Reaction of diphenylphosphanylacetylene with RB(C6F 5)2 reagents: Evidence for a remarkable sequence of synergistic frustrated Lewis pair addition reactions

Article abstract of DOI:10.1021/ic402139g

Diphenylphosphanylethyne (3a) reacts with tris(pentafluorophenyl)borane at room temperature by a typical frustrated Lewis pair (FLP) reaction. It undergoes a sequential series of 1,2-phosphane/borane additions to the alkyne unit in an overall 2:2 molar ra

Full text of DOI:10.1021/ic402139g

Article
pubs.acs.org/IC
Reaction of Diphenylphosphanylacetylene with RB(C6F5)2 Reagents:
Evidence for a Remarkable Sequence of Synergistic Frustrated Lewis
Pair Addition Reactions
Jiangang Yu, Gerald Kehr, Constantin G. Daniliuc,† and Gerhard Erker*
Organisch-Chemisches Institut, Universitat Munster, Corrensstrasse 40, 48149 Munster, Germany
̈
̈
̈
S
* Supporting Information
ABSTRACT: Diphenylphosphanylethyne (3a) reacts with tris-
(pentafluorophenyl)borane at room temperature by a typical
frustrated Lewis pair (FLP) reaction. It undergoes a sequential
series of 1,2-phosphane/borane additions to the alkyne unit in
an overall 2:2 molar ratio to selectively form the dimeric pro-
duct 5a. Product 5 features a pentafulvene-reminiscent structure
with a pair of phosphonium units in the ring and B(C6F5)3 sub-
stituents at the periphery. At elevated temperature, the reac-
tion becomes less selective, now favoring the formation of cis- and trans-1,1-carboboration products from a 1:1 stoichiometry.
After photolytic trans/cis isomerization, the vicinal FLP 6a becomes the major product, featuring an intramolecular P···B
interaction. The reaction of 3a with H3CB(C6F5)2 also gives a heterocyclic dimer (11), except that here a substituent H/CH3
exchange by an addition/elimination pathway has taken place. In the B(C6F5)3-derived system, we were able to trap an alleged
intermediate of this rearrangement reaction by adding n-butyl isocyanide. Five products in the Ph2P- and (p-tolyl)2P-derived
systems were characterized by X-ray diffraction
Scheme 1). This was not isolated, but it was characterized by, e.g., a
31P NMR signal at δ 4.3, a 11B NMR resonance at δ −8.8, and an
acetylene CH 1H NMR resonance at δ 1.54 (1H, 3JPH = 8.9 Hz).
INTRODUCTION
■
Phosphane/borane (P/B) frustrated Lewis pairs (FLPs)1 can
react with terminal acetylenes either by deprotonation, followed
by alkynyl anion addition, e.g., to the borane Lewis acid,2 or by
synergistic 1,2-addition of the P/B pair to the CC triple bond.3
Alternatively, strongly electrophilic RB(C6F5)2 boranes undergo
1,1-carboboration reactions4−6 with various alkynes, especially
when good migrating groups are present at the acetylenic
substrate, such as, e.g., PR2,7,8 SiR3,9 SR,10 and even H.5,6 This
may pose a serious selectivity problem when singly phosphanyl-
substituted alkynes, such as, e.g., Ph2PCCH (3a), are treated
with the RB(C6F5)2 reagents. Principally, one might envisage
that this would be a typical case of 1,1-carboboration with facile
internal phosphanyl migration. However, the 3a/RB(C6F5)2
combination itself may constitute a P/B FLP that might be
able to add to another acetylene unit in the typical FLP way. We
investigated some such systems and found a remarkable array of
competing reaction pathways being followed depending on the
specific reaction conditions applied.
Scheme 1
RESULTS AND DISCUSSION
■
The diarylphosphanylacetylenes 3a (Ar = phenyl) and 3b (Ar =
p-tolyl) were prepared in a two-step process by the treatment of
lithiated (trimethylsilyl)acetylene (1) with the respective Ar2PCl
reagents followed by deprotection.11
The treatment of 3a with 1 molar equiv of the strong boron
Lewis acid B(C6F5)3 was first carried out under direct NMR
observation in a deuterated solvent (toluene-d8). We observed
the formation of the adduct 4a at low temperature (−60 °C;12 see
Received: August 21, 2013
Published: September 26, 2013
© 2013 American Chemical Society
11661
dx.doi.org/10.1021/ic402139g | Inorg. Chem. 2013, 52, 11661−11668

Inorganic Chemistry
Article
The reaction of 3a with B(C6F5)3 was then carried out on a
preparative scale and found to proceed smoothly to the product
5a in a toluene solution (1 h, room temperature). Workup involv-
ing precipitation from dichloromethane at −30 °C eventually
gave compound 5a as a white solid, which was isolated in ca. 60%
yield (see Scheme 1).
In solution (CD2Cl2), compound 5a features pairs of clearly
separated 11B (δ −13.1 and −15.1) and 31P NMR (δ 53.8 and
2
15.5, JPP ≈ 145 Hz) signals. They are located in the typical
1
borate and phosphonium chemical shift range. The olefinic H
NMR ([B]C4)H (see Figure 2 for the numbering scheme)
resonance occurs as a dd at δ 9.40 (3JPH = 53.7 and 31.3 Hz), and
the corresponding endocyclic (C3)H signal is at δ 7.37 (dd, 3JPH
=
53.2 Hz, 2JPH = 28.6 Hz). The 13C NMR signals of the exocyclic
CC double bond were located at δ 210.9 [([B]C4)H] and
1
1
107.9 (C1, JPC = 86.7 Hz, JPC = 66.4 Hz), respectively. The
corresponding 13C NMR signals of the endocyclic CC bond
were found at δ 138.7 [(C3)H, 1JPC = 79.6 Hz] and 167.7 (C2,
br), respectively.
Figure 1. Molecular structure of the 1,1-carboboration product 6a
(thermal ellipsoids are shown with 30% probability). Selected bond
lengths (Å), angles (deg), and dihedral angles (deg): C1−C2 1.348(3),
C1−P1 1.775(2), C2−B1 1.651(3), B1−P1 2.045(2); C1−P1−B1
77.1(1), C2−B1−P1 79.4(1), P1−C1−C2 98.4(1), C1−C2−B1
105.2(2); P1−C1−C2−B1 −1.(2), C1−C2−B1−P1 0.9(1).
We assume that product 5a was formed in a typical sequence of
1,2-P/B FLP addition reactions3 to the CC triple bonds of a
pair of the starting material 3a (see Scheme 2). Probably, 3a
Scheme 2
The borane has added to an acetylenic carbon atom and induced
1,2-migration of the PPh2 substituent concomitant with 1,2-
migration of a C6F5 substituent from boron to carbon. The
resulting olefinic product 6a consequently contains a geminal
pair of C6F5 and B(C6F5)2 substituents at one former acetylene
carbon and a H/PPh2 pair at the other. In the isolated isomer, the
phosphanyl and boryl substituents were found to be cis to each
other. They show a direct P···B interaction, as is typical of
unsaturated vicinal P/B FLPs of this type.7
The reaction of (p-tolyl)2PCCH (3b) with B(C6F5)3 takes a
similar course. We first observed P/B adduct formation at ca.
−60 °C [4b: δ −9.9 (11B NMR), 4.1 (31P NMR)]. In contrast to
the Ph2P-substituted system 4a, the B(C6F5)3 adduct 4b is much
more thermally robust. It required prolonged stirring at ambient
temperature to be consumed. In this case, the formation of the
follow-up products is much less selective (for details, see the
Supporting Information). Prolonged stirring of the mixture (4b)
at room temperature eventually resulted in formation of the dimeric
FLP addition product 5b admixed with the 1,1-carboboration
products 6b and 7b and an additional not yet unequivocally
identified fourth product. Workup eventually gave the coupling
product 5b in 52% yield as a white solid.
Compound 5b was characterized by X-ray diffraction (single
crystals were obtained by keeping a saturated CH2Cl2 solution at
room temperature for several days). Structure determination
showed that the product was produced from the reaction of
2 mol equiv of each 3b and B(C6F5)3. The resulting cyclodimer
features a central five-membered heterocycle that contains a pair
of Ar2P units. All of the endocyclic carbon atoms are sp2-
hybridized. A B(C6F5)3 substituent is found bonded to carbon
atom C2 of the endocyclic CC double bond. Carbon atom C1
is part of an exocyclic CC double bond, to the end of which
(C4) the second B(C6F5)3 substituent is bonded (see Figure 2).
Heating of the 3b/B(C6F5)3 reaction mixture for 1 h at 80 °C
gave a ca. 26:32:27 mixture of the products 5b, 6b, and 7b (see
Scheme 1; for details, see the Supporting Information). Com-
pound 7b again was tentatively assigned by its NMR spectra from
the mixture. After removal of the product 5b, the filtrate was
photolyzed for 3 h, and eventually we isolated the 1,1-carboboration
forms a reactive FLP (in equilibrium with their Lewis acid/Lewis
base adduct) with B(C6F5)3 that is able to add to the CC triple
bond of another 3a molecule to form the intermediate 8a. This
can then itself react with an external B(C6F5)3 Lewis acid by FLP
addition to the remaining CC triple bond of 8a to directly
yield the observed dimeric product 5a.
The reaction is markedly less selective at elevated temperature.
The reaction between 3a and B(C6F5)3 in toluene at 80 °C (1 h)
gives a mixture of three products in a ca. 39:26:31 ratio. One
product is the cyclic dimer 5a, which was formed by a typical FLP
reaction sequence; the two new products are both probably
arising from competing 1,1-carboboration reactions. One
product was identified as the cyclic P/B FLP 6a (see below).
To the other we tentatively ascribed the structure of its respective
trans isomer 7a (see Scheme 1). This would be in accordance
with the observation that 1,1-carboboration reactions often
proceed stereounselectively to give cis/trans product mixtures.6
In addition, we photolyzed the reaction mixture and found
that compound 7a was cleanly isomerized to 6a. After ca. 3 h
of irradiation, the original 39:26:31 mixture of products 5a,
6a, and 7a had changed to a ca. 41:54 mixture of 5a and 6a.
The ratios were determined from 31P NMR spectra from an in
situ experiment (for details, see the Supporting Information).
From a stepwise workup procedure, we eventually isolated
the 1,1-carboboration product 6a as a white solid in ca. 12%
yield.
The X-ray crystal structure analysis of compound 6a (single
crystals were obtained from the slow diffusion of pentane into a
saturated CH2Cl2 solution at −30 °C) shows the typical pattern
of a product formed by 1,1-carboboration (see Figure 1).
11662
dx.doi.org/10.1021/ic402139g | Inorg. Chem. 2013, 52, 11661−11668

Inorganic Chemistry
Article
the single CH− group at the bridge was located at δ 7.29 (2JPH
=
12.9 Hz) with corresponding 13C NMR signals at δ 126.5 (C−,
1JPC = 58.5 Hz) and 170.2 (C[B], br), respectively.
We then reacted diphenylphosphanylacetylene 3a with 1 mol
equiv of the borane H3CB(C6F5)2.13 The reaction took 5 h at 80 °C.
The product was identified by X-ray crystal structure analysis as
the dimeric hetercyclic derivative 11 (see Figure 4). Compound
Figure 2. Molecular structure of compound 5b (thermal ellipsoids are
shown with 30% probability). Selected bond lengths (Å) and angles
(deg): C1−P2 1.785(4), P2−C3 1.783(4), C3−C2 1.325(5), C2−P1
1.839(4), C1−P1 1.813(4), C1−C4 1.353(5), C2−B2 1.681(5), C4−
B1 1.654(5); C1−P2−C3 97.4(2), C1−P1−C2 100.9(2), C1−C4−B1
135.7(3), C2−B2−C81 110.4(3), P1−C1−P2 107.9(2).
product 6b in ca. 19% yield. It was characterized by X-ray
diffraction (see Figure 3) and shown to represent an example of
an FLP with a reasonably strong P···B interaction.
Figure 4. View of the molecular structure of compound 11 (thermal
ellipsoids are shown with 30% probability). Selected bond lengths (Å)
and angles (deg): C1−P1 1.802(3), P1−C2 1.814(3), C2−C3 1.340(4),
P2−C3 1.791(3), P2−C1 1.783(2), C1−C4 1.359(3), B1−C4
1.631(4), B2−C2 1.653(4), B2−C6 1.629(4); C1−P2−C3 98.0(1),
C1−P1−C2 101.4(1), C1−C4−B1 120.5(2), B1−C4−C5 119.0(2),
C2−B2−C6 112.3(2), C2−B2−C81 111.6(2).
11 has a framework analogous to that already found for com-
pound 5b (see above), but it bears a slightly, but nevertheless,
distinctly different substituent pattern. For 11, we have found a
five-membered heterocyclic core structure that contains the pair
of phosphonium units that is typical for this type of an “FLP
dimer”. It features the B(C6F5)2CH3 substituent at the endo-
cyclic sp2-hybridized carbon atom C2 and an exocyclic CC
double bond attached at carbon atom C1. The adjacent carbon
atom C4, however, has a CH3 group bonded to it and, con-
sequently, it also bears a B(H)(C6F5)2 substituent. In the end,
we have found a situation where at this end of the dimer a CH3
substituent and an H substituent have exchanged their expected
positions.
Figure 3. Molecular structure of the FLP 6b (thermal ellipsoids are
shown with 30% probability). Selected bond lengths (Å), angles (deg),
and dihedral angles (deg): C1−C2 1.359(4), C1−P1 1.770(3), C2−B1
1.627(4), B1−P1 2.057(3); C1−P1−B1 76.4(1), C2−B1−P1 79.8(2),
P1−C1−C2 98.6(2), C1−C2−B1 105.1(2); P1−C1−C2−B1 −2.7(2),
C1−C2−B1−P1 2.3(2).
This specific composition of compound 11 has been
confirmed in solution (CD2Cl2) by its NMR spectra. It shows
the typical pair of 31P NMR resonances [δ 33.1 and 22.2 (2JPP
∼
158 Hz)] and the B(C6F5)2CH3 11B NMR resonance at δ −11.9.
The second 11B NMR resonance occurs at δ −15.9; it is split into
a doublet due to the bonded hydride (1JBH ∼ 88 Hz). The
1
corresponding [B]H H NMR resonance was located as a
Compound 6b shows the typical NMR features of the CC
unsaturated FLP system, namely, heteronuclei NMR resonances
at δ −4.7 (11B NMR) and 12.0 (31P NMR), respectively. It shows
the 19F NMR signals of the pair of C6F5 substituents at boron at δ
−131.3, −158.2, and −165.2 [Δ19Fm,p = 7.0] and the
corresponding signals of the migrated C6F5 group at δ −137.8,
−153.1, and −163.6 [Δ19Fm,p= 10.5]. The 1H NMR resonance of
partially relaxed broadened 1:1:1:1 quartet at δ 3.36. The methyl
group that was shifted from boron to the adjacent carbon atom
(C4) during the reaction gives rise to a 1H NMR signal at δ 2.16
(corresponding 13C NMR resonance at δ 31.3). The 13C NMR
signals of the exocyclic CC double bond occur at δ 226.7
(C[CH3][B]) and δ 101.5 (1JPC = 95.5 and 67.0 Hz),
respectively. The endocyclic CC double bond gives rise to
11663
dx.doi.org/10.1021/ic402139g | Inorg. Chem. 2013, 52, 11661−11668

Inorganic Chemistry
Article
NMR features at δ 140.0 [1JPC = 75.1 Hz, C−, corresponding
1H NMR resonance at δ 7.31 (JPH = 52.4 and 29.0 Hz)] and 173.0
(br), respectively.
The formation of compound 11 in the reaction between 3a
and H3CB(C6F5)2 indicates that there has been a H/CH3
exchange reaction taking place along the reaction pathway
involving the “normal” dimer 9 (for details, see the Supporting
Information). We assume that the geminal pair of phosphonium
substituents makes the terminus of the adjacent exocyclic CC
double bond sufficiently electrophilic that it becomes amenable
to nucleophilic methyl attack from the adjacent borate anion.
This would lead to the intermediate 10c. Subsequent 1,2-hydride
migration to boron would represent a viable possibility to explain the
formation of the observed and isolated product 11 (see Scheme 3).
Scheme 3
Figure 5. Molecular structure of compound 12a (thermal ellipsoids are
shown with 30% probability). Selected bond lengths (Å) and angles
(deg): C2−P1 1.832(5), P1−C1 1.736(4), C2−C3 1.336(6), C3−P2
1.786(4), P2−C1 1.714(5), C1−C4 1.573(6), C2−B2 1.656(6), C4−
B1 1.667(6), C5−B1 1.623(9); C3−P2−C1 99.9(2), C1−P1−C2
104.3(2), C1−C4−B1 124.5(4), C4−B1−C5 111.2(4), B1−C5−N1
172.8(5), P1−C1−P2 108.0(2).
delocalization over both phosphorus atoms.15 The sp3-
hybridized carbon atom C4 is bonded to it. Carbon atom C4 is
four-coordinated, having C6F5, H, and boryl substituents. The
B(C6F5)2 group has formed an adduct with the added n-butyl
isocyanide donor.
So, it seems that in this reaction the isonitrile has trapped the
free borane Lewis acid of an isomer of 5a, namely, of the reactive
intermediate 10a that was formed (in an equilibrium situation)
with 5a by a 1,2-C6F5 shift from boron to carbon. This is the
analogous reaction that has been proposed for the formation
of the substituent exchange product 11 (see Scheme 3), except in
this case a C6F5 group has migrated (see Scheme 4).
This view has been supported by the outcome of a trapping
reaction starting from the heterocycle 5a. Stirring compound 5a
for 10 min with 1 equiv of n-butyl isocyanide in a dichloro-
methane solution at room temperature led to formation of the
isonitrile/borane adduct 12a, which was isolated in 83% yield
after workup (see Scheme 4). The product was characterized by
Compound 12a shows an AX pattern of 31P NMR resonances
at δ 56.3 and 22.3 (2JPP ∼ 150 Hz). It shows two 11B NMR signals
(δ −13.5 and −17.9). The isonitrile sp-hybridized carbon
resonance of compound 12a occurs at δ 127.7. The 13C NMR
resonances of the −CH[B]C6F5 substituent (C4) was found at δ
Scheme 4
1
20.4 (br, H NMR δ 4.73); the adjacent “ylidic” carbon (C1)
shows a 13C NMR signal at δ 15.6 (1JPC ∼ 118 and 90 Hz). The
corresponding 13C signals of the endocyclic CC unit were
1
located at δ 162.1 (C[B], br) and 140.8 (C−, JPC
=
86.3 Hz); 1H NMR δ 6.80 (JPH = 55.8 and 33.1 Hz), respectively.
CONCLUSIONS
■
P/B FLPs are known to react with terminal alkynes. Either they
can undergo an acid−base reaction, yielding a phosphonium/
alkynylborate salt, or they can simply add 1,2 to the CC triple
bond. Alternatively, alkynes can undergo 1,1-carboboration
reactions just with the borane component of the FLP alone
without involving the phosphane at all.
carbon, hydrogen, and nitrogen elemental analysis, spectroscopy,
and X-ray diffraction (single crystals were obtained from the slow
diffusion of pentane into a saturated CH2Cl2 solution at −30 °C).
The crystal structure analysis has revealed that compound 12a
contains the intact unsaturated five-membered heterocyclic core
(see Figure 5). The B(C6F5)3 substituent is bonded to its
endocyclic CC double bond. The “tip” of the five-membered
heterocycle is made up of a single sp2-hybridized carbon atom
(C1). Formally, it is part of an ylidic structure,14 but it features
The here-employed 3a/borane system represents an interest-
ing hybrid between these principal reaction alternatives. The
substrate 3a contains both a phosphane and an alkyne functional
group. Therefore, it can undergo a 1,1-carboboration reaction, pro-
bably proceeding with PPh2 migration, to give a 1-phosphanyl-2-
borylalkene product. At least in its cis isomer, the phosphane
11664
dx.doi.org/10.1021/ic402139g | Inorg. Chem. 2013, 52, 11661−11668

Inorganic Chemistry
Article
1
−60 °C. H NMR (600 MHz, 213 K, toluene-d8): δ 7.28 (m, 4H,
o-tolyl), 6.37 (m, 4H, m-tolyl), 1.64 (s, 3H, CH3), 1.57 (d, 2JPH = 9.0 Hz,
1H, CH). 13C{1H} NMR (151 MHz): δ 148.8 (dm, 1JFC ≈ 240 Hz,
component of this newly formed vicinal FLP is involved, because
in the product 6a, it features a P···B interaction.
However, this attractive reaction pathway has only been
observed at high reaction temperature, and then the 1,1-car-
boboration reaction (to give 6a and 7a) is only a competing
reaction with 1,2-P/B FLP addition. The reaction becomes quite
selective in favor of the FLP addition reaction alternative at room
temperature. Here we have found formation of the five-mem-
bered heterocyclic “dimeric” product 5a (and, consequently, also
5b) to prevail under these milder reaction conditions. Even in the
case of the 3a/H3CB(C6F5)2 reaction, this pathway seems to be
favored, although it is followed in this specific case by a
subsequent rearrangement reaction.
We conclude that we have found a unique reaction system
where the bifunctional alkyne 3a reacts very selectively with a
strongly electrophilic borane by a typical FLP reaction pathway
to yield the interesting 2-fold P/B alkyne addition product 5a.
The 1,1-carboboration pathway, which is always an alternative, is
in this case only observed as a competing reaction at elevated
temperature, i.e., in a regime where the 3 + B(C6F5)3 reaction
system has become quite unselective. These observations may
help us and others to determine reaction conditions for selective
FLP reactions without accompanying reaction alternatives
becoming too dominant.
1
C6F5), 143.2 (p-tolyl), 140.6 (dm, JFC ≈ 250 Hz, C6F5), 137.3 (dm,
1JFC ≈ 250 Hz, C6F5), 132.9 (d, 2JPC = 8.3 Hz, o-tolyl), 129.5 (d, 3JPC
=
11.0 Hz, m-tolyl), 121.1 (d, 1JPC = 60.1 Hz, i-tolyl), 115.2 (br, i-C6F5),
101.0 (dm, 2JPC ≈ 12 Hz, CH), 72.2 (d, 1JPC = 108.0 Hz, CP), 20.7
(CH3). 11B{1H} NMR (192 MHz): δ −9.9 (ν1/2 ≈ 700 Hz). 31P{1H}
NMR (243 MHz): δ 4.1 (ν1/2 ≈ 40 Hz). 19F NMR (564 MHz): δ −127.1
(br, 2F, o-C6F5), −155.2 (br, 1F, p-C6F5), −163.7 (br, 2F, m-C6F5)
[Δδ19Fm,p = 8.5].
Synthesis of Compound 5a. The mixing of diphenylphosphan-
ylethyne (0.11 g, 0.50 mmol) with tris(pentafluorophenyl)borane (0.26 g,
0.50 mmol) in toluene (6 mL) at room temperature led to a light-brown
solution. After 1 h of stirring, all volatiles were removed in vacuo. The
obtained residue was dissolved in CH2Cl2 (1 mL). Then the solution
was kept overnight at −30 °C. Subsequently, the white precipitate was
isolated by cannula filtration and dried in vacuo to give the product (0.21 g,
0.15 mmol, 60%) as a white powder. Mp: 320 °C (dec). Elem anal. Calcd
1
for C64H22B2F30P2: C, 53.22; H, 1.54. Found: C, 52.94; H, 1.45. H
NMR (600 MHz, 299 K, CD2Cl2): δ 9.40 (dd, 3JPH = 53.7 and 31.3 Hz,
1H, BCH), 7.85 (m, 2H, p-PhA), 7.77 (m, 2H, p-PhB), 7.58 (m, 4H, m-
PhA), 7.56 (m, 4H, o-PhB), 7.51 (m, 4H, m-PhB), 7.47 (m, 4H, o-PhA),
3
2
7.37 (dd, JPH = 53.2 Hz, JPH = 28.6 Hz, 1H, PCH). 13C{1H} NMR
(151 MHz): δ 210.9 (br m, BCH), 167.7 (br, BCP), 138.7 (d, 1JPC = 79.6
Hz, PCH), 136.3 (d, 4JPC = 3.1 Hz, p-PhA), 135.6 (d, 4JPC = 3.1 Hz, p-
PhB), 134.0 (d, 3JPC = 10.1 Hz, o-PhB), 133.7 (d, 3JPC = 11.6 Hz, o-PhA),
130.5 (d, 3JPC = 13.5 Hz, m-PhA), 129.9 (d, 3JPC = 13.0 Hz, m-PhB), 118.3
(d, 1JPC = 83.0 Hz, i-PhB), 116.5 (d, 1JPC = 87.9 Hz, i-PhA), 107.9 (dd,
1JPC = 86.7, 1JPC = 66.4 Hz, PCP) (C6F5 not listed). 11B{1H} NMR (192
MHz): δ −13.1 (ν1/2 ≈ 34 Hz), −15.1 (ν1/2 ≈ 27 Hz). 31P{1H} NMR
(243 MHz): δ 53.8 (d, 2JPP ≈ 145 Hz), 15.5 (d, 2JPP ≈ 145 Hz). 19F NMR
(564 MHz): δ −128.3, −130.3 (each br, each 2F, o-C6F5), −159.2 (t,
3JFF = 20.9 Hz), −159.3 (t, 3JFF = 20.9 Hz, each 1F, p-C6F5), −164.4 (m,
4F, m-C6F5) [Δ19Fm,p = 5.2 and 5.1].
EXPERIMENTAL SECTION
■
General Procedures. Standard Schlenk-type glassware (or glove-
box) under an atmosphere of argon was used in the syntheses involving
air- and/or moisture-sensitive compounds. Solvents were dried, and
X-ray crystal structure analyses were performed. Data sets were collected
with a Nonius Kappa CCD diffractometer. Programs used: data collec-
tion, COLLECT;16 data reduction, Denzo-SMN;17 absorption correc-
tion, Denzo;18 structure solution, SHELXS-97;19 structure refinement,
SHELXL-97;20 graphics, XP (BrukerAXS, 2000). Thermal ellipsoids are
shown with 30% probability, R values are given for observed reflections,
and wR2 values are given for all reflections. Exceptions and special
features: Two disordered over two position dichloromethane molecules
were found in the asymmetric unit of compound 5b. Several restraints
(SAMI, SAME, ISOR, and SADI) were used in order to improve the
refinement stability. Compound 6a crystallized with one disordered
over two position toluene molecules in the asymmetric unit. Several
restraints (SAMI, SAME, ISOR, and SADI) were used in order to
improve the refinement stability. In compound 11, the hydrogen at the
B1 atom was refined freely. Compound 12a contains an unidentified
disordered solvent molecule in the asymmetrical unit, which could not
be satisfactorily refined. The program SQUEEZE21 was therefore used to
mathematically remove the effect of the solvent. The quoted formula
and derived parameters are not included in the squeezed solvent
molecule.
Synthesis of Compound 5b. Di-p-tolylphosphanylethyne (0.12 g,
0.50 mmol) and tris(pentafluorophenyl)borane (0.26 g, 0.50 mmol)
were dissolved in toluene (2 mL) and stirred at room temperature for 7
days until the solution turned brown. Then all volatiles were removed in
vacuo, and the obtained residue was washed with cold CH2Cl2 (2 ×
0.5 mL). Drying of the solid in vacuo yielded 5b (0.19 g, 0.13 mmol,
52%) as a white powder. Single crystals of 5b suitable for X-ray single
crystal structure analysis were obtained by keeping a saturated CH2Cl2
solution at room temperature for 1 week. Mp: 300 °C (dec). Elem anal.
Calcd for C68H30B2F30P2: C, 54.43; H, 2.02. Found: C, 54.62; H, 2.05.
1H NMR (600 MHz, 299 K, CD2Cl2): δ 9.28 (dd, 3JPH = 53.2 and 30.9
Hz, 1H, BCH), 7.43 (m, 4H, o-tolylA), 7.37 (m, 8H, o,m-tolylB), 7.31 (m,
4H, m-tolylA), 7.26 (dd, 3JPH = 54.0 Hz, 2JPH = 28.2 Hz, 1H, PCH), 2.52
B
A
(s, 6H, CH3 ), 2.47 (s, 6H, CH3 ). 13C{1H} NMR (151 MHz): δ 209.8
(br m, BCH), 167.3 (br, BCP), 148.4 (d, 4JPC = 3.2 Hz, p-tolylB), 147.4
(d, 4JPC = 3.1 Hz, p-tolylA), 138.3 (d, 1JPC = 80.0 Hz, PCH), 133.9 (d,
2JPC = 11.1 Hz, o-tolylA), 133.6 (d, 2JPC = 12.1 Hz, o-tolylB), 131.2 (d,
3JPC = 14.1 Hz, m-tolylB), 130.4 (d, 3JPC = 13.6 Hz, m-tolylA), 115.1 (d,
1JPC = 86.0 Hz, i-tolylA), 113.0 (dd, 1JPC = 90.5 Hz, J = 3.7 Hz, i-tolylB),
Generation of Compound 4a (NMR Scale). Diphenylphospha-
nylethyne (11 mg, 50 μmol) and tris(pentafluorophenyl)borane (26 mg,
50 μmol) were mixed in toluene-d8 (1.0 mL) at −78 °C in an NMR tube.
Then the reaction mixture was directly measured by NMR experiments
B
109.0 (dd, 1JPC = 86.9 and 67.0 Hz, PCP), 22.0 (d, 5JPC = 1.6 Hz, CH3 ),
5
A
21.7 (d, JPC = 1.5 Hz, CH3 ) [C6F5 not listed]. 11B{1H} NMR (192
MHz): δ −13.2 (ν1/2 ≈ 35 Hz), −15.2 (ν1/2 ≈ 30 Hz). 31P{1H} NMR
(243 MHz): δ 53.0 (d, 2JPP ∼ 146 Hz), 14.5 (d, 2JPP ∼ 146 Hz). 19F NMR
(564 MHz): δ −128.4, −130.3 (each br, each 2F, o-C6F5), −159.7 (t,
3JFF = 20.1 Hz), −159.9 (t, 3JFF = 20.0 Hz, each 1F, p-C6F5), −164.8 (m,
4F, m-C6F5).
1
starting at −60 °C. H NMR (600 MHz, 213 K, toluene-d8): δ 7.29
(m, 4H, o-Ph), 6.66 (m, 2H, p-Ph), 6.49 (m, 4H, m-Ph), 1.54 (d, 3JPH
8.9 Hz, 1H, CH). 13C{1H} NMR (151 MHz): δ 148.7 (dm, 1JFC
=
≈
≈
1
1
240 Hz, C6F5), 140.6 (dm, JFC ≈ 255 Hz, C6F5), 137.2 (dm, JFC
250 Hz, C6F5), 132.8 (o-Ph), 132.3 (p-Ph), 128.7 (m-Ph) [from the
ghsqc experiment], 124.1 (d, 1JPC = 58.0 Hz, i-Ph), 114.9 (br, i-C6F5),
101.8 (dm, 2JPC = 9.9 Hz, CH), 71.5 (dm, 1JPC = 107.8 Hz, CP).
11B{1H} NMR (192 MHz): δ −8.8 (ν1/2 ≈ 800 Hz). 31P{1H} NMR (243
MHz): δ 4.3 (ν1/2 ≈ 40 Hz). 19F NMR (564 MHz): δ −127.2 (br, 2F,
o-C6F5), −155.3 (br, 1F, p-C6F5), −163.9 (br, 2F, m-C6F5) [Δδ19Fm,p = 8.6].
Generation of Compound 4b (NMR Scale). After di-p-tolylphos-
phanylethyne (12 mg, 50 μmol) and tris(pentafluorophenyl)borane
(26 mg, 50 μmol) were mixed in toluene-d8 (1.0 mL) at −78 °C in a
NMR tube, the reaction mixture was measured by NMR experiments at
X-ray Crystal Structure Analysis of Compound 5b. Formula
C68H30B2F30P2·2CH2Cl2, M = 1670.33, colorless crystal, 0.18 × 0.13 ×
0.07 mm, a = 13.2281(7) Å, b = 13.9512(5) Å, c = 19.8440(11) Å, α =
86.049(5)°, β = 84.316(4)°, γ = 67.594(4)°, V = 3367.1(3) Å3, ρcalc
=
1.647 g cm−3, μ = 3.211 mm−1, empirical absorption correction (0.595 ≤
T ≤ 0.806), Z = 2, triclinic, space group P1 (No. 2), λ = 1.54178 Å,
̅
T = 223(2) K, ω and φ scans, 46868 reflections collected ( h, k, l),
(sin θ)/λ = 0.60 Å−1, 11646 independent (Rint = 0.066) and 9492
11665
dx.doi.org/10.1021/ic402139g | Inorg. Chem. 2013, 52, 11661−11668

Inorganic Chemistry
Article
observed reflections [I > 2σ(I)], 1033 refined parameters, R1 = 0.074,
wR2 = 0.205, max (min) residual electron density 0.83 (−0.53) e Å−3.
Hydrogen atoms were calculated and refined as riding atoms.
Z = 2, triclinic, space group P1 (No. 2), λ = 1.54178 Å, T = 223(2) K, ω
̅
and φ scans, 20191 reflections collected ( h, k, l), [(sin θ)/λ] =
0.60 Å−1, 5217 independent (Rint = 0.059) and 4206 observed reflections
[I > 2σ(I)], 462 refined parameters, R1 = 0.050, wR2 = 0.142, max (min)
residual electron density 0.51 (−0.24) e Å−3. Hydrogen atoms were
calculated and refined as riding atoms.
Synthesis of Compound 6a. Immediately after diphenylphospha-
nylethyne (84 mg, 0.40 mmol) and tris(pentafluorophenyl)borane
(0.20 g, 0.40 mmol) were mixed in toluene (4.0 mL), the reaction
mixture was heated for 1 h at 80 °C. Then the light-brown reaction
mixture was concentrated to approximately one-third in vacuo and kept
stirring at room temperature overnight. The obtained precipitate was
collected by cannula filtration and dried in vacuo to give 5a (60 mg,
42 μmol, 21%) as a white powder. The yellow filtrate was then irradiated
under UV light (high-pressure mercury vapor lamp: HPK 125 W, Pyrex
filter) for 3 h until the solution turned colorless. Subsequently, the
solvent was removed in vacuo, and the residue was crystallized from a
pentane solution to give 6a (35 mg, 48 μmol, 12%) as a white powder.
Single crystals of 6a suitable for X-ray single crystal structure analysis
were obtained by the slow diffusion of pentane into a saturated CH2Cl2
solution at −30 °C. Mp: 158 °C. Elem anal. Calcd for C32H11BF15P: C,
Synthesis of Compound 11. Diphenylphosphanylethyne (0.11 g,
0.50 mmol) and methylbis(pentafluorophenyl)borane (0.18 g, 0.50 mmol)
were dissolved in toluene (6.0 mL) and stirred for 5 h at 80 °C until the
solution turned brown. Then the reaction mixture was kept at low
temperature (−30 °C), and some colorless crystals precipitated. The
crystals were collected by cannula filtration and dried in vacuo to give
compound 11 (0.12 g, 0.11 mmol, 42%). Crystals of 11 suitable for X-
ray single crystal structure analysis were obtained by keeping a saturated
toluene solution at room temperature for 2 days. Mp: 244 °C. Elem anal.
Calcd for C54H28B2F20P2: C, 56.88; H, 2.47. Found: C, 56.73; H, 2.76.
1H NMR (600 MHz, 299 K, CD2Cl2): δ 7.84 (m, 4H, o-PhA), 7.81 (m,
2H, p-PhA), 7.71 (m, 2H, p-PhB), 7.67 (m, 4H, o-PhB), 7.64 (m, 4H,
m-PhA), 7.56 (m, 4H, m-PhB), 7.31 (dd, 3JPH = 52.4 Hz, 2JPH = 29.0 Hz,
1H, CH), 3.36 (1:1:1:1 q partially relaxed, 1JBH ≈ 90 Hz, 1H, BH),
2.16 (s, 3H, CH3), 0.00 (s, 3H, BCH3). 13C{1H} NMR (151 MHz): δ
226.7 (br, CB), 173.0 (br, BCP), 140.0 (d, 2JPC = 75.1 Hz, CH),
135.3 (d, J = 3.1 Hz, p-PhA), 134.8 (d, J = 3.3 Hz, p-PhB), 133.60, 133.57
(each d, 2JPC = 11.5 Hz, o-PhA,B), 130.3 (d, 3JPC = 12.9 Hz, m-PhA), 130.0
(d, 3JPC = 13.6 Hz, m-PhB), 119.7 (dm, 1JPC = 91.3 Hz, i-PhB), 118.7 (dm,
1JPC = 83.1 Hz, i-PhA), 101.5 (dd, 1JPC = 95.5 and 67.0 Hz, PCP), 31.3
(br, CH3), 10.5 (br, BCH3) [C6F5 not listed]. 11B NMR (192 MHz): δ
−11.9 (ν1/2 ≈ 100 Hz), −15.9 (1JBH ≈ 88 Hz). 31P{1H} NMR (243
MHz): δ 33.1 (dm, 2JPP ∼ 158 Hz), 22.2 (dm, 2JPP ∼ 158 Hz). 19F NMR
53.22; H, 1.54. Found: C, 52.94; H, 1.45. 1H NMR (500 MHz, 299 K,
2
CD2Cl2): δ 7.53 (m, 2H, p-Ph), 7.41 (m, 4H, m-Ph), 7.34 (d, JPH
=
12.4 Hz, 1H, CH) [from the ghsqc experiment], 7.33 (m, 4H, o-Ph).
13C{1H} NMR (126 MHz): δ 171.0 (br, CB), 132.4 (d, 4JPC = 3.0 Hz,
p-Ph), 132.1 (d, 2JPC = 9.5 Hz, o-Ph), 129.5 (d, 3JPC = 11.6 Hz, m-Ph),
125.8 (dm, 1JPC = 58.1 Hz, CH), 125.8 (d, 1JPC = 45.6 Hz, i-Ph) [C6F5
is not listed]. 11B{1H} NMR (160 MHz): δ −4.3. 31P{1H} NMR (202
MHz): δ 11.8 (ν1/2 ≈ 80 Hz). 19F NMR (470 MHz): δ −137.6 (m, 2F, o),
−152.8 (t, 3JFF = 20.4 Hz, 1F, p), −163.4 (m, 2F, m) (C6F5) [Δδ19Fm,p
=
10.6], −131.2 (m, 4F, o), −157.9 (t, 3JFF = 19.6 Hz, 2F, p), −165.0 (m,
4F, m) [B(C6F5)2] [Δδ19Fm,p = 7.1].
(564 MHz): δ −131.0, −131.5 (each m, each 2F, o-C6F5), −161.6 (t, 3JFF
=
X-ray Crystal Structure Analysis of Compound 6a. Formula
C32H11B2F15P·C7H8, M = 814.32, colorless crystal, 0.33 × 0.26 ×
0.22 mm, a = 11.1554(10) Å, b = 20.4812(14) Å, c = 15.9966(7) Å, β =
104.768(5)°, V = 3534.1(4) Å3, ρcalc = 1.530 g cm−3, μ = 1.688 mm−1,
empirical absorption correction (0.605 ≤ T ≤ 0.707), Z = 4, monoclinic,
space group P21/c (No. 14), λ = 1.54178 Å, T = 223(2) K, ω and φ scans,
25467 reflections collected ( h, k, l), (sin θ)/λ = 0.60 Å−1, 6126
independent (Rint = 0.037) and 5493 observed reflections [I > 2σ(I)],
569 refined parameters, R1 = 0.039, wR2 = 0.103, max (min) residual
electron density 0.30 (−0.20) e Å−3. Hydrogen atoms calculated and
refined as riding atoms.
Synthesis of Compound 6b. Di-p-tolylphosphanylethyne (92 mg,
0.40 mmol) and tris(pentafluorophenyl)borane (0.20 g, 0.40 mmol)
were dissolved in toluene (4 mL) and stirred for 1 h at 80 °C until the
solution turned brown. Then the reaction mixture was concentrated in
vacuo and kept stirring at room temperature overnight until a white solid
precipitated. The solid was collected by cannula filtration and dried in
vacuo to give 5b (52 mg, 35 μmol, 18%) as a white powder. Subsequently,
the filtrate was irradiated by UV light (high-pressure mercury vapor
lamp: HPK 125 W, Pyrex filter) for 3 h until the solution turned
colorless. The solvent was removed in vacuo, and the residue crystallized
from pentane to give 6b as a white powder (60 mg, 80 μmol, 19%).
Crystals of 6b suitable for X-ray single crystal structure analysis were
obtained by the slow diffusion of pentane into a saturated CH2Cl2
solution at −30 °C. Mp: 168 °C (dec). Elem anal. Calcd for C34H15BF15P:
C, 54.43; H, 2.02. Found: C, 54.62; H, 2.05. 1H NMR (600 MHz, 299 K,
CD2Cl2): δ 7.29 (d, 2JPH = 12.9 Hz, 1H, CH), 7.21 (m, 4H, m-tolyl),
7.18 (m, 4H, o-tolyl), 2.37 (s, 6H, CH3). 13C{1H} NMR (151 MHz): δ
170.2 (br, CB), 143.3 (d, 4JPC = 2.5 Hz, p-tolyl), 132.0 (d, 2JPC = 9.8
Hz, o-tolyl), 130.2 (d, 3JPC = 11.2 Hz, m-tolyl), 126.5 (dm, 1JPC = 58.5
19.8 Hz), −161.7 (t, 3JFF = 21.0 Hz, each 1F, p-C6F5), −165.6, −165.7
(each m, each 2F, m-C6F5) [Δδ19Fm,p = 4.0].
X-ray Crystal Structure Analysis of Compound 11. Formula
C54H28B2F20P2·2C7H8, M = 1324.59, colorless crystal, 0.22 × 0.12 ×
0.12 mm, a = 13.2776(4) Å, b = 13.9853(8) Å, c = 16.3101(9) Å, α =
93.485(3)°, β = 97.639(2)°, γ = 93.710(4)°, V = 2988.1(3) Å3, ρcalc
=
1.472 g cm−3, μ = 1.603 mm−1, empirical absorption correction (0.719 ≤
T ≤ 0.830), Z = 2, triclinic, space group P1 (No. 2), λ = 1.54178 Å, T =
̅
223(2) K, ω and φ scans, 45392 reflections collected ( h, k, l), (sin θ)/
λ = 0.60 Å−1, 10349 independent (Rint = 0.053) and 8413 observed
reflections [I > 2σ(I)], 837 refined parameters, R1 = 0.055, wR2 = 0.153,
max (min) residual electron density 0.50 (−0.35) e Å−3. The hydrogen
at the B1 atom was refined freely; others were calculated and refined as
riding atoms.
Synthesis of Compound 12a. Caution! Many isocyanides are toxic
and must be handled with due care. The combination of compound 5a
(29 mg, 20 μmol) with n-butyl isocyanide (1.7 mg, 20 μmol) in CH2Cl2
(1 mL) led instantaneously to a light-yellow solution. After the reaction
mixture was stirred for 10 min, all volatiles were removed in vacuo and
the obtained residue was washed with cold pentane (3 × 2 mL).
The product (25 mg, 16.5 μmol, 83%) was obtained as light yellow
powder. Crystals of 12a suitable for X-ray single crystal structure analysis
were obtained by the slow diffusion of pentane into a saturated CH2Cl2
solution at −30 °C. Mp: 215 °C (dec). Elem anal. Calcd for C69H31B2F30NP2:
C, 54.25; H, 2.05; N, 0.92. Found: C, 54.07; H, 1.96; N, 0.87. IR (KBr):
ν
̃
/cm−1 = 2308 (CN). 1H NMR (600 MHz, 299 K, CD2Cl2): δ 8.02
(m, 2H, o-PhA), 7.97 (m, 2H, o-PhB), 7.78 (m, 1H, p-PhA), 7.72 (m, 4H,
o-PhC), 7.70 (m, 4H, m-PhA), 7.67 (m, 1H, p-PhB), 7.61 (m, 1H, p-PhC),
7.50 (m, 4H, m-PhB), 7.49 (m, 4H, m-PhC), 7.39 (m, 1H, p-PhD), 7.20
1
5
Hz, CH), 122.4 (d, JPC = 48.0 Hz, i-tolyl), 21.7 (d, JPC = 1.4 Hz,
(m, 2H, o-PhD), 7.14 (m, 2H, m-PhD), 6.80 (br dd, 3JPH = 55.8 Hz, 2JPH
=
CH3) [C6F5 is not listed]. 11B{1H} NMR (192 MHz): δ = −4.7 (ν1/2
≈
33.1 Hz, 1H, CH), 4.73 (m, 1H, BCH), 2.84 (t, 3JHH = 7.3 Hz, 2H,
NCH2), 1.59 (m, 2H, CH2), 1.30 (m, 2H, CH2Me), 0.91 (t, 3JHH = 7.4 Hz,
3H, CH3). 13C{1H} NMR (151 MHz): δ 162.1 (br, BCP), 140.8 (dm,
200 Hz). 31P{1H} NMR (243 MHz): δ = 12.0 (ν1/2 ≈ 90 Hz). 19F NMR
(564 MHz): δ −131.3 (m, 4F, o), −158.2 (tm, 3JFF = 19.3 Hz, 2F, p), −165.2
(m, 4F, m) (B(C6F5)2) [Δδ19Fm,p = 7.0], −137.8 (m, 2F, o), −153.1 (t,
3JFF = 21.0 Hz, 1F, p), −163.6 (m, 2F, m) (C6F5) [Δδ19Fm,p = 10.5].
X-ray Crystal Structure Analysis of Compound 6b. Formula
C34H15BF15P, M = 750.24, colorless crystal, 0.20 × 0.15 × 0.08 mm,
a = 8.9861(1) Å, b = 12.7129(2) Å, c = 14.7045(1) Å, α = 71.570(6)°,
β = 83.088(8)°, γ = 74.813(10)°, V = 1536.7(3) Å3, ρcalc = 1.621 g cm−3,
μ = 1.882 mm−1, empirical absorption correction (0.704 ≤ T ≤ 0.864),
1JPC = 86.3 Hz, CH), 135.2 (br, o-PhB), 133.60−133.38 (m, o,p-PhA,C
,
p-PhB), 131.9 (br d, 2JPC = 9.0 Hz, o-PhD), 131.6 (d, 4JPC = 2.8 Hz, p-
PhD), 130.0 (dm, JPC = 80.6 Hz, i-PhA), 129.7 (d, JPC = 11.7 Hz, m-
PhA), 129.1 (d, 3JPC = 12.1 Hz, m-PhC), 128.5 (d, 3JPC = 12.0 Hz, m-PhB),
127.9 (d, 1JPC = 81.5 Hz, i-PhD), 127.7 (br, NC), 127.5 (d, 3JPC = 11.5
1
3
Hz, m-PhD), 126.0 (dd, JPC = 85.0 Hz, J = 3.6 Hz, i-PhC), 120.9 (d,
1
1JPC = 81.7 Hz, i-PhB), 44.7 (NCH2), 29.4 (CH2), 20.4 (br, BCH), 20.0
11666
dx.doi.org/10.1021/ic402139g | Inorg. Chem. 2013, 52, 11661−11668

Inorganic Chemistry
Article
(CH2Me), 15.6 (dd, 1JPC = 117.9 and 89.5 Hz, PCP), 13.1 (CH3) [C6F5
not listed]. 11B{1H} NMR (192 MHz): δ −13.5 (ν1/2 ≈ 35 Hz), −17.9
(ν1/2 ≈ 200 Hz). 31P{1H} NMR (243 MHz): δ 56.3 (dm, 2JPP ∼ 150 Hz),
22.3 (dm, 2JPP ∼ 150 Hz). 19F NMR (470 MHz, 193 K, CD2Cl2): δ −
121.6 (1F), −124.9 (1F), −129.9 (1F), −130.7 (1F), −131.4 (4F), −
132.7 (1F), −133.3 (1F), −137.7 (1F), −141.9 (1F) (each m, o), −155.7
(1F), −156.6 (1F), −157.8 (1F), −160.4 (1F), −160.8 (1F), −161.2
(1F) (each m, each 1F, p), −159.9 (1F), −162.2 (1F), −162.4 (1F), −
162.8 (1F), −162.9 (1F), −164.2 (2F), −164.4 (1F), −165.5 (1F), −
165.8 (1F), −166.1 (1F), −166.4 (1F) (each m, m)(C6F5).
X-ray Crystal Structure Analysis of Compound 12a. Formula
C69H31B2F30NP2, M = 1527.51, colorless crystal, 0.28 × 0.08 × 0.03 mm,
a = 13.7600(7) Å, b = 23.8790(20) Å, c = 21.9660(30) Å, β = 94.374(6)°,
V = 7196.5(12) Å3, ρcalc = 1.410 g cm−3, μ = 1.622 mm−1, empirical
absorption correction (0.659 ≤ T ≤ 0.953), Z = 4, monoclinic, space
group P21/n (No. 14), λ = 1.54178 Å, T = 223(2) K, ω and φ scans,
59373 reflections collected ( h, k, l), (sin θ)/λ = 0.60 Å−1, 12072
independent (Rint = 0.011) and 6860 observed reflections [I > 2σ(I)],
938 refined parameters, R1 = 0.071, wR2 = 0.222, max (min) residual
electron density 0.36 (−0.41) e Å−3. Hydrogen atoms calculated and
refined as riding atoms.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: erker@uni-muenster.de.
Author Contributions
†X-ray structure analyses.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support from the European Research Council is
gratefully acknowledged.
REFERENCES
■
(1) (a) Stephan, D. W.; Erker, G. Angew. Chem., Int. Ed. 2010, 49, 46−
76. See also: (b) Frustrated Lewis Pairs I, Uncovering and
Understanding. In Topics in Current Chemistry; Erker, G., Stephan, D.
W., Eds.; Springer: Heidelberg, Germany, 2013; Vol. 332. (c) Frustrated
Lewis Pairs II, Expanding the Scope. In Topics in Current Chemistry
Erker, G., Stephan, D. W., Eds.; Springer: Heidelberg, Germany, 2013;
Vol. 334.
Synthesis of Compound 12b. Caution! Many isocyanides are toxic
and must be handled with due care. The combination of compound 5b
(50 mg, 30 μmol) with n-butyl isocyanide (2.8 mg, 30 μmol) in CH2Cl2
(1 mL) led instantaneously to a light-yellow solution. After the reaction
mixture was stirred for 10 min, the solvent was removed in vacuo and the
obtained residue was washed with cold pentane (3 × 2 mL). The
product (40 mg, 76%) was obtained as a light-yellow powder. Mp:
203 °C (dec). Elem anal. Calcd for C73H39B2F30NP2: C, 55.37; H, 2.48;
(2) (a) Dureen, M. A.; Stephan, D. W. J. Am. Chem. Soc. 2009, 131,
8396−8397. (b) Dureen, M. A.; Brown, C. C.; Stephan, D. W.
Organometallics 2010, 29, 6594−6607. (c) Liedtke, R.; Frohlich, R.;
̈
Kehr, G.; Erker, G. Organometallics 2011, 30, 5222−5232. (d) Voss, T.;
Mahdi, T.; Otten, E.; Frohlich, R.; Kehr, G.; Stephan, D. W.; Erker, G.
̈
Organometallics 2012, 31, 2367−2378. (e) Zhao, X.; Liang, L.; Stephan,
N, 0.88. Found: C, 55.22; H, 2.97; N, 0.78. IR (KBr): ν
̃
/cm−1 = 2349
D. W. Chem. Commun. 2012, 48, 10189−10191.
(CN). 1H NMR (600 MHz, 299 K, CD2Cl2): δ 7.94 (m, 2H, o-tolylA),
7.87 (br m, 2H, o-tolylB), 7.56 (m, 2H, o-tolylC), 7.51 (m, m-tolylA), 7.30
(m, 2H, m-tolylB), 7.26 (m, 2H, m-tolylC), 7.01 (m, 2H, o-tolylD), 6.91
(m, m-tolylD), 6.70 (br dd, 3JPH = 54.3 Hz, 2JPH = 32.5 Hz, 1H, CH),
(3) (a) Momming, C. M.; Kehr, G.; Wibbeling, B.; Frohlich, R.;
̈
̈
Schirmer, B.; Grimme, S.; Erker, G. Angew. Chem., Int. Ed. 2010, 49,
2414−2417. (b) Rosorius, C.; Kehr, G.; Frohlich, R.; Grimme, S.; Erker,
G. Organometallics 2011, 30, 4211−4219.
̈
A
4.73 (br m, 1H, BCH), 2.82 (m, 2H, NCH2), 2.51 (s, tolylCH3 ), 2.48 (s,
(4) (a) Wrackmeyer, B. Coord. Chem. Rev. 1995, 145, 125−156.
(b) Wrackmeyer, B. Heteroataom Chem. 2006, 17, 188−208.
(5) (a) Jiang, C.; Blacque, O.; Berke, H. Organometallics 2009, 29,
125−133. (b) Fan, C.; Piers, W. E.; Parvez, M.; McDonald, R.
Organometallics 2010, 29, 5132−5139.
B
C
D
tolylCH3 ), 2.46 (s, tolylCH3 ), 2.35 (s, tolylCH3 ), 1.58 (m, 2H, CH2),
1.29 (m, 2H, CH2Me), 0.92 (t, 3JHH = 7.4 Hz, 3H, CH3). 13C{1H} NMR
4
(151 MHz): δ 161.8 (br, BCP), 144.82 (d, JPC = 3.1 Hz), 144.81
(d, 4JPC = 3.1 Hz, p-tolylB,C), 144.4 (d, 4JPC = 3.0 Hz, p-tolylA), 142.7 (d,
4JPC = 3.1 Hz, p-tolylD), 140.6 (dm, 1JPC = 86.9 Hz, CH), 135.3 (br m,
(6) (a) Chen, C.; Kehr, G.; Frohlich, R.; Erker, G. J. Am. Chem. Soc.
̈
2010, 132, 13594−13595. (b) Chen, C.; Frohlich, R.; Kehr, G.; Erker, G.
̈
o-tolylB), 133.6 (t, J = 10.3 Hz, o-tolylA), 133.3 (d, JPC = 10.7 Hz,
2
Chem. Commun. 2010, 46, 3580−3582. (c) Chen, C.; Eweiner, F.;
o-tolylC), 131.6 (br d, 2JPC = 8.3 Hz, o-tolylD), 130.4 (d, 3JPC = 12.2 Hz,
m-tolylA), 129.6 (d, 3JPC = 12.4 Hz, m-tolylC), 129.2 (d, 3JPC = 12.4 Hz,
m-tolylB), 128.0 (d, 3JPC = 11.8 Hz, m-tolylD), 127.9 (br, NC) [from
the ghmbc experiment], 127.1 (dm, 1JPC1 = 82.3 Hz, i-tolylA), 125.3 (dm,
Wibbeling, B.; Frohlich, R.; Senda, S.; Ohki, Y.; Tatsumi, K.; Grimme, S.;
̈
Kehr, G.; Erker, G. Chem.Asian J. 2010, 5, 2199−2208. (d) Chen, C.;
Voss, T.; Frohlich, R.; Kehr, G.; Erker, G. Org. Lett. 2011, 13, 62−65.
̈
(7) (a) Ekkert, O.; Kehr, G.; Frohlich, R.; Erker, G. Chem. Commun.
̈
1JPC = 82.5 Hz, i-tolylD), 122.7 (dd, JPC = 87.2 Hz, JPC = 3.4 Hz,
3
2011, 47, 10482−10484. (b) Ekkert, O.; Kehr, G.; Frohlich, R.; Erker, G.
̈
i-tolylC), 117.4 (dm, 1JPC = 81.8 Hz, i-tolylB), 44.5 (NCH2), 29.4 (CH2),
J. Am. Chem. Soc. 2011, 133, 4610−4616. (c) Liedtke, R.; Kehr, G.;
21.7 (d, J = 1.5 Hz, tolylCH3 ), 21.6 (d, J = 1.3 Hz, tolylCH3 ), 21.5 (br d,
A
B
Frohlich, R.; Daniliuc, C. G.; Wibbeling, B.; Petersen, J. L.; Erker, G.
̈
J = 1.0 Hz, tolylCH3 ), 21.1 (d, J = 1.6 Hz, tolylCH3 ), 20.5 (br, BCH),
20.0 (CH2Me), 15.6 (dd, 1JPC = 119.7 and 90.9 Hz, PCP), 13.1 (CH3)
[C6F5 not listed]. 11B{1H} NMR (192 MHz): δ −13.6 (ν1/2 ≈ 35 Hz),
−18.0 (ν1/2 ≈ 250 Hz). 31P{1H} NMR (243 MHz): δ 54.7 (d, 2JPP ∼ 150
Hz), 21.4 (d, 2JPP ∼ 150 Hz). 19F NMR (470 MHz, 193 K): δ −121.2
(1F), −124.9 (1F), −129.9 (1F), −130.2 (1F), −131.2 (2F), −131.4
(1F), −131.5 (1F), −132.8 (1F), −133.1 (1F), −137.5 (1F), −142.2
(1F) (each m, o), −156.0, −157.2, −158.6, −161.0, −161.8, −161.8
(each 1F, each m, p), −161.5 (1F), −162.4 (1F), −162.5 (1F), −163.3
(1F), −163.5 (1F), −164.4 (3F), −166.0 (1F), −166.1 (1F), −166.6
(1F), −166.7 (1F) (each m, m)(C6F5).
C
D
Helv. Chim. Acta 2012, 95, 2515−2527.
(8) Mobus, J.; Bonnin, Q.; Ueda, K.; Frohlich, R.; Itami, K.; Kehr, G.;
̈
̈
Erker, G. Angew. Chem., Int. Ed. 2012, 51, 1954−1957.
(9) (a) Ugolotti, J.; Dierker, G.; Frohlich, R.; Kehr, G.; Erker, G. J.
̈
Organomet. Chem. 2011, 696, 1184−1188. (b) Dierker, G.; Ugolotti, J.;
Kehr, G.; Frohlich, R.; Erker, G. Adv. Synth. Catal. 2009, 351, 1080−
̈
1088.
(10) Eller, C.; Kehr, G.; Daniliuc, C. G.; Frohlich, R.; Erker, G.
̈
Organometallics 2013, 32, 384−386.
(11) Kondoh, A.; Yorimitsu, H.; Oshima, K. J. Am. Chem. Soc. 2007,
129, 4099−4104.
(12) See for a comparison: Spies, P.; Frohlich, R.; Kehr, G.; Erker, G.;
̈
Grimme, S. Chem.Eur. J. 2008, 14, 333−343.
ASSOCIATED CONTENT
(13) For other abstraction reactions of methyl anion equivalents by
boranes, see, for example: (a) Guram, A. S.; Jordan, R. F. J. Org. Chem.
1993, 58, 5595−5597. (b) Wu, Z.; Jordan, R. F.; Petersen, J. L. J. Am.
Chem. Soc. 1995, 117, 5867−5868. (c) Beswick, C. L.; Marks, T. J. J. Am.
Chem. Soc. 2000, 122, 10358−10370. (d) Niehues, M.; Erker, G.; Kehr,
■
S
* Supporting Information
Text and figures giving further experimental and spectroscopic
details and CIF files giving crystallographic data for 5b, 6a, 6b,
11, and 12a. This material is available free of charge via the
Internet at http://pubs.acs.org.
G.; Schwab, P.; Frohlich, R.; Blacque, O.; Berke, H. Organometallics
̈
2002, 21, 2905−2911.
11667
dx.doi.org/10.1021/ic402139g | Inorg. Chem. 2013, 52, 11661−11668

Inorganic Chemistry
Article
(14) See for a comparison: Doring, S.; Erker, G.; Frohlich, R.; Meyer,
̈
̈
O.; Bergander, K. Organometallics 1998, 17, 2183−2187.
(15) Spannhoff, K.; Kehr, G.; Kehr, S.; Frohlich, R.; Erker, G. Dalton
̈
Trans. 2008, 3339−3344.
(16) Hooft, R. W. W. COLLECT; Bruker AXS: Delft, The Netherlands,
2008.
(17) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307−
326.
(18) Otwinowski, Z.; Borek, D.; Majewski, W.; Minor, W. Acta
Crystallogr. 2003, A59, 228−234.
(19) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467−473.
(20) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112−122.
(21) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7−13.
11668
dx.doi.org/10.1021/ic402139g | Inorg. Chem. 2013, 52, 11661−11668