CO2 and formate complexes of phosphine/borane frustrated Lewis pairs

Article abstract of DOI:10.1002/chem.201100286

The reaction of a solution of B(C₆F₄H)₃ and either iPr₃P or tBu₃P with CO₂ afforded the species R₃P(CO₂)B(C₆F₄H) ₃ (R=iPr (1), tBu (2)

Full text of DOI:10.1002/chem.201100286

DOI: 10.1002/chem.201100286
CO2 and Formate Complexes of Phosphine/Borane Frustrated Lewis Pairs
Ilona Peuser,[a, b] Rebecca C. Neu,[a, b] Xiaoxi Zhao,[a] Matthias Ulrich,[a]
Birgitta Schirmer,[b] Jens A. Tannert,[b] Gerald Kehr,[b] Roland Frçhlich,[b]
Stefan Grimme,*[b] Gerhard Erker,*[b] and Douglas W. Stephan*[a]
Abstract: The reaction of a solution of
(C6F4H)3 and either iPr3P or tBu3P
with CO2 afforded the species R3P-
(CO2)B(C6F4H)3 (R=iPr (1), tBu (2)).
In a similar fashion the boranes, RB-
(C6F5)2 (R=hexyl, cyclohexyl (Cy),
norbornyl), ClB(C6F5)2, or PhB(C6F5)2
were combined with tBu3P and CO2 to
give the species tBu3P(CO2)BR(C6F5)2
prepared by reaction of the precursor
frustrated Lewis pair (FLP) with H2.
Subsequent reactions of 9 and 10 with
with tBu3P treated with an equivalent
of formic acid gave [(C6F5)2BR-
ACHUTNGRENU(NG HCO2)]ACHTUGNTREN[NUGN tBu3PH] (R=hexyl (13), Cy
(14), norbornyl (15)). Subsequent addi-
tion of an additional equivalent of
borane provides a second synthetic
route to 11 and 12. Crystallographic
studies of compounds 2–6 and 8–14 are
reported and discussed. Further under-
standing of the FLP complexation and
activation of CO2 is provided by com-
putational studies.
B
G
A
E
CO2
afforded
the
species
[((C6F5)2BR)
N
U
A
Cy (11), norbornyl (12)). In related
chemistry, combinations of the boranes
RBACHTNUTGRNEG(UN C6F5)2 (R=hexyl, Cy, norbornyl)
G
N
G
(R=hexyl (3), Cy (4), norbornyl (5),
Cl (6), Ph (7)). Similarly, the com-
pounds [tBu3PH]ACHTUNGTRENNUNG[RBHACHTUNTGREN(NUGN C6F5)2] (R=
Keywords: boranes
dioxide fixation
frustrated Lewis pairs · phosphines
·
carbon
·
formate
·
hexyl (8), Cy (9), norbornyl (10)) were
Introduction
reactivity of CO2. Although CO2 reacts with strong nucleo-
philes and coordinatively unsaturated transition metal spe-
cies, the presence of hydroxide results in the formation of
bicarbonate salts.[7] On the other hand, reactions of main-
group systems with CO2 have only just begun to garner at-
tention. For example, recent reports have described the iso-
lation of a CO2 adduct of a nitrogen base[8] and the carboxy-
lation of N-heterocyclic carbenes[9] that undergo subsequent
catalytic reduction to methanol. Similarly, reactions of CO2
with silyl, germyl and strontium amides have been de-
scribed.[10]
The phenomenon of global warming is largely attributable
to the increasing concentration of carbon dioxide in the at-
mosphere.[1] A variety of materials including zeolites, silica
gels, aluminas, activated carbons,[2] as well as sophisticated
metal–organic frameworks (MOFs)[3] have been developed
in an effort to sequester this greenhouse gas. Although these
approaches are creative, they are based on large-scale stor-
age of bound CO2. An alternative to these methods involves
the conversion of carbon dioxide to a C1 chemical feed-
stock.[4] In fact, some years ago, the conversion of CO2 to
methanol was put forward by Olah et al. as the basis for the
“methanol economy”.[5] To this end, efforts to develop ho-
mogeneous and heterogeneous catalytic processes have tar-
geted the conversion of CO2 into alternative fuels and or-
ganic building blocks.[4,6] A fundamental challenge in this
field is the remarkable thermodynamic stability and limited
Our own efforts have focused on the development of new
strategies for the activation of small molecules employing
simple main-group systems. Frustrated Lewis pairs (FLPs)
have proven to be highly reactive systems derived from the
synergistic action of unquenched Lewis acidic and basic sites
on the substrate.[11] The first reports of such reactivity dem-
onstrated the activation of H2 by combinations of sterically
encumbered phosphines and boranes and their subsequent
use in hydrogenation catalysis.[12] Since then, a broadening
range of FLPs has been used in hydrogenation catalysis[13]
and in reactivity with a variety of substrates including disul-
[a] I. Peuser, R. C. Neu, X. Zhao, Dr. M. Ulrich, Prof. Dr. D. W. Stephan
Department of Chemistry, University of Toronto
80 St. George Street, Toronto, ON, M5S 3H6 (Canada)
E-mail: dstephan@chem.utoronto.ca
fides, B H bonds,[14] olefins,[15,16] alkynes,[16,17] cyclopro-
À
panes,[18] N2O,[19] and CO2.[20–22] Much of this work has been
recently reviewed.[11]
[b] I. Peuser, R. C. Neu, B. Schirmer, J. A. Tannert, Dr. G. Kehr,
Dr. R. Frçhlich, Prof. Dr. S. Grimme, Prof. Dr. G. Erker
Organisch-Chemisches Institut der Universitꢁt Mꢂnster
Corrensstrasse 40, 48149 Mꢂnster (Germany)
E-mail: grimmes@uni-muenster.de
In recent work, we have communicated the use of sterical-
ly encumbered phosphines and boranes in the reversible
binding of CO2 (Scheme 1, A and B).[20] In subsequent work
OꢀHare and co-workers demonstrated the stoichiometric re-
duction of amine/borane FLP–CO2 complexes to methanol
under rather forcing conditions (4 d, 1608C).[21] Shortly
erker@uni-muenster.de
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201100286.
9640
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Chem. Eur. J. 2011, 17, 9640 – 9650

FULL PAPER
It is noteworthy that in contrast with the formation of 1,
reaction of iPr3P with B
of CO2, even under a CO2 atmosphere. Rather, nucleophilic
aromatic substitution at the para position of B(C6F5)3 by the
phosphine yields the zwitterionic isomer iPr3P(p-C6F4)B(F)-
(C6F5)2.[24] The formation of 1 results from the inability of
this FLP to undergo para-substitution, thus demonstrating a
desirable feature of B(C6F4H)3.
The boranes RB(C6F5)2 (R=hexyl, cyclohexyl (Cy), nor-
bornyl) were generated through in situ hydroboration of the
appropriate olefin precursor by HB(C6F5)2. These resulting
boranes were then individually combined with tBu3P under
an atmosphere of CO2, giving the species R3P(CO2)BR-
(C6F5)2 (R=hexyl (3), Cy (4), norbornyl (5)) in yields of 75,
ACHTNUGTERN(NGNU C6F5)3 does not result in the capture
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
Scheme 1. CO2 Complexes of FLPs.
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
thereafter, we demonstrated that P/Al-based FLPs[22a]
(Scheme 1, C) react with NH3BH3 effecting similar reduc-
tion in 5 min at 258C.[22b] Most recently, Piers et al. demon-
strated that FLP systems could effect the catalytic deoxyge-
native hydrosilylation of CO2 to methane.[23a] In this full
report, we examine reactions of phosphine/borane FLP sys-
tems with CO2 in greater detail. The impact of variations of
the Lewis acids on bound CO2 and the chemistry that af-
fords related formate derivatives is probed. The understand-
ing of the nature of these systems is further augmented by
computational studies.
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
71, and 86%, respectively (Scheme 2). These compounds ex-
hibited similar spectroscopic parameters to those described
for 1 and 2. Although these compounds were isolable and
stable at low temperature, each of these species was ob-
served to lose CO2 above À158C.
In a similar fashion, reactions of ClBACHTUNGTRENN(GU C6F5)2 or PhBACHTUNGTRENNUNG(C6F5)2
with tBu3P under a CO2 atmosphere afforded the com-
pounds tBu3P(CO2)B(C6F5)2R (R=Cl (6), Ph (7)) in 79 and
Results and Discussion
N
ACHTUNGTRENNUNG
55% yields (Scheme 2). Similar to 3–5 these compounds
were also sensitive, undergoing facile loss of CO2, regenerat-
ing the respective FLP. Nonetheless some of these latter
species were stable for a few hours in CD2Cl2 at room tem-
perature.
Crystallographic studies confirmed the structures of 2–6
(Figures 1–3) in which the CO2 is bound through the carbon
atom to P and to B through one of the O atoms. As the
In a fashion similar to that previously communicated for the
synthesis of tBu3P
(C6F4H)3 and either iPr3P or tBu3P in CH2Cl2 under an at-
(C6F5)3,[20] reaction of a solution of
ACHTUNGTRENNUNG(CO2)BACHTUTGNRENNUGN
BACHTUNGTRENNUNG
mosphere of carbon dioxide proceeded smoothly to yield
the white solids 1 and 2 in 77 and 59%, respectively. These
products exhibited 31P{1H} NMR resonances at d=37.3 and
45.4 ppm, and 11B{1H} NMR resonances at d=À2.3 and
À2.4 ppm, respectively, which are in accordance with the
quaterization of the boron center.[23b] Both compounds dis-
played signals at about d=À134 and À143 ppm in the
19F NMR spectra. The 13C NMR spectra of 1 and 2 showed
resonances expected for the constituent phosphorus and
boron fragments as well as signals at d=161.6 and
162.2 ppm, which exhibited C–P couplings of J=112 and
93 Hz, respectively. These latter signals were consistent with
À
the presence of P C bonds derived from phosphine binding
to CO2. Infrared spectra showed absorptions at n˜ =1700 and
1699 cmÀ1 for 1 and 2, respectively, attributable to a C=O
stretch vibration. Collectively, these data support the formu-
lations of these products as R3PACHTUNGTRNENUG(CO2)BACHTUNTGREN(NUGN C6F4H)3 (R=iPr
(1), tBu (2); Scheme 2).
Figure 1. POV depiction of 2.
À
phosphine fragments are identical in these species, the P C
bond length in 2–6 are indistinguishable averaging 1.89(1) ꢄ
À
with the exception of 5 where the P C bond length is
À
1.896(3) ꢄ (Table 1). Although the B O bond lengths in
these compounds range from 1.527(3)–1.592(3), the longest
À
À
B O bond length is in 5. The shortest B O bond length is
1.527(3) ꢄ in 6, consistent with the Lewis acidity of ClB-
À
G
1.281(5)–1.300(2) ꢄ in 2–6, whereas the terminal C=O bond
lengths in 2, 3, 4, and 6 average 1.204(4) ꢄ. Only compound
5 deviates from these typical values. This seems to be attrib-
Scheme 2. Synthesis of compounds 1–7.
Chem. Eur. J. 2011, 17, 9640 – 9650
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9641

D. W. Stephan, S. Grimme, G. Erker et al.
Table 1. Selected bond lengths and IR data for different B/P FLP–CO2
Complexes.
À
À
À
Compound
P C
[ꢄ]
C O
[ꢄ]
C=O
[ꢄ]
O B
[ꢄ]
n˜
[cmÀ1
]
U
A
B
2
3
4
1.893(1)
1.900(3)
1.892(2)
1.896(4)
1.893(3)
1.896(3)
1.888(2)
1.299(2)
1.284(4)
1.300(2)
1.281(5)
1.289(4)
1.284(3)
1.297(3)
1.208(2)
1.209(4)
1.203(2)
1.208(5)
1.206(4)
1.210(3)
1.201(3)
1.547(2)
1.550(4)
1.556(2)
1.579(5)
1.587(4)
1.592(3)
1.527(3)
1695
1694
1699
1693
1698
1686
1702
5
6
tions, the compounds [tBu3PH]ACHTNUGTRENN[GU RBHACHTUNGTNER(NUGN C6F5)2] (R=hexyl (8),
Cy (9), norbornyl (10)) were prepared initially generating
the borane in situ, followed by combination with tBu3P and
subsequent exposure to 2 bar H2 at room temperature. The
resulting salts 8–10 were isolated in 60, 66, and 77% yield,
respectively. These compounds exhibited typical PH and BH
À
spectroscopic signatures. The P H fragments in 8–10 gave
rise to H NMR signals at d=5.46, 5.49, and 5.28 ppm with
1
P,H coupling constants of J=436.6, 437.2, and 432.5 Hz, re-
À
spectively. The corresponding B H resonances were ob-
served at d=2.72, 2.44, and 2.46 ppm, respectively, with the
associated 11B{1H} signals at d=À18.4, À17.6, and
À18.5 ppm, respectively. Analogous preparation of the deu-
terated analogues [tBu3PD]ACHTUNTRGENN[UG RBDAHCTUTGNREN(NUGN C6F5)2] (R=hexyl ([D2]8),
Cy, ([D2]9), norbornyl ([D2]10)) were confirmed by the ob-
2
À
servations of H NMR resonances attributable to the P D
fragments at d=5.45, 5.49, and 5.30 ppm, respectively, with
P,D coupling constants of J=66.1, 66.9, and 66.8 Hz, respec-
À
tively. The resonances for the corresponding B D units
Figure 2. POV depictions of a) 3, b) 4, and c) 5.
were observed at d=2.71, 2.49, and 2.50 ppm, respectively.
The formation of the products 8, 9, and 10 was further con-
firmed by X-ray crystallographic studies (Figure 4). The
metric parameters of these salts were unexceptional.
Subsequent reactions of 9 and 10 with CO2 were under-
taken. Heating a solution of 9 to 608C overnight under CO2,
resulted in the formation of a new species 11. The product
11 was recrystallized from dichloromethane/pentane afford-
ing 45% yield based on one equivalent of 9. NMR data for
11 revealed a broad 11B NMR resonance at d=5.1 ppm, as
1
well as the H NMR resonances including a singlet at d=
8.04 ppm and a 13C{1H} NMR signal at d=173.4 ppm. These
data are in accordance with the existence of a bridging for-
mate unit. Infrared absorption at n˜ =1631 cmÀ1 also supports
1
this proposition. A doublet at d=5.09 ppm in the H NMR
Figure 3. POV depictions of 6.
spectrum exhibits P,H coupling of J=427.7 Hz, consistent
with the presence of the phosphonium cation [tBu3PH]+,
supporting the formulation of 11 as [tBu3PH]
(m-HCO2)] (Scheme 3). Similarly, the reaction of 10 afforded
the analogous species [tBu3PH][(norbornylB(C6F5)2)2A(m-
ACHTNUGERTN[NUGN ((C6F5)2BCy)2-
uted to a combination of steric bulk of the norbornyl sub-
stituent and the lesser Lewis acidity of the borane.
ACHTUNGTRENNUNG
A
CHTUNGTRENNUNG
All of the above-described compounds evolve CO2 upon
warming. Indeed in some cases, the compounds were found
to be unstable at room temperature. Similarly, exposure of
these complexes to H2 resulted in the liberation of CO2 and
the subsequent heterolytic activation of H2 to give the corre-
HCO2)] (12) as a 1:1 mixture of the respective pairs of rac
and meso diastereomers, which exhibited similar core spec-
tral parameters as observed for 11. The formation of 11 and
12 was confirmed by X-ray crystallography (Figure 5). The
anions of these salts are comprised of two borane fragments
À
sponding [tBu3PH]
G
bridged by a formate unit. The resulting B O distances in
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CO2 and Formate Complexes
FULL PAPER
Figure 5. POV depictions of the anions of a) 11 and b) 12.
À
the O-C-O angle is 121.2(5)8. The average of these B O dis-
tances is slightly longer than those seen in the recently re-
ported salt [TMPH]
2,2,6,6-tetramethylpiperidine; B O: 1.587(3), 1.584(3) ꢄ; C
(m-HCO2)][23s] (TMP=
ACHTUGTNRENNUG[((C6F5)3B)2ACHUTNGTRENNUGN
À
À
À
À
O: 1.256(3), 1.268(3) ꢄ), whereas the C O distances (B(1)
À
O(1) 1.611(7), B(2) O(2) 1.567(7), 1.253(6), 1.254(6) ꢄ) in
11 are slightly shorter. The B O distance of 1.566(4) ꢄ in 12
is similar to that in 11, whereas the C O distances of
À
Figure 4. POV depictions of a) 8, b) 9, and c) 10.
À
1.249(3) ꢄ is slightly shorter.
the anion of 11 are 1.611(7) and 1.567(7) ꢄ, the correspond-
In related chemistry, the boranes RBACHTGNUTERNNU(G C6F5)2 (R=hexyl,
À
ing C O distances in 11 are 1.253(6) and 1.254(6) ꢄ, and
Cy, norbornyl) were combined with one equivalent of tBu3P
and treated with one equivalent of formic acid. These reac-
tions occur rapidly and afford the formation of the new spe-
cies 13–15, respectively. These products exhibit 31P and
1H NMR resonances consistent with the presence of the
phosphonium cation [tBu3PH]+. The 1H NMR data also
show resonances at d=8.29, 8.20, and 8.17 ppm suggesting
the formation of the formato–borate anions, thus inferring
the formation of these products as [tBu3PH]
ACHTNUGRTNE[NUGN (C6F5)2BR-
AHCTUNGRTEGNUN(N HCO2)] (R=hexyl (13), Cy (14), norbornyl (15)). X-ray
crystallographic studies confirmed these interpretations
(Figure 6).
Additionally, some selected compounds were modeled
computationally. In general, good congruence between the
experimentally measured X-ray geometries and the calculat-
ed geometries is observed (Figure 7).[25] However, some de-
Scheme 3. Synthesis of compounds 8–15.
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9643

D. W. Stephan, S. Grimme, G. Erker et al.
Table 2. Computed reaction energies of PtBu3 and RBACHTUNRTGNE(GNU C6F5)2 (a). b) For-
mation of 3, 4, 6, and 6a relative to separate reactants, and c) formation
of 3, 4, 6, and 6a relative to the FLP and CO2.[a]
Compound
R
TPSS-D2
B2PLYP-D3//TPSS-D2
a
b
c
hexyl
Cy
Cl
H
hexyl
Cy
Cl
H
hexyl
Cy
Cl
À13.1
À9.7
À10.4
À7.3
À13.5
À27.8
À28.5
À31.2
À30.6
À31.4
À15.4
À21.5
À17.1
À3.6
À10.8
À20.9
À24.9
À27.1
À28.5
À27.7
À14.5
À19.8
À17.7
À6.9
3
4
6
6a
3
4
6
6a
H
[a] The def2-TZVP basis set was used. All energies are given in [kcal
molÀ1].
the reactants (Table 2b) and relative to the FLP and CO2
(Table 2c). In the following we will focus our discussion on
the data from the B2PLYP-D3 calculations, which have an
estimated accuracy of about 5–10% (TPSS-D2 data give
similar trends, see the Experimental Section).
Figure 6. POV depictions of the anions of a) 13 and b) 14.
All computed reactions are strongly exothermic. The
values for the phosphine–borane interactions (Table 2a)
range from À7 to À21 kcalmolÀ1. The reaction energies for
the formation of 3, 4, and 6 with respect to free reactants
vary only between À25 to À28 kcalmolÀ1. The smaller
energy values with respect to the FLP and CO2 (Table 2c)
simply reflect the different stabilities of the FLP, whereas
the energetics of the bonds formed are rather similar. The
formation of compound 4 is the most exothermic (see
Table 2c). Similarly, the corresponding FLP forms the stron-
gest P–B interactions, although it is almost isoenergetic with
the interaction of PtBu3 and CH3ACTHUNTRGENNUG(CH2)5BCAHTUNTGRENN(UNG C6F5)2.
These calculations also provide some insight regarding the
impact of borane substituents on the compound stability.
Formation of the FLP from PtBu3 and CyB
the highest energy of those calculated. The corresponding
values for the FLPs derived from CH3A(CH2)5B(C6F5)2 and
ClB
(C6F5)2 are about 3 kcalmolÀ1 lower and differ by only
ACHTNUGTNER(NGNU C6F5)2 results in
C
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
0.4 kcalmolÀ1. This reflects the smaller size of the Cl sub-
stituent and the higher flexibility of the n-hexyl chain. On
the other hand, the n-hexyl group is still bulkier than Cl and
this leads to a CO2 uptake energy for 4 that is comparable
to the one computed for the formation of 6.
Only the theoretically considered compound 6a differs
from the others as it gives rise to the lowest FLP self-
quench energy of all tested compounds as well as the small-
est reaction energy relative to the FLP (À6.9 kcalmolÀ1).
This infers a preference for the formation of the FLP as the
reaction with CO2 does not seem feasible as the energy gain
for this step is comparatively small and may even generate a
loss upon consideration of entropic corrections. Nonetheless,
it is noteworthy that the overall reaction energy of 6a is
very similar to that of compound 6, which suggests similar
behavior towards release of CO2.
Figure 7. Overlay of X-ray structure (green) and DFT-D2 optimized
structure (red) of a) 3 and b) 6.
viations between computed and experimental structures are
seen in the “outer” regions of the bulky substituents. This
presumably arises from crystal packing effects.[26] The inter-
action energies of PtBu3 with the boranes RBACHTUNGRTNEUNG(C6F5)2 (n-
hexyl, R=Cy, Cl, H) were calculated (Table 2a). The forma-
tion reaction energy values for compounds 3, 4, 6, and 6a
(see Table 2) were calculated and are reported relative to
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CO2 and Formate Complexes
FULL PAPER
13C{1H} NMR (101 MHz, CD2Cl2, 298 K): d=161.3 (d, 1J
PCO2), 148.4 (dm, 1J(F,C)=235 Hz, o-C6F4H), 146.0 (dm, 1J
240 Hz, m-C6F4H), 127.4 (br, i-C6F4H), 103.7 (t, 2J
(F,C)=23 Hz, p-CH),
(P,C)=3 Hz, iPr); 19F NMR
(377 MHz, CD2Cl2, 298 K): d=À134.7 (m, 6F; o-C6F4H), À143.1 ppm (m,
6F; m-C6F4H); 11B{1H} NMR (128 MHz, CD2Cl2, 298 K): d=À2.3 ppm
(br); 31P{1H} NMR (162 MHz, CD2Cl2, 298 K): d=37.3 ppm; IR (KBr):
n˜ =1700 cmÀ1 (C=O); elemental analysis calcd (%) for C28H24BF12O2P
(662.2): calcd: C 50.78, H 3.65; found: C 50.88, H 3.89.
ACHTUNGTRENNUNG
Conclusion
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
In summary, a variety of FLPs comprised of phosphine and
an electrophilic borane have been shown to bind CO2 af-
fording zwitterionic products of the form R3PCO2B-
1
2
22.2 (d, JACTHNUGERTN(NUNG P,C)=34.5 Hz, iPr), 17.0 ppm (d, JACHTUNGTRENNUNG
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
Analytical data for 2: yield: 180.0 mg (0.256 mmol, 59%); 1H NMR
(400 MHz, CD2Cl2, 298 K): d=6.85 (tt, 3J(H,F)=9.7, 4J
ACTHNUGTRENNUGN ACHTUNGTRENNNUG
3H; p-CH), 1.60 ppm (d, 3J
ACHTUNGTRENNUNG
CTHUNGTRENNUNG
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
E
ACHTUNGTRENNUNG
19.5 Hz, tBu), 30.7 ppm (tBu); 19F NMR (377 MHz, CD2Cl2, 298 K): d=
À133.8 (m, 6F; o-C6F4H), À143.2 ppm (m, 6F; m-C6F4H); 31P{1H} NMR
(162 MHz, CD2Cl2, 298 K): d=45.4 ppm; 11B{1H} NMR (128 MHz,
CD2Cl2, 298 K): d=À2.4 ppm; IR (KBr): n˜ =1699 cmÀ1 (C=O); elemental
analysis calcd (%) for C31H30BF12O2P (704.33): C 52.86, H 4.29; found C
53.05, H 4.47.
that although FLPs can capture CO2 and formate fragments,
the thermal instability of the CO2 adducts precludes deriva-
tization. It is for this reason that we now are exploring new
FLP systems that offer stronger Lewis acids. Efforts to
employ such new FLPs to effect reduction of CO2 or to uti-
lize CO2 in synthetic chemistry are underway.
Synthesis of tBu3PACHTUGNTRENUNN(G CO2)BRACHTNURTEGGN(NUN C6F5)2 ACHTGUNTREN(NUGN R=hexyl (3), Cy (4), norbornyl (5)):
These compounds were prepared in a similar fashion and thus only one
synthetic protocol is detailed. (C6F5)2BH (111.0 mg, 0.316 mmol) was sus-
pended in pentane (2 mL). Through
a syringe 1-hexene (40 mL,
0.316 mmol) was added and the solution was stirred for 10 min. After-
wards, tBu3P (64.0 mg, 0.316 mmol) was also dissolved in pentane (1 mL)
and added to the first solution. The reaction flask was cooled down to
À508C, degassed and then filled with CO2 (2.0 bar) and stirred for 5 min.
The immediately precipitated white solid was separated from the pentane
solution by removing the solvent with a cannula and the product was
dried in vacuo for 5 min also at low temperature. Crystals suitable for X-
ray analysis were obtained from a dichloromethane solution by slow dif-
fusion of pentane at À358C. Analytical data for 3: yield: 160 mg
(0.237 mmol, 75%); 1H NMR (400 MHz, CD2Cl2, 243 K): d=1.57 (d, 3J-
Experimental Section
General considerations: All manipulations were performed on a double-
manifold N2 (H2)/vacuum line with Schlenk-type glassware or in an N2-
filled inert atmospheres glovebox. The N2 and H2 gases were dried by
passage through a Dririte column. Solvents (Aldrich) were dried by using
an Innovative Technologies solvent system (toluene, hexane, pentane,
CH2Cl2). NMR spectra were obtained on a Bruker ARX 300 spectrome-
ter (1H: 300 MHz, 13C: 75 MHz), Bruker Avance 400 MHz spectrometer
(1H: 400 MHz, 13C: 101 MHz, 19F: 376 MHz, 11B: 128 MHz, 31P:
162 MHz) or, Varian Inova 500 (1H: 500 MHz, 13C: 126 MHz, 19F:
470 MHz, 11B: 160 MHz). 1H NMR and 13C NMR chemical shifts (d) are
given relative to TMS and referenced to the solvent signal (19F relative to
external CFCl3; 11B relative to external BF3·Et2O). NMR assignments are
supported by additional 1D and 2D NMR experiments. Assignments
marked with a superscript t are tentative assignments extracted from the
COSY, GHMBC and GHSQC NMR experiments. NMR spectra were re-
corded in CD2Cl2 unless otherwise stated and chemical shifts are report-
ed in ppm. NMR solvents were purchased from Cambridge Isotopes,
dried over CaH2 (CD2Cl2 and CDCl3), vacuum-distilled prior to use and
stored over 4 ꢄ molecular sieves in the glovebox. Elemental analyses
were performed on a Elementar Vario El III; IR spectra were recorded
on a Varian 3100 FT-IR (Excalibur Series). Melting points were obtained
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
(C-4), 30.0 (tBu), 26.6 (C-2), 23.5 (C-1), 22.9 (C-5), 14.2 ppm (C-6);
19F NMR (377 MHz, CD2Cl2, 243 K): d=À133.8 (dd, 3J
(F,F)=24.7, 4J-
ACHTUNGTRENNUNG
ACHTUGNTRENN(NUG F,F)=20.6 Hz, 1F; p-C6F5),
(F,F)=7.6 Hz, 2F; o-C6F5), À161.9 (t, 3J
À166.1 ppm (m, 1F; m-C6F5) [Dd19Fm,p =4.2 ppm]; 31P{1H} NMR
(162 MHz, CD2Cl2, 243 K): d=41.3 ppm (u1/2 ꢀ2 Hz); temperature of
CO2 loss: À148C; IR (KBr): n˜ =1693 cmÀ1 (s, C=O); elemental analysis
calcd (%) for C31H40BF10O2P (676.4): C 55.04, H 5.96; found: C 55.26, H
6.31.
with
a DSC Q20 (TA Instruments). The boranes RBCAHTUNTGNRUEGN(C6F5)2 (R=
(CH2)5CH3, Cy, (norbornyl), Cl, Ph) were prepared by literature meth-
Analytical data for 4: yield: 140 mg (0.208 mmol, 71%); 1H NMR
(500 MHz, CD2Cl2, 243 K): d=1.54 (d, 3J
ACHTUNGTRENNUNG
ods.[27]
Synthesis of R3P
pounds were prepared in a similar fashion and thus only one synthetic
protocol is detailed. A solution of B(p-C6F4H)3 (81.0 mg, 0.177 mmol) in
ACHTUNGTRENNUNG(CO2)BAHCTUNRTGE(GNNNU p-C6F4H)3 ACHTNGUTREN(NUGN R=iPr (1), tBu (2)): These com-
ACHTUNGTRENNUNG
91.9 Hz, PCO2), 147.4 (dm, 1J
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
ꢀ240 Hz, m,p-C6F5), not observed (i-C6F5), 40.2 (d, 1J
ACHTUNGTRENNUNG
dichloromethane (2 mL) was mixed with iPr3P (290.0 mg of a 10 wt% so-
lution in hexane, 0.181 mmol) and cooled to À 648C. The solution was
pressurized with CO2 and allowed to warm to ambient temperature. The
reaction mixture gradually became turbid. After stirring overnight, all
volatiles were removed in vacuo at 08C to yield the crude product as a
colorless, powdery residue. The residue was extracted with cold dichloro-
methane (3ꢅ2 mL) and pentane (ca. 2 mL) was added in a dropwise
fashion. The mixture was filtered and the mother liquor was evaporated
to dryness in vacuo. The colorless residue was recrystallized by storing a
cold, saturated dichloromethane/pentane solution (ca. 1:1) at À358C for
several days. Analytical data for 1: yield: 90.0 mg (136.0 mmol, 77%);
tBu), 32.0 (br, C-1), 29.9, 28.6, 27.6 (br, CH2), 29.9 ppm (tBu); 19F NMR
(470 MHz, CD2Cl2, 243 K): d=À132.0 (br, 2F; o-C6F5), À161.6 (br, 1F;
p-C6F5), À166.0 ppm (br, 2F; m-C6F5) [Dd19Fm,p =4.4 ppm]; 31P{1H} NMR
(202 MHz, CD2Cl2, 243 K): d=41.0 ppm (u1/2 ꢀ9 Hz); temperature of
CO2 loss: À168C; IR (KBr): n˜ =1698 cmÀ1 (s, C=O); elemental analysis
calcd (%) for C31H38BF10O2P (674.4): C 55.21, H 5.68; found: C 55.01, H
5.77.
Analytical data for 5: yield: 340 mg (0.495 mmol, 86%). At low tempera-
ture the solubility of 5 is very poor. At room temperature the system re-
leased CO2 partially, leading to an equilibrium of (norbornyl)BACHTUNGTRENNUNG(C6F5)2/
PtBu3 and compound 5 in a ratio of 4:1. 1H NMR (500 MHz, CD2Cl2,
1H NMR (400 MHz, CD2Cl2, 298 K): d=6.87 (tt, 3J
7.0 Hz, 3H; p-CH), 2.79 (dsept, 2J(P,H)=14.0, 3J
iPr), 1.41 ppm (dd, 3J(P,H)=16.5, 3J
(H,H)=7.1 Hz, 18H; iPr);
A
ACHTUNGTRNE(NUNG H,F)=
3
A
U
298 K): d=2.05/196 (each m, 1H; 1,4-H), 1.61 (d, J
(P,H)=14.2 Hz, 27H;
A
U
tBu), 1.42/1.17 (each m, 2H; 5-Ht), 1.41/1.28 (each m, 2H; 6-Ht), n.o. (2-
Chem. Eur. J. 2011, 17, 9640 – 9650
ꢃ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9645

D. W. Stephan, S. Grimme, G. Erker et al.
H), 1.31 (m, 4H; 3-Ht), 0.74/0.28 ppm (each brm, 2H; 7-Ht);
13C{1H} NMR (126 MHz, CD2Cl2, 298 K): d=n.o. (CO), 39.7, 37.0 (C-
1,4), 40.6 (tBu), 37.1 (C-7), 34.9 (C-3t), n.o. (C-2), 34.6 (C-6t), 30.4 (tBu),
29.2 ppm (C-5t); 19F NMR (470 MHz, CD2Cl2, 243 K): d=À130.2 (br, 2F;
ble for X-ray analysis were obtained from a dichloromethane solution by
slow diffusion of pentane at À358C.
Analytical data for 8: yield: 180.0 mg (0.284 mmol, 60%); 1H NMR
(500 MHz, CD2Cl2, 298 K): d=5.46 (d, 1J
G
o-C6F5), À151.1 (br, 1F; p-C6F5), À162.3 ppm (br, 2F, m-C6F5) [Dd19Fm,p
=
3
(br, 1H; BH), 1.64 (d, J
N
11.2 ppm] [(norbornyl)BACHTNUTGRNEUNG
(C6F5)2/PtBu3: ca. 80%]; 19F NMR (470 MHz,
0.80 (each m, 2H; CH2), 0.85 ppm (t, 3J
13C{1H} NMR (126 MHz, CD2Cl2, 298 K): d=148.5 (dm, J
CD2Cl2, 243 K): d=À130.5, À131.5 (each br, 2F; o-C6F5), À161.7, À162.1
(each t, 3J
G
1
o-C6F5), 137.6 (dm, J
U
1
2F; m-C6F5) [Dd19Fm,p ꢀ(4.5Æ0.3) ppm] [5: ca. 20%]; 31P{1H} NMR
(202 MHz, CD2Cl2, 298 K): d=62.4 (u1/2 ꢀ3 Hz, tBu3P: ca. 80%), 57.8 (u1/
2 ꢀ2 Hz, tBu3PH+: traces], 42.5 ppm (u1/2 ꢀ3 Hz, 5: ca. 20%]; tempera-
ture of CO2 loss: À168C; IR (KBr): n˜ =1686 cmÀ1 (s, C=O); elemental
analysis calcd (%) for: C32H38BF10O2P (686.4): C 55.99, H 5.58; found: C
55.08, H 5.23.
m-C6F5), 129.8 (br, i-C6F5), 37.9 (d, J
A
(br), 23.4 (br), 23.3 (CH2), 30.3 (tBu), 14.4 ppm (C-6); 19F NMR
(470 MHz, CD2Cl2, 298 K): d=À132.9 (m, 2F; o-C6F5), À165.8 (br, 1F;
p-C6F5), À167.6 ppm (m, 2F; m-C6F5) [Dd19Fm,p =1.8 ppm]; 11B{1H} NMR
(160 MHz, CD2Cl2, 298 K): d=À18.4 (u1/2 ꢀ200 Hz); 31P NMR (202 MHz,
CD2Cl2, 298 K): d=57.7 (dm, 1J
(%) for C30H42BF10P (634.4): C 56.80, H 6.67; found: C 56.27, H 6.40.
G
Preparation of tBu3P
ACHTUNGTRENNUNG(CO2)BACHTUNTGREN(NUGN C6F5)2Cl (6): A 50 mL schlenk flask was
Analytical data for 9: yield: 203.0 mg (0.321 mmol, 66%); 1H NMR
charged with ClB(C6F5)2 (150.0 mg, 0.394 mmol) and tBu3P (80.0 mg,
ACHTUNGTRENNUNG
(500 MHz, CD2Cl2, 298 K): d=5.49 (d, 1J
ACTHNUTRGNE(NUG P,H)=437.2 Hz, 1H; PH), 2.44
0.395 mmol) in bromobenzene (10 mL). The bright yellow solution was
degassed and backfilled with CO2 (1 bar). The reaction mixture was then
stirred for two hours at room temperature. At this time, pentane (20 mL)
was added precipitating an off-white solid. The solvent was decanted and
the crude product was washed with pentane (3ꢅ5 mL). The product 6
was then dried in vacuo for two hours. Yield: 193.0 mg (79%). Crystals
suitable for X-ray diffraction were grown from a layered CH2Cl2/cyclo-
hexane solution at 258C. 1H NMR (600 MHz, CD2Cl2, 298 K): d=
(brm, 1H; BH), 1.66 (d, 3J
ACTHNUGRTENUNG(P,H)=15.6 Hz, 27H; tBu), 1.64/1.17 (each m,
t
1H; 4CH2), 1.61/1.21 (each m, 2H; 3,5CH2 ), 1.49/0.84 (each m, 2H;
t
2,6CH2 ), 1.09 ppm (br, 1H; 1-H); 13C{1H} NMR (126 MHz, CD2Cl2,
298 K): d=148.2 (dm, 1J
G
ACHTUNGTRENNUNG
ꢀ246 Hz, p-C6F5), 136.5 (dm, 1J
ACHTUNGTRENNUNG
t
C6F5), 37.9 (d, 1J
(tBu), 29.6 ppm
(P,C)=25.9 Hz, tBu), 35.2 (2,6CH2 ), 30.7 (br, C-1), 30.3
ACHTUNGTRENNUNG
(
t
3,5CH2 ), 28.6 (4CH2); 19F NMR (470 MHz, 298 K,
CD2Cl2): d=À132.0 (m, 2F; o-C6F5), À166.0 (m, 1F; p-C6F5),
ACHTUNGTRENNUNG
1.68 ppm (d, 3J(P,H)=14.5 Hz, tBu); 13C{1H} NMR (151 MHz, CD2Cl2,
À167.6 ppm (m, 2F; m-C6F5) [Dd19Fm,p =1.6 ppm]; 11B NMR (160 MHz,
298 K): d=161.0 (d, 1J(P,C)=93.4 Hz, PCO2), 147.8 (dm, 1J
ACTHNUGTRENNUGN ACHTUNGTRENNNUG
1
298 K, CD2Cl2): d=À17.6 ppm (d, J
ACHTUNGTRENNUNG
ꢀ238 Hz, o-C6F5), 140.0 (dm, 1J
ACHTUNGTRENNUNG
1
298 K, CD2Cl2): d=57.7 ppm (dm, J
A
(F,C)ꢀ256 Hz, m-C6F5), n.o. (i-C6F5), 41.3 (d, 1J
ACHTUNGTRENNUNG
calcd (%) for C30H40BF10P (632.4): C 56.98, H 6.38; found: C 56.43, H
6.38.
30.5 ppm (tBu); 19F NMR (564 MHz, CD2Cl2, 298 K): d=À133.8 (m, 2F;
3
o-C6F5), À159.5 (t, J
G
Analytical data for 10: yield: 144 mg (0.223 mmol, 77%); 1H NMR
C6F5), [Dd19Fm,p =6.1 ppm]; 11B{1H} NMR (192 MHz, CD2Cl2, 298 K): d=
2.1 ppm (u1/2 ꢀ150 Hz); 31P{1H} NMR (243 MHz, CD2Cl2, 298 K): d=
45.0 ppm (u1/2 ꢀ2 Hz); IR (KBr): n˜ =1702 cmÀ1 (C=O); elemental analy-
sis calcd (%) for C25H27BClF10O2P (626.7): C, 47.88; H, 4.34, found: C,
47.89; H, 4.46.
(500 MHz, CD2Cl2, 298 K): d=5.28 (d, 1J
ACHTUNGTRENNUNG
3
t
ACTHNUTRGNEUNG
Ht), 1.65 (d, J(P,H)=15.7 Hz, 27H; tBu), 1.59/0.87 (each m, 1H; 7CH2 ),
t
t
1.44/1.19 (each m, 1H; 5CH2 ), 1.43/1.12 (each m, 1H; 6CH2 ), 1.18 (m,
1H; 2-H), 1.13/1.00 ppm (each m, 1H; 3CH2 ); 13C{1H} NMR (126 MHz,
t
CD2Cl2, 298 K): d=147.5 (dm, 1J
ACHTUNGTRENNUNG
(F,C)ꢀ233 Hz, o-C6F5), 137.5 (dm, 1J-
Preparation of tBu3PCO2B
ACHTNUGTERN(NGNU C6F5)2Ph (7): A 100 mL Schlenk flask was
1
charged with PhB(C6F5)2 (0.100 g, 0.237 mmol) and tBu3P (0.048 g,
ACHTUNGTRENNUNG
N
U
C6F5), 42.2 (br, C-1t), 38.5 (br, 3CH2 ), 38.4 (br, C-4t), 38.0 (d, 1J
ACHTUNGTRENNUNG(P,C)=
0.237 mmol) in pentane (10 mL) and bromobenzene (1 mL). The reaction
mixture was degassed and backfilled with CO2 (1 bar). The reaction in-
stantly became cloudy and was stirred for a further 12 h. The white pre-
cipitate was allowed to settle and the solvent was decanted. The product
was washed with pentane (3ꢅ5 mL) and dried in vacuo for 2 h. Yield:
0.087 g (55%); 1H NMR (400 MHz, CD2Cl2, 298 K): d=7.68 (d, 3J-
7
t
5
t
27.0 Hz, tBu), 36.6 (br, CH2 ), 34.8 (br, C-2), 34.3 (br, CH2 ), 30.3 (tBu),
t
30.2 ppm (br, 6CH2 ); 19F NMR (470 MHz, CD2Cl2, 298 K): d=À131.9
(m, 2F; o-C6F5A), À132.2 (m, 2F; o-C6F5B), À166.0 (t, 3J
ACHTUNGTREN(NUNG F,F)=20.3 Hz,
1F; p-C6F5A), À166.1 (t, 3J(F,F)=20.2 Hz, 1F; p-C6F5B), À167.6 (m, 2F;
R
m-C6F5B), À167.7 ppm (m, 2F; m-C6F5A), [Dd19Fm,p =1.7A, 1.5B ppm];
A
U
11B NMR (160 MHz, CD2Cl2, 298 K): d=À18.5 (d, 1J
(B,H)ꢀ90 Hz);
31P NMR (202 MHz, CD2Cl2, 298 K): d=58.7 (dm, J
(P,H)ꢀ433 Hz); ele-
1
A
ACHTUNGTRENNUNG
mental analysis calcd (%) for C31H40BF10P (644.4): C 57.78, H 6.26;
found: C 57.68, H 6.20.
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
Generation of [tBu3PD]
norbornyl ([D2]10)): These compounds were prepared in a similar fash-
ion and thus only one preparation is detailed. HB(C6F5)2 (165.0 mg,
ACHTUNTGERN[NUG RBDHCAUTNGTERNN(UGN C6F5)2] (R=hexyl ([D2]8), Cy ([D2]9),
AHCTUNGTRENNUNG
20.0 Hz, tBu); 29.3 ppm (tBu); 19F NMR (377 MHz, CD2Cl2, 298 K): d=
AHCTUNGTRENNUNG
3
3
À130.5 (d, J
(F,F)=23.0 Hz, 4F; o-C6F5), À160.0 (t, J
ACHTUNGTREN(NUGN F,F)=21.0 Hz, 2F;
0.477 mmol) was suspended in pentane (2 mL). Through a syringe 1-
hexene (60 mL, 0.477 mmol) was added dropwise and the mixture was
stirred for 10 min. tBu3P (94.0 mg, 0.477 mmol) was also dissolved in pen-
tane (2 mL) and added to the first solution. The degassed reaction flask
was then filled with D2 (2.0 bar) at ambient temperature for 10 min and
stirred overnight. The precipitated white solid was separated from the
pentane solution by removing the solvent with a cannula. The product
was washed with pentane (2ꢅ4 mL) and dried in vacuo for two hours.
p-C6F5), À164.7 ppm (m, 4F; m-C6F5); 11B{1H} NMR (128 MHz, CD2Cl2,
298 K): d=0.83 ppm; 31P{1H} NMR (162 MHz, CD2Cl2, 298 K): d=
1
43.9 ppm (d, J
(P,C)=92 Hz); IR (KBr): n˜ =1695 cmÀ1 (C=O); elemental
analysis calcd (%) for C31H32BF10O2P (668.3): C 55.67, H 4.83; found: C
55.60, H 5.09.
Preparation of [tBu3PH]ACHTNUTRGENN[UG RBHCAHTUNGTREN(NUGN C6F5)2] (R=hexyl (8), Cy (9), norbornyl
(10)): These compounds were prepared in a similar fashion and thus only
one preparation is detailed. (C6F5)2BH (165.0 mg, 0.477 mmol) was sus-
pended in pentane (2 mL). Through
0.477 mmol) was added dropwise and the mixture was stirred for 10 min.
tBu3P (94.0 mg, 0.477 mmol) was also dissolved in pentane (2 mL) and
added to the first solution. The degassed reaction flask was then filled
with H2 (2.0 bar) at ambient temperature for 10 min and stirred over-
night. The precipitated white solid was separated from the pentane solu-
tion by removing the solvent with a cannula. The product was washed
with pentane (2ꢅ4 mL) and dried in vacuo for two hours. Crystals suita-
Analytical data for [D2]8: yield: 212.0 mg (0.333 mmol, 70%); 2H NMR
(77 MHz, CH2Cl2, 298 K): d=5.45 (d, 1J
ACTHNUTRGNEUNG(P,D)=66.1 Hz, 1D; PD),
a syringe 1-hexene (60 mL,
2.72 ppm (br, 1D; BD).
Analytical data for [D2]9: yield: 116.0 mg (0.183 mmol, 75%); 2H NMR
(77 MHz, CH2Cl2, 298 K): d=5.49 (d, 1J
ACTHNUTRGNEUNG(P,D)=66.9 Hz, 1D; PD),
2.49 ppm (br, 1D; BD).
Analytical data for [D2]10: yield: 212 mg (0.328 mmol, 77%); 2H NMR
(77 MHz, CH2Cl2, 298 K): d=5.30 (d, 1J
ACTHNUTRGNEUNG(P,D)=66.8 Hz, 1D; PD),
2.50 ppm (br, 1D; BD);
9646
www.chemeurj.org
ꢃ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 9640 – 9650

CO2 and Formate Complexes
FULL PAPER
Synthesis of [tBu3PH]
G
E
product was washed with pentane (2ꢅ10 mL) and dried in vacuo for one
hour. Crystals suitable for X-ray analysis were obtained from dichloro-
methane by slow diffusion of pentane at À358C.
(12)): These compounds were prepared in an analogous manner and thus
only one preparation is detailed. In addition these species were prepared
by two methods.
Analytical data for 13: yield: 250.0 mg (0.368 mmol, 85%); 1H NMR
(600 MHz, CD2Cl2, 298 K): d=8.29 (s, 1H; CHO2), 5.81 (brd, 1J
N
Method 1: Compound 9 (203.0 mg, 0.321 mmol) was dissolved in bromo-
benzene (6 mL), the solution was added to a thick-walled reaction flask,
degassed and filled with CO2. The reaction mixture was heated to 608C
overnight. Afterwards, the solvent was removed in vacuo and the crude
3
448.9 Hz, 1H; PH), 1.64 (d, J
N
1.05 (each m, 2H; CH2), 1.01 (m, 2H; 1-H), 0.84 ppm (m, 3H; 6-H);
13C{1H} NMR (151 MHz, CD2Cl2, 298 K): d=166.4 (HCO2), 148.0 (dm,
1
1J
1J
N
(F,C)ꢀ254 Hz, p-C6F5), 137.2 (dm,
product was recrystallized from
(F,C)ꢀ237 Hz, m-C6F5), n.o. (i-C6F5), 37.7 (d, 1J
ACHTUNGTRENNUNG
(1:1). Crystals of 11 suitable for X-ray analysis were obtained from di-
chloromethane by slow diffusion of pentane at À358C.
30.3 (tBu), 34.0, 32.6, 26.6, 23.3 (CH2), 25.2 (br, C-1), 14.4 ppm (C-6);
19F NMR (564 MHz, CD2Cl2, 298 K): d=À133.9 (m, 2F; o-C6F5), À163.3
Method 2: (C6F5)2BH (375.0 mg, 1.084 mmol) was dissolved in bromoben-
zene (3 mL). Through a syringe cyclohexene (110 mL, 1.084 mmol) was
added dropwise and the solution was stirred for 10 min. tBu3P (110.0 mg,
0.542 mmol) was also dissolved in bromobenzene (2 mL) and added to
the first solution. Afterwards, formic acid (20 mL, 0.542 mmol) was added
through a syringe and the reaction mixture was stirred overnight at ambi-
ent temperature. After removal of half of the solvent and addition of
pentane (12 mL), the suspension was stored in a freezer for one hour. Af-
terwards, the solvent was removed with a syringe and washed twice with
pentane (2ꢅ10 mL) and dried in vacuo for one hour.
(t, 3J
(F,F)=20.7 Hz, 1F; p-C6F5), À166.8 ppm (m, 2F; m-C6F5)
[Dd19Fm,p =3.5 ppm]; 11B{1H} NMR (192 MHz, CD2Cl2, 298 K): d=
0.6 ppm (u1/2 ꢀ200 Hz); 31P NMR (243 MHz, CD2Cl2, 298 K): d=55.1
(brd, 1J
ACHTUNGTRENNUNG
elemental analysis calcd (%) for C31H42BF10O2P (678.4): C 54.88, H 6.24;
found: C 54.80, H 5.91.
Analytical data for 14: yield: 230.0 mg (0.340 mmol, 78%); 1H NMR
(500 MHz, CD2Cl2, 298 K): d=8.20 (s, 1H; CHO2), 5.82 (brd, 1J
ACHTUNGTRENNUNG(P,H)=
443.2 Hz, 1H; PH), 1.64 (d, 3J
N
t
m, 2H; 3,5CH2 ), 1.63/1.07 (each m, 1H; 4CH2), 1.62/0.72 (each m, 2H;
Analytical data for 11: Method 1: yield: 95.0 mg (0.067 mmol, 45%; max-
imum yield: 50%); Method 2: yield: 545.0 mg (0.493 mmol, 91%);
1H NMR (600 MHz, CD2Cl2, 298 K): d=8.04 (s, 1H; CHO2), 5.09 (d, 1J-
t
2,6CH2 ), 1.30 ppm (br, 1H; 1-H); 13C{1H} NMR (126 MHz, CD2Cl2,
298 K): d=166.4 (HCO2), 148.2 (dm, 1J
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG ACHTUNGTREN(NGUN P,H)=15.8 Hz, 27H; tBu), 1.62/
(P,H)=427.7 Hz, 1H; PH), 1.66 (d, 3J
(dm, 1J(F,C)=245 Hz, p-C6F5), 136.6 (dm, 1J
ACTHNUGTRENNUGN ACHTUNGTRENNNUG
4
1.04 (each m, 2H; CH2), 1.60/1.20 (each m, 4H; 3,5CH2 ), 1.50/0.61 (each
124.6 (br, i-C6F5), 37.7 (d, 1J
t
m, 4H; 2,6CH2 ), 1.27 ppm (m, 2H; 1-H); 13C{1H} NMR (151 MHz,
t
(
2,6CH2 ), 30.3 (tBu), 29.3 (3,5CH2 ), 28.3 ppm (4CH2); 19F NMR (470 MHz,
CD2Cl2, 298 K): d=173.4 (HCO), 147.8 (dm, 1J
ACHTUNGTRENNUNG
CD2Cl2, 298 K): d=À132.3 (m, 2F; o-C6F5), À163.0 (t, 3J
139.2 (dm, 1J
G
1F; p-C6F5), À166.4 ppm (m, 2F; m-C6F5) [Dd19Fm,p =3.4 ppm];
C6F5), 121.3 (br, i-C6F5), 38.1 (d, 1J
11B{1H} NMR (160 MHz, CD2Cl2, 298 K): d=1.5 ppm (u1/2 ꢀ200 Hz);
2,6CH2 ), 28.8
31P NMR (202 MHz, CD2Cl2, 298 K): d=55.4 ppm (dm, 1J
ACHTUNGTRENNUNG(P,H)
30.3 (tBu), 30.0
(
(564 MHz, CD2Cl2, 298 K): d=À132.6 (m, 2F; o-C6F5), À161.1 (t, 3J-
ꢀ444 Hz); IR (KBr): n˜ =1689 (s), 1645 (m), 1516 (s), 1464 cmÀ1 (s); ele-
mental analysis calcd (%) for C31H40BF10O2P (676.4): C 55.08, H 5.96;
found: C 54.64, H 5.71.
A
5.6 ppm]; 11B NMR (192 MHz, CD2Cl2, 298 K): d=5.1 ppm (u1/2
ꢀ500 Hz); 31P NMR (243 MHz, 298 K, CD2Cl2): d=60.5 (dm, 1J
Analytical data for 15: yield: 280.0 mg (0.407 mmol, 70%); 1H NMR
~428 Hz); IR (KBr): n˜ =1631 cmÀ1 (s); elemental analysis calcd (%) for
(600 MHz, CD2Cl2, 298 K): d=8.17 (s, 1H; CHO2), 5.81 (d, 1J
ACHTUNGTRENNUNG
C49H52B2F20O2P (1105.5): C 53.24, H 4.74; found: C 52.83, H 4.61.
Analytical data for 12: Method 1: yield: 75.0 mg (0.066 mmol, 46%; max-
imum yield: 50%); Method 2: yield: 417.0 mg (0.369 mmol, 71%); 1:1
mixture of pairs of diastereomers; 1H NMR (500 MHz, CD2Cl2, 298 K):
AHCTUNGTRENNUNG
(P,H)=15.5 Hz, 27H; tBu), 1.44/1.31 (each m, 1H; 5-Ht), 1.44/1.15 (each
m, 1H; 6-Ht), 1.35 (m, 1H; 2-H), 1.27/1.12 (each m, 1H; 3-Ht), 0.92/
0.84 ppm (each brm, 1H; 7-Ht); 13C{1H} NMR (151 MHz, CD2Cl2,
d=8.04 (s, 1H; CHO2), 5.13 (d, 1J
ACHTUNGTRENNUNG
298 K): d=165.9 (HCO2), 148.1 (dm, 1J
ACHTUNGTRENNUNG
2H; 4-Ht), 1.92/1.91 (each m, S2H; 1-Ht), 1.66 (d, 3J
ACHTUNGTRENNUNG
(dm, 1J
125.4 (br, i-C6F5), 40.2 (C-1t), 37.7 (d, 1J
AHCTUNGTRENNUNG
N
ACHTUNGTRENNUNG
27H; tBu), 1.42/1.12 (each m, 2H; 5-Ht), 1.40/1.22 (each m, 2H; 6-Ht),
1.30 (m, 2H; 2-H), 1.17 (m, 4H; 3-Ht), 0.79/0.70 ppm (each brm, 2H; 7-
Ht); 13C{1H} NMR (126 MHz, CD2Cl2, 298 K): d=172.7, 172.6 (CHO2),
37.4 (C-7), 35.7 (br, C-2), 35.5 (C-3t), 34.7 (C-5t), 30.3 (tBu), 29.4 ppm (C-
6t); 19F NMR (564 MHz, CD2Cl2, 298 K): d=À132.1 (m, 2F; o-C6F5A),
1
1
147.9 (dm, J
N
G
À133.3 (m, 2F; o-C6F5B), À162.6 (t, 3J
(F,F)=20.0 Hz, 1F; p-C6F5A),
ACHTUNGTRENNUNG
137.3 (dm, 1J
ACHTUNGTRENNUNG
À163.4 (t, 3J(F,F)=20.5 Hz, 1F; p-C6F5B), À166.4 (m, 2F; m-C6F5A),
U
ACHTUNGTRENNUNG
(d, 1J(P,C)=26.8 Hz, tBu), 37.4, 37.32 (C-4t), 37.30. 37.28 (m, C-7t), 35.1
À166.8 ppm (m, 2F; m-C6F5B) [Dd19Fm,p =3.8A, 3.4B ppm]; 11B{1H} NMR
(br, C-3t), 34.7 (br, C-2), 34.5, 34.4 (C-6t), 30.4 (tBu), 29.2 ppm (br, C-5t);
19F NMR (470 MHz, CD2Cl2, 298 K): d=À131.9, À132.0, (each m, 2F; o-
C6F5A), À132.9, À133.0, (each m, 2F; o-C6F5B), À160.6, À160.7 (each t, 3J-
(192 MHz, CD2Cl2, 298 K): d=1.0 ppm (u1/2 ꢀ170 Hz); 31P NMR
(243 MHz, CD2Cl2, 298 K): d=55.5 ppm (dm, 1J
(P,H)ꢀ450 Hz); IR
(KBr): n˜ =1681 (s), 1645 (m), 1515 (s), 1464 cmÀ1 (s); elemental analysis
calcd (%) for C32H40BF10O2P (688.4): C 55.83, H 5.86; found: 55.42, H
5.49.
(F,F)=20.0 Hz, 1F; p-C6F5A), À161.3, À161.4 (each t, 3J
1F; p-C6F5B), À165.4, À165.5 (each m, 2F; m-C6F5A), À165.8,
À165.9 ppm (each m, 2F; m-C6F5B); 11B{1H} NMR (160 MHz, CD2Cl2,
298 K): d=4.3 ppm (u1/2 ꢀ500 Hz); 31P NMR (202 MHz, CD2Cl2, 298 K):
X-ray data collection and reduction (Toronto): Crystals were coated in
Paratone-N oil in a glovebox, mounted on a MiTegen Micromount and
placed under an N2 stream, thus maintaining a dry, O2-free environment
for each crystal. The data were collected on a Bruker Apex II diffractom-
eter with MoKa radiation (l=0.71069). The frames were integrated with
the Bruker SAINT[36] software package by using a narrow-frame algo-
rithm. Data were corrected for absorption effects by using the empirical
multi-scan method (SADABS[37]).
d=60.1 (dm, 1J
(P,H)ꢀ429 Hz); IR (KBr): n˜ =1638 (s); elemental analy-
sis calcd (%) for C51H52B2F20O2P (1129.5): C 54.23, H 4.64; found C
54.09, H 3.42.
Synthesis of [tBu3PH]
bornyl (15)): These compounds were prepared in a similar fashion and
thus only one preparation is detailed. HB(C6F5)2 (150.0 mg, 0.434 mmol)
ACHTUNGTRENNUNG[(C6F5)2BRACHTUNGTNER(NUGN O2CH)] (R=hexyl (13), Cy (14), nor-
AHCTUNGTRENNUNG
was dissolved in toluene (4 mL). Through a syringe 1-hexene (54 mL,
0.434 mmol) was added dropwise and stirred for 10 min. tBu3P (88.0 mg,
0.434 mmol) was also dissolved in toluene (2 mL) and added to the first
solution. Afterwards, formic acid (16 mL, 0.434 mmol) was added through
a syringe and the reaction mixture was stirred for one hour at ambient
temperature. After addition of pentane (10 mL) a white solid precipitat-
ed from the solution and the supernatant solution was decanted. The
X-ray data collection and reduction (Mꢀnster): Crystals were coated in
FOMBLIN Y oil, mounted on a glass fiber and placed under an N2
stream, thus maintaining a dry, O2-free environment for each crystal. The
data were collected on Nonius Kappa CCD diffractometers, both with
APEXII detectors, in case of Mo radiation a rotating anode generator
equipped with Montel mirrors was used. The frames were integrated with
Chem. Eur. J. 2011, 17, 9640 – 9650
ꢃ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9647

D. W. Stephan, S. Grimme, G. Erker et al.
the DENZO[38] software package including absorption corrections by
using the empirical multi-scan method.
and allowed to ride on the carbon to which they are bonded assuming a
À
C H bond length of 0.95 ꢄ. Hydrogen-atom temperature factors were
fixed at 1.10 times the isotropic temperature factor of the carbon atom to
which they are bonded. The hydrogen-atom contributions were calculat-
ed, but not refined. The locations of the largest peaks in the final differ-
ence Fourier map calculation as well as the magnitude of the residual
electron densities in each case were of no chemical significance. Addi-
tional details are provided in the Supporting Information.
Structure solution and refinement (Toronto): Non-hydrogen atomic scat-
tering factors were taken from the literature tabulations.[28] The heavy
atom positions were determined by using direct methods employing the
SHELXTL[39] direct methods routine. The remaining non-hydrogen
atoms were located from successive difference Fourier map calculations.
The refinements were carried out by using full-matrix least squares tech-
niques on F, minimizing the function w
G
Structure solution and refinement (Mꢀnster): Non-hydrogen atomic scat-
tering factors were taken from the literature tabulations.[28] The heavy
atom positions were determined by using direct or Patterson methods
employing the SHELXS[40] routine. The remaining non-hydrogen atoms
were located from successive difference Fourier map calculations. The re-
finements were carried out by using full-matrix least squares techniques
2
2
fined as 4Fo /2s (Fo ) and Fo and Fc are the observed and calculated struc-
ture factor amplitudes, respectively. In the final cycles of each refine-
ment, anisotropic temperature factors were assigned to all non-hydrogen
atoms except in cases of disorder or insufficient data. In the latter cases
À
atoms were treated isotropically. C H atom positions were calculated
Table 3. Crystallographic data.
2·CH2Cl2
3
4·CH2Cl2
5·CH2Cl2
6
formula
C32H32BCl2F12O2P
789.26
monoclinic
C2/c
37.5992(19)
9.1190(5)
21.6909(11)
90.00
114.066(2)
90.00
C31H40BF10O2P
676.41
monoclinic
P21/n
9.0306(3)
17.9639(7)
21.8857(9)
90.00
100.321(2)
90.00
3493.0(2)
4
C32H40BCl2F10O2P
759.32
C33H40BCl2F10O2P
771.33
C25H27BClF10O2P
626.70
monoclinic
C2/c
32.4596(9)
8.6466(3)
22.3184(8)
90.00
119.588(3)
90.00
5447.20(3)
8
M [gmolÀ1
]
crystal system
space group
a [ꢄ]
b [ꢄ]
c [ꢄ]
triclinic
triclinic
¯
¯
P1
P1
9.4143(1)
11.9296(1)
16.8587(1)
81.528(1)
76.336(1)
71.861(1)
1742.77(3)
2
9.4213(5)
11.8188(6)
17.1466(9)
81.847(2)
75.654(3)
72.219(3)
1756.82(16)
2
a [8]
b [8]
g [8]
V [ꢄ3]
Z
6790.6(6)
8
l [ꢄ]
0.71073
150(2)
1.544
1.54178
223(2)
1.286
1.54178
223(2)
1.447
1.54178
223(2)
1.458
1.54178
223(2)
1.528
T [K]
1calcd [gcmÀ3
]
Rint
0.0677
0.335
0.058
14.11
0.077
28.57
0.053
28.44
0.044
26.46
m [cmÀ1
]
total data
unique data
71040
10291
7198
47055
6216
5245
22342
6029
4406
22979
6161
5085
17806
4810
4195
2
data>2s
N
)
variables
460
350
442
470
370
R
(>2s)
0.0538
0.095
0.053
0.054
0.042
Rw
0.1627
0.281
0.131
0.146
0.115
GOF
1.026
1.039
1.014
1.027
1.021
9
10
11
12
13
14·CH2Cl2
formula
C30H42BF10
634.42
monoclinic
P21/c
20.1797(5)
17.3034(5)
20.1334(5)
90.00
112.293(2)
90.00
6504.7(3)
8
C31H40BF10P
644.41
monoclinic
P21/c
11.7360(2)
23.5022(5)
12.3519(3)
90.00
111.8070(10)
90.00
C49H42B2F20O2P
C51H51B2F20O2P
1128.51
monoclinic
C2/c
15.5966(11)
18.1216(8)
18.3225(5)
90.00
93.638(3)
90.00
5168.1(5)
4
C31H40BF10O2P
C32H44BCl2F10O2P
763.35
M [gmolÀ1
]
1095.42
monoclinic
P21/n
15.6851(11)
16.2344(13)
20.0983(15)
90.00
104.151(2)
90.00
4962.5(6)
4
676.41
orthorhombic
P212121
9.0103(2)
14.8207(3)
24.2492(6)
90.00
90.00
90.00
3238.21(13)
4
crystal system
space group
a [ꢄ]
b [ꢄ]
c [ꢄ]
triclinic
¯
P1
9.0425(2)
12.2269(2)
17.8775(4)
70.717(7)
83.012(7)
88.212(6)
1851.74(7)
2
a [8]
b [8]
g [8]
V [ꢄ3]
Z
3163.12(12)
4
l [ꢄ]
1.54178
223(2)
1.296
0.71073
150(2)
1.353
0.71073
150(2)
1.466
1.54178
223(2)
1.482
0.71073
223(2)
1.387
0.71073
223(2)
1.369
T [K]
1calcd [gcmÀ3
]
Rint
0.062
14.30
0.0523
0.166
0.0543
0.170
0.055
14.82
0.049
1.70
0.049
2.97
m [cmÀ1
]
total data
unique data
52378
11422
8049
27924
7175
4757
35999
8727
5796
22832
4448
3576
22953
7560
6669
17365
8615
7075
2
data>2s
N
)
variables
777
388
691
402
416
443
R
(>2s)
0.075
0.0713
0.099
0073
0.089
0.070
Rw
GOF
0.224
1.010
0.2069
1.028
0.2682
1.029
0.215
1.008
0.261
1.099
0.173
1.083
9648
www.chemeurj.org
ꢃ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 9640 – 9650

CO2 and Formate Complexes
FULL PAPER
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finement, anisotropic temperature factors were assigned to all non-hydro-
gen atoms except in cases of disorder or insufficient data. In the latter
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À
suming C H bond lengths between 0.94 and 0.99 ꢄ depending on the
type of the carbon atom. Hydrogen-atom temperature factors were fixed
at 1.20 or 1.50 times the isotropic temperature factor of the carbon atom
to which they are bonded. The locations of the largest peaks in the final
difference Fourier map calculation as well as the magnitude of the residu-
al electron densities in each case were of no chemical significance.
For the crystallographic data see Table 3. Additional data for the struc-
tural studies are deposited in the Cambridge Crystallographic database.
CCDC-806867 (2), 806868 (3), 806869 (4), 806870 (5), 806871 (6), 806872
(7), 806873 (8), 806874 (9), 806875 (10), 806876 (11), 806877 (12), and
806878 (13) contain the supplementary crystallographic 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.
Computational studies: Selected compounds have been investigated by
means of state-of-the-art quantum chemical methods. As a starting point
we used the X-ray structures and performed geometry optimizations with
the meta-GGA density functional TPSS[25] applying the large Gaussian
AO basis set def2-TZVP,[29] the resolution of the identity approxima-
tion[30] and an empirical dispersion correction (DFT-D2)[31] as provided
by the ORCA 2.7 (rev. 1383) program package.[32] Subsequent single-
point calculations with the accurate double-hybrid functional B2PLYP[33]
and the same basis set have been carried out by using the Turbomole 6.0
suite of programs.[34] Because inter- and intramolecular dispersion inter-
actions play a crucial role in systems like FLPs with bulky and weakly in-
teracting substituents, the newly developed DFT-D3 dispersion correction
was consistently applied.[35]
Acknowledgements
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Financial support from the Fonds der Chemischen Industrie and the gift
of solvents from BASF is gratefully acknowledged by Professors Grimme
and Erker. Professor Stephan is grateful for the financial support of
NSERC of Canada and the award of a Canada Research Chair and a
Killam Research Fellowship. X.Z. is grateful for the award of an
NSERC-CGS scholarship.
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Received: January 26, 2011
Published online: July 11, 2011
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