). 13C{1H} NMR (126
X-ray crystal structure analysis of 17: formula C34H10BF20OP,
M = 856.20, colorless crystal, 0.25 Â 0.15 Â 0.05 mm, a = 10.6020(3)
Å, b = 17.5414(6) Å, c = 18.9734(6) Å, β = 90.290(2)°, V = 3528.5(2) Å3,
F
calc = 1.612 g cmÀ3, μ = 1.955 mmÀ1, empirical absorption correction
(0.641 e T e 0.909), Z = 4, monoclinic, space group P21/n (No. 14),
λ = 1.54178 Å, T = 223 K, ω and j scans, 19 821 reflections collected
((h, Àk, Àl), [(sin θ)/λ] = 0.60 ÅÀ1, 5790 independent (Rint = 0.068)
and 4198 observed reflections [I g 2σ(I)], 515 refined parameters, R =
0.085, wR2 = 0.259, solvent molecules could not be identified; therefore
the SQUEEZE routine was used, group C31ÀC36 refined with thermal
4
MHz, [D2]-dichloromethane, 298 K): δ 22.7 (br d, JP,H = 17.9 Hz,
CH3), 125.1 (o-Ph), 125.3 (br, dCB), 127.1 (p-Ph), 128.9 (m-Ph),
140.9 (d, 3JP,H = 11.4 Hz, i-Ph), 157.3 (dCH), 159.1 (d, 1JP,C = 118.8
Hz, CdO) [C6F5 not listed]. 11B{1H} NMR (192 MHz, [D2]-dichlor-
omethane, 298 K): δ À4.7 (ν1/2 ≈ 80 Hz). 19F NMR (564 MHz, [D2]-
dichloromethane, 298 K): δ À164.7 (m, 2F, m), À158.1 (m, 1F, p),
À132.8 (br, 2F, o) (BC6F5) [Δδ19Fmp = 6.6], À155.7 (m, 2F, m),
restraints (ISOR), max. residual electron density 0.85 (À0.72) e ÅÀ3
,
hydrogen atoms calculated and refined as riding atoms.
Preparation of Compound 18. Mixture 13/14 (100 mg, 0.13 mmol,
1 equiv) reacted with cinnamic aldehyde (17.5 mg, 0.13 mmol, 1 equiv)
to form a bright yellow reaction solution. The product 18 was obtained
as a white solid (85 mg, 0.098 mmol, 74%). Crystals suitable for X-ray
crystal structure analysis were obtained by slow evaporation of a
saturated solution of 18 in [D2]-dichloromethane at À34 °C. Anal.
Calcd for C36H12BF20OP (864.2 g/mol): C 49.01, H 1.37. Found:
C 49.17, H 1.49. Decomp.: 140 °C. 1H NMR (400 MHz, [D2]-
À137.4 (m, 1F, p), À125.9 (br, 2F, o) (PC6F5) [Δδ19Fmp = 8.3]. 31
P
≈
NMR (243 MHz, [D2]-dichloromethane, 298 K): δ À30.1 (dm, 3JP,H
61 Hz). 31P{1H} NMR (243 MHz, [D2]-dichloromethane, 298 K): δ
À30.1 (m, ν1/2 ≈ 35 Hz).
Preparation of Compound 16b. Mixture 13/14 (200 mg, 0.27 mmol,
1 equiv) reacted with para-tolyl-isocyanate (35.0 mg, 0.27 mmol, 1 equiv)
to yield the product 16b as a white solid (148 mg, 0.17 mmol, 65%).
Anal. Calcd for C35H11BF20OP (883.2 g/mol): C 47.60, H 1.26, N 1.59.
Found: C 47.48, H 0.61, N 1.79. MS-ESI-EM: calcd for (C35-
H11BF20OP)H 884.0436, found 884.04350. Decomp.: 184 °C. 1H
3
4
dichloromethane, 295 K): δ 1.96 (dd, JH,H = 7.0 Hz, JP,H = 3.5 Hz,
3H, CH3), 5.91 (br d, 3JH,H = 7.1 Hz, CH), 6.29 (br d, 3JH,H = 15.8 Hz,
3
3
1H, dCHPh), 6.91 (dd, JH,H = 15.8 Hz, JH,H = 7.5 Hz,
1H, dCHCH), 7.26 (dq, 3JP,H = 63.3 Hz, 3JH,H = 7.0 Hz, 1H, dCH),
7.30 (m, 2H, m-Ph), 7.32 (m, 3H, o-, p-Ph). 13C{1H} NMR (101 MHz,
[D2]-dichloromethane, 295 K): δ 23.1 (br d, 3JP,C = 15.7 Hz, CH3), 84.0
3
NMR (500 MHz, [D6]-benzene, 298 K): δ 1.39 (dd, JH,H = 6.9, Hz,
4JP,H = 3.6 Hz, 3H, CH3), 1.83 (s, 3H, CH3Tol), 6.83 (m, 2H, m-Tol),
(br d, JP,C = 43.5 Hz, CH), 120.2 (m, dCHPh), 127.0 (br, m-Ph),
1
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Organometallics
ARTICLE
129.15 (o-Ph), 129.24 (p-Ph), 133.7 (br, PCB)b, 135.5 (m, i-Ph), 136.1
(m, dCHCH)a, 158.1 (dCH) [C6F5 not listed, a from the ghsqc NMR
experiment, b from the ghmbc NMR experiment]. 11B NMR (96 MHz,
[D2]-dichloromethane, 296 K): δ 0.9 (s, ν1/2 ≈ 100 Hz). 19F NMR (470
MHz, [D2]-dichloromethane, 298 K): δ À165.3 (m, 2F, m), À159.8
(br, 1F, p), À133.8 (br, 2F, o) (BC6F5) [Δδ19Fmp = 5.5], À156.6 (br,
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W. E.; Parvez, M. J. Am. Chem. Soc. 2010, 132, 10660–10661. (d)
Dureen, M. A.; Stephan, D. W. J. Am. Chem. Soc. 2010, 132, 13559–
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2F, m), À139.3 (br, 1F, p), À125.9 (br, 2F, o) (PC6F5) [Δδ19Fmp
=
17.3]. 19F NMR (470 MHz, [D2]-dichloromethane, 233 K): δ À164.9
A
(m, 2F, m), À160.0 (m, 1F, p), À135.1 (m, 2F, o) (BC6F5 ) [Δδ19Fmp
=
B
5.5], À164.9 (m, 2F, m)À159.0 (m, 1F, p), À132.7 (m, 2F, o) (BC6F5 )
[Δδ19Fmp =5.9],À157.4 (m, 2F, m), À138.8 (m, 1F, p), À126.9(m, 2F, o)
(PC6F5A) [Δδ19Fmp = 18.6], À155.4 (m, 2F, m), À138.6 (m, 1F, p),
B
À125.0 (m, 2F, o) (PC6F5 ) [Δδ19Fmp = 16.6]. 31P{1H} NMR (243
MHz, [D2]-dichloromethane, 296 K): δ À6.9 (br, ν1/2 ≈ 70 Hz).
X-ray crystal structure analysis of 18: formula C36H12BF20OP 2
3
CH2Cl2, M = 1052.09, colorless crystal, 0.23 Â 0.20 Â 0.14 mm,
a = 10.9273(4) Å, b = 11.9928(4) Å, c = 16.7507(8) Å, R = 70.979(5)°,
β = 89.996(4)°, γ = 73.451(5)°, V = 1978.89(14) Å3, Fcalc = 1.766
g cmÀ3, μ = 4.303 mmÀ1, empirical absorption correction (0.438 e T e
0.584), Z = 2, triclinic, space group P1 (No. 2), λ = 1.54178 Å, T = 223 K,
ω and j scans, 26 239 reflections collected ((h, Àk, Àl), [(sin θ)/λ] =
0.60 ÅÀ1, 6850 independent (Rint = 0.049) and 5901 observed reflec-
tions [I g 2σ(I)], 587 refined parameters, R = 0.044, wR2 = 0.113, max.
residual electron density 0.33 (À0.41) e ÅÀ3, hydrogen atoms calculated
and refined as riding atoms.
’ ASSOCIATED CONTENT
S
Supporting Information. Additional experimental and
b
spectroscopic details. CIF files for compounds 15a, 15b, 17,
and 18. This material is available free of charge via the Internet at
http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: erker@uni-muenster.de.
’ ACKNOWLEDGMENT
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Financial Support from the Deutsche Forschungsgemein-
schaft is greatly acknowledged. We thank Boulder Scientific
Company for a gift of B(C6F5)3.
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